liu.seSearch for publications in DiVA
Change search
Refine search result
234567 201 - 250 of 320
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 201.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wren, Joakim
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Heating in a Stenosed Coronary Artery With Pulsating Flow and Non-Newtonian Viscosity2009In: ASME 2008 Summer Bioengineering Conference: Parts A and B, The American Society of Mechanical Engineers (ASME) , 2009, no PART A, p. 331-332Conference paper (Refereed)
    Abstract [en]

    Cardiovascular disease is the most prevalent cause of death in the developed countries and most deaths are due to coronary atherosclerosis [1]. During the development of atherosclerosis, several stages can be distinguished including vulnerable plaque. This group of plaque has an inclination for erosion and rupture and is therefore of particular interest. Due to the inflammatory response of vulnerable plaque including an increased metabolism and thereby a locally increased temperature, it is possible to detect such warm cores by intracoronally temperature measurement under some prerequisitions. Temperature differences up to 2.2 K on the surface of carotid plaques have been measured [2], but the relation between plaque vulnerability, inflammatory response, temperature increase and possibility to detection by means of temperature measurement is far from fully perceived.

  • 202.
    Lantz, Jonas
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Henriksson, Lilian
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Persson, Anders
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Importance Of Including Papillary Muscles And Trabeculae In Cardiac Flow Simulations2016In: Proceedings of the 2016 Summer Biomechanics, Bioengineering and Biotransport Conference, Organizing Committee for the 2016 Summer Biomechanics, Bioengineering and Biotransport , 2016Conference paper (Other academic)
  • 203.
    Lantz, Jonas
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Faculty of Medicine and Health Sciences.
    Henriksson, Lilian
    Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Persson, Anders
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Patient-Specific Simulation of Cardiac Blood Flow From High-Resolution Computed Tomography2016In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 138, no 12Article in journal (Refereed)
    Abstract [en]

    Cardiac hemodynamics can be computed from medical imaging data, and results could potentially aid in cardiac diagnosis and treatment optimization. However, simulations are often based on simplified geometries, ignoring features such as papillary muscles and trabeculae due to their complex shape, limitations in image acquisitions, and challenges in computational modeling. This severely hampers the use of computational fluid dynamics in clinical practice. The overall aim of this study was to develop a novel numerical framework that incorporated these geometrical features. The model included the left atrium, ventricle, ascending aorta, and heart valves. The framework used image registration to obtain patient-specific wall motion, automatic remeshing to handle topological changes due to the complex trabeculae motion, and a fast interpolation routine to obtain intermediate meshes during the simulations. Velocity fields and residence time were evaluated, and they indicated that papillary muscles and trabeculae strongly interacted with the blood, which could not be observed in a simplified model. The framework resulted in a model with outstanding geometrical detail, demonstrating the feasibility as well as the importance of a framework that is capable of simulating blood flow in physiologically realistic hearts.

  • 204.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Large eddy simulation of LDL surface concentration in a subject specific human aorta2012In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 45, no 3, p. 537-542Article in journal (Refereed)
    Abstract [en]

    The development of atherosclerosis is correlated to the accumulation of lipids in the arterial wall, which, in turn, may be caused by the build-up of low-density lipoproteins (LDL) on the arterial surface. The goal of this study was to model blood flow within a subject specific human aorta, and to study how the LDL surface concentration changed during a cardiac cycle. With measured velocity profiles as boundary conditions, a scale-resolving technique (large eddy simulation, LES) was used to compute the pulsatile blood flow that was in the transitional regime. The relationship between wall shear stress (WSS) and LDL surface concentration was investigated, and it was found that the accumulation of LDL correlated well with WSS. In general, regions of low WSS corresponded to regions of increased LDL concentration and vice versa. The instantaneous LDL values changed significantly during a cardiac cycle; during systole the surface concentration was low due to increased convective fluid transport, while in diastole there was an increased accumulation of LDL on the surface. Therefore, the near-wall velocity was investigated at four representative locations, and it was concluded that in regions with disturbed flow the LDL concentration had significant temporal changes, indicating that LDL accumulation is sensitive to not only the WSS but also near-wall flow.

    Download full text (pdf)
    fulltext
  • 205.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Resolving flow and mass transport in a healthy subject-specific aorta using large eddy simulation2012In: Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1), 2012Conference paper (Refereed)
  • 206.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Resolving Low-Density Lipoprotein (LDL) on the Human Aortic Surface Using Large Eddy Simulation2011In: 64th Annual Meeting of the APS Division of Fluid Dynamics, 2011Conference paper (Refereed)
  • 207.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Estimation of Wall Shear Stress in a Human Aorta Using Fluid-Structure Interaction2011In: The 6th international symposium on biomechanics in vascular biology and cardiovascular disease, 2011Conference paper (Refereed)
  • 208.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    MR-Based Imaging for Patient Specific, Fully Coupled 2-way Fluid-Structure Interaction of the Human Aorta2010Conference paper (Other academic)
  • 209.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wall shear stress in a subject specific human aorta - Influence of fluid-structure interaction2011In: International Journal of Applied Mechanics, ISSN 1758-8251, Vol. 3, no 4, p. 759-778Article in journal (Refereed)
    Abstract [en]

    Vascular wall shear stress (WSS) has been correlated to the development of atherosclerosis in arteries. As WSS depends on the blood flow dynamics, it is sensitive to pulsatile effects and local changes in geometry. The aim of this study is therefore to investigate if the effect of wall motion changes the WSS or if a rigid wall assumption is sufficient. Magnetic resonance imaging (MRI) was used to acquire subject specific geometry and flow rates in a human aorta, which were used as inputs in numerical models. Both rigid wall models and fluid-structure interaction (FSI) models were considered, and used to calculate the WSS on the aortic wall. A physiological range of different wall stiffnesses in the FSI simulations was used in order to investigate its effect on the flow dynamics. MRI measurements of velocity in the descending aorta were used as validation of the numerical models, and good agreement was achieved. It was found that the influence of wall motion was low on time-averaged WSS and oscillating shear index, but when regarding instantaneous WSS values the e.ect from the wall motion was clearly visible. Therefore, if instantaneous WSS is to be investigated, a FSI simulation should be considered.

    Download full text (pdf)
    fulltext
  • 210.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wall shear stress in an MRI-Based Subject-Specific Human Aorta Using Fluid-Structure Interaction2010In: Proceedings of the ASME 2010 Summer Bioengineering Conference (SBC2010), NY, USA: ASME , 2010, p. 563-564Conference paper (Other academic)
    Abstract [en]

    Wall shear stress (WSS) is well established as an indicator of increased risk for development of atherosclerotic plaques, platelet activation and thrombus formation [1]. Prediction and simulation of the sites of wall shear stresses that are deemed dangerous before intervention would be of great aid to the surgeon. However, the geometries used for these types of simulations are often approximated to be rigid. To more accurately capture the flow and arterial wall response of a realistic human aorta, fluid-structure interaction (FSI) which allows movement of the wall, is needed. Hence, the pressure wave and its effect on the wall motion are resolved and enables a more physiological model as compared to a rigid wall case.

  • 211.
    Lantz, Jonas
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Science & Engineering. Swedish E Science Research Centre SeRC, Sweden.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Länne, Toste
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Östergötlands Läns Landsting, Heart and Medicine Center, Department of Thoracic and Vascular Surgery.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Is aortic wall shear stress affected by aging? An image-based numerical study with two age groups2015In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 37, no 3, p. 265-271Article in journal (Refereed)
    Abstract [en]

    The size of the larger arteries increases during the entire life, but not much is known about how the change in size affects the blood flow. This study compares the flow field in a group of young males (N = 10, age = 23.5 +/- 1.4), with a group of older males (N = 8, age = 58.0 +/- 2.8). Aortic geometries were obtained by magnetic resonance imaging, and the aortic blood flow field was computed using computational fluid dynamics. The aortic wall shear stress was obtained from the computations, and it was concluded that time-averaged wall shear stress decreased with increased age, probably as a consequence of increased aortic diameter and decreased stroke volume, which in turn reduces the shear rates in the aorta. However, the oscillatory shear index, which is a measure of the oscillatory nature of the wall shear stress vector, seemed to be unaffected by aging.

  • 212.
    Leskovec, Martin
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Method Development for Heat Transfer Predictions in Channel Flows: An efficient CFD approach for ribbed stationary channels2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Gas turbines are today used in numerous industrial and aeronautical applications. To increase the specific power output and efficiency, a high turbine inlet gas temperature is desired. The high temperature leads to the need of cooling critical components in the hot gas path. Siemens Industrial Turbomachinery AB, SIT AB, in Finspång manufactures gas turbines where the internal cooling of critical components is done through serpentine channels. To utilize the cooling air as efficiently as possible, vortex creating objects are placed inside the channel which result in higher heat transfer. To compute the heat transfer in the channel, correlation based approaches that will give a uniform value for an entire channel are often used.

    This thesis contains two parts. First, investigating how an automated CAE process can be developed that is able to be incorporated into the SIT AB CAE process of today and with a future vision of a, basically, "one-click-CFD" approach for non-generic geometries. Secondly, how CFD simulations for predicting heat transfer levels inside the cooling channels with high accuracy and that captures local features of heat transfer can be performed.

    The suggested CAE approach involves the CAD-tool NX for geometry creation and for managing an entire CFD project the ANSYS software Workbench, combined with ANSYS Meshing for generation of computational grid, CFX-pre and CFX for pre-processing and solving and CFD-post for post-processing. This approach is suggested for generic geometries due to the simplicity in incorporating it into existing CAE processes. For the future vision of non-generic geometries, the inhouse developed project manager Concept is suggested. It allows for customized coupling between a broader range of available software tools.

    To validate the CFX model and to investigate how the CFD calculations should be performed, two cases were set up, one where the CFD model and the inhouse code was compared to experimental data of a generic geometry and one where the CFD model and the inhouse code were compared at engine-like conditions. The results for the experimental case resulted in heat transfer coefficients from the CFD model that were 30% off from experimental data, and the inhouse code maximum deviation was 10%. Compared to previous numerical studies this was considered to be of acceptable accuracy, and the location of data extraction points were considered to cause the deviation in the CFD model. For the engine-like case both CFD and inhouse code predicted the heat transfer level as expected. The simulations were performed in steady state mode on automatically generated meshes with the SST-Reattachment turbulence model. The Reynolds number varied from 10 000 to 80 000 and the meshes were around 4-10M elements in size.

    Download full text (pdf)
    2016 - Method Development for Heat Transfer Predictions in Channel Flows - An efficient CFD approach for ribbed stationary channels - Leskovec
  • 213.
    Lind, Malin
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Josefsson, Karl Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    A CFD Method for Simulation of Gas-Liquid Flow in Cooling Systems: An Eulerian-Eulerian Approach2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When designing modern engines it is important to construct a cooling system that cools the engine structure efficiently. Within the cooling system there is always a certain amount of air which can accumulate and form air pockets in critical areas, such as the water jacket, which can lead to wall degradation. A Computational Fluid Dynamics (CFD) method in STAR-CCM+ from CD-adapco, was derived at Volvo Cars in order to study the accumulation of air bubbles in the water jacket. The method was derived by investigating and evaluating already existing methods. The method initially considered as the best suited was the Eulerian-Eulerian approach. The method was validated against three simpler geometries where experimental data was available. The Eulerian-Eulerian approach treats both phases, liquid and gas, as continuous phases. The idea with the method is to solve the Navier-Stokes equation, the continuity equation and the energy equation for both phases using the Eulerian approach, therefore called Eulerian-Eulerian. The interaction between the two phases was important to model properly which was done by including several interaction models within STAR-CCM+. By tuning different coefficients, which were investigated by a thorough parameter study, the method resembled the experimental data in a satisfying way. The best suited mesh for these simpler geometries was a directed mesh. However, the mesh in the water jacket was automatically generated by STAR-CCM+ and the simpler cases were therefore validated with an automated mesh as well. To capture the experimental data the convection scheme for volume fraction had to be of second order when simulating with automated mesh. This resulted in convergence issues when implementing the method on the water jacket. Instead first order convection scheme, which did not present as satisfying results as second order, had to be implemented. Simulations of the water jacket were performed with two different velocities, that were 10 m/s and 19 m/s, and different flow split ratios for the three outlets. Air with volume fraction 0.1 was injected at the inlet during the first 0.5 s followed by 0.5-1.1 s of further simulation without injecting air. Increased velocity resulted in increased flow through of gas, whereas no big difference could be seen between the different outlet flow split ratios. At two different zones lower pressure was found which resulted in gas holdup. To be able to validate the results from the water jacket, experiments would be necessary to perform in order to provide experimental data for comparison. Velocity profiles from the derived two-phase method resemble the velocity profiles from the one-phase simulation from Volvo, which indicated that the two-phase method did not affect the solution in a remarkable way. Granted that the zones of lower pressure and gas holdup normally coincides, the pressure field from the one-phase simulation could be directly studied, which would lower the computational costs significantly.

    Download full text (pdf)
    fulltext
  • 214.
    Linde, Måns
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Economic and Environmental Benefits of the ORC and the Willingness to Invest: A case study from a wastewater treatment plant and a small-scale combined heat and power plant2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In Sweden, as many other European countries, centralized large-scale electricity production has traditionally been used to meet the electricity and heat demand. During recent years however, small-scale producers have gained more ground and contributes more to the total electricity generation. Industrial systems such as sewage plants and small-scale district heating plants both have potential thermal power sources available and utilizing this to generate electricity could be an important contribution towards increasing the ratio and effectiveness of renewable energy sources and reduce the primary energy supply. The potential of the Organic Rankine Cycle has been acknowledged by many, with commercial development increasing exponentially during the recent decades. Unlike the traditional Rankine cycle which uses water as a working fluid, the ORC uses a refrigerant with a lower evaporation temperature, which makes it possible to produce electricity from heat of lower temperatures.

    This thesis has through reading literature and plant visits analyzed the effect of implementing an operation strategy at two different plants where ORCs has been installed. One wastewater treatment plant in Norrköping and one combined heat and power plant in Ronneby, Sweden. The operation strategy includes moving production of electricity to high demand hours as well as analyzing options for increasing the efficiency at the plants. In addition, this thesis also includes a questionnaire made in order to analyze what obstacles and motivations that affect the willingness to invest in ORC technology in Sweden.

    The result from this provides useful information for future work in order to see an increased establishment of the ORC on the Swedish market.The results show that by implementing an operation strategy at plant Norrköping the avoided electricity and heat cost from installing the ORC could be increased by 47% and the avoided emissions increased by 436%. For plant Ronneby the avoided electricity cost could be increased by 8% and the avoided emissions increased by 31%.

    The questionnaire shows that different plants have different prerequisites and viewpoints when it comes to investing in ORC technology. This can for example be differences in budget for investments, the workload of the employees or if there is available fuel to run the ORC. From this finding it becomes clear that if one wish to see an increase in ORC technology in today’s industry, it becomes vital to look at each individual plant and assess the situation from there. However, a trend shows that the reduced electricity cost and the reduction in global emissions are two strong motivations for heat plants and wastewater treatment plants to invest in ORC systems.

    Download full text (pdf)
    fulltext
  • 215.
    Lindqvist, Jakob
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Faber, Niklas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Performance evaluation in post integrated organic Rankine cycle systems: A study on operational systems utilizing low grade heat2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Organic Rankine cycles can be integrated with district heating systems and in applications of biogas digestion. Evaluating the performance of the installations by Againity AB in Ronneby and Norrköping, Sweden, is a unique opportunity which can support the establishment of ORC technology in the waste heat recovery market, unveiling its feasibilities and limitations.

    Operational data gathered from October 2017 until April 2018, provides this thesis with information about the ORC-systems. A method using Coolprop and Matlab has been used to detect steady-state series in the Ronneby installation using moving standard deviation and inclination criteria. By screening the data and selecting these series, analytical equations can be used to determine the performance of the installations and map the linear relationship between variables like pressure and generator power.

    The largest impact on the system in Ronneby is developed in the condenser. Large coolant volume flow creates large heat sink capacity and higher generator efficiency and power. However, with increasing generator power the condenser pressure decrease. Lower condenser pressure results in a decreased evaporation pressure, which could be maintained if the pump was able to run at higher frequencies.

    The Plant in Norrköping needs further studies and a review of its sensors. The code in Matlab is a resource to Againity and Linköpings university for future work in performance evaluation. It can be used to detect errors in energy balance, local readings, and picture the machines' performance graphically.

    Download full text (pdf)
    Faber Lindqvist 2018
  • 216.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Doppler prediction of transvalvular gradient and stenotic orifice area.1988In: American Journal of Cardiology, ISSN 0002-9149, E-ISSN 1879-1913, Vol. 61, no 11, p. 958-959Article in journal (Refereed)
  • 217.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    MITRAL PRESSURE HALF-TIME TECHNIQUE FOR ASSESSING SEVERITY OF MITRAL-STENOSIS - ESSENTIAL PARAMETERS1989In: IMAGES OF THE TWENTY-FIRST CENTURY, PTS 1-6, 1989, Vol. 11Conference paper (Refereed)
    Abstract [en]

    The flow through a stenotic mitral valve, which is mainly determined by the cross-sectional area of the valve and the pressure difference across it, is discussed. The gradient half-time is an attempt to describe the area from the decline in transmitral pressure difference alone. The gradient half-time increases with increasing severity of the stenosis. Besides the area of the mitral valve, there are other factors influencing the gradient half-time. Such factors are the transported volume and the initial pressure gradient. The compliance of the cardiac chambers and the pulmonary venous flow also influence the gradient half-time, but through changes in the pressure difference across the valve. The problem can therefore be analyzed either with or without inclusion of compliance in the calculations

  • 218.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Pressure half-time does not always predict mitral valve area correctly.1988In: Journal of the American Society of Echocardiography, ISSN 0894-7317, E-ISSN 1097-6795, Vol. 1, no 5, p. 313-321Article in journal (Refereed)
    Abstract [en]

    A theory is presented elucidating factors that influence the pressure half-time. By combining the Bernoulli and continuity equations and making certain assumptions about the shape of the atrioventricular pressure difference decay, it can be shown that valve area, volume transported across that area, and initial pressure difference influence the pressure half-time according to a formula in which the pressure half-time is related to V/(Ao square root of delta po), where V is the transported volume across the orifice with the area Ao, and delta po is the initial pressure difference across that area. In a subsequent hydraulic model experiment pressure half-time was determined for three different hole areas, with various initial volumes and initial pressure gradients. We did not obtain a unique relation between the pressure half-time and area. Instead the results supported our theory, and we found a close linear relationship between area and V/(T0.5 square root of delta po) (correlation coefficient [r] = 0.998), as predicted in the theory (T0.5 = pressure half-time). Clinical examples in which the pressure half-time may be misleading in the assessment of severity of mitral stenosis are presented.

  • 219.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    BARCLAY, SA
    XIONG, Changsheng
    ANDERSSON, Gunnar
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    ECHOCARDIOGRAPHIC ASSESSMENT OF HEART-VALVE REGURGITANT FLOW USING THE FLOW CONVERGENCE METHOD1991In: PROCEEDINGS OF THE ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOL 13, PTS 1-5, 1991, p. 191-192Conference paper (Refereed)
  • 220.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    KARLSSON, M
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    ERLANDSON, BE
    HYPERTHERMIA OF THE PROSTATE FROM A HEAT TRANSFER POINT OF VIEW1994In: PROCEEDINGS OF THE 16TH ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY - ENGINEERING ADVANCES: NEW OPPORTUNITIES FOR BIOMEDICAL ENGINEERS, PTS 1&2, 1994, Vol. 2, p. 768-769Conference paper (Refereed)
    Abstract [en]

    The finite element method is used to analyse the heat transfer at hyperthermia treatment of the prostate. The microwave antenna is enclosed in a water cooled intra urethral catheter. The purpose of this study is modeling and simulation of the temperature field during local microwave hyperthermal treatment of the prostate. Numerical calculations of the temperature field and the heat flux are necessary in order to get better knowledge of possibilities and restrictions of the method. The influence on the treatment from an incorrect location of the antenna has been studied. The location of the antenna is essential for a successful treatment. The effect of possible phase change processes associated with the heating is included in the analysis. A phase transition has a significant influence on the shape and the propagation speed of the temperature field. For the combination of microwave heating of the tissue and heat transfer from it there exists a transition zone of finite size instead of a transition front

  • 221.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    KARLSSON, Matts
    ANDERSSON, Gunnar
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Hyperthermia treatment of the prostate - A complex heat transfer problem1993In: NUMERICAL METHODS IN THERMAL PROBLEMS, VOL VIII, PTS 1 AND 2, 1993, p. 1239-1250Conference paper (Refereed)
  • 222.
    Loyd, Dan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    KARLSSON, Matts
    ERLANDSSON, Björn Erik
    SJODIN, Jan Gunnar
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Heat transfer analysis of hyperthermia treatment of the prostate1995In: COMPUTER SIMULATIONS IN BIOMEDICINE, 1995, p. 617-624Conference paper (Refereed)
  • 223.
    Lundvall, Johan
    et al.
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    Weinerfelt, Per
    Linköping University, Department of Mathematics, Applied Mathematics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Reconstruction of velocity data, using optimization2003In: Computational Fluid and Solid Mechanics 2003 / [ed] K.J. Bathe, 2003, p. 2324-2327Conference paper (Other academic)
    Abstract [en]

    From a given velocity field u*, a flow field that satisfies a given differential equation and minimize some norm is determined. The gradient for the optimization is updated using adjoint technique. The numerical solution of the non-linear partial differential equation is done using a multigrid scheme. The test case shows promising results. The method handles missing data as well as disturbances.

    This chapter discusses reconstruction of velocity data, using optimization. There is a growing interest in obtaining velocity data on a higher temporal and/or spatial resolution than is currently possible to measure. The problem originates from a vast array of topics—such as meteorology, hydrology, wind tunnel, or water tunnel experiments—and from noninvasive medical measurement devices, such as 3D time-resolved-phase-contrast magnetic resonance imaging. The rapid development in computer performance gave birth to new methods, based on optimization and simultaneous numerical solution of partial differential equations, well-suited for the task of up-sampling. The data may be of several kinds—low spatial and/or temporal resolution with or without areas of missing and/or uncertain data. It determines a flow field that satisfies a given differential equation and minimize some norm from a given velocity field. The gradient for the optimization can be updated through adjoint technique. The numerical solution of the nonlinear partial differential equation can be done through a multigrid scheme. The method handles missing data as well as disturbances.

  • 224.
    Lång, Marcus
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    CFD-Method for 3D Aerodynamic Adjoint Simulations: For External Automotive Aerodynamics2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today’s rules and regulations regarding emissions from combustion vehicles are very strict and the travel range per tank and/or charge, especially for electric vehicles, is a crucial factor which will always be considered by the customers. Hence, automotive manufacturers strive to boost fuel and battery economy. This can, to a great extent, be done by improving the aerodynamics of the vehicle for lower drag. The conventional CFD process for aerodynamic development is relatively time consuming and there is rarely enough timeor resources to find the optimal design in all regions of the vehicle. Hence, the adjoint solver was investigated to make the aerodynamic development process more efficient by providing sensitivities of the geometry with respect to drag force.

    The adjoint solver was investigated both through a literature review as well as by performing CFD and adjoint simulations. The CFD and adjoint simulations were performed using Fluent 2019 R1 and the realizable k-ε turbulence model. It was found that it is important to monitor surface sensitivities during the solution in addition to the adjoint residuals to assess convergence of the adjoint simulation. It is also recommended to analyse regions of high residuals in the domain to ensure that they are far away from the surface(s) of interest. Investigations regarding different stabilization schemes as well different meshes for the adjoint solver were performed.

    It was concluded that the residual minimization scheme (RMS) is the preferred stabilization scheme. It was found that a coarser mesh can be used to reduce localized transient behaviour if the adjoint solver has trouble converging. It was found that a simplified model of a fully detailed car geometry is necessary to reduce the complexity and the resolution of the mesh to be able to use the RMS and to avoid local instabilities. A proposed CFD and adjoint procedure with guidelines and recommendation was developed.

    Download full text (pdf)
    fulltext
  • 225.
    Lönning, Jonathan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Experimental Investigation of Fuel Mixing Concepts for 3rd Generation DLE Burners: Evaluation Through Water Rig and Atmospheric Combustion Rig Measurements2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    New Siemens burner concepts thought to produce a more homogeneous air/fuel mix-ture and a better distribution of the fuel over the burner cross section have been evaluated. A homogeneous air/fuel mixture is known to produce the lowest levels of emitted oxides of nitrogen (NOx) which is a main objective for Siemens Industrial Turbomachinery AB (SIT). It is desired that a burner concept can be found which further reduces the amount of emitted NOx but at the same time maintains a moderate pressure drop.

    A water rig was used in in order to evaluate the mixing performance of the new concepts. A video camera, a laser and a fluorescent substance, simulating fuel, was used to record movies of the burner mixing tube cross section. The movies were post processed in Matlab using in-house scripts where intensity and RMSD fields were obtained. These fields were used to compare the fuel mixing ability of totally 21 new burner concepts to the burner concept currently applied in the SGT-800.

    The water rig experiments have shown that a more homogeneous air/fuel mixture, compared to the reference burner, is possible to achieve with 11 out of the 21 tested concepts. The water rig has shown a repeatability within 5%.

    The water rig results obtained from a test with the reference burner were also compared to CFD simulation results. The water rig showed good agreement to the CFD simulation when comparing the trends of the fuel mixing ability.

    Two of the newly developed concepts were also tested in the Atmospheric Combustion Rig (ACR) at SIT to evaluate the pressure drop and emitted NOx in atmospheric conditions. One of these concepts showed a deterioration of the fuel mixing performance based on the water rig experiments while the other showed an improvement. The expectations of these concepts in terms of emitted NOx were therefore a significant deterioration and improvement, respectively. The results showed that both concepts performed quite similar with a moderate reduction of emitted NOx. The unexpected results have been derived to the pressure dependence of NOx, burner to burner differences from manufacturing and the small amount of available measurement points. The measured pressure drop over the burners reached unacceptable levels and the design of the new concepts therefore needs further improvements.

    Download full text (pdf)
    Jonathan_Lönning_master_thesis_2016
  • 226.
    Maleki, Shohreh
    et al.
    Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska Institute, Sweden.
    Björck, Hanna M.
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences.
    Folkersen, Lasse
    Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska Institute, Sweden.
    Nilsson, R.
    Computational Medicine, Karolinska Institutet, Stockholm.
    Renner, Johan
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Caidahl, K.
    Clinical Physiology, Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
    Franco‐Cereceda, A.
    7Cardiothoracic Surgery Unit, Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
    Länne, Toste
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Thoracic and Vascular Surgery.
    Eriksson, Per
    Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska Institute, Sweden.
    Identification of a novel flow-mediated gene expression signature in patients with bicuspid aortic valve2013In: Journal of Molecular Medicine, ISSN 0946-2716, E-ISSN 1432-1440, Vol. 91, no 1, p. 129-139Article in journal (Refereed)
    Abstract [en]

    Rationale: Individuals with bicuspid aortic valve (BAV) are at significantly higher risk of developing serious aortic complications including aortic aneurysm and dissection than individuals with a tricuspid aortic valve (TAV). Studies have indicated an altered aortic blood flow in patients with BAV, however the extent to which altered flow may influence the pathological state of BAV aorta is still unclear.

    Objective: To dissect flow-mediated gene expression potentially leading to increased aneurysm susceptibility in patients with BAV.

    Methods and Results: A large collection of publically available microarray data sets were screened for consistent co-expression with KLF2, KLF4, TIE1, THBD, and PKD2, five previously well-characterized flow-regulated genes. This identified 122 genes with coexpression probability of >0.5. Of these, 44 genes satisfied two additional filtering criteria in ascending aorta (127 arrays). The criteria were significant correlation with one or more of the 5 query genes (R>0.40) and differential expression between patients with BAV and TAV. No gene fulfilled the criteria in mammary artery (88 arrays). A large proportion of the identified genes were angiogenesis related genes. Further, 55% of the genes differentially expressed between BAV and TAV showed differential expression in disturbed vs. uniform flow pattern regions in rat aorta. Protein expression of ZFP36, PKD2 and GPR116 were analyzed by immunohistochemistry and their association with BAV were further discussed.

    Conclusions: With a new strategy to dissect flow-mediated gene expression, we identified novel genes associated with valve morphology. The complex pattern of blood flow, as a consequence of BAV

  • 227.
    Marashi, Seyedeh Sepideh
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Network Modeling Application to Laminar Flame Speed and NOx Prediction in Industrial Gas Turbines2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The arising environmental concerns make emission reduction from combustion devices one of the greatest challenges of the century. Modern dry low-NOx emission combustion systems often operate under lean premixed turbulent conditions. In order to design and operate these systems efficiently, it is necessary to have a thorough understanding of combustion process in these devices.

    In premixed combustion, flame speed determines the conversion rate of fuel. The flame speed under highly turbulent conditions is defined as turbulent flame speed. Turbulent flame speed depends on laminar flame speed, which is a property of the combustible mixture.

    The goal of this thesis is to estimate laminar flame speed and NOx emissions under certain conditions for specific industrial gas turbines. For this purpose, an in-house one-dimensional code, GENE-AC, is used.

    At first, a data validation is performed in order to select an optimized chemical reaction mechanism which can be used safely with the fuels of interest in gas turbines. Results show that GRI-Mech 3.0 performs well in most cases. This mechanism is selected for further simulations.

    Secondly, laminar flame speed is calculated using GRI-Mech 3.0 at SGT-800 conditions. Results show that at gas turbine conditions, increasing ambient temperature and fuel to air ratio enhances flame speed, mainly due to faster reaction rates. Moreover, laminar flame speed is highly affected by fuel composition. In particular, adding hydrogen to a fuel changes chemical processes significantly, because hydrogen is relatively light and highly diffusive. Calculations are conducted over a range of equivalence ratios and hydrogen fractions in methane at atmospheric as well as gas turbine operating conditions. Results reveal some trends for changes in laminar flame speed, depending on hydrogen content in the mixture.

    The final part of the thesis involves the development of a reactor network model for the SGT-700 combustor in order to predict NOx emissions. The network model is built in GENE-AC based on results from available computational fluid dynamics (CFD) simulations of the combustor. The model is developed for full load conditions with variable pilot fuel ratios. The NOx emissions are predicted using GRI-Mech 3.0 mechanism. A parametric study shows the dependency of NOx emissions on equivalence ratio and residence time. For SGT-700 running on natural gas, NOx emissions are fitted to measurement data by tuning equivalence ratio and residence time. The model is then tested for a range of ambient temperatures and fuel compositions. It is found that, although the model can correctly predict the trends of ambient temperature and fuel effects on NOx emissions, these effects are to some extent over-estimated. Using future engine tests and amending calibration can improve the results.

    Download full text (pdf)
    Marashi-Thesis-2013-NetworkModeling
  • 228.
    Markl, Michael
    et al.
    University Hospital Freiburg.
    Kilner, Philip J
    Royal Brompton .
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Comprehensive 4D velocity mapping of the heart and great vessels by cardiovascular magnetic resonance2011In: JOURNAL OF CARDIOVASCULAR MAGNETIC RESONANCE, ISSN 1097-6647, Vol. 13, no 7Article, review/survey (Refereed)
    Abstract [en]

    Background: Phase contrast cardiovascular magnetic resonance (CMR) is able to measure all three directional components of the velocities of blood flow relative to the three spatial dimensions and the time course of the heart cycle. In this article, methods used for the acquisition, visualization, and quantification of such datasets are reviewed and illustrated. Methods: Currently, the acquisition of 3D cine (4D) phase contrast velocity data, synchronized relative to both cardiac and respiratory movements takes about ten minutes or more, even when using parallel imaging and optimized pulse sequence design. The large resulting datasets need appropriate post processing for the visualization of multidirectional flow, for example as vector fields, pathlines or streamlines, or for retrospective volumetric quantification. Applications: Multidirectional velocity acquisitions have provided 3D visualization of large scale flow features of the healthy heart and great vessels, and have shown altered patterns of flow in abnormal chambers and vessels. Clinically relevant examples include retrograde streams in atheromatous descending aortas as potential thromboembolic pathways in patients with cryptogenic stroke and marked variations of flow visualized in common aortic pathologies. Compared to standard clinical tools, 4D velocity mapping offers the potential for retrospective quantification of flow and other hemodynamic parameters. Conclusions: Multidirectional, 3D cine velocity acquisitions are contributing to the understanding of normal and pathologically altered blood flow features. Although more rapid and user-friendly strategies for acquisition and analysis may be needed before 4D velocity acquisitions come to be adopted in routine clinical CMR, their capacity to measure multidirectional flows throughout a study volume has contributed novel insights into cardiovascular fluid dynamics in health and disease.

    Download full text (pdf)
    FULLTEXT01
  • 229.
    Martinez, Luis Iñaki
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Investigation of CFD conjugate heat transfer simulation methods for engine components at SCANIA CV AB2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The main objective of this Master Thesis project is the development of a new methodology to perform Computational Fluid Dynamics (CFD) conjugate heat transfer simulations for internal combustion engines, at the Fluid and Combustion Simulations Department (NMGD) at Scania CV AB, Södertalje, Sweden. This new method allows to overcome the drawbacks identified in the former methodology, providing the ability to use the more advanced polyhedral mesh type to generate good quality grids in complex geometries like water cooling jackets, and integrating all the different components of the engine cylinder in one unique multi-material mesh. In the method developed, these advantages can be used while optimizing the process to perform the simulations, and obtaining improved accuracy in the temperature field of engine components surrounding the water cooling jacket when compared to the experimental data from Scania CV AB tests rigs.

    The present work exposes the limitations encountered within the former methodology and presents a theoretical background to explain the physics involved, describing the computational tools and procedures to solve these complex fluid and thermal problems in a practical and cost-effective way, by the use of CFD.A mesh sensitivity analysis performed during this study reveals that a mesh with low y+ values, close to 1 in the water cooling jacket, is needed to obtain an accurate temperature distribution along the cylinder head, as well as to accurately identify boiling regions in the coolant domain.

    Another advantage of the proposed methodology is that it provides new capabilities like the implementation of thermal contact resistance in periodical contact regions of the engine components, improving the accuracy of the results in terms of temperature profiles of parts like valves, seats and guides.

    The results from this project are satisfactory, providing a reliable new methodology for multi-material thermal simulations, improving the efficiency of the work to be performed in the NMGD department, with a better use of the available engineering and computational resources, simplifying all the stages of multi-material projects, from the geometry preparation and meshing, to the post-processing tasks.

    Download full text (pdf)
    fulltext
  • 230.
    Modin, Daniel
    et al.
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, The Institute of Technology.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Länne, Toste
    Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Thoracic and Vascular Surgery.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, The Institute of Technology.
    Evaluation of Aortic Geometries created by MRI Data in Man2011In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 31, no 6, p. 485-491Article in journal (Refereed)
    Abstract [en]

    The development of atherosclerotic plaques has been associated with the patterns of wall shear stress (WSS). However, much is still uncertain with the methods used to calculate WSS. Correct vessel geometries are mandatory to get reliable estimations and the purpose of this study was to evaluate an in vivo method for creating aortic 3D geometry in man based on data from magnetic resonance imaging (MRI) with ultrasound as reference.

    Methods: The aortas of ten healthy males, 23.4 ± 1.6 years of age, were examined with MRI, and 3D geometries were created with manual segmentation of the images. Lumen diameters (LD) were measured in the abdominal aorta (AA) and the thoracic aorta (TA) with non-invasive B-mode ultrasound as a reference.

    Results: The anteroposterior diameter of the AA was 13.6 ± 1.1 mm for the MRI and 13.8 ± 1.3 mm for the ultrasound (NS). Intraobserver variability (CV) for MRI and ultrasound was <0.92% and <0.40% respectively . Interobserver variability MRI and ultrasound was 0.96% and 0.56% respectively. The diameter of the TA was 19.2 ± 1.4 mm for the MRI, and the intraobserver variability (CV) were <0.78% and interobserver variability (CV) were 0.92%.

    Conclusion: Specific arterial geometries can be constructed with a high degree of accuracy using MRI. This indicate that the MRI geometries may be used to create realistic and correct geometries in the calculation of WSS in the aorta of man.

    Download full text (pdf)
    fulltext
  • 231.
    Munjulury, Raghu Chaitanya
    et al.
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Nadali Najafabadi, Hossein
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Safavi, Edris
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Ölvander, Johan
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Petter, Krus
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    A comprehensive computational multidisciplinary design optimization approach for a tidal power plant turbine2017In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 9, no 3, p. 1-13, article id 1687814017695174Article in journal (Refereed)
    Abstract [en]

    Multidisciplinary design optimization has become a powerful technique to facilitate continuous improvement of complex and multidisciplinary products. Parametric modeling is an essential part with tremendous impact on the flexibility and robustness of multidisciplinary design optimization. This article investigates the effect of relational and non-relational parameterization techniques on the robustness and flexibility of the conceptual design of a multidisciplinary product. Bench marking between relational and non-relational parameterization and their effect on flexibility and robustness indicate that the relational parameterization is an efficient method in the multidisciplinary design optimization process. The inherent properties of the method contribute to an efficient parametric modeling with improved communication between different disciplines. This enhances the performance of the multidisciplinary design optimization process and allows a more flexible and robust design. The considered disciplines are computer-aided design, computational fluid dynamics, finite element analysis, and dynamic simulation. A high-fidelity geometry created in a computer-aided design environment is computer-aided design centric approach and later used in computational fluid dynamics, finite element analysis for a better understanding of the product as it leads to precise outcomes. The proposed approach is implemented for the conceptual design of a novel product, a tidal power plant developed by Minesto AB using a multidisciplinary design optimization process.

    Download full text (pdf)
    fulltext
  • 232.
    Mårtensson, Jonathan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics .
    Method development for investigation of real effects on flow around vanes2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the development of turbo machinery components it's desirable to not spend more time than necessary when setting up aero-thermal calculations to investigate uncertainties in the design. This report aims to describe general thoughts used in the development of an ICEM-mesh script and the possible configurations in the script file which enables the user to build mesh-grids with/without clearance gap at the hub and/or shroud for different blade geometries. It also aims to illustrate the performance analysis made on the Vinci LH2 turbine, a next generation upper stage engine to the Ariane 5 rocket, in which the effect of the tip gap size on the efficiency has been studied.

    The calculations made have shown good agreement with experimental data. The efficiency loss due to the mixing of fluid where leakage flow passes the tip gap, which results in growth of a strong vortex, and the fluid passing the blade tip, with almost no work extracted from it, has shown a quite linear efficiency dependence depending on the tip gap size.

    Download full text (pdf)
    FULLTEXT01
  • 233. Order onlineBuy this publication >>
    Nadali Najafabadi, Hossein
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    On Film Cooling of Turbine Guide Vanes: From Experiments and CFD-Simulations to Correlation Development2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    To achieve high thermal efficiency in modern gas turbines, the turbine-inlet temperature has to be increased. In response to such requisites and to prevent thermal failure of the components exposed to hot gas streams, the use of different cooling techniques, including film cooling, is essential. Finding an optimum film cooling design has become a challenge as it is influenced by a large number of flow and geometrical parameters. This study is dedicated to some important aspects of film cooling of a turbine guide vane and consists of three parts.

    The first part is associated with an experimental investigation of the suction and pressure side cooling by means of a transient IR-Thermography technique under engine representative conditions. It is shown that the overall film cooling performance of the suction side can be improved by adding showerhead cooling if fan-shaped holes are used, while cylindrical holes may not necessarily benefit from a showerhead. According to the findings, investigation of an optimum cooling design for the suction side is not only a function of hole shape, blowing ratio, state of approaching flow, etc., but is also highly dependent on the presence/absence of showerhead cooling as well as the number of cooling rows. In this regard, it is also discussed that the combined effect of the adiabatic film effectiveness (AFE) and the heat transfer coefficient (HTC) should be considered in such study. As for the pressure side cooling, it is found that either the showerhead or a single row of cylindrical cooling holes can enhance the HTC substantially, whereas a combination of the two or using fan-shaped holes indicates considerably lower HTC. An important conclusion is that adding more than one cooling row will not augment the HTC and will even decrease it under certain circumstances.

    In the second part, computational fluid dynamics (CFD) investigations have shown that film cooling holes subjected to higher flow acceleration will maintain a higher level of AFE. Although this was found to be valid for both suction and pressure side, due to an overall lower acceleration for the pressure side, a lower AFE was achieved. Moreover, the CFD results indicate that fan-shaped holes with low area ratio (dictated by design constraints for medium-size gas turbines), suffer from cooling jet separation and hence reduction in AFE for blowing ratios above unity. Verification of these conclusions by experiments suggests that CFD can be used more extensively, e.g. for parametric studies.

    The last part deals with method development for deriving correlations based on experimental data to support engineers in the design stage. The proposed method and the ultimate correlation model could successfully correlate the laterally averaged AFE to the downstream distance, the blowing ratio and the local pressure coefficient representing the effect of approaching flow. The applicability of the method has been examined and the high level of predictability of the final model demonstrates its suitability to be used for design purposes in the future.

    List of papers
    1. Film Cooling Performance of a Turbine Vane Suction Side: The Showerhead Effect on Film Cooling Hole Placement for Cylindrical and Fan-Shaped Holes
    Open this publication in new window or tab >>Film Cooling Performance of a Turbine Vane Suction Side: The Showerhead Effect on Film Cooling Hole Placement for Cylindrical and Fan-Shaped Holes
    2015 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 137, no 9, article id 091005Article in journal (Refereed) Published
    Abstract [en]

    In this paper, the transient IR-thermography method is used to investigate the effect of showerhead cooling on the film-cooling performance of the suction side of a turbine guide vane working under engine-representative conditions. The resulting adiabatic film effectiveness, heat transfer coefficient (HTC) augmentation, and net heat flux reduction (NHFR) due to insertion of rows of cooling holes at two different locations in the presence and absence of the showerhead cooling are presented. One row of cooling holes is located in the relatively high convex surface curvature region, while the other is situated closer to the maximum throat velocity. In the latter case, a double staggered row of fan-shaped cooling holes has been considered for cross-comparison with the single row at the same position. Both cylindrical and fan-shaped holes have been examined, where the characteristics of fan-shaped holes are based on design constraints for medium size gas turbines. The blowing rates tested are 0.6, 0.9, and 1.2 for single and double cooling rows, whereas the showerhead blowing is maintained at constant nominal blowing rate. The adiabatic film effectiveness results indicate that most noticable effects from the showerhead can be seen for the cooling row located on the higher convex surface curvature. This observation holds for both cylindrical and fan-shaped holes. These findings suggest that while the showerhead blowing does not have much impact on this cooling row from HTC enhancement perspective, it is influential in determination of the HTC augmentation for the cooling row close to the maximum throat velocity. The double-row fan-shaped cooling seems to be less affected by an upstream showerhead blowing when considering HTC enhancement, but it makes a major contribution in defining adiabatic film effectiveness. The NHFR results highlight the fact that cylindrical holes are not significantly affected by the showerhead cooling regardless of their position, but showerhead blowing can play an important role in determining the overall film-cooling performance of fan-shaped holes (for both the cooling row located on the higher convex surface curvature and the cooling row close to the maximum throat velocity), for both the single and the double row cases.

    Place, publisher, year, edition, pages
    ASME Press, 2015
    Keywords
    Film cooling, Showerhead cooling, Cylindrical holes, Fan-shaped holes, Gas Turbine
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-116936 (URN)10.1115/1.4029966 (DOI)000377794200005 ()
    Projects
    Turbo Power Program
    Note

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Sweden AB; Royal Institute of Technology through the Swedish research program TURBO POWER

    Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2017-12-04Bibliographically approved
    2. Film Cooling Performance of Multiple Arrays of Cylindrical and Fan-Shaped Holes
    Open this publication in new window or tab >>Film Cooling Performance of Multiple Arrays of Cylindrical and Fan-Shaped Holes
    Show others...
    2015 (English)In: Journal of Propulsion and Power, ISSN 0748-4658, E-ISSN 1533-3876, Vol. 31, no 6, p. 1621-1630Article in journal (Refereed) Published
    Abstract [en]

    Experimental investigations are performed on the suction side of a cooled turbineguide vane. Transient IR thermography is used to evaluate film cooling performanceof cylindrical and fan-shaped holes in a test facility representing engine conditions.Adiabatic film effectiveness (AFE) and net heat flux reduction (NHFR) results due tocoolant injection through double and multiple rows in the presence and absence of anupstream showerhead are presented. Two double staggered rows at different positionshave been cross-compared; one at a relatively high convex curvature region and theother close to the maximum throat velocity. A combination of the two double rowsis considered to be multiple rows. The tested blowing ratios are in the interval of[0.6 – 1.2] and [0.3 – 1.2] for double and multiple rows, respectively. The showerheadcooling is maintained at nominal blowing ratio. The findings suggest that the choice ofbest cooling hole shape for film cooling design can be highly influenced by the numberof cooling rows to be used and also the presence (or absence) of showerhead cooling.It is worth noting that the outcome may differ depending on the quantity of interest, i.e. AFE or NHFR.

    Place, publisher, year, edition, pages
    American Institute of Aeronautics and Astronautics, 2015
    Keywords
    Film Cooling, Gas Turbine, Film Effectiveness, Net Heat Flux Reduction, Cylindrical Holes, Fan-shaped Holes
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-117030 (URN)10.2514/1.B35618 (DOI)000368248000011 ()
    Projects
    Turbo Power Program
    Note

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery, AB; GKN Aerospace Sweden, AB; Royal Institute of Technology through the Swedish research program TURBO POWER

    Vid tiden för disputationen förelåg publikationen endast som manuskript

    Available from: 2015-04-11 Created: 2015-04-11 Last updated: 2019-11-11Bibliographically approved
    3. Film Cooling Jet Injection Effect in Heat Transfer Coefficient Augmentation for the Pressure Side Cooling of Turbine Vane
    Open this publication in new window or tab >>Film Cooling Jet Injection Effect in Heat Transfer Coefficient Augmentation for the Pressure Side Cooling of Turbine Vane
    2014 (English)In: ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, American Society of Mechanical Engineers , 2014, Vol. 5B, p. Paper No. GT2014-26055-Conference paper, Published paper (Refereed)
    Abstract [en]

    Improving film cooling performance of turbine vanes and blades is often achieved through application of multiple arrays of cooling holes on the suction side, the showerhead region and the pressure side. This study investigates the pressure side cooling under the influence of single and multiple rows of cooling in the presence of a showerhead from a heat transfer coefficient augmentation perspective. Experiments are conducted on a prototype turbine vane working at engine representative conditions. Transient IR thermography is used to measure time-resolved surface temperature and the semi-infinite method is utilized to calculate the heat transfer coefficient on a low conductive material. Investigations are performed for cylindrical and fan-shaped holes covering blowing ratio 0.6 and 1.8 at density ratio of about unity. The freestream turbulence is approximately 5% close to the leading edge.

    The resulting heat transfer coefficient enhancement, the ratio of HTC with to that without film cooling, from different case scenarios have been compared to showerhead cooling only. Findings of the study highlight the importance of showerhead cooling to be used with additional row of cooling on the pressure side in order to reduce heat transfer coefficient enhancement. In addition, it is shown that extra rows of cooling will not significantly influence heat transfer augmentation, regardless of the cooling hole shape.

    Place, publisher, year, edition, pages
    American Society of Mechanical Engineers, 2014
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-111022 (URN)10.1115/GT2014-26055 (DOI)000362139100038 ()978-0-7918-4572-1 (ISBN)
    Conference
    ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Düsseldorf, Germany, June 16–20, 2014
    Available from: 2014-10-03 Created: 2014-10-03 Last updated: 2019-11-11Bibliographically approved
    4. CFD Based Sensitivity Analysis of Influencing Flow Parameters for Cylindrical and Shaped Holes in a Gas Turbine Vane
    Open this publication in new window or tab >>CFD Based Sensitivity Analysis of Influencing Flow Parameters for Cylindrical and Shaped Holes in a Gas Turbine Vane
    2012 (English)In: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, Volume 4: Heat Transfer, Parts A and B Copenhagen, Denmark, June 11–15, 2012, ASME Press, 2012, Vol. 4, p. 1501-1509Conference paper, Published paper (Refereed)
    Abstract [en]

    In this study a CFD based sensitivity analysis is performedincluding the flow parameter blowing ratio, the geometrical parametercooling hole shape and the effect of approaching flow(hole position), investigating the film cooling performance of areal vane configuration working at engine like conditions. Forthis purpose numerical results from the commercial CFD codeFLUENT using the Spalart-Allmaras turbulence model has beenvalidated versus experimental results on the same vane includingthe film cooling hole configurations. Blowing ratios ranging from(0.2-1.8) have been considered. In addition, film cooling performanceof rows of cooling holes at six different positions locatedaround the suction and pressure side of the vane are investigatedfor studying the influence of flow acceleration present in turbinevanes. These flow parameters are investigated for both cylindricaland fan-shaped holes. Investigations are performed at afixed unity density ratio. It has been found that for fan-shapedholes film cooling performance is higher for cooling holes locatedat positions whit a high accelerated flow. On the otherhand, film cooling performance of cylindrical holes are found tobe affected less by acceleration. Due to the low velocity and lowacceleration on the pressure side the hole position seems to haverelatively low influence on the cooling performance.

    Place, publisher, year, edition, pages
    ASME Press, 2012
    Keywords
    Computational Fluid Dynamics, Film Cooling, Fan-shaped Holes, Cylindrical Holes
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-116938 (URN)10.1115/GT2012-69023 (DOI)978-0-7918-4470-0 (ISBN)
    Conference
    ASME Turbo Expo 2012, June 11-12, Copenhagen, Denmark
    Projects
    Turbo Power Program
    Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2016-03-14Bibliographically approved
    5. Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient
    Open this publication in new window or tab >>Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient
    2012 (English)In: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, Volume 4: Heat Transfer, Parts A and B, Copenhagen, Denmark, June 11–15, 2012, ASME Press, 2012, Vol. 4, p. 1491-1500Conference paper, Published paper (Refereed)
    Abstract [en]

    Most of the proposed correlations for prediction of gas turbinefilm cooling performance in the open literature rely on experimentsconducted on flat plates. These correlations neglectadverse pressure gradient effects present in the flow field for airfoillike configurations. The continuous change in flow characteristicsin the main flow field from leading edge to trailingedge that will affect the film cooling performance is also neglected.In this study correlations are derived from measurementsconducted on a gas turbine vane working at engine likeconditions. This will take into account the effect of hole positionand the local flow situation. Indeed, cooling holes locatedat three (five) different positions with blowing ratio ranges from0.3-2.5 (0.9-6) have been considered along the suction (pressure)sides. The non-dimensional pressure coefficient CP, at the exitlocation of each hole has been introduced as a new variable toderive a single correlation for either suction or pressure sides.Three main variables: downstream distance, blowing ratio, andlocal CP together with the two way interaction between thesevariables are introduced into a commercial statistical analysisprogram, Minitab. Stepwise regression analysis has been performedto highlight factors with greatest influence on the correlationmodel. Appropriateness of the derived model is measuredbased on the adjusted coefficient of determination, R2ad j. Correlationsare derived for eight different configurations: for suctionand pressure sides, cylindrical and fan-shaped holes and in thepresence and absence of showerhead cooling. Despite the complexity of the flow due to high blowing ratio (existence of lift off)and also variation of film cooling performance from one positionto another, the calculated R2adj values indicate a high predictabilityof the proposed correlation model. The suggested correlationmodel can be useful for optimizing the location of one or severalrows of cooling holes around the vane and also one single rowperformance.

    Place, publisher, year, edition, pages
    ASME Press, 2012
    Keywords
    Film Cooling, Gas Turbine, Film effectiveness, Correlation, Fan-shaped Holes, Cylindrical Holes
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-116987 (URN)10.1115/GT2012-69021 (DOI)000335868900132 ()978-0-7918-4470-0 (ISBN)
    Conference
    ASME Turbo Expo 2012, June 11–15, Copenhagen, Denmark
    Projects
    Turbo Power Program
    Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2017-03-07Bibliographically approved
    Download full text (pdf)
    fulltext
    Download (pdf)
    omslag
    Download (jpg)
    presentationsbild
  • 234.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Andersson, Magnus
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Assessment in a Learning-Centered Course Design Framework2016In: Proceedings of the International CDIO Conference, 2016, p. 791-800, article id 161Conference paper (Refereed)
    Abstract [en]

    It is important for course designers to establish assessments in accordance to intended learning outcomes and course activities in order to promote deep learning in higher education. In this context a learning-centered course design (LCCD) framework could be utilized to interconnect the assessments towards the high level learning objectives and learning activities. The primary objective of this paper is to highlight the effectiveness of using such a framework with the emphasis on assessment component for developing a new course, Fluid Mechanics, at Linköping University, Sweden. This study indicated an implementation of the LCCD framework, which facilitate establishment of CDIO Standards 8 and 11. This has been achieved by designing an assessment method that involves active learning activities in accordance to the intended learning outcomes. The inherent property of this approach, the integration between different components of teaching, is thus the key feature in achieving the highlighted standards and contributes in enhancing the student’s knowledge, skills and attitude within the subject.

    Download full text (pdf)
    fulltext
  • 235.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Farhanieh, Arman
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Gårdhagen, Roland
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    On the Characteristics of the Jet in Film Cooling Applications2016In: PROCEEDINGS OF THE 5TH INTERNATIONAL CONFERENCE ON JETS, WAKES AND SEPARATED FLOWS (ICJWSF2015), SPRINGER INT PUBLISHING AG , 2016, Vol. 185, p. 449-455Conference paper (Refereed)
    Abstract [en]

    Numerical and experimental investigations are conducted to study the jet characteristics on the pressure side of a film-cooled turbine guide vane. CFD simulations, including both the steady RANS turbulence model, k - omega shear stress transport (SST), as well as the hybrid approach, Scale-Adaptive Simulation (SAS), are utilized to comprehend the turbulent flow structures and the vortex dynamics associated to the film cooling jet. For this purpose the commercial CFD code FLUENT has been utilized to study flow with injection of coolant through fan-shaped holes for two blowing ratios (0.6 and 1.2). Although, both turbulence models predict the vortical structures and jet dynamics similarly, the findings suggest that by resolving large energy containing vortices, the SAS model can improve the modeling of mixing properties and thereby approximation of the surface temperature.

  • 236.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Bradley, Andreas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wren, Joakim
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Kinell, Mats
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    CFD Simulations Using Reduced Models for Film Cooling Design2011In: 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2011, American Institute of Aeronautics and Astronautics, 2011, p. AiAA 2011-710-Conference paper (Other academic)
    Abstract [en]

    Film cooling technologies are widely used for attaining high efficiency in gas turbine engines. In this study we have investigated the potential for reduced models to capture different aspects of film cooling by means of CFD at low turn-around time while maintaining the accuracy at a reasonable level. CFD simulations and experiments were carried out for an engine-like setting. Subsequently, the computational domain was reduced in two steps in order to decrease the simulation time. Results for all models are compared with experimental data, including aerodynamic validation, heat transfer coefficient and film effectiveness. The aerodynamic results are very similar for experiments and simulations, and the heat transfer coefficient and film cooling effectiveness showed similarities within the expected range. Thus, this strategy could be very useful for e.g. early vane and film cooling design.

  • 237.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Kinell, Mats
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Film Cooling Jet Injection Effect in Heat Transfer Coefficient Augmentation for the Pressure Side Cooling of Turbine Vane2014In: ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, American Society of Mechanical Engineers , 2014, Vol. 5B, p. Paper No. GT2014-26055-Conference paper (Refereed)
    Abstract [en]

    Improving film cooling performance of turbine vanes and blades is often achieved through application of multiple arrays of cooling holes on the suction side, the showerhead region and the pressure side. This study investigates the pressure side cooling under the influence of single and multiple rows of cooling in the presence of a showerhead from a heat transfer coefficient augmentation perspective. Experiments are conducted on a prototype turbine vane working at engine representative conditions. Transient IR thermography is used to measure time-resolved surface temperature and the semi-infinite method is utilized to calculate the heat transfer coefficient on a low conductive material. Investigations are performed for cylindrical and fan-shaped holes covering blowing ratio 0.6 and 1.8 at density ratio of about unity. The freestream turbulence is approximately 5% close to the leading edge.

    The resulting heat transfer coefficient enhancement, the ratio of HTC with to that without film cooling, from different case scenarios have been compared to showerhead cooling only. Findings of the study highlight the importance of showerhead cooling to be used with additional row of cooling on the pressure side in order to reduce heat transfer coefficient enhancement. In addition, it is shown that extra rows of cooling will not significantly influence heat transfer augmentation, regardless of the cooling hole shape.

  • 238.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Kinell, Mats
    Siemens Industrial Turbomachinery AB.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB.
    Film Cooling Performance of a Turbine Vane Suction Side: The Showerhead Effect on Film Cooling Hole Placement for Cylindrical and Fan-Shaped Holes2015In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 137, no 9, article id 091005Article in journal (Refereed)
    Abstract [en]

    In this paper, the transient IR-thermography method is used to investigate the effect of showerhead cooling on the film-cooling performance of the suction side of a turbine guide vane working under engine-representative conditions. The resulting adiabatic film effectiveness, heat transfer coefficient (HTC) augmentation, and net heat flux reduction (NHFR) due to insertion of rows of cooling holes at two different locations in the presence and absence of the showerhead cooling are presented. One row of cooling holes is located in the relatively high convex surface curvature region, while the other is situated closer to the maximum throat velocity. In the latter case, a double staggered row of fan-shaped cooling holes has been considered for cross-comparison with the single row at the same position. Both cylindrical and fan-shaped holes have been examined, where the characteristics of fan-shaped holes are based on design constraints for medium size gas turbines. The blowing rates tested are 0.6, 0.9, and 1.2 for single and double cooling rows, whereas the showerhead blowing is maintained at constant nominal blowing rate. The adiabatic film effectiveness results indicate that most noticable effects from the showerhead can be seen for the cooling row located on the higher convex surface curvature. This observation holds for both cylindrical and fan-shaped holes. These findings suggest that while the showerhead blowing does not have much impact on this cooling row from HTC enhancement perspective, it is influential in determination of the HTC augmentation for the cooling row close to the maximum throat velocity. The double-row fan-shaped cooling seems to be less affected by an upstream showerhead blowing when considering HTC enhancement, but it makes a major contribution in defining adiabatic film effectiveness. The NHFR results highlight the fact that cylindrical holes are not significantly affected by the showerhead cooling regardless of their position, but showerhead blowing can play an important role in determining the overall film-cooling performance of fan-shaped holes (for both the cooling row located on the higher convex surface curvature and the cooling row close to the maximum throat velocity), for both the single and the double row cases.

  • 239.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Kinell, Mats
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB, Finspong, Sweden.
    Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient2012In: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, Volume 4: Heat Transfer, Parts A and B, Copenhagen, Denmark, June 11–15, 2012, ASME Press, 2012, Vol. 4, p. 1491-1500Conference paper (Refereed)
    Abstract [en]

    Most of the proposed correlations for prediction of gas turbinefilm cooling performance in the open literature rely on experimentsconducted on flat plates. These correlations neglectadverse pressure gradient effects present in the flow field for airfoillike configurations. The continuous change in flow characteristicsin the main flow field from leading edge to trailingedge that will affect the film cooling performance is also neglected.In this study correlations are derived from measurementsconducted on a gas turbine vane working at engine likeconditions. This will take into account the effect of hole positionand the local flow situation. Indeed, cooling holes locatedat three (five) different positions with blowing ratio ranges from0.3-2.5 (0.9-6) have been considered along the suction (pressure)sides. The non-dimensional pressure coefficient CP, at the exitlocation of each hole has been introduced as a new variable toderive a single correlation for either suction or pressure sides.Three main variables: downstream distance, blowing ratio, andlocal CP together with the two way interaction between thesevariables are introduced into a commercial statistical analysisprogram, Minitab. Stepwise regression analysis has been performedto highlight factors with greatest influence on the correlationmodel. Appropriateness of the derived model is measuredbased on the adjusted coefficient of determination, R2ad j. Correlationsare derived for eight different configurations: for suctionand pressure sides, cylindrical and fan-shaped holes and in thepresence and absence of showerhead cooling. Despite the complexity of the flow due to high blowing ratio (existence of lift off)and also variation of film cooling performance from one positionto another, the calculated R2adj values indicate a high predictabilityof the proposed correlation model. The suggested correlationmodel can be useful for optimizing the location of one or severalrows of cooling holes around the vane and also one single rowperformance.

  • 240.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB.
    Kinell, Mats
    Siemens Industrial Turbomachinery AB.
    CFD Based Sensitivity Analysis of Influencing Flow Parameters for Cylindrical and Shaped Holes in a Gas Turbine Vane2012In: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, Volume 4: Heat Transfer, Parts A and B Copenhagen, Denmark, June 11–15, 2012, ASME Press, 2012, Vol. 4, p. 1501-1509Conference paper (Refereed)
    Abstract [en]

    In this study a CFD based sensitivity analysis is performedincluding the flow parameter blowing ratio, the geometrical parametercooling hole shape and the effect of approaching flow(hole position), investigating the film cooling performance of areal vane configuration working at engine like conditions. Forthis purpose numerical results from the commercial CFD codeFLUENT using the Spalart-Allmaras turbulence model has beenvalidated versus experimental results on the same vane includingthe film cooling hole configurations. Blowing ratios ranging from(0.2-1.8) have been considered. In addition, film cooling performanceof rows of cooling holes at six different positions locatedaround the suction and pressure side of the vane are investigatedfor studying the influence of flow acceleration present in turbinevanes. These flow parameters are investigated for both cylindricaland fan-shaped holes. Investigations are performed at afixed unity density ratio. It has been found that for fan-shapedholes film cooling performance is higher for cooling holes locatedat positions whit a high accelerated flow. On the otherhand, film cooling performance of cylindrical holes are found tobe affected less by acceleration. Due to the low velocity and lowacceleration on the pressure side the hole position seems to haverelatively low influence on the cooling performance.

  • 241.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Utriainen, Esa
    Kinell, Mats
    Multi-variable Correlation for Cylindrical Holes at Suction and Pressure sides of A Turbine Vane2012Conference paper (Other academic)
    Abstract [en]

    Reliable correlations for predicting film cooling performance is one of the major considerations in the cooling analysis of today's gas turbine engines. In this study correlations have been derived for cylindrical holes positioned at three different positions on both the suction and pressure sides of a vane configuration at engine like settings. The blowing ratio ranges between 0.3-2.2 for the suction side and 0.9-6.55 for the pressure side. The density ratio is one. The correlation model derived here is inspired from Bunker with modifications in definition of the variables and adding extra terms. The extra terms obtained from the main variables are introduced into a stepwise regression method (statistical analysis) to find predictors with the highest contribution percentage. These variables are then utilized in the correlation for increasing model predictability. The proposed correlation is compared with existing correlations in terms of adjusted coefficient of determination R2 adj , where significant improvement is obtained. The applicability of the model to shaped holes is also discussed. Copyright © 2012 American Institute of Aeronautics and Astronautics, Inc.

  • 242.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Utriainen, Esa
    Kinell, Mats
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    A Modified Correlation for Film Effectiveness Prediction of Cylindrical Holes at the Suction Side of A turbine Guide Vane2011In: Proceedings of the 6th Baltic Heat Transfer Conference, Tampere Convention Bureau , 2011Conference paper (Other academic)
  • 243.
    Nadali Najafabadi, Hossein
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Utriainen, Esa
    Siemens Industrial Turbomachinery AB, Sweden.
    Kinell, Mats
    Siemens Industrial Turbomachinery AB, Sweden.
    Wang, Lieke
    Siemens Industrial Turbomachinery AB, Sweden.
    Film Cooling Performance of Multiple Arrays of Cylindrical and Fan-Shaped Holes2015In: Journal of Propulsion and Power, ISSN 0748-4658, E-ISSN 1533-3876, Vol. 31, no 6, p. 1621-1630Article in journal (Refereed)
    Abstract [en]

    Experimental investigations are performed on the suction side of a cooled turbineguide vane. Transient IR thermography is used to evaluate film cooling performanceof cylindrical and fan-shaped holes in a test facility representing engine conditions.Adiabatic film effectiveness (AFE) and net heat flux reduction (NHFR) results due tocoolant injection through double and multiple rows in the presence and absence of anupstream showerhead are presented. Two double staggered rows at different positionshave been cross-compared; one at a relatively high convex curvature region and theother close to the maximum throat velocity. A combination of the two double rowsis considered to be multiple rows. The tested blowing ratios are in the interval of[0.6 – 1.2] and [0.3 – 1.2] for double and multiple rows, respectively. The showerheadcooling is maintained at nominal blowing ratio. The findings suggest that the choice ofbest cooling hole shape for film cooling design can be highly influenced by the numberof cooling rows to be used and also the presence (or absence) of showerhead cooling.It is worth noting that the outcome may differ depending on the quantity of interest, i.e. AFE or NHFR.

  • 244.
    Nadalina Jafabadi, Hossein
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics .
    Investigation of Film Cooling Strategies CFD versus Experiments -Potential for Using Reduced Models2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The ability and efficiency of today’s gas turbine engines are highly dependent on development of cooling technologies, among which film cooling is one of the most important. Investigations have been conducted towards discovering different aspects of film cooling, utilizing both experiments and performing CFD simulations. Although, investigation by using CFD analysis is less expensive in general, the results obtained from CFD calculations should be validated by means of experimental results. In addition to validation, in cases like simulating a turbine vane, performing CFD simulations can be time consuming. Therefore, it is essential to find approaches that can reduce the computational cost while results are validated by experiments.

    This study has shown the potential for reduced models to be utilized for investigation of different aspects of film cooling by means of CFD at low turn-around time. This has been accomplished by first carrying out CFD simulations and experiments for an engine-like setting for a full vane. Then the computational domain is reduced in two steps where all results are compared with experiments including aerodynamic validation, heat transfer coefficient and film effectiveness. While the aerodynamic results are in close agreement with experiments, the heat transfer coefficient and film effectiveness results have also shown similarities within the expected range.

    Thus this study has shown that this approach can be very useful for e.g. early vane and film cooling design.

    Download full text (pdf)
    FULLTEXT01
  • 245.
    Naronikar, Aditya
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Riström, Anton
    Luleå University of Technology, Luleå.
    CFD and Experimental Study of Refuelling and Venting a Fuel System2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In 1999, California Air Resources Board (CARB) implemented a regulation that required all gasoline cars sold in California be fitted with an Onboard Refueling Vapor Recovery System (ORVR). The ORVR system is designed to prevent Volatile Organic Compounds (VOCs) from escaping into the atmosphere during refuelling by storing the gas vapours in a carbon canister. Due to the complex nature of the fuel system, making design changes could have large implications on the ORVR performance of the vehicle. It is therefore desirable to develop a CFD model that can predict the effects of design changes, thereby reducing the need to perform physical tests on each design iteration. This master thesis project was performed at the Fuel Systems department at Volvo Cars in order to help reduce project lead times and product development costs by incorporating CFD as a part of the fuel system development cycle. The CFD results obtained were validated through experimental tests that were also performed as part of this project.

    In this master thesis project, a CFD model was developed to simulate the refuelling of gasoline for a California specification Volvo XC90 with an OPW-11B pump pistol. The model was set up in STAR-CCM+ using the Eulerian Volume of Fluid model for multiphase flow, the RANS realizable k-epsilon turbulence model and the two layer all y+ wall treatment. The effects of the carbon canister were modelled as a porous baffle interface in the simulations where viscous and inertial resistances of the porous media were adjusted to obtain a desired pressure drop across the canister. This method proved to be a suitable simplification for this study. The effects of evaporation as well as a chemical adsorption model for the carbon canister have been excluded from the project due to time limitations.

    It was found that the CFD simulations were in good agreement with the experimental results, especially with respect to capturing the overall behaviour of the fuel system during refuelling. It was found that resolving the flow spatially (and temporally) in the filler pipe was a crucial part in ensuring solver stability. A pressure difference between experiment and simulation was also observed as a consequence of excluding evaporation from the CFD model.

    After the CFD model had been verified and validated, changes to different parts of the fuel system were investigated to observe their effects on ORVR performance. These included changing the recirculation line diameter, changing the carbon canister properties and changing the angle of how the pump pistol was inserted into the capless unit. It was found that the recirculation line diameter is a very sensitive design parameter and increasing the diameter would result in fuel vapour leaking back out into the atmosphere. Similarly, increasing the back pressure by swapping to a different carbon canister would result in the leakage of fuel vapour. On the other hand, insignificant changes in system behaviour were observed when the fuel pistol angle was changed.

    Download full text (pdf)
    fulltext
  • 246.
    Nikolov, Zhivko
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Effect of upstream turbulence on truck aerodynamics2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aerodynamic team at SCANIA has discovered the need to investigate the effect of the upstream turbulence conditions on the aerodynamics of the trucks. This need comes from the fact that there are differences between the drag coefficients obtained using computational fluid dynamics (CFD) and the on-road measurements. This difference can lead to wrong predictions of fuel consumption and emissions, which can cause incorrect evaluation of design changes. In this study the problem of modeling upstream turbulence in CFD simulations is addressed together with its effect on the aerodynamics of the trucks. To achieve this, representative values of turbulence intensity and length scale were found from the work of different researchers, who performed on-road measurements for various conditions. These values were then used in a method by Jakob Mann to generate a synthetic turbulence field. This field was then used to generate time varying velocity components, added to the mean velocity at the inlet of a CFD simulation. After the implementation of the method it was discovered that the conditions at the test section of the virtual wind tunnel were representative of the on-road measurements. The results showed drag increase and wake length decrease, similar to previous studies performed on simple geometries. It also showed that the higher mixing of the flow increases the drag by surface pressure increase of forward facing surfaces and pressure decrease at the base.

    These conclusions may be extended to other bluff body geometries and it shows the importance of good design around gaps. The comparison between two truck geometries showed that a truck with better aerodynamics in a smooth flow shows less drag increase with introduction of upstream turbulence.

    Download full text (pdf)
    fulltext
  • 247.
    Nilsson, Elias
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    One-Dimensional Human Thermoregulatory Model of Fighter Pilots in Cockpit Environments2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During flight missions, fighter pilots are in general exposed to vast amounts of stress including mild hypoxia, vibrations, high accelerations, and thermal discomfort. It is interesting to predict potential risks with a certain mission or flight case due to these stresses to increase safety for fighter pilots. The most predominant risk is typically thermal discomfort which can lead to serious health concerns. Extensive exposure to high or low temperature in combination with a demanding work situation weakens the physical and mental state of the pilot and can eventually lead to life-threatening conditions. One method to estimate the physical and mental state of a person is to measure the body core temperature. The body core temperature cannot be measured continuously during flight and needs to be estimated by using for instance a human thermoregulatory model.

    In this study, a model of the human thermoregulatory system and the cockpit environment is developed. Current thermoregulatory models are not customized for fighter pilots but a model developed by Fiala et al. in 2001, which has previously shown good performance in both cold and warm environments as well as for various activation levels for the studied person, is used as a theoretical foundation. Clothing layers are implemented in the model corresponding to clothes used by pilots in the Swedish air force flying the fighter aircraft Gripen E in warm outside conditions. Cooling garments and air conditioning systems as well as avionics, canopy, and cockpit air are included in the model to get a realistic description of the cockpit environment. Input to the model is a flight case containing data with altitude and velocity of the fighter during a mission.

    human heat transfer; body temperature regulation; physiological model;cooling garment; cockpit modeling

    Download full text (pdf)
    fulltext
  • 248.
    Omer, Muhammad
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics .
    Impingement Cooling: Heat Transfer Measurement by Liquid Crystal Thermography2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In modern gas turbines parts of combustion chamber and turbine section are under heavy heat load, for example, the rotor inlet temperature is far higher than the melting point of the rotor blade material. These high temperatures causes thermal stresses in the material, therefore it is very important to cool the components for safe operation and to achieve desired component life. But on the other hand the cooling reduces the turbine efficiency, for that reason it is vital to understand and optimize the cooling technique.

    In this project Thermochromic Liquid Crystals (TLCs) are used to measure distribution of heat transfer coefficient over a scaled up combustor liner section. TLCs change their color with the variation of temperature in a particular temperature range. The color-temperature change relation of a TLC is sharp and precise; therefore TLCs are used to measure surface temperature by painting the TLC over a test surface. This method is called Liquid Crystal Thermography (LCT). LCT is getting popular in industry due to its high-resolution results, repeatability and ease of use.

    Test model in present study consists of two plates, target plate and impingement plate. Cooling of the target plate is achieved by impingement of air coming through holes in the impingement plate. The downstream surface of the impingement plate is then cooled by cross flow and re-impingement of the coolant air.

    Heat transfer on the target plate is not uniform; areas under the jet which are called stagnation points have high heat transfer as compare to the areas away from the center of jet. It is almost the same situation for the impingement plate but the location of stagnation point is different. A transient technique is used to measure this non-uniform heat transfer distribution. It is assumed that the plates are semi-infinitely thick and there is no lateral heat transfer in the plates. To fulfill the assumptions a calculated time limit is followed and the test plates are made of Plexiglas which has very low thermal conductivity.

    The transient technique requires a step-change in the mainstream temperature of the test section. However, in practical a delayed increase in mainstream temperature is attained. This issue is dealt by applying Duhamel’s theorem on the step-change heat transfer equation. MATLAB is used to get the Hue data of the recorded video frames and calculate the time taken for each pixel to reach a predefined surface temperature. Having all temperatures and time values the heat transfer equation is iteratively solved to get the value of heat transfer coefficient of each and every pixel of the test surface.

    In total fifteen tests are conducted with different Reynolds number and different jet-to-target plate distances. It is concluded that for both the target and impingement plates, a high Reynolds number provides better overall heat transfer and increase in jet-to-target distance

    decreases the overall heat transfer.

    Download full text (pdf)
    FULLTEXT01
  • 249.
    Ottosson, Oscar
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    CFD Simulation of Urea Evaporation in STAR-CCM+2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Diesel engines produce large amounts of nitrogen oxides (NOX) while running. Nitrogen oxides are highly toxic and also contribute towards the formation of tropospheric ozone. Increasingly stringent legislation regarding the amount of nitrogen oxides that are allowed to be emitted from diesel-powered vehicles has forced manufacturers of diesel-engines to develop after-treatment systems that reduce the amount of nitrogen oxides in the exhaust. One of the main components in such a system is selective catalytic reduction (SCR), where nitrogen oxides are reduced to diatomic nitrogen and water with the help of ammonia. A vital part of this process is the spraying of a urea-water-solution (UWS), which is needed in order to produce the reducing agent ammonia. UWS spraying introduces the risk of solid deposits (such as biuret, ammelide and ammeline) forming in the after-treatment system, should the flow conditions be unfavourable. Risk factors include high temperatures, but also low dynamics and high thickness of the resulting liquid film that forms as the UWS spray hits the surfaces of the after-treatment system. It is thus essential that manufacturers of SCR after-treatment systems have correct data on how much UWS that should be sprayed into the exhaust for any given flow condition. Experimental tests are thoroughly used to assess this but are very expensive and are thus limited to prototype testing during product development. When assessing a wider range of concepts and geometries early on in the product development stage, simulation tools such as computational fluid dynamics (CFD) are used instead.

    One of the most computationally heavy processes to simulate within a SCR after-treatment system is the UWS spray and its interaction with surfaces inside the after-treatment system, where correct prediction of the formation of solid deposits are of great importance. Most CFD models used for this purpose hold a relatively good level of accuracy and are utilized throughout the whole industry where SCR aftertreatment is applied. Despite this, these models are limited in the fact that they are only able to cover timescales in the scope of seconds to minutes while using a tolerable amount of computational power. However, the time spectrum for solid deposit formation is minutes to hours.

    Scania is one of Sweden’s biggest developers of SCR after-treatment, with the technology being incorporated directly into its silencers. AVL Fire is the main UWS spray simulation tool for engineers at Scania at the moment. One major drawback of using AVL Fire for UWS spray simulations is that it is deemed too time-consuming to set up new cases and too unstable during simulation, which makes it too costly in terms of expensive engineering hours.

    This project has investigated the potential of using STAR-CCM+ for UWS spray simulations at Scania instead. A standard method has been evaluated, as well as parameters that will prove useful in further investigations of a potential speedup method. The studied method in STAR-CCM+ is easy to setup and the simulation process is robust and stable. Various other perks come from using STAR-CCM+ as well, such as: a user-friendly interface, easy and powerful mesh-generation and great post-process capabilities.

    Several different parameters have been investigated for their impact on the studied method, such as mesh refinement of the spray injector area and the number of parcels injected every time-step through the spray injector (simply put the resolution of the spray). A possible speedup by freezing the momentum equations when allowed and lowering the amount of inner iterations has also been investigated.

    A handful of operating conditions have been studied for two different geometries. The attained simulation results display correlations with physical measurements, but further assessment for identifying the risk of solid deposit needs to be performed on the studied cases to assess the full accuracy of solid deposit prediction of the studied method. Recommendations for future work includes fully implementing and evaluating the speedup method available for spray simulations in STAR-CCM+ as well as directly comparing how the accuracy and performance of the method relates to that of the method used in AVL Fire for spray simulations.

    Download full text (pdf)
    Exjobbsrapport
  • 250.
    Parras Blázquez, Pedro Santiago
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    CFD Analysis of Pressure Instabilities in Stator-Rotor Disc Cavity Systems2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The continuous demand to improve turbine performance has led manufactures to focus on aspects that have been previously considered of secondary importance such as the secondary air system. The purpose of this system is to cool the components and prevent ingestion of hot gas into the stator-rotor cavity that could lead to low frequency pressure fluctuations called Cavity Flow Instabilities. These instabilities could cause unpredictable rotor vibrations and damage several components.

    A CFD method capable of detecting cavity flow instabilities in a rotor-stator disk cavity system is investigated, based on the 360◦model of the cavity without anystator vanes and rotor blades. Boundary conditions are simplified by considering steady and uniform flow in the main gas path. Different turbulence models are tested such as Realizable k−ε,k−ω SST, DDES, and SAS. In order to test the performance of the method, different purge flow levels are simulated.

    The most successful results, are predicted by the Realizable k−ε turbulence model. This model predicts two rotating low pressure structures in the cavity, for low purge flow levels. These pressure structures rotate at approximately 80% of the rotor speed. Furthermore, the spectra analysis of the pressure shows a reasonable agreement with the experimental results in terms of the frequency, showing a distinct region of low frequencies pressure instabilities. Nonetheless, this method overpredicts the amplitudes by a factor of 3-7 depending on the frequency. In addition, regions of one order of magnitude higher in frequency is also predicted. The DDES model shows similar findings but the amplitudes in the pressure spectra associated to the low frequencies are lower. Additionally, SAS also predicts the pressure in-stabilities but, in this case, the amplitudes are closer to RANS simulations, yet the high frequencies disappear. Unfortunately, k−ω SST, did not predict these pressure instabilities.

    Further research is still needed in many of the aspects of this work, from the simplifications up to the turbulence models. However, it is concluded from this work that this method could be a useful tool for turbine design as it decreases the need for testing and prototype manufacturing.

    Download full text (pdf)
    fulltext
234567 201 - 250 of 320
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf