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CFD Simulations for Film Cooling: Reduced Models at Engine Like Conditions
Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In gas turbines some parts are exposed to combustion gases with temperatures well above the melting temperature of the material. Therefore, various cooling techniques are utilized in order to protect the parts exposed to these hot gases. One such technique, film cooling, is a common and well established way to protect the exposed parts. Film cooling involves the ejection of cold air on the surface of the parts that are to be protected, thus creating a film of colder air between the surface and the hot gases.

Computational Fluid Dynamics (CFD) is a way of calculating fluid flow, and can be used to calculate the effectiveness of a cooling film in film cooling applications. CFD is demanding in terms of computer power, especially when advanced methods are to be used. Even the simpler methods, such as Reynolds Average Navier-Stokes (RANS), can be quite demanding, time and computer power-wise, and require resources not always available. Finding ways of limiting the needed computer power is therefore of large interest.

The aim of this thesis is to reduce the computational time of film cooling CFD-simulations, by using reduced models. To achieve this, simulations has been conducted and compared to experiments. The investigated setup is of an enginelike equipment, where a guide vane is investigated for heat transfer coefficient and film effectiveness. The geometry in the experimental setup is constructed in such a way as to give the same pressure distribution around the guide vane as can be seen in a real gas turbine, although at lower temperatures than those in the real turbine. The CFD-simulations conducted on the test rig includes RANS-simulations using the realizable k- and the SST k-! turbulence models.

The reduced model contains only the central part of the vane. The walls of the test rig is replaced with periodic boundary conditions. This narrow model gives good agreement with the full model for heat transfer coefficient. Due to the large computational cost required to conduct simulations with cooling on the full model no comparison were made between the cooled narrow and cooled full model.

To further reduce the size of the computational domain, two additional models were investigated. The first one involves a reduction of the full domain to only include the section being studied, in this case the suction side of the guide vane.

This infers a reduction of the mesh size to less than ten percent of the size of what a mesh of the cooled full domain would be. The next step to reduce the size of the model and mesh is to make a narrow version of the already shortened model. The results for these two models show that they perform adequately to each other and (in the cases where a comparison is possible), to the full domain.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 44 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1593
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-91716OAI: oai:DiVA.org:liu-91716DiVA: diva2:618778
Presentation
2013-05-31, Sal C3, C-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-04-30 Created: 2013-04-30 Last updated: 2017-12-14Bibliographically approved
List of papers
1. Fan Shaped And Cylindrical Holes Studied in a Vane Film Cooling Test Rig
Open this publication in new window or tab >>Fan Shaped And Cylindrical Holes Studied in a Vane Film Cooling Test Rig
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2010 (English)In: Proceedings of the Asme Turbo Expo 2010, Vol 4, Pts a and B, 2010, 1777-1784 p.Conference paper, Published paper (Refereed)
Abstract [en]

In order to optimize the vane film cooling and thereby increase the efficiency of a gas turbine, different film cooling configurations were experimentally investigated. Dynamic similarity was obtained regarding main flow Reynolds number, airfoil pressure coefficient, adiabatic wall temperature and film cooling ejection ratio. The maximum reached Mach number was 0.52. The geometry of the test section, consisting of one vane and two flow paths, was modified in order to meet the dimensionless pressure coefficient distribution around the airfoil experienced by a full stage airfoil. This would ascertain that scaled but engine realistic pressure gradients would be achieved in the rig test.

During the test, the cold airfoil was suddenly imposed to a hot main stream and the evaluation of both the film cooling effectiveness and the heat transfer coefficient distribution on the visiable surface could be done at one single test using timeresolved temperature measurements obtained through IR thermography. A high resolution MWIR camera was used together with a silicon viewing window. The post-processing allowed for corrections regarding emissions and determination of the desired parameters on the vane surface.

Results, heat transfer coefficients and film cooling effectiveness, for fan shaped and cylindrical film cooling holes configurations are compared. The results show clear benefit of using shaped holes over cylindrical ditto, especially on the suction side where near hole film effectiveness is enhanced by approximately 25%, but the results also show that this benefit diminishes to nothing in the suction side trailing edge region.

The local heat transfer coefficients are generally lower for the shaped hole configurations. Contrary to the film effectiveness the shaped holes configurations show lower heat transfer coefficients also at the suction side trailing edge region, making use of the shaped hole configurations superior to cylindrical ones as the heat flux to the surface is reduced.

Numerical predictions using a boundary layer code, TEXSTAN, and CFD, for a smooth wall configuration corresponds well with the measured results.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91707 (URN)10.1115/GT2010-23308 (DOI)000290693500155 ()978-0-7918-4399-4 (ISBN)978-0-7918-3872-3 (ISBN)
Conference
ASME Turbo Expo 2010: Power for Land, Sea, and Air, GT 2010; Glasgow; United Kingdom
Available from: 2013-04-30 Created: 2013-04-30 Last updated: 2016-03-14Bibliographically approved
2. Towards Efficient CFD-Simulations of Engine LikeTurbine Guide Vane Film Cooling
Open this publication in new window or tab >>Towards Efficient CFD-Simulations of Engine LikeTurbine Guide Vane Film Cooling
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2011 (English)Conference paper, Published paper (Other academic)
Abstract [en]

It is well known that the efficiency of a gas turbine can be increased by using higher combustion temperatures and that this demands improved cooling. This study focuses on strategies to decrease the turnaround time for numerical predictions of film cooling while keeping the ability to resolve details of the flow. Simulations have been carried out for a real vane geometry at close to engine-like conditions and results are compared with corresponding experiments. The investigation includes an un-cooled situation for aerodynamic validation and to determine baseline heat transfer coefficent. Simulations and experiments of film effectiveness and heat transfer coefficient and their dependence of blowing ratio are investigated.

Place, publisher, year, edition, pages
ARC Aerospace Research Central, 2011
Keyword
Film cooling, gas turbines, CFD
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-75567 (URN)10.2514/6.2011-708 (DOI)978-1-60086-950-1 (ISBN)
Conference
49th AIAA Aerospace Science Meeting including the New Horizons Forum and Aerospace Exposition, January 4-7, Orlando, Florida, USA
Available from: 2012-03-08 Created: 2012-03-08 Last updated: 2016-03-14Bibliographically approved
3. CFD Simulations Using Reduced Models for Film Cooling Design
Open this publication in new window or tab >>CFD Simulations Using Reduced Models for Film Cooling Design
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2011 (English)In: 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2011, American Institute of Aeronautics and Astronautics, 2011, AiAA 2011-710- p.Conference paper, Published 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.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2011
Keyword
Film Cooling, Gas Turbines, CFD
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-76905 (URN)10.2514/6.2011-710 (DOI)978-1-60086-950-1 (ISBN)
Conference
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 4–7 January 2011, Orlando, Florida
Available from: 2012-04-24 Created: 2012-04-24 Last updated: 2016-05-11Bibliographically approved

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