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Turbulent Flow in Constricted Blood Vessels: Quantification of Wall Shear Stress Using Large Eddy Simulation
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).
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The genesis of atherosclerosis has previously been shown to be affected by the frictional load from the blood on the vessel wall, called the wall shear stress (WSS). Assessment of WSS can therefore provide important information for diagnoses, intervention planning, and follow‐up. Calculation of WSS requires high‐resolved velocity data from the vessel, which in turn can be obtained using computational fluid dynamics (CFD). In this work large eddy simulation LES was successfully used to simulate transitional flow in idealized as well as subject specific vessel models. It was shown that a scale resolving technique is to prefer for this application, since much valuable information otherwise is lost. Besides, Reynolds‐Averaged Navier‐Stokes (RANS) models have generally failed to predict this type of flow.

Non‐pulsating flows of Reynolds numbers up to 2 000 in a circular constricted pipe showed that turbulence is likely to occur in the post‐stenotic region, which resulted in a complex WSS pattern characterized by large spatial as well temporal fluctuations in all directions along the wall. Time averaged streamwise WSS was relatively high, while time averaged circumferential WSS was low, meaning that endothelial cells in that region would be exposed to oscillations in a stretched state in the streamwise direction and in a relaxed state in the circumferential direction.

Since every vessel is unique, so is also its WSS pattern. Hence the CFD simulations must be done in subject specific vessel models. Such can be created from anatomical information acquired with magnetic resonance imaging (MRI). MRI can also be used to obtain velocity boundary conditions for the simulation. This technique was used to investigate pulsating flow in a subject specific normal human aorta. It was shown that even the flow in healthy vessels can be very disturbed and turbulence like, and even for this case large WSS variations were seen. It was also shown that regions around branches from the aorta, known to be susceptible for atherosclerosis, were characterized by high time averaged WSS and high oscillatory shear index.

Finally, the predictive capability of CFD was investigated. An idealized model of a human aorta with a coarctation and post‐stenotic dilatation was studied before and after a possible repair of the constriction. The results suggested that small remaining abnormalities in the geometry may deteriorate the chances for a successful treatment. Also, high values of shear rate and Reynolds stresses were found in the dilatation after the constriction, which previous works have shown means increased risk for thrombus formation and hemolysis.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 57 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1558
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-100918DOI: 10.3384/diss.diva-100918ISBN: 978-91-7519-473-8 (print)OAI: oai:DiVA.org:liu-100918DiVA: diva2:664323
Public defence
2013-12-10, C3, hus C, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-11-14 Created: 2013-11-14 Last updated: 2017-03-27Bibliographically approved
List of papers
1. Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
Open this publication in new window or tab >>Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
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2006 (English)In: Medical Image Computing and Computer-Assisted Intervention – MICCAI 2006: 9th International Conference, Copenhagen, Denmark, October 1-6, 2006. Proceedings, Part I / [ed] Rasmus Larsen, Mads Nielsen and Jon Sporring, Springer Berlin/Heidelberg, 2006, 1, Vol. 4190, 257-263 p.Conference paper, Published paper (Refereed)
Abstract [en]

Patient specific modelling of the blood flow through the human aorta is performed using computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). Velocity patterns are compared between computer simulations and measurements. The workflow includes several steps: MRI measurement to obtain both geometry and velocity, an automatic levelset segmentation followed by meshing of the geometrical model and CFD setup to perform the simulations follwed by the actual simulations. The computational results agree well with the measured data.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2006 Edition: 1
Series
Lecture Notes in Computer Science, ISSN 0302-9743 (print), 1611-3349 (online) ; 4190
National Category
Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-36902 (URN)10.1007/11866565_32 (DOI)000241556300032 ()32988 (Local ID)3-5404-4707-5 (ISBN)978-3-540-44727-6 (ISBN)978-3-540-44707-8 (ISBN)32988 (Archive number)32988 (OAI)
Conference
The 9th MICCAI Conference, Copenhagen, Denmark, 1-6 October 2006
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-03-27Bibliographically approved
2. Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application
Open this publication in new window or tab >>Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application
2011 (English)In: WSEAS Transactions on Biology and Biomedicine, ISSN 1109-9518, Vol. 8, no 3, 86-101 p.Article in journal (Refereed) Published
Abstract [en]

Turbulent flow in the cardiovascular system may increase the risk for severe arterial disease. This workaddresses the feasibility of Large Eddy Simulation (LES) using a general purpose code as a tool for assessmentof cardiovascular flow and investigates Wall Shear Stress (WSS) in steady as well as pulsating turbulent pipeflow. Poiseuille flow was specified at the inlet, and with a suitable ammount of perturbations at the inlet it waspossible to predict experimental data. The extent of the recirculation zone was affected by the inlet disturbances,and magnitude as well as direction of the WSS vector varied significantly at the reattachment point. For thepulsating flow, WSS shows a complex pattern with different spatial and temporal variation along the pipe. Thewall shear stress gradient was calculated on the entire post-stenotic surface and each component in the gradientwas investigated. The off-diagonal components in the gradient are usually assumed to be small, but here they werefound to be on the same order of magnitude as the diagonal terms. This work demonstrates the need for a scaleresolving simulation technique to accurately model cardiovascular flows.

Keyword
Turbulence, Large Eddy Simulation, Cardiovascular Flow, Wall Shear Stress
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-73211 (URN)
Available from: 2011-12-22 Created: 2011-12-22 Last updated: 2016-03-14
3. Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
Open this publication in new window or tab >>Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
2010 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 132, no 6Article in journal (Refereed) Published
Abstract [en]

Large eddy simulation was applied for flow of Re = 2000 in a stenosed pipe in order to undertake a thorough investigation of the wall shear stress (WSS) in turbulent flow. A decomposition of the WSS into time averaged and fluctuating components is proposed. It was concluded that a scale resolving technique is required to completely describe the WSS pattern in a subject specific vessel model, since the poststenotic region was dominated by large axial and circumferential fluctuations. Three poststenotic regions of different WSS characteristics were identified. The recirculation zone was subject to a time averaged WSS in the retrograde direction and large fluctuations. After reattachment there was an ante grade shear and smaller fluctuations than in the recirculation zone. At the reattachment the fluctuations were the largest, but no direction dominated over time. Due to symmetry the circumferential time average was always zero. Thus, in a blood vessel, the axial fluctuations would affect endothelial cells in a stretched state, whereas the circumferential fluctuations would act in a relaxed direction.

Place, publisher, year, edition, pages
American Society Mechanical Engineers, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58347 (URN)10.1115/1.4001075 (DOI)000278965500002 ()
Available from: 2010-08-13 Created: 2010-08-11 Last updated: 2017-12-12
4. Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
Open this publication in new window or tab >>Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
2012 (English)In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 34, no 8, 1139-1148 p.Article in journal (Refereed) Published
Abstract [en]

In this study, large-eddy simulation (LES) is employed to calculate the disturbed flow field and the wall shear stress (WSS) in a subject specific human aorta. Velocity and geometry measurements using magnetic resonance imaging (MRI) are taken as input to the model to provide accurate boundary conditions and to assure the physiological relevance. In total, 50 consecutive cardiac cycles were simulated from which a phase average was computed to get a statistically reliable result. A decomposition similar to Reynolds decomposition is introduced, where the WSS signal is divided into a pulsating part (due to the mass flow rate) and a fluctuating part (originating from the disturbed flow). Oscillatory shear index (OSI) is plotted against time-averaged WSS in a novel way, and locations on the aortic wall where elevated values existed could easily be found. In general, high and oscillating WSS values were found in the vicinity of the branches in the aortic arch, while low and oscillating WSS were present in the inner curvature of the descending aorta. The decomposition of WSS into a pulsating and a fluctuating part increases the understanding of how WSS affects the aortic wall, which enables both qualitative and quantitative comparisons.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Human aorta, Atherosclerosis, Wall shear stress, Computational fluid dynamics, Scale resolving turbulence model, Reynolds decomposition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-84887 (URN)10.1016/j.medengphy.2011.12.002 (DOI)000309028800016 ()
Note

Funding Agencies|Swedish research council|VR 2007-4085VR 2010-4282|National Supercomputer Centre (NSC)|SNIC022/09-11|

Available from: 2012-11-01 Created: 2012-10-26 Last updated: 2017-12-07
5. Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning
Open this publication in new window or tab >>Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning
2015 (English)In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 7, no 2Article in journal (Refereed) Published
Abstract [en]

Large eddy simulation was applied to investigate hemodynamics in a model with coarctation of the aorta (CoA) and post-stenotic dilatation. Special focus was put on the role of hemodynamics for success of CoA repair. Several parameters previously identified as related to cardiovascular disease were studied. Known risk factors were observed both with CoA and after repair, and the restoration of the anatomy seems to be crucial for a successful result.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation / SAGE Publications, 2015
Keyword
Coarctation of the Aorta, CFD, Intervention Planning, Turbulence, Wall Shear Stress, Shear Rate
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-100917 (URN)10.1155/2014/971418 (DOI)000354083600087 ()
Available from: 2013-11-14 Created: 2013-11-14 Last updated: 2017-12-06Bibliographically approved

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