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Turbulent Flow in Constricted Blood Vessels: Quantification of Wall Shear Stress Using Large Eddy Simulation
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
2013 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2013. , s. 57
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1558
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-100918DOI: 10.3384/diss.diva-100918ISBN: 978-91-7519-473-8 (tryckt)OAI: oai:DiVA.org:liu-100918DiVA, id: diva2:664323
Disputas
2013-12-10, C3, hus C, Campus Valla, Linköpings universitet, Linköping, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2013-11-14 Laget: 2013-11-14 Sist oppdatert: 2019-12-03bibliografisk kontrollert
Delarbeid
1. Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
Åpne denne publikasjonen i ny fane eller vindu >>Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
Vise andre…
2006 (engelsk)Inngår i: 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, s. 257-263Konferansepaper, Publicerat paper (Fagfellevurdert)
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.

sted, utgiver, år, opplag, sider
Springer Berlin/Heidelberg, 2006 Opplag: 1
Serie
Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 4190
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-36902 (URN)10.1007/11866565_32 (DOI)000241556300032 ()32988 (Lokal ID)3-5404-4707-5 (ISBN)978-3-540-44727-6 (ISBN)978-3-540-44707-8 (ISBN)32988 (Arkivnummer)32988 (OAI)
Konferanse
The 9th MICCAI Conference, Copenhagen, Denmark, 1-6 October 2006
Tilgjengelig fra: 2009-10-10 Laget: 2009-10-10 Sist oppdatert: 2018-02-20bibliografisk kontrollert
2. Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application
Åpne denne publikasjonen i ny fane eller vindu >>Large Eddy Simulation of Stenotic Flow for Wall Shear Stress Estimation - Validation and Application
2011 (engelsk)Inngår i: WSEAS Transactions on Biology and Biomedicine, ISSN 1109-9518, Vol. 8, nr 3, s. 86-101Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
Turbulence, Large Eddy Simulation, Cardiovascular Flow, Wall Shear Stress
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-73211 (URN)
Tilgjengelig fra: 2011-12-22 Laget: 2011-12-22 Sist oppdatert: 2016-03-14
3. Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
Åpne denne publikasjonen i ny fane eller vindu >>Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
2010 (engelsk)Inngår i: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 132, nr 6Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
American Society Mechanical Engineers, 2010
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-58347 (URN)10.1115/1.4001075 (DOI)000278965500002 ()
Tilgjengelig fra: 2010-08-13 Laget: 2010-08-11 Sist oppdatert: 2017-12-12
4. Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
Åpne denne publikasjonen i ny fane eller vindu >>Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
2012 (engelsk)Inngår i: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 34, nr 8, s. 1139-1148Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2012
Emneord
Human aorta, Atherosclerosis, Wall shear stress, Computational fluid dynamics, Scale resolving turbulence model, Reynolds decomposition
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-84887 (URN)10.1016/j.medengphy.2011.12.002 (DOI)000309028800016 ()
Merknad

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

Tilgjengelig fra: 2012-11-01 Laget: 2012-10-26 Sist oppdatert: 2017-12-07
5. Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning
Åpne denne publikasjonen i ny fane eller vindu >>Large Eddy Simulation of Pulsating Flow Before and After CoA Repair - CFD for Intervention Planning
2015 (engelsk)Inngår i: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 7, nr 2Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Hindawi Publishing Corporation / SAGE Publications, 2015
Emneord
Coarctation of the Aorta, CFD, Intervention Planning, Turbulence, Wall Shear Stress, Shear Rate
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-100917 (URN)10.1155/2014/971418 (DOI)000354083600087 ()
Tilgjengelig fra: 2013-11-14 Laget: 2013-11-14 Sist oppdatert: 2017-12-06bibliografisk kontrollert

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