Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation Bachelor’s Thesis by Athanasios Margaritis AEM: 5516 Supervisor: Anestis I. Kalfas, Associate Professor Aristotle University of Thessaloniki Faculty of Engineering School of Mechanical Engineering Laboratory of Fluid Mechanics and Turbomachinery
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Numerical Analysis of Blood Flow Through the Human Carotid Artery
BifurcationBachelor’s Thesis
by Athanasios MargaritisAEM: 5516
Supervisor: Anestis I. Kalfas, Associate Professor
Aristotle University of ThessalonikiFaculty of Engineering
School of Mechanical EngineeringLaboratory of Fluid Mechanics and
Turbomachinery
Contents• Introduction• Literature Survey• Methods• Results• Discussion• ConclusionsoLimitationsoSuggestions for Further Research
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
IntroductionThe purpose of this study
• Engineering Diploma First Cycle Thesis (Bachelor’s Thesis)• Atherosclerotic diseases are the main cause of mortality – morbidity• Blood flow through Carotid Artery important for atherogenesis• Study flow through the Carotid Artery using Measurements, Imaging and
CFD• Target: use CFD for prognosis, diagnosis and treatment of
cardiovascular diseases
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
IntroductionThe stages of this study
• Six 3D geometries reconstructed using 2D MRI images from 3 volunteers• Geometry correction and computational mesh generation using
ANSA• Universal average periodic boundary conditions coded in
MATLAB and C• Solution using commercial CFD software, ANSYS Fluent• Results presentation using ANSYS CFD-Post and μΕΤΑ
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
Literature SurveyPrevious Studies Reviewed
• Numerous relevant previous studies (since 1960, intensified after 2000)• CFD applications for studying of blood flow through the arterial tree or carotid
artery• Studies of wave propagation through the arterial tree• Research on arterial wall properties (elasticity, viscoelasticity, compliance
• No recirculation or helicity during systolic acceleration• Helical flow after velocity
peak, during systolic deceleration• Low WSS on the outer walls
of the ICA bulb and ECA, due to secondary flows.
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
ResultsStreamlines and Secondary Flows
(4/5)
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Figure 13. Streamlines for the LCAB and RCAB of Subjects 1,2,3 during the systolic deceleration phase of the cardiac cycle.
• Results presented during the systolic deceleration phase• Secondary and helical flows
occur downstream of the bifurcation• Smaller bifurcation angle
results in larger secondary flow regions, retained further downstream
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
ResultsLow Wall Shear Stress Regions
(5/5)
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Figure 14. Low WSS regions for the LCAB and RCAB of Subjects 1,2,3 during the systolic deceleration phase of the cardiac cycle.
• Results presented at the peak of the systolic acceleration phase• Lowest Wall Shear Stress
regions appear on the outer walls of both the ECA and the ICA bulb• Areas correlate well with
secondary flow regions
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
DiscussionEffects of the Viscosity Model• Minor effect of blood’s viscosity
model• Near-infinite shear rate near the wall
• Non-Newtonian, Carreau-Yassuda model• Negligible variations in the results• Smoother time-variation of WSS values• Slight mitigation of extreme peak
values(minimum – maximum)
• Newtonian model accuracy is sufficient• Further research for viscosity model• For Fluid-Structure Interactions• For multiphase simulation of blood
(1/4)
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Figure 15. Comparison of results for the Newtonian and the Carreau-Yassuda viscosity models.
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
DiscussionWall Shear Stress Distribution
• Wall Shear Stress is the most important factor for cardiovascular diseases• Endothelium alignment and LDL accumulation and intrusion
• Current results agree with previously reported findings• Maximum values of at the bifurcation apex at the end of the
systolic acceleration phase• Lower values away from the apex and during the rest of the cardiac
cycle• Physiological values of
• Lowest values on the outer walls of ICA bulb and ECA with • Risk for atherogenesis in regions where
(2/4)
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
DiscussionRecirculation and Secondary Flows
(3/4)
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
• Velocity profiles are disturbed, far from parabolic near the bifurcation• Flow separation, recirculation and helical secondary flows• Near the outer walls, downstream of the bifurcation• Induced due to artery branching and curvature• During the systolic deceleration phase of the cardiac cycle
• Flow inversion occurs during diastole• Effect of bifurcation angle• High bifurcation angle leads to massive secondary flow regions, limited at
the root of each branch at the bifurcation• Low bifurcation angle leads to smaller secondary flow regions, retained
further downstream through the ICA and ECA branches, main flow close to the inner walls
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
DiscussionPeriodic Time Evolution
(4/4)
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
• Flow field variation during cardiac cycle not emphasized in previous literature• Secondary and helical flow regions after systolic acceleration peak• Maximum WSS values at the end of systolic acceleration, much
lower during the rest of the cardiac cycle• Flow inversion during diastolic phase• Shear-thinning behaviour of blood mitigates peak WSS values
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
Conclusions
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
• Insignificant variation between the Newtonian and the Carreau-Yassuda viscosity models• Minor effect mostly regarding peak WSS values• Further examination required for multiphase or FSI simulations• Negligible increase in complexity – Carreau-Yassuda may be easily used
• Wall Shear Stress distributions in perfect agreement with previous literature• Accurate models and commercial ANSYS Fluent solver
• Secondary flow regions correlate with low, oscillating WSS regions• Occur on the outer walls of the ICA and ECA branches, at the beginning of
the bifurcation
• Flow inversion may occur during the diastolic phase of the cardiac cycle
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
Limitations
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
• Universal boundary conditions instead of patient-specific measurements• Parabolic inlet velocity profile – negligible error• Fixed mass flow split and pressure differences
• Imaging and reconstruction techniques• Limited MRI accuracy• Effect of posture and operator during MRI• Manual geometry reconstruction and correction – human error
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
Suggestions for Further Research
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
• Clarification of the importance of different simulation models for each case• Turbulent or Laminar• Single-phase or Multi-phase• Newtonian or Non-Newtonian
• Implementation of fully coupled Fluid-Structure Interaction simulations• Include wave propagation phenomena
• Use of Windkessel models as boundary conditions for the arterial tree
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation
Thank you.
Aristotle University of Thessaloniki
Athanasios Margaritis
Laboratory of Fluid Mechanics and Turbomachinery
Dipl. Ing. Athanasios Margaritis
Numerical Analysis of Blood Flow Through the Human Carotid Artery Bifurcation