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Isfahan University of Technology Numerical simulation of flow fields in a bypass anastomosis with stenosis Elnaz Zohravi Elnaz zohravi@me iut ac ir April 13 2009 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Prof Ebrahim Shirani eshirani@cc iut ac ir AbstractA potential interaction between the local hemodynamics and the artery wall response has been suggested forvascular graft failure by intimal hyperplasia IH Among the various hemodynamic factors wall shear stresshas been implicated as the primary factor responsible for the development of IH In order to explore the role ofhemodynamics in the formation of IH in complete bypass graft code ADINA is used The fluid flow through a stenosed artery and its bypass graft in a complete bypass can substantially influence theoutcome of bypass surgery To help improve our understanding of this and related issues the steady andunsteady Navier Stokes flows are computed in a 3 D idealized arterial bypass system with partially occludedhost artery At first steady flow in a complete bypass tube was simulated The study was to consider a completeflow field which included both the bypass and the host tubes The changes of the hemodynamics wereinvestigated with three parameters the inlet flow Reynolds number Re anastomotic angle and the positionof the occlusion in the host tube The baseline flow field was set up with Re 200 45 and the centeredposition of occlusion The parametric study was then conducted on combination of Re 100 200 400 45 60 and three occlusion positions left center and right It was found that in the baseline case largeslow recirculation flows could be seen in the host tube both upstream and downstream of the occlusion Theseparation points were on the opposite walls to the junctions Recirculation zones were also found near the toeand in the proximal outer wall of the bypass tube Their sizes were about one diameter of the tube or smaller Insome cases pairing vortices could be seen in the host tube upstream of the occlusion The shear rate distributionassociated with the flow fields was presented The flow pattern obtained was satisfying to those observedexperimentally by other investigators The difference of the flow fields between a complete bypass and simpleanastomosis was discussed Both the residual flow issued from the stenosis which is potentially important at an earlier stage aftergrafting and the complex flow structure induced by the bypass graft are investigated Four geometric models including symmetric stenoses 0 56 75 100 in the host artery and a major aspect of the bypass system namely the effect of area reduction are considered By analyzing the flow characteristics in theseconfigurations it is found that 1 substantial area reduction leads to flow recirculation in both upstream anddownstream of the stenosis and in the host artery near the toe while diminishes the recirculation zone in thebypass graft near the bifurcation junction and 2 the curvature of the bypass graft can modify the fluid flowstructure in the entire bypass system Finally pulsatile waveforms were introduced to study the hemodynamics in a bypass anastomosis underunsteady flow condition Time dependent and steady state results were compared to gain an insight towards thefeasibility of using steady condition as a representative of the long term averaged flow behavior within arteries Keywords bypass intimal hyperplasia anastomotic angle wall shear stress stenosis pulsatile flow

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اينتيمال هايپر پلاژيا , زاويه اتصال , تنش برشي , جريان نوساني