Study of Physiological Flow Through an Abdominal Aortic Aneurysm (AAA)

Abstract

Pulsatile flow in an axisymmetric rigid-walled model of an abdominal aortic aneurysm (AAA) has been analyzed numerically for various aneurysm dilations considering blood as a Newtonian fluid and Non-Newtonian fluid respectively. Physiologically realistic waveform which include Reynolds number between 97 to 407 is used as pulsatile flow inlet. A finite volume method is used to solve the governing equation for two dimensional, unsteady, laminar flow of an incompressible fluid. Comparisons with previously published work on the basis of special case were performed and found to be in excellent agreement. The flow pattern is analyzed by Streamline, Axial velocity, Wall shear stress(WSS), Wall pressure, Wall shear stress gradient, Pressure gradient etc. Results are observed at five different time, such as maximum systolic acceleration(point A), maximum systolic velocity(point B), maximum systolic deceleration(point C), minimum systolic velocity(point D) and maximum diastolic velocity(point E). At point D and point E vortex is generated near the centre of aneurysm. Centre of vortex moves towards the downstream as the percentage of dilation increases. Wall shear stress (WSS) becomes maximum at point B, but static pressure becomes maximum at point C. Axial velocity at the centre line becomes minimum at the centre of aneurysm for the point A, B, and C while it becomes minimum at the end of aneurysm for point D and E. For comparing the aneurysms with different dilations time average parameters are used that are obtained from 15 different times. As the percentage of aneurysm increases maximum value of time average wall shear stress(TAWSS), time average pressure (TAP), time average wall shear stress gradient (TAWSSG), time average pressure gradient (TAPG), Oscillating shear index (OSI) becomes higher. Similar results are obtained when blood is considered as Non-Newtonian fluid. At point B,WSS along wall becomes higher for Non-Newtonian fluid as compared to Newtonian fluid. The impact of Non-Newtonian blood flow characteristics on pressure compared to Newtonian model is found insignificant.