Computation of physiological bifurcation flows using a patched grid

Abstract

A finite volume method in a boundary-fitted coordinate system together with a zonal grid method is employed to compute the flow field of a real-shape two-dimensional aortic bifurcation. The steady terms in the governing equations are treated by a fully explicit scheme. The zonal gridding procedure is discussed in detail. The numerical method is first tested in a laminar backward facing step flow to demonstrate the features of the method. The effect of the interface treatment on the flow fields can be significant. A 90° T-junction is then computed. The results are in good agreement with the available experimental data. The method is then applied to simulate the flows of an atherosclerotic human aorta. Both the steady and pulsatile flows are considered. It is shown that the mean shear stresses in recirculation regions of a pulsatile flow cannot be adequately described by a corresponding steady flow with a mean Reynolds number. In pulsatile flows, a sinusoidal input pulse and a realistic input pulse are both used in the computations. It is found that the “averaged” flow behavior is similar in both cases. However, the details of the flow field are significantly different. During pulsatile flow, permanent eddies are not present. That is, for a certain period in a cycle, the entire wall is free from eddies. On the other hand, in another period, the overall wall is almost completely in the reversing flow near the walls. These phenomena have been observed by other authors experimentally. Distributions of wall shear stresses and locations of recirculation zones in a realistic flow are shown and discussed briefly.