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The fluid flow through a stenosed artery and its bypass graft in an anastomosis can substantially influence the outcome of bypass surgery. To help improve our understanding of this and related issues, the steady Navier-Stokes flows are computed in an idealized arterial bypass system with partially occluded host artery. Both the residual flow issued from the stenosis--which is potentially important at an earlier stage after grafting--and the complex flow structure induced by the bypass graft are investigated. Seven geometric models, including symmetric and asymmetric stenoses in the host artery, and two major aspects of the bypass system, namely, the effects of area reduction and stenosis asymmetry, are considered. By analyzing the flow characteristics in these configurations, it is found that (1) substantial area reduction leads to flow recirculation in both upstream and downstream of the stenosis and in the host artery near the toe, while diminishes the recirculation zone in the bypass graft near the bifurcation junction, (2) the asymmetry and position of the stenosis can affect the location and size of these recirculation zones, and (3) the curvature of the bypass graft can modify the fluid flow structure in the entire bypass system.

In the present study, flow fields in the threedimensional, tangentially crossing micro-channels were studied. The effect of the relevant geometrical parameters such as the aspect ratio, contact surface area, surface to volume factor, flow rate and cross angle on the flow turning was reported. When the geometries and the flow conditions of the two crossing channels were the same, the fraction of turning flow was found to be dependent on the aspect ratio of the channel as reported previously in the literature. However, if the configuration and flow conditions of the two channels were different, the results need to be clarified. A parameter of non-dimensionalized surface to volume ratio was devised to characterize the flow turning. And the parameter was tested against its validity using numerical simulation and the available experimental data. The experiments on the crossing angle were conducted to show that larger angle in general yielded higher turning flow ratio. The results are expected to be useful in the passive control of flow in micro-fluidic devices among others.

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