The study of pulsatile flow in stenosed vessels is of particular importance because of its significance in relation to blood flow in human pathophysiology. To date, however, there have been few comprehensive publications detailing systematic numerical simulations of turbulent pulsatile flow through stenotic tubes evaluated against comparable experiments. In this paper, two-equation turbulence modeling has been explored for sinusoidally pulsatile flow in 75% and 90% area reduction stenosed vessels, which undergoes a transition from laminar to turbulent flow as well as relaminarization. Wilcox's standard k-omega model and a transitional variant of the same model are employed for the numerical simulations. Steady flow through the stenosed tubes was considered first to establish the grid resolution and the correct inlet conditions on the basis of comprehensive comparisons of the detailed velocity and turbulence fields to experimental data. Inlet conditions based on Womersley flow were imposed at the inlet for all pulsatile cases and the results were compared to experimental data from the literature. In general, the transitional version of the k-omega model is shown to give a better overall representation of both steady and pulsatile flow. The standard model consistently over predicts turbulence at and downstream of the stenosis, which leads to premature recovery of the flow. While the transitional model often under-predicts the magnitude of the turbulence, the trends are well-described and the velocity field is superior to that predicted using the standard model. On the basis of this study, there appears to be some promise for simulating physiological pulsatile flows using a relatively simple two-equation turbulence model.

Experimental tests and computational fluid dynamics (CFD) simulations using the commercial code FLUENT were carried out to investigate the effects of the fan support hub geometry on the component heat transfer and cooling air flow through a simplified model of an electric motor for an automotive cooling-fan system, since little is known about the thermofluid dynamics of such machines. It has been found that the presence of radial ribs on the fan hub has a significant effect on drawing cooling air through the motor, particularly at lower air flowrates, regardless of the rotational speed. In addition, the rotational speed, hub diameter, fin height, and rib width are important parameters for inducing flow inside the hub while the tip gap and hub depth are not as influential. Increasing the number of ribs or fins has little impact on the performance of the hub. Good agreement was found between the experimental and predicted temperatures from heat transfer simulations of the motor for representative underhood environmental conditions. The present work shows that a valuable CFD tool can be developed to predict the temperature distribution inside the motor and offers a guide to the methodology whereby design modifications may be made to improve motor performance for a given application.

No abstract