DNS of transitional pulsatile flow through a constriction: coherent structures and Reynolds stress budgets

Direct Numerical Simulations of pulsatile flow through channels and pipes with a constriction will be presented. Overall our simulations verify some of flow features reported in earlier experiments in the literature. In particular, during the acceleration phase a shear layer that forms at the stenosis becomes unstable and sheds an array of vortices. The vortices break down as they interact with the wall leading to the formation of boundary layers with turbulent-like characteristics shortly after the mean reattachment point. The simulations provide a detailed description of the instantaneous flow and the spatial-temporal evolution of the structures responsible for the generation of turbulence. The relation of theses structures to the phase averaged statistics and especially the budgets of turbulent kinetic energy and the Reynolds stresses will be discussed in detail. Finally the effect of Reynolds number and the frequency and amplitude of the oscillating flow rate on the flow patterns will be given.