Department of Applied Mathematics, University of Waterloo
Two dimensional vortices generated by oscillatory flow over ripples: early stages
In this talk, we consider three increasingly asymmetric oscillatory flows over two ripple profiles, one of which is asymmetric and represents a small deviation from a symmetric ripple. For each of these cases, the vorticity and velocity fields are analyzed for the first three cycles. The Reynolds number is mostly limited to 1250, with a few cases also run at 5000. It can be observed that two vortices of opposite vorticity are generated during each cycle, one each during the forward and backward flows. These vortices pair up and trace a path that extends higher up as the asymmetry of the flow or ripple shape is amplified. This effect is a consequence of the increasing difference between the vorticities of the individual vortices in each vortex pair. After about three periods, the motion becomes more and more chaotic due to the interaction of the newly generated vortices with the older ones.