Time Resolved PIV Measurements of the Flow Field Associated With the Interaction of Concentrated and Distributed Vorticity

摘要

Time resolved particle image velocimetry was used to investigate new aspects of the flow field associated with a vortex ring/ moving wall interaction. These physical simulations represent aspects of the instantaneous flow field interactions known to exist in turbulent wall-bounded flows. To allow for an explicit study of these interactions and avoid background turbulence, unsteady, laminar, vortex ring experiments were conducted with reproducible initial conditions. For the case when the vorticity in the bottom core of the ring and shear layer have opposite sign, the passage of the vortex ring above the wall results in a lifting of the near wall fluid. This gives rise to the formation of a primary hairpin vortex with the same sign vorticity as the top core of the vortex ring. The results obtained indicate that the ring rebounds from the wall for these interactions at increasing angles for increasing incident angles. Furthermore, the hairpin lift up occurs over shorter time scales when the incidence angle of the vortex ring was increased. The results provide further insight into how vortical structures interact and the associated momentum transport mechanisms relevant to turbulent flows.