PIV studies of coherent structures generated at the end of a stack of parallel plates in a standing wave acoustic field

Oscillating flow near the end of a stack of parallel plates placed in a standing wave resonator is investigated using particle image velocimetry (PIV). The Reynolds number, Re _d , based on the plate thickness and the velocity amplitude at the entrance to the stack, is controlled by varying the acoustic excitation (so-called drive ratio) and by using two configurations of the stacks. As the Reynolds number changes, a range of distinct flow patterns is reported for the fluid being ejected from the stack. Symmetrical and asymmetrical vortex shedding phenomena are shown and two distinct modes of generating "vortex streets" are identified.