Transitory Behavior of Synthetic Jets

The transitory behavior of an isolated synthetic (zero net mass flux) jet was investigated experimentally using PIV and hot-wire anemometry. In the present work, the synthetic jet was produced over a broad range of length- and time-scales, where three formation frequencies, f = 300, 917, and 3100Hz, several stroke lengths (between 5 and 50 times the slit width) and Reynolds numbers (between 85 and 408) were tested. The transitory behavior, following the onset of the input signal, in planes along and across the slit was measured. It was found that the time it takes the synthetic jet to become fully developed depends on the stroke length, formation frequency and Reynolds number. In general, the transients consist of four stages associated with the merging of vortices in both cross-stream and spanwise planes that grow in size, which lead to the pinch off of the leading vortex before the jet reaches its steady-state.