Visualization of synthetic jet formation in air

Abstract

This experimental study deals with a round synthetic jet (SJ) issuing into quiescent surroundings. Flow visualization in air is used to identify different flow field regimes. Hot-wire anemometry and theoretical evaluations are used to quantify parameters in terms of the Reynolds (Re) and Stokes (S) numbers. To verify the theoretical evaluation, additional experiments were performed using the laser Doppler vibrometry. Four regimes of oscillatory suction and extrusion are distinguished and presented by means of a Re–S parameter map: (a) creeping flow without SJ formation, (b) SJ formation and propagation without vortex rollup, (c) SJ with vortex rollup, and (d) vortex structure breakdown, instability and transition to turbulence. Differences in the SJ regimes at low, moderate and high Stokes numbers are found. While all four (a–d) regimes are identified for lower (S < 10) and moderate (S = 10–30) Stokes numbers, the SJ formation process for higher Re and S is coupled with the laminar–turbulent transition. The results are reasonably consistent with those in the available literature.