Interactions between adjacent synthetic-jet-generated vortices of high Strouhal number

This experimental study characterizes the development and interaction of vortices generated by the synthetic jets of the Strouhal numbers (St) from 0.17 to 0.92, issuing from either single, dual, or triple rectangular orifices. Particle image velocimetry is used for flow measurements. A synthetic jet results from the periodic motion of diaphragm mounted beneath each orifice plate, generating counter-rotating vortex pairs. It has been found that, if St is sufficiently high, these paired vortices are confined near the orifice by the suction stroke, forming the near-wall fluid oscillation or confined oscillatory flow; otherwise, a traditional-jet-like flow forms. In dual high-St synthetic jets, when a phase difference (θ) exists between the driving waveforms of adjacent jets, the confined vortex dynamics change, inducing a cross-stream motion toward the phase-leading jet. This effect occurs most strongly at θ = 0.5π. For three adjacent synthetic jets also with θ = 0.5π, the cross-stream motion is substantially enhanced. These findings are significant for the application of high-St synthetic jet arrays in flow control, particularly for the manipulation of the turbulent boundary layer.