Investigation of Phase and Spacing effects in Synthetic Jet Actuator arrays

Experiments have been undertaken with two small-scale Synthetic Jet Actuators in a zero-pressure gradient boundary-layer, in order to investigate the effect of relative input signal phase. CTA anemometry techniques were used, demonstrating that changes in the downstream flow structure could be observed. Time-averaged streamwise velocity profiles demonstrated that a case with a 270 o phase difference between the upstream and downstream actuator resulted in a more concentrated movement of near-wall fluid towards the vortex core than a 90 o case. Significant differences in the PSD analyses of downstream streamwise velocity time histories were found, suggesting that input signal phase could influence the stability and hence effectiveness of flow structures used in flowcontrol applications. Further investigation using phase-locked CTA data acquisition showed that the relative positions of the two adjacent vortex rings were reversed between cases, suggesting that the resulting induced velocities could affect the stability of the combined synthetic jet.