Influence of Strouhal number and phase difference on the flow behavior of a synthetic jet array

A computational study is presented to characterize the flow behavior of independently controlled multiple synthetic jet actuators (SJA). For fixed geometric configuration and Reynolds number (⁠$Re$⁠) $300$⁠, the influence of Strouhal number (⁠$St=0.028–0.172$⁠) and phase difference $(∅=0°–180°$⁠) between the actuators on the evolution, and interaction of the vortices are highlighted. Directivity plots are employed to illustrate the effect of $∅$ on the vectoring behavior of a synthetic jet array (SJ array). It has been observed that a high jet vectoring angle (⁠$β$⁠) is achieved while operating the SJ array at low $St$⁠. The vectoring angle seems to be independent of $∅$ for the low and high $St$⁠. However, for an intermediate $St=0.086$⁠, the vectoring angle varies with the $∅$⁠. The phase averaged vorticity contour for $St=0.028$ reveals that the evolution of the anti-clockwise vortex from the leading actuator (SJA1) decides the vectoring of the jet. By contrast, for higher $Sts$(⁠$0.115$ and $0.13$⁠), the remnant vortices play a significant role in vectoring the jets toward the leading actuator. Based on the cross-stream distribution of time-averaged streamwise velocity, three distinct flow regimes are characterized: near-field, intermediate-field, and far-field. The strength of the jet is quantified by the downstream distribution of the jet momentum flux. Proper evolution of the vortices results in the enhancement of the jet momentum flux. It is recommended to operate the SJ array at an intermediate $St$ (⁠$0.086$⁠) to vary the jet vectoring angle with phase differences as well as to achieve maximum jet momentum flux.