Interaction of twin synthetic jets in attached and separated boundary layers: effects of yaw angle and phase difference

Abstract

This paper further extends our understanding of the interaction between twin synthetic jets (SJs) in attached and separated laminar boundary layers, following our previous works on twin SJs at zero yaw angle (Wen and Tang in J Fluids Eng Trans ASME 139:091203, 2017). In current investigation, the twin-SJ-induced streamwise vortices and their influence on attached and separated laminar boundary layers are examined at two nonzero yaw angles and four phase differences. Dye visualization and CFD simulations are conducted to compare the interaction of SJ-induced three-dimensional streamwise vortices and their impacts on the attached boundary layer. Two-dimensional PIV measurements are then conducted to evaluate the control effect of the twin SJs on the separated boundary layer. Our previous works have revealed that at zero yaw angle, the twin SJs interact in a constructive way regardless of their phase difference. Here, we further find that when the twin SJs operate with nonzero yaw angles, their interaction can be destructive due to the nonzero lateral distance, but the level of destruction can be mitigated by adjusting their phase difference. The strength of twin-SJ induced vortices and their impacts in the near-wall region are evaluated through streamwise vorticity flux and excess wall shear stress, respectively. In the separated boundary layer, although generally decreasing with the increase of yaw angle, significant influence of twin SJs can still be observed by varying the phase difference.