Mechanisms of SWBLI control by using a surface arc plasma actuator array

Mechanisms for controlling the shock wave boundary layer interaction (SWBLI) by a plasma actuator array are investigated by two experiments. Low-frequency and high-frequency actuation modes are compared. The experimental results yield valuable insights into the control mechanism of SWBLI using a surface arc plasma actuator array. The schlieren snapshots and the mean and root mean square error of the image sequence and pressure measurements are analyzed to determine the control mechanisms. The high-frame schlieren images for flow visualization indicate a significant modification of the separation shock in both experiments due to thermal injection. More importantly, because the high-frequency actuation mode operates at relatively low energy, it can provide quasi-continuous perturbations, providing stable control for separation shock weakening. The Iband/Itotal ratio for low-frequency unsteadiness obtained from the pressure spectrum is reduced below 5% at 10 kHz forcing. The integrated schlieren intensity IRMS and power spectrum indicate a dominant vortex forcing effect as an additional actuation mechanism in addition to the gas heating effect that may affect the separation shock and its interaction with the boundary layer. As the plasma actuation is activated, numerous periodic streamwise vortices and small-scale trailing vortices are produced in the high-frequency actuation mode, resulting in an enhancement of the mixture upstream of the interaction region and promoting the momentum transfer to the boundary layer. In addition, the large-scale turbulence structures characterized by low-frequency unsteadiness are subject to artificial vortex shedding by the plasma perturbation, further increasing the momentum transfer in the boundary layer. We propose a conceptual model describing the vortical activity due to actuation and the interaction between plasma actuation and the SWBLI flow. Thus, a hybrid mechanism of SWBLI control associated with vortical activity exists.