Response of the shock wave/boundary layer interaction to the plasma synthetic jet

Abstract

Control of shock wave/boundary layer interaction (SWBLI) is of high practical importance for supersonic aircraft drag reducing. Lots of flow control strategies including passive and active control techniques have been put forward to minimize negative effect of SWBLI.Plasma aerodynamic control technique is considered as a potential one due to its flexibility in manipulating the supersonic flow. The goal of this research is to investigate the control effect of the novel actuator called plasma synthetic jet on the SWBLI.The effect of counter-flow plasma synthetic jet actuator on the SWBLI is investigated experimentally in this paper. The experiments are conducted in a supersonic wind tunnel at Mach number Ma=3.1. The test model is a blunt body with a plasma synthetic jet actuator installed inside its head which is used to create aerodynamic perturbations, and with a conical compression ramp in the rear, enabling the creation of SWBLI flow configuration. The plasma synthetic jet actuator is designed to inject pulsed hot gas by arc discharge into a small cavity in the direction perpendicular to the normal shock wave induced by the blunt body. The schlieren method is used for flow measurement and the flow characteristics are studied according to a sequence of schlieren images (1024512 pixel resolution) captured by a high speed charge-couple device camera with a framing rate of 58 kHz, triggered externally, and an exposure time of 1 s. Additionally, the mechanism of this control strategy on the SWBLI induced by the ramp is revealed by using the numerical method.The characteristics of the plasma synthetic jet in quiescent air are firstly studied. The results show a sudden reduction of averaged jet velocity under the resistance of the air. In addition, some small-scale flow structures in the jet are observed which may enhance the turbulence in the upstream boundary layer. The flow topology of interaction modified by actuation with frequencies of f=1 kHz and f=3 kHz are respectively analyzed. It is shown that by using this type of control strategy, the attached shock is locally degraded with the attachment point moving upward. The separation bubble is suppressed, hence making the separation shock move downstream. In addition, an extensive impact effect is exerted to the interaction region by actuation at f=1 kHz because more hot gas is produced by the actuator. Therefore, the actuator is found to be capable of significantly mitigating the negative effects induced by the SWBLI. The numerical work focuses on the interaction between the jet and the flow after the normal shock. The results show that large-scale vortex is induced by the interaction which increases turbulence and accelerates the flow near the wall during its moving downstream and dissipation, demonstrating turbulence enhancement in the boundary layer and a variation of upstream flow characteristics are the key factors for separation reduction and shock wave mitigation.