激波/边界层干扰对等离子体合成射流的响应特性

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

利用高速纹影系统和数值模拟方法研究了激波/边界层干扰对逆流喷射的等离子体合成射流的响应特性,并揭示了流动控制机理.实验在来流马赫数Ma=3.1的风洞中进行,测试模型采用钝头体和压缩斜坡的组合模型,等离子体合成射流激励器安装在钝头体头部.纹影系统捕捉了放电频率为f=1 kHz和f=3 kHz的激励对附体激波形态和分离激波运动的控制效果.等离子体合成射流使压缩斜坡激波/边界层干扰区域的起始点向下游移动,分离泡尺寸减小,附体激波强度减弱,发生弯曲,再附点移向上游,与此同时分离激波向附体激波逼近.与f=3 kHz激励相比,f=1 kHz激励的射流流量更大,对激波/边界层干扰的影响范围更广、控制效果更好.通过数值模拟,揭示了射流与来流相互作用对下游流场的作用机理:射流与来流相互作用诱导出大尺度旋涡,大尺度旋涡耗散发展增强了近壁面流场的湍流度;压缩斜坡上游近壁面的流场性质发生变化,进而导致了压缩斜坡激波/边界层干扰区域流动的变化.

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（1024 x 512 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（is.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.