The rapid flow evolution between a plasma jet and a 20° compression ramp flow is captured by a high-speed schlieren system at Mach 2.0. Several interesting flow phenomena are observed for the first time. The pulsed jet, which generates strong perturbations, forces the crossflow boundary layer to separate and forms a forward moving shock. A typical shock-on-shock interaction occurs when the precursor shock intersects with the original shock. The interaction is initially regular, and then it transforms into an irregular one with a Mach stem connecting the precursor shock and original ramp shock.

A large interval plasma synthetic jet actuator (PSJA) with multiple slots under low pressure condition was designed to control the flow-field for high-altitude vehicle.Since the breakdown voltage decreased rapidly under low pressure condition,the distance of cathode and anode can be extended to 26 mm,much larger than that of traditional PSJA.This optimization also could make the cavity and output of actuator extend remarkably.The discharge characteristics and flow-field were researched by electric parameter measurement system and high-speed schlieren technology,respectively.The results showed that the initial jet velocity of the actuator reached 761m/s,indicating the actuator had excellent application prospect in high speed flow control.In addition,comparing with the normal perforated jet generated by the actuator,the compression wave and plasma jet appeared in an ellipse shape with a large flat portion,contributing to enhance the perturbation and momentum exchange capability.

Görtler-like vortices (GLVs) are ubiquitous in supersonic flows and have a significant influence on the local flow. However, the existence of these streamwise vortices in impinging shock wave/turbulent boundary layer interaction (ISTBLI) has been a topic in dispute for decades. By the ice-cluster based planar laser scattering technique and a simplified aerodynamic model, we obtain and analyze high-resolution images acquired at two orthogonal planes. The results support the presence of GLVs in the ISTBLI flow. A possible mechanism of their generation is provided.

The plasma synthetic jet is a new active flow control technique, which has great potentials for supersonic flow control A plasma synthetic jet actuator (PSJA) for supersonic flow control which operates under low ambient pressure is designed In order to explore the transient jet flowfield, high-speed Schlieren and electronic measurement systems are utilized to test the single-shot operating characteristics of the actuator under two ambient pressure conditions. The evolution of the jet boundary, which depicts the transient jet flowfield and can be used to estimate the flow control capability, is captured. It is found that the ambient pressure is the primary reason to affect the arc energy deposition, which directly determines the velocity of blast wave and jet front. In addition, the flow patterns of PSJA under various ambient pressures show some similarities. The jet evolution can be divided into three stages, i.e. pressure dominant stage, the inertia dominant stage and vortex ring dominant stage. During the pressure dominant stage, the PSJA could be treated as jet. For the inertia dominant stage, the Froude number decreases from 2263.82 to 21.73, indicating the inertia effect gets weakened with an intensified buoyancy effect, but the inertia effect still holds the dominant position, and this stage may be considered as the end mark of the injection process. As for the vortex ring dominant stage, large scale vortex ring becomes significant and the jet front velocity is very low but with apparent fluctuation.

Gortler-like vortices (GLVs) are ubiquitous in supersonic flows and have a significant influence on the local flow. However, the existence of these streamwise vortices in impinging shock wave/turbulent boundary layer interaction (ISTBLI) has been a topic in dispute for decades. By the ice-cluster based planar laser scattering technique and a simplified aerodynamic model, we obtain and analyze high-resolution images acquired at two orthogonal planes. The results support the presence of GLVs in the ISTBLI flow. A possible mechanism of their generation is provided. Published by AIP Publishing.

A plasma synthetic jet actuator with oblique orifice was designed.The discharge characteristics and flow field characteristics were researched by electric parameter measurement system and high-speed Schlieren technology.Results showed that compared with the actuator with normal orifice,the injection flow induced by the jet actuator with oblique orifice tended to attach the wall and behave with significant asymmetry,enhancing the jet flow control capability.Moreover,the effect of buoyancy on the evolution of high temperature plasma jet flow was observed,the normal velocity induced by the buoyancy effect altered the flow direction,and this effect got stronger at the end of the evolution.

In order to study a new type of plasma synthetic jet actuator with normal slot,the instantaneous flow field characteristics and discharging characteristics were researched by high-speed Schlieren technology and electric parameter measurement system. The results show that the initial jet velocity of normal slot actuator is 1.4 times to that with same exit area normal orifice. While the jet velocity of normal slot actuator tends to damp rapid-ly and the jet duration is much shorter,which indicate that the momentum exchange between the jet flow and the ambient flow are more violent. Moreover, the three dimensional flow field of normal slot actuator was observed and analyzed firstly, it shows that the precursor shock is more flat and the jet flow has a large uniform portion. Therefore,the normal slot actuator has great advantages in enhancing the work frequency and widening the range of flow control.

等离子体合成射流控制技术因其具有不需要外部气源、工作频带宽、射流速度高、射流净质量通量为零、低功耗、激励器形式多样、环境适应性强等特点,成为了目前针对高速流场主动流动控制技术中应用潜能大、 有望实现实际工程应用突破的流动控制装置.传统的等离子体激励器的出口多为垂直于流向或与流向成一定夹角,故垂直于流向的动量分量会对激励器的流动控制能力产生影响.为增强流向动量注入能力,拟设计一种新型的水平动量注入型等离子体合成射流激励器.主要内容有:采用外部电路电参数测量与高速纹影技术,对激励器常压下单周期工作特性与重频工作特性进行了初步研究.对水平动量注入型等离子体合成射流激励器的射流结构进行了分析,探究了该激励器工作频率对射流流场的流场特性与控制能力的影响.最后在高速纹影测量的基础上,开展了激励器高频工作时均出口动压的研究.实验表明:水平动量注入型激励器单周期射流初始速度达到220 m/s,单周期激波初始速度达到477 m/s.此外,工作频率对于激励器的影响主要体现在对激励器控制范围的影响,当激励器工作频率增高时,在相同位置时激励器的动压输入能力下降.

Graphical Abstract NPLS image of surface A at M 0 = 3

A rectangular hypersonic inlet is tested at the low-speed mode (Ma 5), the design mode (Ma 6), and the overspeed mode (Ma7) to enrich the understanding of hypersonic-inlet unstart. A flow plug is placed at the duct exit to simulate the combustion-induced high pressure and initiate the inlet unstart. High-speed schlieren imaging and time-resolved pressure measurements are used simultaneously to record the unsteady-flow structures and surface pressures of the unstart process. The results indicate that the unstart processes are basically the same for the low-speed mode and the design mode. An unstart phenomenon dominated by the ramp-side flow separation, which exhibits violent fluctuations along the entire duct with a low frequency, is observed at these two operating modes. While operating at the overspeed mode, the strong shear layer, induced by the Mach reflection of the coalesced external oblique shock, divides the internal flow into two parts. The cowl side is filled by fully subsonic flow after the compression of the detached normal shock, and the ramp side mainly contains supersonic flow downstream of the shear-layer-induced oblique shock. Therefore, a real-time adjustment of the detached cowl shock to the downstream high pressure is formed, keeping the entire flowfield of the inlet from oscillation in a much wider range of throttling ratio. With a further increase of the throttling ratio, an oscillation dominated by the cowl-side reversed flow occurs. The oscillation phenomenon exhibits relatively gentle fluctuations, and the characteristic frequencies are mainly determined by the shock train in front of the throat section.