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A plasma synthetic jet actuator with a high-frequency oblique slot was designed for supersonic flow control. The actuator's periodic operation characteristics were investigated using electrical parameter measurements and high-speed schlieren techniques. Experimental findings indicate that the actuator can stably operate within the frequency range of 0–2400 Hz. With increasing operating frequency, the breakdown voltage, maximum current, and discharge energy decrease, while the energy efficiency of the discharge increases. Moreover, the experiment revealed for the first time that an increase in the number of charged particles within the cavity leads to a decrease in breakdown voltage, and the concentration of charged particles reaches saturation at approximately 1200 Hz. High-speed schlieren observations indicate substantial inter-cycle influences in the periodic jet. At higher operating frequencies, the impact of inter-cycle flow field effects becomes more pronounced. The oblique slot plasma synthetic jet exhibits clear directionality in the distribution of shock waves and jet. The oblique slot jet also shows a significant wall attachment effect. These characteristics are beneficial for enhancing the flow control capability of the actuator. At 1200 Hz, the actuator achieves a discharge efficiency of 63% and a maximum jet front velocity of 309 m/s, showcasing its superior overall performance. [ABSTRACT FROM AUTHOR]

Herein, a curved isolator with sidewall contraction of a hypersonic scramjet is extracted and simplified. The flow characteristics in the isolator with an entrance Mach number of 3.46 are studied. The results show that the lateral contraction of the sidewall generates a strong shock and its subsequent reflected shock, which induce glancing shock wave/boundary layer interaction (GSWBLI), rolling up large-scale vortices adjacent to the symmetry plane. As the downstream backpressure increases, the shock train propagates upstream and interacts with the glancing shock and vortices inevitably, forming a typical shock train/glancing shock/boundary layer interaction (STGSBLI) phenomenon. Different from the shock train in a straight isolator, it can be divided into two distinct parts, i.e., the center part and the side part. For the center part, it behaves in a quasi-two-dimensional manner, which is primarily associated with STGSBLI, forcing the low-momentum subsonic flow to principally accumulate near the symmetry plane and weakening the spanwise pressure gradient in the center part. For the side part, it locates behind the glancing and reflected shocks and is much shorter than the center part, resulting in a streamwise extension of the supersonic flow region near the sidewall. As the shock train moves upstream, the quasi-two-dimensional region enlarges and extends to the sidewall. It is demonstrated that the aforementioned two parts of the shock train can also be discovered in curved sidewall-contraction isolators with different centerlines. Therefore, the STGSBLI is the dominant and universal physical phenomenon in isolators with sidewall contraction. [ABSTRACT FROM AUTHOR]

A hypersonic inlet/isolator acts as the "compressor" for scramjet engines through a series of shocks, which induces complex internal flows. This paper comprehensively reviews the recent research achievements, focusing on the shock-dominated internal flow of an inlet/isolator. Considering the specific geometrical feature of the hypersonic inlet, the shock wave/boundary layer interactions (SWBLIs) are characterized by multiple successive shocks. Three types of couplings have been observed between adjacent interaction regions. Moreover, shock and expansion waves, which are induced by the SWBLIs and named "background wave", are reflected in an isolator, forming a background wave/shock train interaction flow. The shock train behavior significantly differs from that in direct-connect facilities under uniform incoming flow conditions, and energy-level-transition-like phenomenon is observed when the shock train intersects with the background wave. Four types of quasi-steady background wave/shock train interactions have been reported, and three types of dynamic transitions have been observed when the shock train passes across the reflection point of the background shock. After the shock train is expelled from the internal duct, the inlet/isolator falls into unstart, and the unsteady shock-dominated flow with violent low-frequency shock oscillation occurs. A typical unstart period contains several stages, including the motion of the shock train in the isolator, large-scale separation in the inlet, and shock oscillation at the external part of the inlet. The flow mechanics of the hypersonic inlet/isolator unstart differs from that of a supersonic inlet. An unstart loop for a hypersonic inlet/isolator has been proposed, including convection wave, shock train, and acoustic wave. Once the induced factor of the unstart is removed, the unstarted shock retreats and the inlet experiences restart with the rebuilding of the supersonic flow. The restart process is highly dependent on the initial flow state and the historical effect. An instantaneous buzz arises before the unstarted shock retreats into the internal duct. Finally, the related passive (e.g., micro-vortex generator, bump, boundary layer bleed and self-circulation secondary flow control method) and active flow control methods (e.g., air jet vortex generator, plasma jet flow control, and solid-particle injection) for weakening the unfavorable impact of these shock-dominated flows are reviewed. Furthermore, the control mechanics and control effects of these flow control methods are analyzed. [ABSTRACT FROM AUTHOR]