Plasma synthetic jets (PSJs) have received widespread attention because of their rapid response capability. The use of PSJ shock and thermal effects for active flow control has been investigated in many recent studies. Through numerical simulation, this study found that the geometric position of a PSJ actuator on an airfoil surface is the key factor affecting flow control effects. Different geometric positions have different effects on the lift-drag characteristics of an airfoil, and the flow control mechanism has different components. The flow control mechanism can be divided into three types: the thermal effect, the coupling of the thermal effect and single shock, and the coupling of thermal effect and multiple-shock rebound. The concept of distance $l_{\mathrm{placement}}$ provides a reference for determining the geometric arrangement of a PSJ actuator. This study showed that in addition to improving the lift-drag characteristics of an airfoil by reducing drag, directly increasing lift is also a new choice. In addition, in a confirmatory experiment, the nanosecond pulse PSJ actuator pushed the bow shock in a Mach 5 flow; the longest distance was about 1% of the characteristic length of the airfoil. In this work, a new type of plasma actuator was used for flow control in hypersonic flow. The influence of the geometric position of the actuator on flow control and the corresponding flow control mechanisms were investigated. This work provide a reference for most work using actuators. For example, the geometric position of an actuator can be selected according to $l_{\mathrm{placement}}$ defined in this work and the parameters of the actuator can be set according to the parameter settings of the PSJA. For aerodynamics research, this work provides a new research idea for improving the aerodynamic performance of aircraft. If drag reduction is difficult to achieve, then increasing lift is also a feasible method. For research on plasma flow control, this work broadens its application to hypersonic flow and reveals that a plasma actuator has two flow control effects at the same time. PSJA conducts flow control through the impact effect of the diffracted wave and the mixing effect of the high-temperature cluster; this provides a reference for relevant personnel.

Pulsed surface arc discharge (PSAD) is one of the essential techniques in flow control. In this paper, the effects of electrode configuration on heat transfer characteristics of PSAD and disturbance characteristics of PSAD on the flow field were investigated by thermal imaging technology and high-speed photography technology. By defining the curvature of curve (COC) of the electrode, we investigated the physical mechanism of the electrode configuration, affecting the PSAD disturbed flow field. The results show that the COC has the optimal solution COCopt. When COC ≤ COCopt, the smaller the COC, the more concentrated the PSAD disturbances to the flow field. When COC > COCopt, the electrode configuration will have an end point effect, resulting in a deviation between the theoretical COC and the real COC. The larger the COC, the stronger the end point effect, and the more concentrated the PSAD disturbances to the flow field. The COC affects the disturbance degree of PSAD to the flow field by distorting the electric field intensity distribution. The change in the electric field intensity causes the fluctuation frequency of the flow field to be inconsistent with the discharge frequency of the PSAD. The stronger the distortion degree of the electric field intensity, the stronger the high-frequency characteristics of the fluctuating frequency of the flow field, and the stronger the high-frequency characteristics of the flow mode of the flow field. In addition, we obtained the value range of COCopt within 0.5–0.7 through theoretical derivation and established a mathematical model of electrode structure's effect on the flow field's flow structure.

This study investigates the characteristics of a shedding vortex around the Coanda surface and its impact on circulation control (CC) performance. Delay detach-eddy simulation based on the two-equation k−ω shear stress transport (SST) turbulence model is performed to solve the flow field. The simulation results show that near the Coanda trailing edge, large vortices periodically shed from the lip above the jet slot, and the shedding vortex is surrounded by a series of strip vortices during its downstream movement. The shedding vortex transfers the disturbance to the jet boundary layer and affects the near-wall velocity. Dynamic mode decomposition shows that the shedding vortex and its high-order harmonic flow structures attenuate very slowly and dominate the flow field. The mode with sub-harmonic frequency of the shedding vortex displays the strip vortices dragged out by the shedding vortex. A larger shedding vortex can intensify the mixing of the jet shear and boundary layers, making the jet velocity decay faster. The size of the shedding vortex can be reduced by decreasing the lip height, thus slowing down the attenuation of the jet velocity and improving the CC performance.

A better understanding of the mechanism of flow separation suppression by dielectric barrier discharge is essential for flow control. This paper investigates the mechanism of improving the aerodynamic performance of the airfoil by dielectric barrier discharge when the Reynolds number is in the range of 6×10⁴~4×10⁵. The results show that the disturbance of the gas discharge to the flow field will form a new flow structure. The fluctuating frequency of the new flow structure determines the ability of the plasma actuator to suppress flow separation. This investigation improves and develops the mechanism of plasma flow control.