The actuations generated by the plasma synthetic jet actuator (PSJA) may become weak under multiple pulses when the discharge frequency increases. In order to further study the frequency characteristics of the actuations, the high-speed Schlieren method is adopted for the experimental study on a nanosecond plasma synthetic jet actuator (NS-PSJA) made of the machinable ceramic. Three typical working states are captured by the numbers of Schlieren measurements, which are continuous, critical, and discontinuous states. For a deep understanding, the relationship between the discharge frequency and the working states of the NS-PSJA is discussed in two aspects: heat and electric charge. The critical and the saturated discharge frequencies are defined, respectively. In addition, the effects of the geometry on the frequency characteristics of the NS-PSJA are also studied such as the shape of the orifice, the electrode spacing, the depth of the cavity, and the height of the electrode. The results suggest that those geometric parameters affect the accumulation of the heat and electric charge, causing the changes of both the critical and the saturated discharge frequencies.

The plasma synthetic jet actuator (PSJA) has been proven to have potential for shock wave control in the supersonic/hypersonic flow. To evaluate the possibility for the PSJA applied in the hypersonic inlet under a Mach number greater than the design value and provide a deeper understanding of its control mechanism, the relevant two-dimensional numerical simulations are carried out. Based on the discussions about the numerical results, the effects are clear of the actuations generated by the PSJAs, including diffracted waves, synthetic jets, and discharged heat, on the oblique shock waves induced by the compression ramps and the aerodynamic performance of the hypersonic inlet. Concretely, the shapes of the oblique waves are changed by propagations of the diffracted waves, whose starting point moved due to the synthetic jets. A deceleration occurs near the surface of the hypersonic inlet caused by the movement of the discharged heat, leading to a thickener boundary layer. Furthermore, the incremental analysis about the total pressure recovery coefficient at the throat shows that the diffracted waves can increase the static pressure at the throat achieving a higher total pressure recovery coefficient, while the discharged heat makes the total pressure recovery coefficient drop due to a lower local Mach number at the throat. The effect of the discharged heat is more obvious than that of the diffracted waves.

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.

An experimental study was conducted with the aim of alleviating the vertical tail buffeting of a 55° delta wing using pulsed nanosecond dielectric barrier discharge plasma actuators. The flow physics in the event of wing stall, flow reattachment, vortex breakdown, shear layer under plasma actuation were obtained and analyzed, and results indicate that plasma actuation promotes flow attachment and manipulates the shear layer. The acceleration results indicate that the structural response of the vertical tail increases with an increasing angle of attack, and the first bending mode response increases most significantly at the post-stall angle. Manipulation of flow field by plasma actuation produces a considerable reduction in buffeting response and mainly controls the first bending mode. The characteristics of velocity fluctuations show two important factors affecting buffeting: the redistribution of loads and the spectrum change of fluctuations, both of which are related to the movement of the impingement point of the shear layer onto the vertical tail controlled by plasma actuation. Theoretical analysis indicates that the impingement point moving downward in the vertical direction of the vertical tail under plasma actuation is the main reason for reduction of the first bending mode response.

To delay the position of vortex breakdown and increase the lift characteristics of the flying wing aircraft, the vortex breakdown characteristics of a flying wing aircraft under jet flow control were studied based on numerical simulation. The design idea of jet excitation selection based on the natural helical mode frequency of the aircraft is proposed. The flow fields and frequency spectrum characteristics of aircraft before and after applying steady and unsteady excitation are analyzed. The results show that under the same jet momentum coefficient, the control method of unsteady excitation has more advantages. The control effect of excitation frequency in the range of helical mode instability frequency is generally better than that outside the helical mode. When the excitation frequency is consistent with the peak value of the main frequency of the upstream helical mode, optimal control effect is obtained, which has the most supplement to the axial velocity and obvious suppression effect on the separation zone. Moreover, periodic energy injection can enhance the peak value characteristics of the main frequency, make the frequency range of the downstream flow field develop toward high frequency, and accelerate the rotation of the flow field after the vortex breakdown.