Reducing turbulent skin friction drag is a fundamental goal for aircraft transportation to conserve energy and decrease emissions. We introduce an annular dielectric barrier discharge plasma actuator (A-DBD-PA) that merges the advantages of near-wall micro-blowing with pulsed plasma flow control to reduce turbulence drag. Wind tunnel experiments on a flat plate assessing the performance of A-DBD-PA revealed that the wall-normal jet on the symmetry plane is critical for turbulent drag reduction in an unsteady flow field. As the duty cycle of plasma actuation increases, it steadies the wall-normal jet, which diminishes shear stress and velocity fluctuations in the boundary layer. This enhanced steadiness fosters induced vortices' formation and evolution, directly impacting the drag reduction rate. Duty cycles below 50% yield a limited drag reduction rate because the airflow's viscous effects predominate over the influence of plasma actuation. Conversely, duty cycles above 50% enhance the interaction of induced vortices, contributing to a stronger disturbance and more effective control, optimizing drag reduction rate up to a maximum of 5.197%.

Slender-body aircraft operating at high angles of attack often experience nonlinear, asymmetric multi-vortex flow structures that generate random, unsteady lateral forces, undermining stability, and maneuverability. Dielectric barrier discharge plasma actuators can eliminate these lateral forces. However, conventional open-loop plasma control method cannot adapt to dynamic flow fields in real time, limiting the overall effectiveness of active flow control. This study introduces a plasma control framework grounded in physical principles and develops plasma actuator design methods to regulate vortex interactions, stabilize flow dynamics, and optimize control efficiency. An intelligent closed-loop flow control strategy based on proximal policy optimization, a deep reinforcement learning algorithm, is utilized to enable real-time plasma parameter adjustments for suppressing lateral force at high angle of attack. The spatiotemporal interaction of plasma-induced and asymmetric vortices was investigated through synchronized pressure measurements and particle image velocimetry. The proximal policy optimization-based parameter optimization model was trained online in an educational open-return wind tunnel and subsequently deployed in a low-speed closed-return wind tunnel. Based on vortex stability analysis and comprehensive results, the closed-loop control algorithm significantly mitigates lateral forces, achieving a 68.5% reduction compared to steady plasma actuation, while improving energy efficiency by 70% over conventional methods.

Dielectric Barrier Discharge (DBD) plasma actuators can generate trains of vortices under burst mode actuation, which is very different from the wall jet flow under steady operation. To clarify the mechanism of DBD under burst mode actuation on separation control, the improved simulation model of burst-mode plasma actuation was developed and validated, and then, the flow field of NACA0015 under 12° and 14° of stall was numerically simulated and compared with the experimental result simultaneously. The results show that the DBD plasma actuator under burst mode actuation is very efficient for separation flow control, and the ability of separation flow control under F⁺ = 10 is more efficient than that under F⁺ = 0.3–5 investigated. The mechanism of burst mode actuation proposed that trains of vortices shed by burst mode actuation could enhance the momentum transfer between the boundary layer and the main flow, and the vortex of large scale shed from the leading edge could merge with the vortices of small scale shed by the DBD plasma actuator with burst mode actuation, which results in the reattachment of separated flow.

Plasma control of forebody asymmetric vortices is mostly achieved by means of dielectric barrier discharge (DBD) plasma actuators. However, DBD actuators suffer from some disadvantages such as a weak induced body force, a single-direction induced jet, and an unclear control mechanism. We carry out wind tunnel experiments involving the forebody vortex control of a slender body at high angles of attack using an innovative extended DBD actuator, which has a stronger capacity to induce an electric wind than a DBD actuator. Through synchronous measurements of the pressure distribution and particle image velocimetry (PIV), the spatiotemporal evolution of the dynamic interactions between plasma-actuation-induced vortices and forebody asymmetric vortices is analyzed. The influence of plasma discharge on the boundary layer separation around a slender body and the spatial topological structures of asymmetric vortices are further surveyed, as the optimized actuation parameters. Extended DBD actuators are found to be more capable of controlling asymmetric vortices than DBD actuators, and a linear proportionality of the sectional lateral force versus the duty ratio is achieved. There exists an optimal normalized reduced frequency (f ⁺ = 2π f _p d/U _∞ = 2.39) for asymmetric vortex control under the present experimental conditions. The research results can provide technical guidance for the control and reuse of forebody asymmetric vortices.

The primary issue regarding the plasma synthetic jet actuator (PSJA) is its performance attenuation at high frequencies. To solve this issue, a self-supplementing, dual-cavity, plasma synthetic jet actuator (SD-PSJA) is designed, and the static properties of the SD-PSJA are investigated through experiments and numerical simulations. The pressure measurement shows that the SD-PSJA has two saturation frequencies (1200 Hz and 2100 Hz), and the experimental results show that both the saturation frequencies decrease as the volume of the bottom cavity of the SD-PSJA increases. As the size of the supplement hole increases, the first saturation frequency increases continuously, while the second saturation frequency shows a trend of first decreasing and then increasing. Numerical simulations show that the working process of the SD-PSJA is similar to that of the PSJA, but the volume of the cavity in the SD-PSJA is smaller than that of the PSJA; the SD-PSJA can supplement air to the top cavity through two holes, thus reducing the refresh time and effectively improving the jet intensity of the actuator at high frequencies.

Reduction of turbulent drag force is one of important works in the design of airplanes and hypersonic aircrafts. The annular plasma synthetic jet (APSJ) has become an interesting and popular flow control method in reducing the drag of turbulent boundary layers. In this paper, a comprehensive experimental study is carried out on the turbulent drag reduction regulated by an array of annular plasma synthetic jet actuators. The effects of the operating parameters such as the actuation voltage, the pulse frequency and the incoming wind speed on the drag reduction rate are studied and discussed in detail. The performances of the plasma actuator array are evaluated and summarized at multiple working conditions. Finally, the coherent structures of turbulence and the hairpin-like vortices are depicted and discussed. The results show that the optimal drag reduction rate is achieved, as the actuation voltage, pulse frequency and incoming wind speed are Vpp = 7 kV, fp= 50 Hz, and U∞ = 7 m/s, respectively. A resonant coupling phenomenon is observed when the pulse frequency of the actuators approaches the characteristic frequency of the coherent structure. The upward sweep flow induced by APSJ actuators may lead to a reduction of the turbulent drag force, but the downward wash flow leads to an increase in the drag. Present study could provide solid experimental data and a helpful guidance for the drag reduction of an airplane.