# Special Issue \"Active Flow Control Technologies for Energy and Propulsive Systems\"  
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Correspondence: [EMAIL_ADDRESS]  
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Theoretical  
In reference [9], the mechanism of high-speed compressor cascade corner separation control with plasma actuations was investigated. Numerical simulations have been performed in order to investigate the control effects of the suction surface as well as the endwall plasma actuations in suppressing flow separation in a high-speed compressor cascade flow. The main flow structures related to the corner separation and the corresponding flow losses are firstly predicted in the absence of active flow control. Then the reduction of the corner separation flow structures through the implementation of suction surface and endwall plasma actuations are investigated. It was shown that plasma actuators improve the high-speed compressor cascade static pressure rise coefficient, while reducing the corresponding total pressure loss and blockage coefficients. In particular, the suction surface plasma actuators are suitable to suppress both corner separation vortex and airfoil separation, and they are more efficient than the endwall plasma actuators in terms of reduction of the total pressure losses However, the endwall plasma actuation is more efficient in the reduction of the flow blockage and improvement of the static pressure rise. In reference [10], plasma actuators have been applied for the optimization of steady and unsteady airloads on a compressor cascade. Plasma actuators have been located both on the pressure and on the suction side of the blade trailing edge, in this way suction side plasma actuation reproduces the effects of mechanical wing spoilers, whereas pressure side plasma actuation acts as a mechanical Gurney flap. Traveling wave mode simulations demonstrate that reductions in the peaks of the blade pitching moment can be obtained on the whole spectrum of interblade phase angles through a proper triggering of pressure/suction side actuation. Hence virtual control surfaces can provide effective load alleviation on the cascade, with potential remarkable reduction of fatigue phenomena. The control of unsteady load is confirmed also in other recent studies [11], that demonstrate the feasibility of using multiple dielectric barrier discharge (multi-DBD) plasma actuators (PAs) as a novel approach for load alleviation and stability control of airfoils in unsteady flow. As flow separation is a critical phenomenon for aircraft, flow separation control over airfoils is an important application, the effectiveness of asymmetrical and symmetrical plasma actuators for enhancing the aerodynamic performances of an airfoil is of great interest. In reference [12], a DBD plasma actuator, attached near the leading edge of an airfoil and operating in burst mode, is shown to be very effective for controlling flow separation at a Reynolds number of \(6.3\times 10^{4}\), when applied to the flows at an angle of attack higher than the stall. In the paper, guidelines for the effective use of DBD plasma actuators are proposed. A DBD plasma actuator is also applied to the flows under cruise conditions. A simple airfoil with an attached DBD actuator presents a higher lift-to-drag ratio than a well-designed airfoil. The high voltage waveform has a great effect on the control authority of the DBD plasma actuator. In reference [13], nanosecond pulsed dielectric barrier discharge (DBD) actuators have been installed on a NACA 0015 airfoil and the operation of the actuator at the dominant experimentally measured flow frequencies at stall conditions was shown to give good control authority. In recent years, fluidic actuators as synthetic jet actuators have been investigated as suitable devices for a wide range of flow control applications. Synthetic jet actuators are zero net mass flux devices, which modify lift and drag forces by altering the boundary layer and wake for a body in crossflow.