# Control of Corner Separation with Plasma Actuation in a High-Speed Compressor Cascade
## 1 Introduction  
Corner separations always occur at the conjunctions between the compressor blade suction surface and the endwall. Modern gas-turbine engines are being designed with highly loaded compressors, and the associated strong adverse pressure gradient will cause the detrimental effects of corner separations to be unacceptable. In practice, it is these separations that greatly limit the compressor blade loading and efficiency by their impact on loss, blockage, and deviation [1; 2; 3]. Throughout the years, both the traditional passive and active flow control methodologies have been used to control the compressor corner separations. Passive flow control methodologies such asboundary layer fences [4; 5], non-axisymmetric endwall contouring [6; 7], and vortex generators [8; 9; 10] etc. can effectively reduce the detrimental effects of corner separations on the design conditions. However, at off-design conditions, extra flow mixing and separations induced by the passive methodologies may increase the flow blockage and loss. On the contrary, active flow control methodologies can be used to control the corner separations at the desired work conditions while being kept turned off at other work conditions to avoid bringing extra blockage and loss to the compressor flow field [11; 12; 13; 14]. Plasma actuation is a typical active flow control methodology and has been proven to be capable of controlling both the compressor stall and corner separations effectively. [PERSON] et al. [15] experimentally studied the control effects of plasma actuation on the corner separations in a low-speed compressor cascade. Their results show that both steady and unsteady plasma actuation on the blade suction surface could control the corner separations effectively, and the unsteady plasma actuation achieved a better control effect. Based on their findings, they concluded that the unsteady plasma actuation could induce more vortex structures, and this was the reason that the unsteady plasma actuation could achieve a better control effect in suppressing the corner separations. Later, [PERSON] and [PERSON] et al. [16; 17; 18; 19] applied the plasma actuation to control the corner separations in a low-speed highly loaded compressor cascade. They used topological and vortex analysis theories to study the physical mechanisms of both the blade suction surface and the endwall plasma actuations in suppressing corner separation and found that the control effects of plasma actuations in suppressing corner separation are closely related to their ability to change the vortex structures within the corner separation. [PERSON] et al. [20; 21] also conducted a series of research on the control of compressor cascade flow separation with plasma actuation. They developed a micro plasma actuator and applied it to control the flow separation in a highly loaded subsonic compressor cascade and found that the plasma actuation could increase the pressure rise ability of the compressor cascade while decreasing the corresponding total pressure loss. Based on their findings, they concluded that increasing the actuation voltage can enhance the control effect of plasma actuation, but, from an energetic point of view, the plasma actuation with lower voltage is more efficient [21]. In 2016, [PERSON] et al. [22] published their studies on the plasma control of the compressor corner separation. They evaluated the effects of plasma actuations placed on the blade suction surface and the endwall respectively by suppressing the corner separation in a low-speed highly loaded compressor cascade with both numerical and experimental methods and found that the plasma actuators mounted upstream of the separation on both the suction surface and the endwall were most effective in suppressing the corner separation, while most of the improvement in total pressure loss stemmed from the suction surface actuator.