# Control of Corner Separation with Plasma Actuation in a High-Speed Compressor Cascade
## 4 Discussion and Conclusions  
Both the suction surface and the endwall plasma actuations can improve the high-speed compressor cascade static pressure rise coefficient, while reducing the corresponding total pressure loss and blockage coefficients. The ability of the plasma actuations to improve the high-speed compressor cascade static pressure rise coefficient is slightly influenced by the incidence angles. However, the abilities of the plasma actuations to reduce the high-speed compressor cascade total pressure loss and blockage coefficients are closely related to the incidence angles. At negative incidence angles, the pressure side separation plays a very important role in the generation of the high-speed compressor cascade total pressure loss and blockage coefficients. As a result, the suction surface and the endwall plasma actuations are quite inefficient in reducing the high-speed compressor cascade total pressure loss as well as blockage coefficients. In future studies, the pressure side plasma actuation may be used to control the high-speed compressor cascade flow separation at negative incidence angles. At large positive incidence angles, both the suction surface and the endwall plasma actuations are very inefficient in suppressing the high-speed compressor cascade corner separations at large scales too. The fact that the scope of the influence of plasma actuations is limited to the regions near solid surfaces is responsible for this phenomenon. For the same reason, with the increase of the body forces of plasma actuators, the relative reduction rate of the high-speed compressor cascade blockage coefficient increases more and more slowly with the suction surface plasma actuation. Thus, in future studies, a brand new three-dimensional plasma actuator, which can influence flow fields far away from solid walls, may be used to control the high-speed compressor cascade corner separations at large scales.  
The suction surface plasma actuation can suppress not only the high-speed compressor cascade corner separation vortex (WV) but also the airfoil separation, so it is more efficient in reducing the total pressure loss of the high-speed compressor cascade. This finding is in accordance with the results of [PERSON] et al. [22], which point out that, compared with the endwall plasma actuation, the plasma actuation on the blade suction surface contributes the most to the improvement in the total pressure loss of the compressor cascade. However, this paper finds that, through suppressing the development of the PV, the endwall plasma actuation is more efficient in reducing the flow blockage and improving the static pressure rise of the high-speed compressor cascade. As a matter of fact, the PV is the main flow structure that determines the characteristics of the high-speed compressor cascade corner separations. Since the formation and development of the PV are determined by the movement of endwall boundary layer, the suction surface plasma actuation is incapable of influencing the PV effectively. Thus it can be concluded that the endwall plasma actuation is more efficient in suppressing the high-speed compressor cascade corner separation than the suction surface plasma actuation. In future studies, based on the mechanisms by which they control the high-speed compressor cascade flow, both the suction surface and the endwall plasma actuation layouts should be optimized to obtain better control effects, while minimizing the power consumption.  
This paper was supported by the National Natural Science Foundation of China (Nos. 51336011, 51376014, 51476004). Thanks go to [PERSON] of DLR for advising on the NACA65-K48 airfoil data.  
[PERSON] performed the simulations and wrote the paper. [PERSON] and [PERSON] contributed to the analysis of the simulation results. [PERSON] and [PERSON] contributed to the design of the plasma actuation layouts.  
The authors declare no conflict of interest.