To discover the characteristic of separated flows and mechanism of plasma flow control on a highly loaded compressor cascade, numerical investigation is conducted. The simulation method is validated by oil flow visualization and pressure distribution. The loss coefficients, streamline patterns, and topology structure as well as vortex structure are analyzed. Results show that the numbers of singular points increase and three pairs of additional singular points of topology structure on solid surface generate with the increase of angle of attack, and the total pressure loss increases greatly. There are several principal vortices inside the cascade passage. The pressure side leg of horse-shoe vortex coexists within a specific region together with passage vortex, but finally merges into the latter. Corner vortex exists independently and does not evolve from the suction side leg of horse-shoe vortex. One pair of radial coupling-vortex exists near blade trailing edge and becomes the main part of backflow on the suction surface. Passage vortex interacts with the concentrated shedding vortex and they evolve into a large-scale vortex rotating in the direction opposite to passage vortex. The singular points and separation lines represent the basic separation feature of cascade passage. Plasma actuation has better effect at low freestream velocity, and the relative reductions of pitch-averaged total pressure loss coefficient with different actuation layouts of five and two pairs of electrodes are up to 30.8% and 26.7% while the angle of attack is 2°. Plasma actuation changes the local topology structure, but does not change the number relation of singular points. One pair of additional singular point of topology structure generates with plasma actuation and one more reattachment line appears, both of which break the separation line on the suction surface.
This paper reports experimental results on the effects of plasma aerodynamic actuation(PAA)on corner separation control in a highly loaded,low speed,linear compressor cascade.Total pressure loss coefficient distribution was adopted to evaluate the corner separation control effect in wind tunnel experiments.Results of pressure measurements and particle image velocimetry(PIV)show that the control effect of pitch-wise PAA on the endwall is much better than that of stream-wise PAA on the suction surface.When both the pitch-wise PAA on the endwall and stream-wise PAA on the suction surface are turned on simultaneously,the control effect is the best among all three PAA types.The mechanisms of nanosecond discharge and microsecond discharge PAA are different in corner separation control.The control effect of microsecond discharge PAA turns out better with the increase of discharge voltage and duty cycle.Compared with microsecond discharge PAA,nanosecond discharge PAA is more effective in preventing corner separation when the freestream velocity increases.Frequency is one of the most important parameters in plasma flow control.The optimum excitation frequency of microsecond discharge PAA is 500 Hz,which is different from the frequency corresponding to the case with a Strouhal number of unity.
To discover the flow behavior in the endwall region and mechanism of plasma flow control on a highly loaded compressor cascade, distributions of static pressure coefficient, total pressure loss coefficient and streamline pattern were investigated. Results show that cross flow from the pressure surface to neighboring suction surface exists under pitch-wise pressure gradient. The deflected endwall boundary layer flow interacts with the incoming flow, and then both of them leave off the endwall in the form of a span-wise vortex. Effect of angle of attack on static pressure is greater than that of free stream velocity. The distinct variations of total pressure loss with endwall actuations are mainly located within the outer verge of a triangular area with high total pressure loss. Effect of pitch-wise actuation on separated flows is much better than that of stream-wise actuation, and both enhance with the increase of angle of attack and actuation strength. An efficient method for plasma flow control in the endwall region is the increase of actuation strength, such as adjusting discharge voltage or changing plasma power supply.
