Flow Control Mechanism Of Low-pressure Turbine By Dielectric Barrier Discharge Plasma Actuator

The working Reynolds number of the low-pressure turbine is at the lowest level of the entire aeroengine.At low Reynolds number,the boundary layer separation is easy to occur,which increases the profile loss.In addition,in order to reduce the weight of the low-pressure turbine,the most effective method is to increase the blade load and reduce the number of blades.But the high load character of the low-pressure turbine changes the transverse pressure distribution in the cascade passage,and increases the reverse pressure gradient at the rear of the suction surface.It leads to the increasing of the secondary flow loss.It can be seen that studying the flow field structure of low-pressure turbine at different Reynolds numbers will provide great help for the flow control.It will be of great significance to enrich the design theory of low-pressure turbine.In this paper,the flow field of the low-pressure turbine cascade at different Reynolds number was numerically simulated.The boundary layer separation in the flow field at low Reynolds number and the main sources of the total pressure loss were analyzed in detail.The induction character of the flat plasma actuator was studied,and the actuator was applied to the flow control of the low-pressure turbine cascade flow field.The effects of plasma actuation at the end wall of the cascade,plasma actuation at the rear of suction surface and combined plasma actuation with actuator arranged at the end wall and the rear of suction surface on the low-pressure turbine cascade flow field were studied.The main conclusions are as follows:(1)The boundary layer separation is easy to occur at the rear part of the suction surface in the case of low Reynolds number,and the total pressure loss in the recirculation zone is high.With the decrease of Reynolds number,the separation point gradually moves towards the leading edge of the cascade,and the size of the separation bubble increases as well.From the leading edge of the cascade,the total pressure loss increases continuously along the streamwise direction.The shear effect caused by the mixing of wake vortices is an important reason for the continuous increase of total pressure loss downstream of the cascade.(2)When the applied voltage rises to about 30 k V,the induced effect of the actuator on the air almost reached the limit.Under the condition that the applied voltage,power frequency and other parameters are constant,the disturbance range of the actuator on the flow field gradually decrease with the increase of incoming flow velocity.(3)When the plasma actuator is applied on the end wall near the leading edge of the cascade,the closer the plasma actuator is to the leading edge of the cascade,the better the control effect of the plasma actuation.The total pressure loss at outlet can be reduced by 8.2%.The plasma actuation decreases the lateral pressure gradient in the cascade passage,and suppressing the lateral movement of low-energy fluids from the pressure side to the suction side.The intensity and height of the passage vortex also decrease.(4)When the plasma actuator is applied on the rear part of the suction surface,the plasma actuator which is located inside the separation bubble has a better effect on reducing the total pressure loss at the outlet.When the applied voltage is about 15 k V,the boundary layer separation are almost suppressed,and the outlet total pressure loss can be reduced by 34%.(5)In the case of the combined plasma actuation with actuators arranged at the end wall and the rear of suction surface,the control effect of combined plasma actuation on flow field is higher than any other cases in reducing the total pressure loss and restraining the boundary layer separation.The total pressure loss at the outlet can be reduced by 48% compared with that in the baseline case.