Numerical Study Of Flow Separation Control Of Compressor Cascade Using DBD Plasma Actuator

With the increase of aeroengine performance, the compressor, as one of the most important parts must have a higher pressure ratio in one stage and less numbers of compressor stages. As the pressure ratio rises, flow separation occurs due to the effect of a large adverse pressure gradient, resulting in an increase in energy loss and a deterioration of the aerodynamic performance. The control of flow separation in the compressor cascade therefore is an important method to increase its aerodynamic performance. Traditional flow control methods, such as suction and blowing, add an additional loss to the compressor cascade, so the application of the plasma actuator becomes a hot research topic due to its advantages, such as less input energy and simple structure.The application of the plasma actuator to flow separation control has been studied by the domestic and foreign scholars from the aspect of theoretical and experimental investigation. And so far, there is no application of plasma actuator to the compressor cascade with a large turning angle.In the present paper, the DBD plasma actuator was applied to the NACA 65 compressor cascade with a large turning angle. First, three types of simplified models were derived based on the public literatures, and numerical simulations on the models were carried out to find the optimum simplified model. And then the optimum model was used in the compressor cascade to control the flow condition. The plasma actuator was installed on the suction surface at different streamwise positions, including 40%,50%, 60% and 70% of the axial chord. Different operating voltages were adopted on the plasma actuator, including 5kv,20kv and 30kv.The results show that it is able to control the flow separation by using the plasma actuator under the design attack angle. In the compressor cascade without the plasma actuator, the separation line on the suction surface starts from 35% of axial chord. After the plasma actuator is used, the starting position of the separation line does not change, but the intensity of the separated flow decreases, and at the same time the height of separation line at the trailing edge reduces. Energy loss presents in the middle of blade because of accumulation of the low-energy fluid and flow separation within the boundary layer. As the plasma actuator locates downstream and the applied voltage increases, the total pressure loss decreases, but it changes little near end wall. Flow under-turning occurs along the whole blade height in the cascade without the plasma actuator. After the plasma actuator is used, the deviation reduces while the flow turning increases near the midspan, but over-turning due to the secondary flow changes little near the hub region. The adverse pressure gradient happens from 15% of axial chord in the compressor cascade without plasma actuator. After the plasma actuator is used, a negative pressure gradient occurs at the interface between the two electrodes, which increases the local flow speed, and hence improves the ability to resist flow separation. The plasma actuator can enhance the airflow energy near the end wall, thus cause the airflow move downstream. In addition, the plasma actuator can act as a fence, which can prevent the low-energy fluid from accumulating towards the midspan. Through the above two functions, the plasma actuator can weaken the intensity of the passage vortex which is caused by the secondary flow, and decrease the influential area of the passage vortex. It therefore can decrease the total loss of compressor cascade.The effects of the plasma actuator was also investigated under off-design incidences by analyzing the exit flow angle, total pressure loss, static pressure along the blade surface and secondary flow. The mechanism of the plasma actuator to control the flow separation is similar to that in the case of design incidence.