New Sawtooth Plasma Actuator Configuration And Mechanism Behind Improved Control Performance

The flow separation control of the airfoil is of great significance in engineering.Flow separation means that during the flight of the aircraft,due to the angle of attack of the airfoil increases,the boundary layer of the airfoil suction side separates from the surface under the effect of the large adverse pressure gradient and form a large wake behind the airfoil,causing the aircraft stall.Based on this background,we analyzed the relevant flow control mechanism and improved the configuration of the plasma actuator to further improve the control effect under high Reynolds number.In this paper,a new configuration sawtooth plasma actuator is developed to control the flow separation of NACA 0015 airfoil at the range of Reynolds number of 0.77×10~5?3.0×10~5.The research is mainly carried out in the following aspects: Firstly,the aerodynamic performance of the airfoil under different actuation modes is measured and determined the optimal control parameters corresponding to different Reynolds numbers.The hot wire anemometer is used to research the development and detachment of the vortex structure,then analyze the changes of the flow field structure at different conditions and positions,and find out the cause of the sudden fluctuation of the instantaneous lift.Through the experiment of the smoke wire flow visualization and particle image velocimetry,the flow separation control mechanism of the new configuration actuator is explored.For the improvement of airfoil aerodynamic performance,research shows that the new actuator can improve the aerodynamic performance of the airfoil more effectively than the traditional method: when the Reynolds number is 0.77×10~5,the optimal control parameters are burst frequency F+ = 0.6,duty cycle DC = 5%,the maximum lift coefficient is increased by 28.6%,the stall angle is delayed by 6o.When the Reynolds number is 3.0×10~5,the optimal control parameters are F+ = 6.0,DC = 60%,the maximum lift coefficient is increased by 9.8%,the stall angle is delayed by 4o.Under the same conditions,the flow control effect of the new configuration actuator is much better than the traditional one.For the mechanism exploration,due to the velocity and flow angle of the plasma-induced jet change periodically along the span direction,an unstable threedimensional disturbance is generated in the flow field.The induced jet generated by the actuation interacts with the natural incoming flow and mixes to form a synthetic flow in the downstream direction.The velocity and angle both periodically change along the spanwise direction,forming lots of vortexes of different scales and strengths.These trajectories of alternating large and small vortices closely follow the suction surface of the airfoil,and move from the leading edge of the airfoil to the trailing edge,which greatly increases the momentum entrainment inside and outside the shear layer.Then,the suction of the upper surface ascending rapidly,so that the differential pressure between the upper and lower surfaces increases,creating additional lift of the airfoil.At the same time,the unstable disturbance promotes the transition of the laminar flow to the turbulent flow and the larger area reattachment of the airfoil surface.