Study On Flow Control Of Airfoil With High Reynolds Number By Synthetic Jet

The lift-drag ratio of airfoil increases with the increase of angle of attack.However,when the angle of attack exceeds a certain critical value,the suction surface of the airfoil will generate a large backpressure gradient with the increase of the angle of attack,which leads to flow separation on the suction surface of the airfoil rear.Flow separation can make the lift of airfoil decrease rapidly,and the drag will continue to rise,resulting in"stall" phenomenon.In this paper,synthetic jet technology is used to control the flow of S809 airfoil at high Reynolds number.The mechanism of synthetic jet controlling the flow separation of airfoil is studied in detail.The orthogonal experimental design method was used to optimize the parameters of synthetic jet,such as jet angle,jet frequency and jet velocity.The control effects of single and two synthetic jets on boundary layer separation of airfoil are compared and analyzed.In addition,the dynamic stall of airfoil controlled by synthetic jet is discussed.The specific conclusions of this paper are as follows:(1)The jet vortices generated by the synthetic jet will induce the high-speed fluid on the suction surface of the airfoil to enter the boundary layer,and the low-speed fluid at the bottom of the boundary layer will be mixed with the high-energy fluid of the mainstream region,thus overcoming the adverse pressure gradient and delaying the flow separation.Two jet actuators can produce higher-speed,higher-flow jets.The suction surface pressure of airfoil controlled by two jet actuators is lower than that controlled by a single jet actuator,and the pressure difference between upper and lower wings is larger.The two jets inject more energy into the flow separation zone of the upper wall surface of the airfoil to better improve the flow separation and improve the aerodynamic characteristics of the airfoil.(2)Jet frequency,jet angle and jet velocity determine the size and location of jet vortices,which have an important impact on the flow field of airfoils.The three parameters are optimized by the orthogonal test design.The lift-drag ratio of airfoil was improved by optimizing the j et parameters.When the inflow angle of attack is equal to 11°,the lift-drag ratio of the airfoil is increased from 37.1 to 48.3 after optimizing the j et parameters.When the inflow angle of attack is equal to 19°,the j et is in a deep stall state,and the lift-drag ratio of the airfoil improved from 13.5 to 16.9 after the optimization of the j et parameters.When the inflow angle of attack is equal to 230°and the airfoil is in full stall state,the lift-drag ratio of the airfoil can not be affected by the jet before optimization,but the value of the lift-drag ratio has been expanded from 2.1 to 12.6 after optimization.Even if the airfoil is in full stall state,the jet scheme optimized by the jet parameters can increase the lift of the airfoil,reduce the drag and improve the aerodynamic performance of the airfoil.Through statistical analysis of experimental data,it is found that the most important factor affecting jet efficiency is jet velocity,followed by j et angle,and finally j et frequency.(3)Under the sinusoidal pitching motion model selected in this paper,synthetic j et control can improve lift coeff-icient of airfoil under dynamic stall.Under the control of the j et,the effect of the jet vortex on the flow separation zone at the trailing edge of the airfoil increases the pressure difference between the upper and lower airfoils.At the same time,the lift coefficient curves of airfoil under dynamic stall and static stall are compared and analyzed.It is found that the oscillation of airfoil can delay stall phenomenon and delay stall attack angle,so that the peak value of lift coeff-icient is larger than that of static condition.