Research On The Forebody Vortex Characteristic And Control By Synthetic Jet In The Static And Dynamic State

When an aircraft characterized by a tangent-ogive shaped forebody flies and maneuvers at large angle of attack,complicated asymmetric vortex flow is generated at the head,which leads to large lateral force and yaw moment.At this time,the aircraft rudders can undergo severe failure,and the aircrafts transverse direction stability deteriorates.So the asymmetric vortex is extremely dangerous,it may causes the aircraft to lose control or enter the spin,and then causes the flight accident.Therefore,there are some focus of this paper on what the aerodynamic characteristic of the asymmetric forebody vortex during the aircraft flight and maneuver action at high angle of attack is;and how to control the froebody vortex including bi-stable state and dynamic state;and whether the spin can be controlled and the maneuverability can be improved by control the forebody vortex.There are some advantages for the synthetic jet method,such as response quickly,zero mass rate,simple structure and light weight,which has been widely applied in active flow control.In this paper,a dual synthetic jet actuator is designed;and the flow characteristics of the actuator is investigated with different voltage,frequency and duty cycle;and the forebody vortex control by the dual synthetic jet actuator is studied in the static and dynamic of the slender body;and the aerodynamic characteristics of slender body in static,pitching motion and free coning motion is obtianed.The main conclusions of this paper are as follows:1.Based on the traditional synthetic jet control technology,a control method providing asymmetric alternately synthetic jet is proposed in this paper.The research shows that the dual synthetic jet actuator alternately produces the jet,the vorticity and momentum;there is a characteristic of frequency selection of the dual synthetic jet actuator,and the average velocity of jet is the largest at resonance frequency;the distribution of flow fields with different asymmetric degrees can be formed at different duty cycle.2.Within the range of relatively high angles of attack,including the angle-of-attack region in a bistable state,the lateral force of the ogive forebody is continuously controlled by the dual synthetic jet actuator.The control changes the bi-stable state,different frequency control forms different distribution state.In the range of the lower frequency control,the unsteady state of the forebody vortex between the bi-stable states is formed,and the forebody vortex follow the cycle of the alternating disturbance at the nose tip.In the range of the intermediate frequency control,because the switching time of the forebody vortex is less than the time of bi-stable transformation,a small swing state of the forebody vortex is formed.In the range of the higher frequency control,the forebody voretx is in a symmetric quasi steady state.Different from the traditional control principle,forebody vortex's oscillation balance position is continuously changed as the duty cycle increases controlled by the dual synthetic jet actuator,but not the time ratio of the forebody vortex stay in the two stable state.3.There is a hysteretic characteristic on the lateral force and normal force of the slender body during the pitching motion,and it greatly influenced by the range of pitching angle and the reduced frequency.According to the flow field information obtained by PIV,it was found that the hysteretic characteristic of the swirling strength,space position,the breakdown location of the forebody vortex and the asymmetrical flow field leads to the hysteresis of aerodynamic force.Compared with the static state,when the slender body pitching down,the asymmetric degree of the forebody vortex distribution is enhanced,breakdown location and the asymmetrical flow field move forward,vice versa.In the dynamic motion,the dual synthetic jet actuator still has the effect to control the forebody vortex,and can reduces the lateral force of the slender body and almost eliminates the hysteresis loop.4.Through the wind tunnel experiment and the flight verification of the model aircraft,it was found that the asymmetric forebody vortex will induces the coning motion and enter the spin,respectively.The dynamic wall effect of the conical motion reduces the control ability of the disturbance at the nose tip to the forebody vortex.However,the disturbance at the nose tip can still achieve the continuous control of the lateral force,the spin recovery and the improvement of the maneuverability of the aircraft flying at a large angle of attack...