Lift Enhancement Of A Flat-plate Airfoil Using Multiple-electrode Plasma Actuator

Mirco-Air Vehicle(MAV)plays an important role in military reconnaissance and agricultural modernization.The increase in lift could allow the MAV to have greater payload capacity,longer endurance,smaller size and lighter weight.Therefore,lift enhacement of MAV has important engineering significance.In this paper,we proposed an innovative method to improve the lift force through momentum inputing into vortical structure by deflcted jet directly.The angle-adjustable deflected jet was produced by sliding discharge plasma actuator in this study.We developed a new actuactor,viz.,five-electrode plasma actuator by adding multiple encapsulated electrodes on tri-electrode sliding discharge plasma actuator.The deflection angle and velocity of plasma actuators were calibrated by schlieren and PIV,respectively.The lift force of a flat-plate airfoil under steady and unsteady controlled by deflected jet induced by five-electrode plamsa actuator was measured by load cell to explore the relationship between lift enhancement and jet angle,and the mechanism of lift ehancement was studied through smoke-wire visualization over flat-plate airfiol and wake measurement done by hot-wire.The experimental results shown that the jet deflection angle induced by the five-electrode plasma actuator was larger than that of the tri-electrode plasma actuator under the same voltage.The deflection angle range of the five-electrode plasma actuator was from 50°to 91°,while the deflection angle range of the tri-electrode plasma actuator was from 8°to 80°.At different deflection angles range from 50°to74°,the maximum velocity of five-electrode plasma actuator reached 1.46m/s and the difference of jet velocity is less than 0.22 m/s.At Reynolds number of 2×10~4 and post-stall angle of attack of 16°,the lift force increased by 88%under steady control of 77°jet.What is more,lift force enhanced by 102.7%under unsteady control of F~+=0.7(F~+=f_bc/U_∞,where f_b,c,U_∞are burst frequency,chord length of airfoil and free-stream velocity,respectively),burst ratio=5%.The lift force varies significantly with the deflecting jet angle.At an angle of attack of 16°,the maximum lift force increased by 88%with control of 77°jet,while under 33°jet control,the lift force only increased by 42%.The jet angles of optimal control are different under different angles of attack.As angle of attack increases from 8°to 16°,the deflection jet angle of optimal control increases from 75°to 77°.Smoke-wire visulazation photographs shown that under control of steady deflected jet,vortical structure forms further downstream and becomes larger which results in deflection of the streamlines towards the airfoil which resulting in lower pressure on suction side of airfoil and hence enhance lift force.