Study On Lift Enhancement Of Airfoil With Free Flaplet

Many researchers have paid lots of attention to the fundamental research on theaerodynamic performance of different Reynolds number airfoil in the last decade,due to the rapid development and creative applications of UAV and MAV.Therefore,the enhancement of aerodynamic performance and flow control mechanism gains further development.When the laminar shear layer separates from the airfoil surface,the flow can reattach to the surface as a turbulent one.There is a region between the separation and reattachment points,which is called laminar separation bubble.As the angle of attack increases,the length of laminar separation bubble decreases and moves forward to the leading edge and thus the lift increases significantly.When the angle of attack increases further,the separation bubble can't reattach on the airfoil surface any more.This phenomenon is known as“bubble burst”which results in the stall of airfoil.During this process,the lift decreases sharply.It's of great significant to develop the flow control technique to improve the aerodynamic performance of airfoil at post stall angle.In this project,the free flaplet installed on the suction surface of airfoil near theleading edge is used to improve the aerodynamic performance of airfoil.Firstly,the airfoil model is NACA 0012 which is a symmetrical wing.The major parameters include the time-mean lift coefficient,time-mean drag coefficient,lift-to-drag ratio,vortex shedding frequency of airfoil,natural frequency of the clockwork spring with flaplet and flow field.Two different Reynolds numbers adopted in the study are Re=1.5×10~5 and Re=2.0×10~5.Three different flaplets with different trailing edges(linear,triangular and semicircle)and three different springs with different elastic modulus are installed on the surface of airfoil.Hence,we can investigate the influence on the aerodynamic performance of the NACA 0012.Based on the experimental results,the Reynolds numbers have negligible impacton the lift and drag of airfoil.The free flaplets can't lead to lift enhancement before the usage of stall angle,but the stall angle is brought forward about 1.5o~4o;Concerning the post-stall,the lift of airfoil with flaplet is improved in a way and the picks-up speed of lift increases more quickly than that without the flaplet.The most optimum control result is obtained at?=5ofor the airfoil with free flaplet.