Empirical Study of the Ground Effect on the Dynamic Stall of a Flapping Wing in Forward Flight

In the present study, the ground effect on the dynamics stall of the flapping wing with the bending deflection angle is experimentally investigated in the forward flight.For this purpose, first, a bending deflection mechanism and the installed facilities for the wind tunnel have been designed and fabricated.Then the simple and bending flapping wings are experimentally examined for h/c=1,1.5, flapping frequency 3.5 Hz and different angles of attack from 00 to 22.50 with velocity 3 m/s. Also, to investigate the effect of flapping frequency and distance from surface on lift force, thrust force and loading power of the simple and bending flapping wings with no angle of attack tested for h/c=1,1.5,2, different flapping frequency from0 Hz to 5 Hz and velocity 3 m/s. Results indicated that decreasing the distance from the surface, dynamic stall of the simple flapping wing occurs at lower angles of attack compared to the bending flapping wing. More specifically, in the minimum distance from the surface (h/c = 1), the stall angle of the simple flapping wing and bending flapping wing (with bending deflection angle of 1070) takes place at 12.50 and 150, respectively. The performance of the bending flapping wing is generally better than the simple flapping wing. Besides, by enhancing flapping frequency and decreasing the distance from the surface, aerodynamic forces and loading power increase.