Experimental Study of Stall-Induced LCOs of Free Vibrating Wing

Stall flutter is a limit cycle oscillation phenomenon occurring when all or part of the flow over a wing separates and re-attaches periodically. This paper reports on experimental investigations carried out on the subsonic stall flutter of a pitch plunge wing wind tunnel model. The object of the experiments was to investigate the aeroelastic effects of the nonlinearity introduced by boundary layer growth and flow separation and the ensuing stall-induced flutter, on a freely vibrating aeroelastic system. The motion of the wing and the pressure distribution around its surface were measured at various conditions. Three types of motion were observed, sometimes at the same wind tunnel airspeed; decay to equilibrium, symmetric limit cycle oscillations (LCO) and asymmetric LCOs. The aerodynamic mechanisms that give rise to these LCOs are described and analyzed. The effect of torsional wing stiffness on the stall flutter response of the wing is also investigated. Finally, repeating the experiments in a smaller wind tunnel showed that wind tunnel blockage has a significant effect on stall flutter