Numerical Investigation of the Effects of Wind Tunnel Model Vibrations on the Measured Aerodynamic Properties of Airfoils and Wings

This paper presents a numerical prediction of the unsteady flow field around oscillating airfoils at high angles of attack by solving unsteady Reynolds-averaged Navier-Stokes equations with SST turbulence model in order to simulate the effects of wind tunnel model vibrations on the aerodynamic properties of airfoils, especially high-aspect-ratio wings in a wind tunnel. The effects of the phase lagging between different modes of oscillations, i.e., the airfoil plunging oscillation mode, the pitching oscillation mode, and the forward-backward oscillation mode, are also studied. It is shown that the vibrations (oscillations) of airfoils can cause the unsteady shedding of large-size separated vortex to precede the stationary stall incidence, hence lead to a stall onset at some earlier (lower) incidence than that in the steady sense. The different phase lagging has different effect on the flow field. When the pitching oscillation mode has small phase lagging behind the plunging oscillation mode, the effect of vibrations is large. Besides, if the amplitude of the oscillations is large enough, and the different modes of vibrations match or combine appropriately, the unsteady stall may occur 2° earlier in angle of attack than the case where airfoils keep stationary.