Study of Gap Physics of Airfoils with Unsteady Flaps

Abstract

Active trailing-edge flaps are a method of aerodynamic control under extensive research to reduce the detrimental effects of dynamic stall. Physical phenomena are poorly understood in the context of active flaps including vorticity and acoustics, separation, and transition. In addition, discrete trailing-edge flaps create a cavity-like flow within the airfoil-flap gap that can complicate these phenomena. This work has explored the physical response of a static airfoil with a discrete noncontoured oscillating flap over a range of freestream parameters. The effects of attached and separated flows, flap oscillation scheduling, airfoil-flap gap size, and freestream speed have all been investigated. Time-accurate predictions were performed using a hybrid Reynolds-averaged Navier–Stokes/large eddy simulation turbulence model. Trailing-edge stall suppression and an increase between aerodynamic response and deflection input were observed as the flap oscillation frequency increased. The lag between response and input also increased approximately linearly with airfoil-flap gap size. Results indicated the transition was unaffected by the flap oscillations. During the frequency content of flow the unsteadiness was consistent with separated flow driven by the flap. Discrete noncontoured flaps are not recommended; if they are required, the size of the gap should be minimized to maintain performance and reduce lag.