Low Reynolds Number Flow Dynamics of a Thin Airfoil with an Actuated Leading Edge

Use of oscillatory actuation of the leading edge of a thin, flat, rigid airfoil, as a potential mechanism for control or improved performance of a micro-air vehicle (MAV), was investigated by performing direct numerical simulations at low Reynolds numbers. The leading edge of the airfoil is hinged at one-third chord length allowing dynamic variations in the effective angle of attack through specified oscillations (flapping). This leading edge actuation results in transient variations in the effective camber and angle of attack that can be used to alleviate the strength of the leading edge vortex at high angles of attack. A fictitious-domain based finite volume approach [Apte et al., JCP 2009] was used to compute the moving boundary problem on a fixed background mesh. The flow solver is three-dimensional, parallel, secondorder accurate, capable of using structured or arbitrarily shaped unstructured meshes and has been validated for a range of canonical test cases including flow over cylinder and sphere at different Reynolds numbers, and flow-induced by inline oscillation of a cylinder. Flow over a plunging SD7003 airfoil at two Reynolds numbers (1000 and 10,000) was computed and results compared with those obtained using AFRL’s high-fidelity solver [Visbal, AIAA J. (2009)] to show good predictive capability. To assess the effect of an actuated leading edge on the flow field and aerodynamic loads, two-dimensional parametric studies were performed on a thin, flat airfoil at 20 degrees angle of attack and Reynolds number of 14,700 (based on the chord length) with sinusoidal actuation of the leading edge over a range of reduced frequencies (k=0.57-11.4) and actuation amplitudes. It was found that high-frequency, low-amplitude actuation of the leading edge significantly alters the leading edge boundary-layer and vortex shedding and increases the mean lift-to-drag ratio. This study indicates that the concept of an actuated leading-edge has potential for development of control techniques to stabilize and maneuver MAVs in response to unsteady perturbations at low Reynolds numbers. The summer research at AFRL’s computational sciences division has resulted in several opportunities for future collaborations with AFRL scientists and researchers. At Oregon State, new projects for senior students are initiated to build and modify the existing physical setup and measure lift and drag coefficients.