Drag-Thrust Transition of the Oscillating NACA0012 Airfoil at Varying Pitch Biases*

The experiments conducted in this research aim to characterize the flow physics governing the harmonically heaving and pitching NACA0012 airfoil at varying pitch biases. By introducing a pitch bias, the NACA0012 airfoil experiences a nonzero mean angle of attack over each cycle, in contrast to the classical case with zero pitch bias. Consequently, the NACA0012 airfoil produces a mean lift force over the course of each cycle in tandem with either a drag or thrust force. The experiments performed comprise of parametric sweeps across reduced frequency, amplitude, Reynolds numbers, and varying pitch biases. The Cornell Cyber-Physics Fluid Dynamics (CPFD) Facility conducts the sweep through this multi-dimensional parameter space by automated batch experimentation. Collectively, the experiments highlight the transition between thrust-producing and drag-producing regimes as well as characterize the kinematics and flow physics that enable efficient production of lift alongside thrust. Particle Image Velocimetry (PIV) experiments are also performed in the CPFD facility to identify modes of vortex shedding and the significance of the Leading Edge Vortex (LEV) in this family of flows.