Lift Production of an Unsteady Self-Propelled Airfoil*

In this research, we study the lift force and vortex formation of an oscillating, self-propelled NACA0012 airfoil. These experiments are enabled by the closed-loop force-feedback system of the Cyber-Physical Fluid Dynamics (CPFD) Facility (Mackowski & Williamson 2011). We employ combined heaving and asymmetric pitching motions on the airfoil, which generate both streamwise and transverse forces. Under its self-generated streamwise forces, the airfoil starts from rest and accelerates to an equilibrium cruising velocity. The asymmetry in pitching motion profile is introduced by a rotational offset, allowing the airfoil to produce a net lift force over a cycle, enabling the wing to carry the weight of a “payload”. Our parameter space is characterized by varying the heaving and pitching amplitudes. Contours of performance metrics form the basis for simple (yet remarkably useful) “Heave-Pitch Diagrams”. By exploring these diagrams, we observe the tradeoffs between lift, propulsion, and energy expenditure. We also investigate the vortex dynamics and flow physics that underpin the efficient production of coupled lift and propulsion, through PIV flow visualization.