Airfoil-vortex interaction and the wake of an oscillating airfoil

Abstract

Laser Doppler velocimetry, a non-intrusive flow measurement technique, was employed to experimentally investigate two-dimensional airfoil-vortex interaction. Vortices were generated by sinusoidally oscillating a NACA 0012 airfoil about its quarter-chord at a reduced frequency of k = 2.05 and an amplitude of ±10° angle of attack. The target airfoil, a NACA 63₂A015, was immersed in the wake, two chord lengths downstream of the vortex generators trailing edge. Phase-averaged velocity measurements of the flow around the target airfoil were made with the airfoil at angles of attack of α = 0° and α = 10°. A close encounter with a counterclockwise rotating vortex was observed for both angles of attack, and a head-on collision, which split the counterclockwise rotating vortex in two, was observed for α = 10°. Vorticity fields were constructed from the velocity measurements and the circulation of the vortex was evaluated throughout the interaction. The surface pressure fluctuations on the airfoil were determined by substituting the measured velocities into the Navier-Stokes equations and numerically integrating the resulting pressure gradients. Furthermore, an extensive investigation of the undisturbed wake of the oscillating airfoil was performed in order to determine the effect of oscillation frequency and amplitude on the wake development.