Birth of starting vortex and establishment of Kutta condition

Abstract

This work provides direct experimental evidence supporting the generation of the airfoil circulation associated with a starting vortex as a viscous-flow process based on global velocity measurements near the trailing edge (TE) of a NACA0012 airfoil at the angle of attack of 6° in a low-speed wind tunnel. The evolving flow topology near the TE exhibits the apparent inviscid flow pattern in a very short initial period, the sequential formation and growth of the starting vortex as a result of near-wall viscous flow development, and the final establishment of the Kutta condition as the starting vortex travels downstream. The evolving flow field in the starting flow over the airfoil is topologically consistent.