Unsteady nature of leading edge vortices

Abstract

Flow visualization and velocity measurements were carried out in leading edge vortices over a delta wing. Very large velocity fluctuations were observed well upstream of breakdown and also in the absence of breakdown. The maximum rms swirl velocity can exceed the free stream velocity depending on the angle of attack. Examination of the probability density functions and spectra suggest that the core of the vortex is characterized by large amplitude, broad band random velocity fluctuations. It was suggested that these large velocity fluctuations are due to apparently random displacements of the vortex core. A simple model of the flow that produced the essential features of the experimental results was presented.