UNSTEADY NATURE OF LEADING-EDGE VORTICES

Flow visualization and velocity measurements were carried out in leadi ng edge vortices over a delta wing. Very large velocity fluctuations w ere observed well upstream of breakdown and also in the absence of bre akdown. The maximum rms swirl velocity can exceed the free stream velo city depending on the angle of attack. Examination of the probability density functions and spectra suggest that the core of the vortex is c haracterized by large amplitude, broad band random velocity fluctuatio ns. 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 res ults was presented. (C) 1997 American Institute of Physics.