VORTEX DYNAMICS IN A PLANE, MODERATE-REYNOLDS-NUMBER SHEAR-LAYER

A completely non-intrusive technique, utilizing synchronized flow visualization and one-point, two-component laser-Doppler velocimetry, has been developed to examine the vortical structure of a homogeneous plane shear layer at a moderate Reynolds number. Results include ensemble-averaged velocity and vorticity maps and, derived from these data, zone-averaged statistics of the basic structure, at 6.2 initial wavelengths downstream of the splitter-plate trailing edge. The velocity field data paint a clear picture of the processes involved in the engulfment or entrainment of free-stream irrotational fluid by the vortices, and the evolution of the material interface separating fluid from the two free streams. The ensemble-averaged vorticity distribution is seen to be of an elliptical cross-section, closely resembling that of the Stuart vortex for a vorticity distribution parameter of 0.4. The effect of jitter which, in the case of zone averages is effectively removed, is assessed by comparison to conventional mean flow properties. It is found that vortex jitter greatly influences u’ and Ruu and, in confirmation of previous results, that a passive vortex does not contribute to the production of large-scale Reynolds stress. © 1990, Cambridge University Press. All rights reserved.