CINEMATIC PARTICLE IMAGE VELOCIMETRY OF HIGH-REYNOLDS-NUMBER TURBULENT FREE SHEAR-LAYER

The objective of this research was to study the time-evolving velocity field in a two-stream, turbulent, planar free shear layer using a cin ematic particle image velocimetry technique, The water shear layer had a velocity ratio of 0.23 and a Reynolds number of 2.62 x 10(4) based on velocity thickness and velocity difference, The cinematic particle image velocimetry system employed an argon-ion laser, a scanning mirro r, and a 35-mm movie camera, Experimental data obtained by this techni que yielded a combined spatial and temporal evolution of the two-dimen sional velocity and spanwise vorticity fields, (The resulting set of 4 00 velocity vector fields is available by contacting the second author .) The detailed velocity field structure of the shear layer was signif icantly different from previous lower Reynolds number flow visualizati ons in that the classical well-defined eddies and braids were replaced with complex three-dimensional agglomerated vortices of both signs, T he velocity held evolution was also notably different from that of the passive scalar field, where the former exhibited stronger temporal va riations and reduced spatial coherency. Temporal and spatial correlati ons yielded transverse distributions of convection velocities based on both streamwise velocity perturbations and vorticity, Additionally, t he spatial autocorrelation was performed to show the average eddy shap e, and a Lagrangian tracking correlation method was used to estimate e ddy lifetime.