ENERGY-DISSIPATION AND VORTEX STRUCTURE IN FREELY DECAYING, STRATIFIED GRID TURBULENCE

Full field digital particle image velocimetry (DPIV) measurements of s trongly stratified grid turbulence have been carried out for long time s (up to Nt approximate to 1000). Quasi-2D vortices were formed that w ere separated vertically by strong horizontal vortex sheets. Dissipati on scales were resolved and the relative dissipation fractions in the horizontal and vertical planes were determined. A simple vortex model, involving a dense packing of discus-shaped structures connected by vo rtex lines that alternate between horizontal and vertical orientation, is shown to be consistent with both the observed velocity and vortici ty fields, and the evolution of the measured length scales in orthogon al planes.