Energy dissipation and vortex structure in freely decaying, stratified grid turbulence

Full field digital particle image velocimetry (DPIV) measurements of strongly stratified grid turbulence have been carried out for long times (up to Nt approximate to 1000). Quasi-2D vortices were formed that were separated vertically by strong horizontal vortex sheets. Dissipation 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 vortex lines that alternate between horizontal and vertical orientation, is shown to be consistent with both the observed velocity and vorticity fields, and the evolution of the measured length scales in orthogonal planes.