Decaying stratified grid turbulence measurements

Decaying grid-generated stratified turbulence experiments were carried out in large towing tanks using 2D PIV and a newly-developed 3D-3C scanning PIV method.The creation of index-matched stable density stratifications in towing tanks up to 20 m long enabled the PIV measurements to be performed during all phases of the decay in order to attain, measure and characterize all regimes -including the elusive strongly-stratified regime (e.g.Brethouwer et al. ( 2007)).The complete set of turbulence statistics permitted the transitions between regimes to to be identified and defined, from quasi-isotropic to weakly-stratified, to strongly-stratified and finally to viscosity-affected, the latter being the late-time regime usually measured when localized turbulence is largely suppressed and the motion is quasi 2D.