Turbulent wakes of stratified flow past a cylinder

Abstract

Laboratory measurements were carried out to investigate the evolution of a turbulent wake behind a right circular cylinder moving in a linearly stratified fluid. The flow field is mainly determined by the internal Froude number Fi and the Reynolds number Re, but at high Re, Fi becomes the only governing parameter. Measurements show that stratified turbulent wakes can be classified into three flow regimes, based on Fi. When Fi<2, the wakes do not grow downstream, and remain at an approximately constant height. For 2<Fi<3, the wakes grow to a maximum height at Nt≊5 and then collapse physically; for Fi≳3, the maximum height is achieved at Nt≊2.5, before the collapse begins. The evolution of such other length scales as the Ozmidov, Kolmogorov, overturning, and Thorpe scales and the maximum Thorpe displacements was measured, and their behavior in the above Fi ranges was delineated. Length scale diagrams for the evolution of stratified turbulence in cylinder wakes were constructed and compared with previous theoretical predictions. The present results provide new insights into the evolution, collapse, and long-term evolution of stratified turbulent flows.