Circulation Structure in a Stratified Cavity Flow

Abstract

Experiments were conducted to study the circulation patterns and mixing processes in a stratified, lid‐driven cavity flow. The ratio of the cavity depth to width used was 1:1 and that of span to width was 3:1. The flow is different from those reported in the literature in up to four ways, viz., recirculation is a dominant feature, temperature control is used to obtain the stratification, the upper and lower boundaries are held at different constant temperatures, and the flows considered are, at most, only partially turbulent. For the geometric configuration used, the following may be concluded about the flow. The flow is strongly three‐dimensional. The number of circulation cells expected in this stratified flow can be estimated from the value of the bulk Richardson number, ${\mathrm{Ri}}_b\text{.}$ Given a local Richardson number, Ri, the entrainment rate, E, is found to be proportional to ${\mathrm{Ri}}^{-1.4}\text{,}$ indicating a shear‐induced mixing process related to the recirculation. Taylor‐Görtler‐like vortices above the thermocline are significant contributors to the mixing process.