Shear-induced mixing and transport from a rectangular cavity

Abstract

Measurements were conducted in the vicinity and downstream of two-dimensional cavities filled with a dense miscible fluid subjected to purging by an overlying wall-bounded turbulent shear flow. Two cavities with aspect ratios 1 and 2 were used, based on previous observations that the mechanism for entraining dense fluid into the flow above is different for these cases. Scaling for the downstream variation of the vertical concentration (buoyancy) distribution of dense fluid is advanced based on dimensional arguments and tested using laser-induced fluorescence measurements. The mean flow and turbulent statistics in the vicinity and downstream of the cavity were also measured. A notable increase of shear stress and turbulent intensities was observed above the higher aspect ratio cavity due to intense vertical exchange between the cavity and the flow above. The influence of the cavity could be detected for several cavity widths, or distances equal to several eddy turnover times. However, the flow above the lower aspect ratio cavity exhibits dramatically less vertical exchange between the cavity and the flow above, as indicated by subtle wisps of fluid transported downstream by the free-stream flow. The shear stress and turbulent intensities for this case have only a minor influence of the cavity.