The Structure of Shear Driven Mixing With an Unstable Thermal Stratification

Abstract

A water channel experiment was used to study the turbulent mixing structure of shear and buoyancy. Density differences between fluid layers were produced by thermal stratification. The experiment was statistically steady and provided a long time period to study the mixing behavior and record data. The mixing process was studied using dye and digitized photographs. Individual images gave a two-dimensional view of the mixing structure. An ensemble average of images gave averaged mixing layer growth rate and the distribution of light and heavy fluid in the mixing layer. The experiment gave a space-time transformation in the streamwise direction which permitted a continuous study of the mixing evolution. The structure of the early growth of a compound shear and buoyancy mixing layer is presented. For the range of flows (δU; = 0 to 1 cm/s) and density differences (0.38 to 2.4 kg/m3), buoyancy was the dominant mixing mechanism.