Dynamics of Mixed Layer in a Nonuniformly Stratified Fluid Heated from Below

Abstract

Unsteady natural convection in a nonuniformly stratified, finite depth layer of water heated from below has been studied. Laboratory experiments were performed using the Mach-Zehnder interferometer as a diagnostic tool for measuring temperature. A shadowgraph technique was used for flow visualization. A simple thermal and a more detailed two-differential equation k–ε turbulence models are used to predict the dynamics of mixed layer which develops when the thermally stratified fluid is heated from below. The thermal model predictions for the mixed layer height agreed to within 5 percent and the mixed layer temperature to within 15 percent of the experimental data obtained in controlled laboratory experiments. Even better agreement between data and predictions were obtained with the k–ε turbulence model. The entrainment processes at the interface between the mixed layer and the stable region as well as turbulence in the layer must be better understood for more realistic modeling of turbulent natural convection in nonuniformly stratified fluids.