Experimental Study of Boundary Effects on Buoyant Jet Dynamics in Linearly Stratified Medium

Abstract

The study of mixing dynamics in stratified environment is very important as it has wide applications ranging from oceanic and atmospheric circulation to astrophysical and engineering flows. The stratification refers to density or temperature variation along height. Here, the entrainment dynamics of vertical turbulent buoyant jet/plume into a linearly stratified medium for varying Brunt Vaisala frequency (N) is presented by analyzing the development of large-scale and small-scale flow patterns. The experimental facility for this study consists of two square acrylic tanks. One of them is the stratification tank, which is linearly stratified (∂ρ/∂z < 0) with the help of water and commercial salt. The second tank is the reservoir tank that is filled with water. The fresh water is injected into the stratified tank to study the plume dynamics. The ensuing evolution of buoyant jet is studied using high-resolution camera and commercial dye, and bulk flow parameters are obtained. The experiments were carried out to the study the wall effects on the buoyant jet characteristics. The first set of experiments were conducted in the rectangular tank having a larger aspect ratio, a = 4, where aspect ratio is defined as the ratio of length (L) to width (W). The second tank has an aspect ratio of approximately a = 1. Mixing characteristics such as spreading height of plume, maximum height of plume and radial intrusion of plume were measured and compared. The results indicate that the presence of wall does change the mixing behavior of the jet when compared to the unbounded wall case.