Sheared stably stratified turbulence and large-scale waves in a lid driven cavity

TL;DR

This study experimentally explores how stable stratification influences turbulence, large-scale flow patterns, and internal gravity waves in a lid-driven cavity, revealing stratification-dependent flow structures and wave phenomena.

Contribution

It provides new insights into the effects of stable stratification on turbulence, flow patterns, and internal gravity waves in a controlled cavity environment.

Findings

Flow patterns depend on stratification strength.

Large-scale nonlinear oscillations interpreted as internal gravity waves.

Wave frequencies are approximately twice the velocity and temperature fluctuation frequencies.

Abstract

We investigated experimentally stably stratified turbulent flows in a lid driven cavity with a non-zero vertical mean temperature gradient in order to identify the parameters governing the mean and turbulent flows and to understand their effects on the momentum and heat transfer. We found that the mean velocity patterns (e.g., the form and the sizes of the large-scale circulations) depend strongly on the degree of the temperature stratification. In the case of strong stable stratification, the strong turbulence region is located in the vicinity of the main large-scale circulation. We detected the large-scale nonlinear oscillations in the case of strong stable stratification which can be interpreted as nonlinear internal gravity waves. The ratio of the main energy-containing frequencies of these waves in velocity and temperature fields in the nonlinear stage is about 2. The amplitude of the waves increases in the region of weak turbulence (near the bottom wall of the cavity), whereby the vertical mean temperature gradient increases.