Turbulence structure in stably stratified open-channel flows

Abstract

Turbulence structure near a shear-free, non wavy gas-liquid interface (free surface) with stable stratification is investigated by means of direct numerical simulation. The influence of stable stratification on the turbulence structure and scalar transfer near the free surface is discussed. Profiles of the turbulence intensities near the free surface indicate that redistribution of the turbulence kinetic energy from the vertical to the horizontal direction (internal energy exchange) occurs in unstratified flow. However, this redistribution is restricted by the stable stratification. These results strongly suggest that vertical motions near the free surface are no longer dominant in stratified flow. As a consequence, scalar transfer across the free surface is deactivated due to the restriction of the vertical motions near the free surface.