Turbulence structure of gravity and turbidity currents

DNS of moderate Reynolds number gravity currents has shown that the vortices in the near-wall region are qualitatively similar to the vortices found in the near-wall region of boundary layers, and the Kelvin-Helmholtz billows at the interface between the high and the low density fluid are similar to the ones observed in mixing layers. In the current work, we perform a quantitative study of the turbulence structure of gravity and turbidity currents at higher Reynolds number using LES. In gravity currents, the streamwise Reynolds stresses in the near-wall region match the ones observed in boundary layers. Wall-normal Reynolds stresses are, however, damped due to stable stratification. In turbidity currents, the bulk density in the near-wall region increases due to particle settling, which results in increased damping of Reynolds stresses due to stronger stratification effects. In the interfacial region, the wall-normal Reynolds stresses in gravity currents are damped as compared to the ones observed in mixing layer. In turbidity currents, however, the Reynolds stresses in the interfacial region match the ones in mixing layers. This is a result of weaker stratification as the density difference across the interfacial region decreases due to particle settling closer to the wall.