Turbidity currents propagating down a slope into a stratified saline ambient fluid

Abstract

Results are presented from highly resolved three-dimensional simulations of turbidity currents down a shallow slope into a stratified saline ambient, for various stratifications and particle settling velocity configurations. The front velocity is computed and the results are compared directly to experimental data by Snow and Sutherland (J Fluid Mech 755:251–273, 2014) and to an existing scaling law for gravity currents in stratified environments but on flat bottoms, with close agreement. The entrainment velocity of the ambient fluid into the current is computed from the DNS data and shows strong space time variability. The intrusion of the current into the ambient fluid is computed and compared to the experimental results of Snow and Sutherland (2014), an existing scaling law proposed by those authors, and a new model with increasing levels of complexity. The numerical results highlight the sensitivity of scaling tools to the choice of entrainment coefficient and their limitations in low entrainment but high settling rate scenarios. The new, simpler scaling relation for the intrusion depth is shown to be more robust and predictive in such cases. The energy budget of the flow is analysed in order to explain the governing processes in terms of energy transfers, with a focus on energy losses and potential to kinetic energy transfers. Particular attention is given to the Stokes losses with varying settling velocities, which validates the prediction of the concentration in the intrusion depth model introduced.