Particle-laden gravity currents interacting with stratified ambient water using direct numerical simulations

Particle-laden gravity currents propagating in stratified environments, such as turbidity currents induced by floods in estuaries or triggered by landslides in oceans, are important and complicated geophysical processes that require multidisciplinary studies. This paper numerically investigates the dynamic features of lock-release particle-laden gravity currents in linear stratification on a flat bed, with the main focus on the front velocity, entrainment ratio, and energy budget. The direct numerical simulations reveal that the suppressive effect of the ambient stratification on the turbulence may cause a particle-laden current to quickly lose momentum so that the near-constant front velocity of the particle-laden current cannot be maintained if no more particles are resuspended. After the acceleration stage, the entrainment ratio of a particle-laden gravity current barely changes with ambient stratification due to a combined effect from suppressed turbulent structures and deposition of particles. The energy-conversion process is accelerated by particle settling and is suppressed by ambient stratification. Specifically, because of the suppressive effect of a stronger stratification on the turbulence, a larger part of the energy is dissipated by microscopic Stokes flow around particles, while a smaller part of the energy is dissipated by the macroscopic convective motion of the fluids.