LES investigation on entrainment in gravity currents

Large Eddy Simulations are used to investigate the dynamics of gravity currents produced by the lock-release technique. Three simulations are carried out varying the initial reduced gravity of the lock fluid. The gravity currents develop two different flow regimes, a slumping phase followed by a self-similar phase, in agreement with the shallow water theory. When the dense fluid is released, a gravity current forms and Kelvin-Helmholtz instabilities develop at the interface between the two fluids, causing entrainment of ambient fluid. Two entrainment parameters, a bulk and a local one, are evaluated from an analysis of the instantaneous increase in volume of the gravity current. Entrainment of ambient fluid is found to occur in both the slumping and the self-similar phases. The analysis of the local entrainment parameter shows the determinant role of Kelvin-Helmholtz instabilities in the entrainment dynamics and mixing.