Numerical Simulation of Turbulent Plumes in a Channel Flow: Settling Velocity and Tilted-Bottom Ramp Effects

Abstract

In the present work, we investigate numerically by means of Direct Numerical Simulation (DNS) the mixing of fresh and salty water in a channel flow configuration along with particle settling processes. In particular, we focus on the influence of the settling velocity in the formation of the fingering instability and the effect of the slope in a bottom tilted ramp. Three-dimensional simulations was done for two settling velocity values while for two-dimensional simulations a slightly tilted ramp inside the computational domain was imposed for 4 different bottom slopes. This ramp is modelled using an Immersed Boundary Method (IBM) in order to mimic submarine configurations. We describe and illustrate the underlying physics of the particle settling processes under the influence of the fresh/salt water mixing layer. We present results without and with various slightly tilted ramps for different Richardson numbers and settling velocities for Reynolds number Re = 1500. The spatial flow structures of the longitudinal vortex formation in the mixing layer turbulence transition as well as the fingering instability caused by the settling particles at early stages of sedimentation process are investigated.