Large Eddy Simulation of Turbulent Density Currents Over Rough Surfaces*

When a heavy density fluid enters an environment with a lighter density, the interaction forms turbulent density currents, a significant type of buoyancy-driven flow. These horizontally moving density currents are critical for ocean mixing and the dispersion of atmospheric pollutants. A large-eddy simulation is conducted on a lock-exchange releasing density current over smooth and rough walls to comprehend the impact of surface roughness on drag effects of density currents. The purpose of the study is to understand the differences between uniform and random roughness elements on the drag characteristics. A previously implemented elegant, immersed boundary-based volume penalization approach where the solid regions are represented as a porous medium with vanishing permeability has been used for this study. The incompressible Navier-Stokes equations are solved with Boussinesq approximations in a finite volume implementation. Various roughness configurations have been utilized to describe the flow's behavior by altering the floor with cubical, cylindrical, and pyramidal geometries. The results have shown that the presence of roughness elements slows down the front because of enhanced drag and uniform pyramid roughness has less drag when compared to cylinders. The effect of Reynold’s number, frictional Reynolds number, and Froude’s number have been studied to provide a universal framework on the effect of roughness in density current.