Fluid-particle interaction regimes during the evolution of turbidity currents from a coupled LES/DEM model

TL;DR

This study uses a coupled LES/DEM model to investigate fluid-particle interactions in turbidity currents, revealing the significant role of vorticity and the energy transfer mechanisms during current evolution.

Contribution

The paper introduces a combined LES/DEM modeling approach to analyze fluid-particle interactions in turbidity currents, providing new insights into vorticity effects and energy transfer.

Findings

Vorticity influences particle lift forces and current evolution.

Positive longitudinal lift promotes initial particle transport.

Only a small fraction of initial potential energy converts to kinetic energy.

Abstract

In this paper, fluid-particle interactions in lock-exchange turbidity currents (TCs) over a flat bed are investigated using a model combining LES and DEM (Large-Eddy Simulation and Discrete Element Method). The reliability of this model is demonstrated via comparing the numerical solutions with measurements of the front positions, fluid velocity profile, and particle concentration profile of lock-exchange TCs. The following physical understandings are obtained. The vorticity field plays an important role for the current evolution by affecting the fluid lift force (i.e., in the direction normal to the fluid-particle slip velocity) acting on the particles. At the very beginning, a longitudinal positive lift force due to strong positive vorticity promotes longitudinal particle transport. Afterwards, the longitudinal lift force decreases and eventually becomes negative, with a magnitude that even exceeds that of the positive longitudinal drag force, because more and more of the settling particles are affected by the negative vorticity near the bottom wall caused by surface friction. Interestingly, in spite of the complex behavior of the fluid-particle interaction forces and their role in TC evolution, only a very small fraction of the initial particle gravitational potential energy is actually transformed into TC kinetic energy (both particle and fluid).