Drag enhancement in a dusty Kolmogorov flow

TL;DR

This study investigates how particles heavier than the fluid influence turbulent drag in a simplified Kolmogorov flow, revealing that increased particle loading enhances drag and turbulence suppression, especially for particles with smaller inertia.

Contribution

It introduces a two-way coupled Eulerian model for dusty flows and demonstrates how particle loading and inertia affect turbulence and drag in a boundary-free setting.

Findings

Increased particle mass loading raises the friction coefficient.

Turbulence suppression is more effective for particles with smaller inertia.

Particles induce a negative feedback via turbophoresis that moderates flow modifications.

Abstract

Particles suspended in a fluid exert feedback forces that can significantly impact the flow, altering the turbulent drag and velocity fluctuations. We study flow modulation induced by particles heavier than the carrier fluid in the framework of an Eulerian two-way coupled model, where particles are represented by a continuum density transported by a compressible velocity field, exchanging momentum with the fluid phase. We implement the model in direct numerical simulations of the turbulent Kolmogorov flow, a simplified setting allowing for studying the momentum balance and the turbulent drag in the absence of boundaries. We show that the amplitude of the mean flow and the turbulence intensity are reduced by increasing particle mass loading with the consequent enhancement of the friction coefficient. Surprisingly, turbulence suppression is stronger for particles of smaller inertia. We understand such a result by mapping the equations for dusty flow, in the limit of vanishing inertia, to a Newtonian flow with an effective forcing reduced by the increase in fluid density due to the presence of particles. We also discuss the negative feedback produced by turbophoresis which mitigates the effects of particles, especially with larger inertia, on the turbulent flow.