The effect of particle density in turbulent channel flow laden with finite size particles in semi-dilute conditions

TL;DR

This study investigates how particle density and volume fraction affect turbulent channel flow with finite-size particles, revealing that volume fraction impacts flow more than density ratio, and high density ratios lead to particle-fluid decoupling.

Contribution

The paper provides new insights into the effects of particle density and volume fraction on turbulent flow, especially highlighting the transition to particle-fluid decoupling at high densities.

Findings

Increasing volume fraction raises flow drag more than increasing density ratio.

Higher density ratios cause particles to migrate towards the channel centerline.

At very high densities, particles behave as a dense gas, decoupling from fluid dynamics.

Abstract

We study the effect of varying the mass and volume fraction of a suspension of rigid spheres dispersed in a turbulent channel flow. We performed several Direct Numerical Simulations using an Immersed Boundary Method for finite-size particles changing the solid to fluid density ratio, the mass fraction and the volume fraction. We find that varying the density ratio between 1 and 10 at constant volume fraction does not alter the flow statistics as much as when varying the volume fraction at constant and at constant mass fraction. Interestingly, the increase in overall drag found when varying the volume fraction is considerably higher than that obtained for increasing density ratios at same volume fraction. The main effect at density ratios of the order of 10 is a strong shear-induced migration towards the centerline of the channel. When the density ratio is further increased up to 1000 the particle dynamics decouple from that of the fluid. The solid phase behaves as a dense gas and the fluid and solid phase statistics drastically change. In this regime, the collision rate is high and dominated by the normal relative velocity among particles.