Turbulent channel flow of dense suspensions of neutrally-buoyant spheres

TL;DR

This study investigates how dense suspensions of neutrally-buoyant spheres affect turbulent channel flow, revealing increased drag, altered velocity profiles, and dominant particle-induced stresses at high volume fractions through direct numerical simulations.

Contribution

It provides new insights into the turbulent behavior of dense suspensions, highlighting the role of particle-induced stresses and their impact on flow properties at high volume fractions.

Findings

Drag increases with volume fraction beyond viscosity effects.

Velocity fluctuations decrease at high particle concentrations.

Particle-induced stresses dominate momentum transfer at high volume fractions.

Abstract

Dense particle suspensions are widely encountered in many applications and in environmental flows. While many previous studies investigate their rheological properties in laminar flows, little is known on the behaviour of these suspensions in the turbulent/inertial regime. The present study aims to fill this gap by investigating the turbulent flow of a Newtonian fluid laden with solid neutrally-buoyant spheres at relatively high volume fractions in a plane channel. Direct Numerical Simulation are performed in the range of volume fractions Phi=0-0.2 with an Immersed Boundary Method used to account for the dispersed phase. The results show that the mean velocity profiles are significantly altered by the presence of a solid phase with a decrease of the von Karman constant in the log-law. The overall drag is found to increase with the volume fraction, more than one would expect just considering the increase of the system viscosity due to the presence of the particles. At the highest volume fraction here investigated, Phi=0.2, the velocity fluctuation intensities and the Reynolds shear stress are found to decrease. The analysis of the mean momentum balance shows that the particle-induced stresses govern the dynamics at high Phi and are the main responsible of the overall drag increase. In the dense limit, we therefore find a decrease of the turbulence activity and a growth of the particle induced stress, where the latter dominates for the Reynolds numbers considered here.