Interface-resolved DNS of vertical particulate channel flow in the turbulent regime

TL;DR

This DNS study investigates the behavior of dilute turbulent particulate flow in a vertical channel, revealing large-scale flow structures and flow modifications caused by particles, with minimal impact from Stokes number variations.

Contribution

The paper presents the first interface-resolved DNS of vertical turbulent particulate flow with thousands of particles, highlighting flow instabilities and structure formation.

Findings

Formation of large-scale streak-like structures

Flow becomes more concave in velocity profile

Turbulence intensity and normal stress anisotropy increase

Abstract

We have conducted a direct numerical simulation (DNS) study of dilute turbulent particulate flow in a vertical plane channel, considering thousands of finite-size rigid particles with resolved phase interfaces. The particle diameter corresponds to approximately 11 wall units and their terminal Reynolds number is set to 136. The fluid flow with bulk Reynolds number 2700 is directed upward, which maintains the particles suspended upon average. Two density ratios were simulated, differing by a factor of 4.5. The corresponding Stokes numbers of the two flow cases were O(10) in the near-wall region and O(1) in the outer flow. We have observed the formation of large-scale elongated streak-like structures with streamwise dimensions of the order of 8 channel half-widths and cross-stream dimensions of the order of one half-width. At the same time, we have found no evidence of significant formation of particle clusters, which suggests that the large structures are due to an intrinsic instability of the flow, triggered by the presence of the particles. It was found that the mean fluid velocity profile tends towards a concave shape, and the turbulence intensity as well as the normal stress anisotropy are strongly increased. The effect of varying the Stokes number while maintaining the buoyancy, particle size and volume fraction constant was relatively weak.