Interface-resolved direct numerical simulation of vertical particulate channel flow in the turbulent regime

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Abstract
We have conducted a direct numerical simulation study of dilute turbulent particulate flow in a vertical plane channel by 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 a bulk Reynolds number of 2700 is directed upward, which maintains the particles suspended on 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 streaklike structures with streamwise dimensions of the order of eight 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, which is triggered by the presence of the particles. It was found that the mean fluid velocity profile tends toward a concave shape, and the turbulence intensity and 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.
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