Direct Numerical Simulation of Four Way-Coupled Gas-Solid Flow and Deposition in a Turbulent Channel Flow

Abstract

This study was concerned with the effects of particle-particle collisions and two-way coupling on the dispersed and carrier phase turbulence fluctuations in a channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle equation of motion included the drag and the shear induced lift forces. The effect of particles on the flow was included in the analysis via a feedback force that acted on the computational grid points. Several simulations for different particle relaxation times and particle mass loadings were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration profiles were determined. It was found that, when particle-particle collisions were included in the computation but two-way coupling effects were ignored, the particle normal fluctuating velocity increased in the wall region causing an increase in the particle deposition velocity. When the particle collisions were neglected but the particle-fluid two-way coupling effects were accounted for, the particle normal fluctuating velocity decreased near the wall causing a decrease in the particle deposition velocity. For the physical case that both inter-particle collisions and two-way coupling effects are present, a series of four-way coupling simulations was performed. It was found that the particle deposition velocity increased with mass loading. The results for the particle concentration profile indicated that the inclusion of either two-way coupling or inter-particle collisions into the computation reduced the accumulation of particles near the wall. Comparisons of the present simulation results with the available experimental data and earlier numerical results were also presented.