(114e) DNS of Particle-Laden Gas Flow with Four-Way Coupling

This study is concerned with the effects of particle–particle collisions and the 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 of the Navier–Stokes equations

via a pseudo-spectral method. The particle equation of motion included the wallcorrected

nonlinear drag force and the wall-induced and shear-induced lift force.

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

particle–particle collisions, particle feedback force and inter-particle interactions on

the particle deposition velocity, fluid and particle fluctuating velocities, and particle

concentration profiles were determined. The effect of particle aerodynamic interactions

was also examined for certain cases.

The simulation results indicated 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 two-way coupling and the

particle normal fluctuating velocity decreased near the wall causing a decrease in

the particle deposition velocity. In the case of the four-way coupling in which both

inter-particle collisions and two-way coupling effects were present, it was found that

the particle deposition velocity increased compared with the one-way coupling case.

When the particle aerodynamic interactions were added to the four-way coupled case

(termed six-way coupled case), no significant changes in the mean fluid and particle

velocities and the fluid and particle fluctuating velocities were obtained.

The results for the particle concentration profile indicated that the inclusion

of two-way coupling or inter-particle collisions into the computation reduced the

accumulation of particles near the wall. It was also observed that particle–particle

collisions and two-way coupling weakened the preferential distribution of particles.

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