Effects of Particle-Particle Collisions on Particle Concentration in a Turbulent Channel Flow

This study is concerned with the effect of inter particle collisions on the particle concentration in turbulent duct flows. 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 Stokes drag, the Saffman lift, and the gravitational forces. The effect of particles on the flow is included in the analysis via a feedback force on the grid points. Several simulations for three classes of particles (28 μm Lycopodia, 50μm glass and 70μm copper) and different mass loadings were performed, and the effect of inter particle collisions on the particle concentration was evaluated and discussed. It was found that the particle-particle collisions reduce the tendency of particles to accumulate near the wall. This might be because collisions decorrelate particles with coherent eddies which are responsible for accumulation of particles near the wall. The spatial distribution of particles at the channel centerplane was compared with the experimental results of Fessler et al. (1994). The simulation results showed that the copper and glass particles had a random distribution while Lycopodium particles showed a non-random distribution with bands of particles that were preferentially concentrated.