STUDY OF THE EFFECTS OF INTER-PARTICLE COLLISIONS ON PARTICLE ACCUMULATION IN TURBULENT CHANNEL FLOWS

Particle-laden turbulence is common in natural phenomena and industrial flows, closely related to human life and production activities. In general, when the volume fraction of particles is less than O\left( 10^ - 4 \right), inter-particle collisions are neglected. Some studies have found that in particle-laden wall turbulence, even at low volume fractions, the effects of turbophoresis and preferential concentration can lead to higher local particle concentrations and frequent particle collisions. However, most existing results focus on homogeneous isotropic turbulence or employ large eddy simulations, and there is a lack of direct numerical simulation studies on particle-laden turbulent channel flows. The quantitative relationship between inter-particle collisions and the degree and morphology of particle clustering remains unclear. In this study, based on the Euler-Lagrangian point-particle framework, at a friction Reynolds number of Re_\tau = 180, we conducted direct numerical simulations to investigate the differences in the accumulation patterns of bidisperse particles in horizontal turbulent channel flows with and without inter-particle collisions. The average mass fraction of particles in the simulations is \bar \phi _m \sim O\left( 1 \right), so the feedback of particles on the flow field is also considered in the model. We found that inter-particle collisions drive near-wall particles to migrate towards the center of the channel, resulting in a flattened wall-normal profile of the average particle concentration, which suppresses particle turbophoresis in wall turbulence. Meanwhile, inter-particle collisions lead to a more uniform distribution of particles within a horizontal thin layer parallel to the wall. In particular, within the viscous sublayer, the anisotropic particle streak structures completely disappear. These results indicate that inter-particle collisions significantly suppress particle turbophoresis and near-wall preferential concentration phenomena in horizontal channel turbulence.