The role of interparticle collisions in turbulent particle-laden channel flow is investigated through a detailed comparison between two-way and four-way coupled point-particle direct numerical simulations. Simulations are performed with particle Stokes number ${\mathrm{St}}^{+}$ ranging from 3 to 300, at a fixed mass loading ${\mathrm{\Phi }}_m=0.6$ and bulk Reynolds number ${\mathrm{Re}}_b=U_{b}h/\nu =5150$. It is found that interparticle collisions significantly modulate the dynamical features of both fluid and particle phases, resulting in a substantial reduction of near-wall particle concentration, enhanced turbulence attenuation, and more pronounced drag reduction especially for high ${\mathrm{St}}^{+}$ cases. These modulating effects mechanistically arise from the following two differences compared with the two-way coupling cases. First, interparticle collisions increase particle velocity fluctuations in the wall-normal direction, which enhances particle dispersion and consequently weakens near-wall particle accumulation. Second, interparticle collisions amplify the slip velocity fluctuations and thereby increase the extra dissipation, which leads to turbulence attenuation and further drag reduction. The above findings suggest that four-way coupling is of fundamental importance for accurate modeling of interphase momentum and energy dynamics in particle-laden turbulent flows.

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• Channel flow
• Fluid-particle interactions
• Interparticle interactions
• Particle-laden flows
• Three-dimensional turbulence
• Direct numerical simulations
• Navier-Stokes equation