Effect of inertial and collisional particles on the skin friction of fully developed turbulent channel flow

Wall friction in particle-laden turbulent channel flows arises from the combined effects of viscous stresses, turbulent momentum transport, and particle–fluid momentum exchange. In this study, direct numerical simulation of a weakly compressible particle-laden turbulent channel flow was performed, and a drag decomposition framework was applied to quantify the viscous, Reynolds-stress-induced and particle-induced contributions to the total skin-friction coefficient. The results show that all particle-laden cases exhibited an overall drag increase relative to single-phase flow; however, the dependence of total drag on mass loading was distinctly non-monotonic. This behavior originated from the competition between the turbulent and particle-induced contributions, while the viscous contribution remained confined to the viscous sublayer and varied only weakly. Wall-normal analyses further revealed that the dominant drag modulation arose from the buffer layer and outer region. When particle collisions were included, the decomposed drag contributions were considerably modified, even in globally dilute suspensions, leading to Stokes-number-dependent biases when the collisions were neglected.