Direct numerical simulation of particle-laden turbulent channel flow over superhydrophobic surfaces

We investigate the effects of superhydrophobic surfaces (SHS) consisting of streamwise-aligned grooves on turbulence dynamics and drag reduction in a fully developed turbulent particle-laden channel flow. The SHS is modeled as a flat boundary with alternating no-slip and free-slip conditions, and a series of two-way coupled point-particle direct numerical simulations are conducted, systematically varying the SHS texture spacing and free-slip area fraction while selecting particle parameters that induce pronounced turbulence modulation and drag reduction. Our results show that particles enhance drag reduction compared to particle-free flows over the same SHS configurations. To elucidate the coupling mechanism between particles and SHS, we analyze turbulence, particle statistics, and secondary flow motions. Particles suppress near-wall vortical structures, reducing Reynolds shear stress and disrupting the phase symmetry of secondary flows. Simultaneously, particle dynamics are influenced by the modulated turbulence, leading to complex nonlinear interactions. The particle–turbulence interactions enhance drag reduction through two competing mechanisms: direct suppression of fluid turbulence and particle-induced stresses. A quantitative analysis of the friction drag coefficient using the drag decomposition reveals that the particle effect on laminar and slip contributions remains relatively weak across various SHS configurations. However, the reduction in fluid turbulence contribution consistently outweighs the particle-phase contribution, leading to an overall enhancement of drag reduction. This study provides insights into the synergistic effects of SHS and particles on drag modulation in turbulent flows.