Modulation of turbulence by dispersed solid particles in a spatially developing flat-plate boundary layer

Direct numerical simulations of particle-laden spatially developing turbulent boundary layers over a flat plate have been performed to investigate the effect of inertial particles on turbulence modulation, using the Eulerian-Lagrangian point-particle approach with two-way coupling. The particles are smaller than the Kolmogorov length scale of the dilute flow, and inter-particle collisions are not considered. The simulation results show that the addition of small solid particles increases the mean streamwise fluid velocity, which in turn leads to a reduction in the boundary layer integral parameters and an increase in the skin-friction drag. These effects become more pronounced as the particle Stokes number and mass loading increase. The streamwise turbulence intensity is slightly enhanced in the close vicinity of the wall but damped in the outer layer. In contrast, the Reynolds stress and the turbulence intensities in the wall-normal and spanwise directions are substantially attenuated across the entire boundary layer, and the levels of attenuation increase monotonically with both particle Stokes number and mass loading. The exchange of kinetic energy between particles and fluid indicates that particle-fluid interactions cause extra energy dissipation, which plays a crucial role in turbulence modulation.