Turbulent channel flow laden with small inertial particles studied using particle-resolved direct numerical simulations*

The present work studies turbulent channel flow laden with small inertial particles from first principles, not relying on the point-particle assumption. Instead, we directly enforce the no-slip and no-penetration condition on the surface of tens of thousands of small spherical particles using an immersed boundary method. We focused on two fundamental questions: (1) how well do standard point-particle methods fare in predicting the particle-resolved data, and (2) how do the small inertial particles affect the momentum transport in the turbulent channel. Concerning the first question, our results show that the dynamics of resolved inertial particles in the one-way coupling regime can be realistically modeled with a simple Schiller-Naumann drag model, together with a simple variant of the Saffman lift force, which is important near the wall. Concerning the second question about the turbulence modulation, two regimes are observed: for smaller mass fractions, the turbulence statistics resemble those of single-phase flow at slightly higher Reynolds number, with near-wall particle accumulation slightly increasing the drag; at higher mass fractions, the particles modulate the turbulent dynamics over the entire flow, and the interphase coupling becomes more complex – fluid Reynolds stresses decrease, but the inertial particle dynamics increase the drag via correlated velocity fluctuations, resulting in an overall drag increase.