Particle dispersion and wall-dependent fluid scales in turbulent bounded flow: implications for local equilibrium models

Theoretical models for particle dispersion in turbulent wall layers are based on closure assumptions for particle-turbulence correlations which strongly depend on the wall-normal coordinate. This paper presents new data for the near-wall dispersion of inertial particles in fully developed turbulent channel flow, obtained using direct numerical simulation (DNS) with a one-way point-particle approach. The link between wall-dependent flow time scales and particle time scales is discussed addressing further the issue of using integral flow time scales to parametrize particle behavior. This is fundamental to validate closure relations in theoretical local-equilibrium models for particle dispersion in wall-bounded flows, where the reduction of the fluid velocity fluctuation in the wall-normal direction is not accompanied by an equivalent reduction of the particle velocity fluctuation.