Boundary Layer Dispersion of Near-Wall Injected Particles of Various Inertias

Abstract

A direct numerical simulation approach was employed along with a Lagrangian particle tracking technique to investigate particle motion and dispersion in a turbulent boundary layer. The present study investigated a range of particle inertias corresponding to outer Stokes numbers varying from 10−4 to 1. In all cases, the ratio of particle terminal velocity to fluid friction velocity was held constant at 10−2 such that the effects of particle inertia would be isolated and dominant with respect to particle dispersion. The particles were injected near the wall at a height of four wall units (with elastic wall collision specified at one wall unit) and their locations recorded at several streamwise planes. Particles having an outer Stokes number much less than unity reach a similar outer flow distribution profile by the time they pass a collection plane located at eight boundary layer thicknesses downstream of injection. Moderately larger particles tended to yield increased wall collisions and increased near-wall concentrations. The increased concentration in the near-wall region (or reduced diffusion away from the wall) is attributed to a coupling of inertia effects and turbulent structures for the non-homogeneous flow (sometimes referred to as turbophoresis). The highest Stokes number particles yield the highest near-wall concentration, but resulted in a decrease in wall collisions in the first few collision bins as it tends to be unaffected by the near-wall structures.