Transport of inertial particles in high-Re turbulent boundary layer

Concentrations and velocities of small inertial particles in high-Re turbulent boundary layers (up to Re_τ = 19000) are measured via laser imaging. Three high-Re flows are combined with three particle sizes to give a range of parameters. Wall-normal profiles of streamwise velocity indicate that the particles slightly but consistently lag the fluid. The concentration profiles indicate a distinct wall-normal region where the Rouse profiles are followed, with significant deviations above and below this region. These deviations are compared to corrections of the Rouse profile. These corrections are made by starting from the advection-diffusion equation (as does Rouse) while making different assumptions. The deviations from Rouse away from the wall are qualitatively consistent with the introduction of a net flux, meaning that the advective flux is not perfectly balanced by the diffusive flux. The Rouse profile assumes this net flux equals zero. However, our data indicates this is not the case and indeed there is a relatively constant non-zero net flux. The deviations close to the wall are qualitatively consistent with a reduced mean settling velocity close to the wall. The Rouse profile assumes this settling velocity to be constant over the whole profile. A reduced settling velocity close to the wall could be caused by preferential sampling of the flow, by turbophoresis or by collisions of particles with the wall.