An Experimental Framework to Study Controlled Unsteady Particle Mobilization*

This work describes an experimental framework to characterize the unsteady mobilization of solid particles from a particle bed. The measurements were carried out in an incoming zero-pressure gradient turbulent boundary layer that proceeded to develop over a particle bed. The bed contained spherical soda lime particles with diameters ranging from 450-600 microns, positioned 3 m from the sandpaper trip. It was determined that at friction Reynolds numbers less than 1600, the naturally occurring large-scale structures mobilized a negligible number of particles. The base flow was then set at a friction Reynolds number of 1600. Large-scale structures were then introduced onto this base flow using a NACA-0010 oscillating airfoil, creating a controllable free-stream disturbance and large-scale shear stress at the particle bed leading to initiation of particle mobilization. This introduced scale's frequency and amplitude could be controlled, and intermittent bursts of large scales could be added. High-speed imagery was utilized to capture the mobilization of the particles under the influence of these large-scale structures. These measurements demonstrated the ability of this framework to initiate particle mobilization through the introduced large-scale structures.