An Experimental Framework to Study Turbulence Induced Particle Mobilization

TL;DR

This paper presents an experimental framework using oscillating airfoils to generate controlled turbulent disturbances, enabling the study of particle mobilization in a turbulent flow and correlating it with flow structures.

Contribution

It introduces a novel experimental setup that allows on-demand particle mobilization by controlling flow disturbance frequency and amplitude.

Findings

Flow scale size is controlled by oscillation frequency.

Energy in the flow scale is controlled by oscillation amplitude.

Particle mobilization correlates with large-scale flow structures.

Abstract

An experimental framework was developed to study the initiation of particle mobilization in a laboratory setting. Large and heavy particles mobilized by a turbulent, gaseous carrier-phase were considered. An airfoil oscillated in the free-stream, generating a tonal free-stream disturbance that perturbed a turbulent boundary layer. The flow developing behind this forced flow was characterized using hot-wire anemometry and particle image velocimetry (PIV). Downstream of the oscillating airfoil mechanism, the turbulent boundary layer responded to the forcing in the form of excess energy at the forcing scale. The signature of this forcing scale was observed to span the entire wall-normal extent of the flow, extending all the way down to the wall. The size of this flow scale was shown to be controlled by changing the frequency of oscillation, while the energy in this flow scale was controlled via the amplitude of oscillation. Demonstrative measurements are presented in which this forced carrier-phase flow mobilized a particle-phase on a particle bed. A PIV-based approach was used to measure the initiation of particle motion as well as the incoming carrier-phase velocity field. The particles on the bed were mobilized ``on-demand'' by the deflection of the airfoil. Consistent with prior work, it was observed that particle mobilization was correlated with the large-scale flow structures of the carrier-phase.