Measurements of the steady streaming flow around oscillating spheres using 3D particle tracking velocimetry

TL;DR

This study measures the three-dimensional steady streaming flow around oscillating spheres using particle tracking velocimetry, revealing discrepancies with theory and suggesting complex multi-particle interactions influence particle self-organization.

Contribution

It provides detailed 3D measurements of streaming flows around oscillating spheres and shows that interactions are more complex than existing theories predict, especially near boundaries.

Findings

Flow topology changes near boundaries

Discrepancies with analytic models

Multi-sphere interactions influence particle behavior

Abstract

Granular particles vibrated in a fluid have been found to exhibit self-organization with attractive and repulsive interactions between the particles. These interactions have been attributed to the steady streaming flow around oscillating particles. Here we examine the steady streaming flow surrounding a vertically oscillating sphere using three dimensional particle tracking velocimetry. We present measurements of the flow with the sphere far from boundaries, close to the bottom wall of the tank, and near another oscillating sphere. The steady velocity field is found to disagree with available analytic calculations. When the sphere is oscillated near the bottom wall the entire topology of the flow changes, resulting in a larger repulsive region than expected. Previous experiments saw attraction between particles in the region where the flow around a single particle is repulsive. We conclude that advection in the streaming flow due to a single particle cannot explain the observed attractive and repulsive interactions, rather non-linear interactions between the flows around two or more spheres must be responsible.