New research results from Fabian Kleischmann & Bernhard Vowinckel in the Journal of fluid mechanics

A recent study by Fabian Kleischmann & Bernhard Vowinckel together with Paolo Luzzatto-Fegiz & Eckart Meiburg from UC Santa Barbara (USA) presents numerical simulations to examine how two identical particles interact in a viscous fluid when exposed to back-and-forth (monochromatic) oscillating flows. By resolving the flow around the particles and ignoring gravity, the researchers isolate the effects of particle inertia. They vary particle spacing and flow frequency and find that the particles either attract or repel each other depending on these parameters. This behavior is consistent across three different particle densities. A universal threshold, following a power law, marks the switch between attraction and repulsion. Flow analysis reveals that fluid-induced vortices play a key role, and the team proposes a circulation-based criterion that reliably distinguishes between attractive and repulsive interactions.