Hydrodynamic interactions and extreme particle clustering in turbulence

TL;DR

This study reveals that inertial particles in turbulence exhibit an explosive increase in clustering near collision distances, challenging existing hydrodynamic interaction theories and indicating unknown physical mechanisms.

Contribution

The paper corrects a previous hydrodynamic interaction theory and demonstrates its failure to explain observed extreme clustering, proposing the need for new physical models.

Findings

RDF of inertial particles scales as r^{-6} near collision radius

Corrected existing hydrodynamic interaction theory fails to match observations

Multiple alternative mechanisms are unlikely explanations for the observed clustering

Abstract

From new detailed experimental data, we found that the Radial Distribution Function (RDF) of inertial particles in turbulence grows explosively with $r^{-6}$ scaling as the collision radius is approached. We corrected a theory by Yavuz et al. (Phys. Rev. Lett. 120, 244504 (2018)) based on hydrodynamic interactions between pairs of weakly inertial particles, and demonstrate that even this corrected theory cannot explain the observed RDF behavior. We explore several alternative mechanisms for the discrepancy that were not included in the theory and show that none of them are likely the explanation, suggesting new, yet to be identified physical mechanisms are at play.