Hydrodynamic interactions and extreme particle clustering in turbulence

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 collision radius is approached. We corrected a theory by Yavuz et al. (Phys. Rev. Lett. 120, 244504 (2018)) based on hydrodynamic interactions between pairs weakly particles, and demonstrate even this cannot explain observed RDF behavior. explore several alternative mechanisms for discrepancy were not included show none them are likely explanation, suggesting new, yet to be identified physical at play.