Insights into sub-Kolmogorov-scale droplet breakup via boundary element simulations

The statistics of sub-Kolmogorov-scale droplet breakup are investigated at a higher Taylor Reynolds number ($Re_{\lambda_T}$) than similar work at low $Re_{\lambda_T}$ (Cristini et al., 2003) to elucidate intermittency and neck pinch off behaviors. To this end, a boundary element method (BEM) is developed to enable simulations of the stochastic Stokes flow about ensembles of droplets along individual trajectories in homogeneous and isotropic turbulence (HIT), made possible through adaptive mesh refinement and fast multipole acceleration. Droplet deformation statistics, near-breakup behavior, and neck thinning statistics at $Re_{\lambda_T}=310$ are presented. Results highlight the effect of the HIT’s strain rate intermittency on the droplet deformation statistics, and investigations of subcritical and critical neck thinning events provide insights into the critical disturbances leading to breakup and transition of the neck contraction to the established viscous pinch-off regime. Both the marked influence of intermittency on the droplet deformation statistics and local strain rate effects very close into the terminal pinch-off regime emphasize the multiscale nature of the problem, even for droplets in the idealized Stokes regime.