Entry and penetration of a superhydrophobic sphere into a deep pool
Phys. Rev. Fluids 11, 014304 – Published 15 January, 2026
DOI: https://doi.org/10.1103/p59t-pnd9
Abstract
This study experimentally examines the entry and penetration of a superhydrophobic sphere into a quiescent deep pool, with special emphasis placed on the primary and secondary pinch-off of the air cavity existing in its wake. By spanning previously underexplored density ratios and impact velocities, this work extends the known regimes of sphere water entry: notably, it demonstrates that lighter spheres, assisted by their wake cavities, can reverse the trajectories from descent to ascent, in contrast to the terminally descending behavior of heavier spheres reported in previous studies. A strong correlation between both primary and secondary pinch-off times with the impact Froude number and dimensionless density is revealed. A semiempirical scaling for cavity volume after primary pinch-off is proposed, offering predictive capability across a broader parameter space. A scalar force balance predicts a drastic decrease in buoyancy at the moment of pinch-off, which is reflected as an abrupt change in the deceleration of the sphere. This behavior is captured from time-resolved trajectory measurements obtained using two orthogonally placed high-speed cameras. These findings provide a comprehensive dataset comprising buoyancy transitions, force balances, and cavity morphologies.
