Experimental study of thermally induced cavity evolution and periodic layered cavities during water entry of heated cylinders

The high-speed water entry of heated cylinders involves strongly coupled physical processes, including free-surface impact, cavity evolution, wall heat transfer, phase-change vaporization, and gas–liquid interfacial instability. To clarify the influence of thermal effects on cavity dynamics, a series of experiments was conducted over different initial cylinder temperatures, entry velocities, and cylinder diameters, combined with high-speed image analysis and a Logvinovich-based cavity reconstruction method. The results show that, within the investigated parameter range, the global cavity evolution remains primarily governed by inertial separation and free-surface closure. Increasing the initial cylinder temperature generally promotes the axial development of the cavity and delays cavity pinch-off, while its effects on the maximum cavity diameter and pinch-off height remain comparatively limited. Under selected high-temperature conditions, periodic layered cavities are observed during the early stage of water entry, and their occurrence depends on the combined effects of thermal conditions, entry velocity, and cylinder size rather than on temperature alone. The observed layered structures are consistent with a possible mechanism involving repeated destabilization, rupture, rewetting, and regrowth of the near-wall vapor structure during the transition toward film boiling. A characteristic scaling model based on vapor-film squeezing and regrowth further suggests that the layered-cavity period tends to increase with cylinder radius and decrease with increasing entry velocity and wall superheat. The measured trends are broadly consistent with the characteristic vapor-film-regrowth timescale predicted by the model. These results provide an experimental and scaling-based framework for understanding the coupled hydrodynamic and thermal mechanisms governing cavity evolution and interfacial unsteadiness during heated-cylinder water entry.