Cavity evolution and cooling process during the water entry of a heated sphere

In this paper, the water-entry process of high-temperature spheres was examined. Due to the intense phase change, the cavities formed by high-temperature spheres differed significantly from those formed by ambient-temperature spheres. Based on distinct cavity evolutionary characteristics, two cavity types were identified: quasi-static cavities occurring at lower initial impact velocities and deep seal cavities occurring at higher initial impact velocities. The variation trends of pinch-off time and characteristic length with respect to initial impact velocity differed among these cavity types due to their unique evolutionary behaviors. Further analysis revealed that although no significant differences in the motion of the sphere were observed among different cavity types, the initial impact velocity significantly influenced it. Higher initial impact velocities resulted in greater drag forces but lower drag coefficients. Next, higher initial impact velocities also induced higher phase change rates in the early stages of the sphere's water entry. Furthermore, the distinct cavity types led to differences in vapor distribution during the process. At the pinch-off time, the quasi-static cavities contained higher vapor content due to their smaller cavity volume. Finally, the cooling process of the sphere also varied with cavity type: for quasi-static cavities, heat flux gradually increased as the gas–liquid interface progressively enveloped the sphere, whereas for deep seal cavities, heat flux remained stable most of the time because the area of the sphere surface near the interface remained stable.