Experimental investigations are conducted on ventilated cavities around an axisymmetric body under streamwise gravity in a gravity-driven vertical water tunnel. A multi-source measurement framework is established to capture cavity morphology, flow field velocity, wall pressure, and local phase state, utilizing the high-speed camera, Particle Image Velocimetry, pressure sensor arrays, and a dual-sensor conductivity probe, respectively. This cooperative system detects the spatial and temporal distribution of a quasi-steady two-phase flow, which contributes to the statistical quantification of the characteristic cavity dimensions: shedding point (location of cavity closure, Lc), pure-gas length (location of reentrant jet tip, Lg), cavity thickness (maximum radius of cavity, Hm), and equivalent length (defined according to the cavity thickness, Lm). The results demonstrate that the measurements from the four independent methods are in excellent agreement under the typical “re-entrant jet dominant” closure mode (Fr = 4.29, 5.57), thereby validating the accuracy and robustness of the established measurement framework. In marked contrast, the significant divergence is observed among the methods under the “interface instability dominant” condition (Fr = 3.13). This divergence clearly reveals the bounded applicability of each technique and underscores the fundamental complexity of the cavity closure mechanism. This work provides a high-resolution and verifiable experimental methodology for investigating the mechanisms of ventilated cavity dimension identification and evolution. Also, it offers a theoretical foundation and a valuable dataset for the design optimization and motion control of underwater vehicles, as well as for the validation of multiphase flow numerical models.
Shu et al. (Thu,) studied this question.
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