Chengwang Xiong

This study experimentally investigates the interfacial instabilities and thermo-hydrodynamic mechanisms of supercavities ventilated by high-temperature condensable vapour. Using high-speed imaging with an AI-based segmentation model, we establish a flow regime map that delineates the supercavitation envelope, identifying a distinct rough supercavity regime associated with the interaction between phase change and turbulence. A key finding is the non-monotonic cavity-length response of condensable vapour ventilation, in which high-flow regression is governed by a condensation-assisted source–sink imbalance, and differs mechanistically from the leakage/closure response observed in air ventilation. Specifically, condensation-induced mass loss acts as an internal sink that can exceed the vapour supply and cause cavity regression. While the cavity diameter remains inertially constrained, its length is highly sensitive to these thermodynamic effects. Spatiotemporal analysis indicates a coupled thermo-hydrodynamic route for the interfacial instability. The observed instability is initiated by thermodynamic self-excitation driven by droplet impingement, under-expanded jet expansion, and contact condensation within the ventilation influence region. These disturbances are convected downstream through a Kelvin–Helmholtz-type shear-layer process. The upper–lower asymmetry of the cavity fluctuations is consistent with gravity-related selection, which preferentially amplifies long-wave perturbations on the upper interface through a Rayleigh–Taylor-type route, and damps fluctuations on the lower interface. These findings extend classical cavitation theory into regimes dominated by rapid phase change, providing new insights into thermo-hydrodynamic coupling in multiphase flows.

The hydrodynamic mechanism governing multi-airgun bubble interactions is fundamental to enhancing low-frequency pressure waves for seabed resource exploration. Regulating this mechanism is a core challenge in clustered airgun design and provides critical insights into initial bubble dynamics following multi-port excitations. This study develops a three-dimensional finite volume model to simulate multiple bubble interactions, validated by spark-generated bubble experiments. The research elucidates the mechanism responsible for enhanced low-frequency pressure waves induced by multi-bubble dynamics, systematically analyzing the effects of inter-bubble distance and coalescence behavior. Key findings indicate that primary pulse amplitude and bubble oscillation ratio peak when the dimensionless distance is approximately twice the maximum bubble radius. The maximum primary pulse amplitudes for three and four bubbles reach 2.14 and 2.58 times that of a single bubble, respectively. Furthermore, annular configurations exhibit lower primary pulse attenuation than linear arrangements. The bubble oscillation period prolongs at smaller distances, directly enhancing low-frequency output. This study reveals the underlying hydrodynamic mechanism, offering a theoretical basis for optimizing airgun arrays to balance low-frequency signal enhancement and primary pulse energy preservation.

This study investigates the fundamental dynamics of a single pulsating bubble collapsing in the complex corner geometry formed by a rigid wall and an adjacent ice plate. Coupled experiments using spark-induced bubbles under various ice thicknesses and wall–ice angles were conducted and complemented by Arbitrary Lagrangian–Eulerian numerical simulations, which were validated with deviations below 10%. The results reveal a rich variety of jetting phenomena governed by the interplay between the wall–ice angle and the dynamic state of the ice boundary. We have identified and categorized four distinct and repeatable jetting modes: Fracture-redirected Jet (FRJ), bisector jet, divergent jet, and split jet (SJ). These modes are shown to be a direct consequence of the initial boundary geometry. For example, ice fracture dynamically changes the boundary from rigid to a free surface, redirecting the jet (FRJ), while a small gap at the wall–ice interface can trigger bubble fission (SJ). The resulting ice fracture patterns and structural pressure footprints serve as clear physical manifestations of these distinct fluid dynamic modes. This work establishes a direct link from initial geometric conditions to the resulting bubble jet dynamics, providing a fundamental understanding of bubble collapse in confined, complex environments.

The present study employs a two-way coupled multi-scale method to simulate and analyze the cloud cavitation flow around a hydrofoil, based on which the distribution of cavitation erosion risk on the hydrofoil is evaluated. The numerical results demonstrate that the multi-scale method can capture not only the overall evolution characteristics of cloud cavitation but also the generation, growth, and collapse of small-scale bubbles. Throughout the majority of a cavitation cycle, the scale of the Lagrange bubbles roughly follows a logarithmic Gaussian distribution. However, it shows a double-peak characteristic as a result of bubble production from both the sheet cavity and the shedding cloud. The distribution of local erosion risk, which is closely aligned with experimental findings, is assessed based on the collapse of small-scale bubbles. The erosion risk is greatest near the closure line of the sheet cavity, which is due not only to the collapse of bubbles around the shedding cloud but also to the shedding and breakdown of small-scale vapor structures during the development of the reentrant jet. During the cavitation cycle, the erosion risk is highest when the shedding cloud forms and the erosion risk decreases as it moves downstream. The multi-scale numerical analysis reveals that the cavitation number alone is insufficient for characterizing cavitation and its erosive effects. For a given cavitation number, the mean diameter of Lagrange bubbles increases with the inflow velocity. Furthermore, the total impact energy from bubble collapse on a hydrofoil follows a power-law dependence on the inflow velocity.