Numerical investigation of asymmetric cavity dynamics during high-speed water exit at shallow angles

During the high-speed water exit of vehicles at shallow angles (θ<20°), prolonged interaction with the free surface significantly enhances the influence of geometric and initial motion parameters on cavity evolution and trajectory stability. In this study, a numerical method coupling three-degree-of-freedom motion equations with the volume of fluid model investigates the mechanisms of nose shape and water-exit angle on trans-media cavity dynamics. Results reveal that the conical nose exhibits a self-regulating mechanism, adjusting its effective deadrise angle via angle of attack variations to yield the weakest cavity asymmetry. Conversely, the flat nose experiences strong flow separation; its high sensitivity to trans-media pressure gradients causes the most severe asymmetry. The hemispherical nose lacks both traits, exhibiting asymmetry primarily driven by the free-surface effect. Furthermore, at a 10° exit angle, the low fluid inertia of the thin water layer causes the pitch rate to exceed the velocity deflection rate. This disparity triggers a positive feedback loop involving trajectory deviation and tail slamming. Steeper water-exit angles increase fluid inertia, suppressing this feedback and enabling the vehicle to stably skim the cavity lip. Ultimately, nose shape and exit angle collectively dictate the free-surface effect's intensity. This study elucidates the fundamental mechanisms governing shallow-angle trans-media exits, providing insights into cavity asymmetry, motion characteristics, and hydrodynamic loading.