Study on Cavitation Dynamics in Vertical Launch Based on Ventilation and Cylinder Pressure Control

• This paper focuses on the vertical cylinder exit process of underwater vehicles, aiming to reveal the underlying hydrodynamic mechanisms governed by the synergistic control of active ventilation and cylinder pressure under low-velocity conditions. • This study employs the commercial software ANSYS Fluent to conduct Computational Fluid Dynamics (CFD) simulations of the vehicle's vertical cylinder exit process. • Main conclusions are drawn: • Confined gas-liquid momentum competition during cross-medium launch is elucidated. • Active ventilation exhibits an asymmetric regulation paradox on tail impact loads. • Critical residual pressure ratio exceeding 0.802 neutralizes water hammer impacts. • A three-tier evolutionary suppression mechanism for explosive venting is proposed. To mitigate destructive transient impact loads induced by gas-liquid momentum interference during constrained cross-medium vertical launches, this study quantitatively deconstructs the intervention mechanisms of active ventilation rate (Q) and residual cylinder pressure ratio (D Pr ) utilizing high-precision VOF and moving mesh technologies. Baseline analyses reveal that the deep-water adverse pressure gradient drives a high-speed re-entry jet, whose subsequent high-frequency cavitation pinch-off and ensuing water hammer effect constitute the fundamental root of extreme base impact loads. Modulating solely the ventilation rate exhibits an asymmetric hydrodynamic paradox: extremely low rates (e.g., 70.57 kg/s) trigger explosive venting, forming a gas-cushioning layer that attenuates water hammer impacts yet fails to sustain shoulder cavitation. Conversely, high rates maintain cavitation but provoke a severe delayed secondary pressure surge reaching 2.4 MPa. To simultaneously achieve cavitation maintenance and load suppression, a critical suppression threshold is precisely calibrated at D Pr ≈ 0.802. Surpassing this threshold induces a significant momentum phase transition and a three-tier evolution. Here, abundant internal exhaust constructs an impenetrable aerodynamic supporting barrier, transitioning the system from a destructive pinch-off collapse to a quasi-steady depressurization mode, thereby completely flattening transient load peaks. This study rigorously elucidates the interphase momentum competitive laws, providing definitive theoretical criteria for flow control in next-generation cross-medium launch systems.