Numerical investigation on the early-stage high-speed water entry of trans-media vehicle with spike

Compared with low-speed water entry, high-speed water entry involves stronger impact loads and more complex multiphase flow phenomena. Accurate prediction of flowfield evolution and impact load is therefore essential for the development of trans-media vehicles. In this study, a solver enhancement based on overInterPhaseChangeDyMFoam is proposed by combining the volume of fluid method with the Schnerr–Sauer cavitation model and incorporating air effects into a two-phase cavitation framework. This solver enables simulations of cavitation during high-speed water entry and is validated against published experimental and theoretical results. The validated solver is then used to investigate the early-stage water-entry process of a spiked trans-media vehicle, with emphasis on flowfield development and hydrodynamic response. These results show that the spike effectively induces flow separation and establishes a stable low-pressure region near the vehicle nose, thereby promoting rapid supercavity formation. The cavity maintains a slender geometry and exhibits quasi-self-similar evolution, whereas radial expansion follows a nonlinear growth trend. As the cavity gradually envelops the vehicle body, the wetted area decreases markedly. Consequently, the drag coefficient rapidly approaches a low quasi-steady level, vehicle deceleration is suppressed, and penetration depth increases approximately linearly with time.