Geometric-scale-induced distortion of cavity and multiphase flow structures during water entry

Cavity formation during water entry fundamentally governs the organization of surrounding multiphase flow structures. However, geometric scaling can introduce significant distortion in cavity morphology and flow field, challenging the assumption of hydrodynamic similarity. This study numerically investigates the scale-dependent distortion of cavity dynamics and associated flow structures for geometrically scaled bodies. These results demonstrate that cavity-dominated multiphase flows are highly sensitive to geometric scaling, leading to systematic distortion in the flow field and turbulence structure. Although global kinematic features remain comparable, reduced-scale models exhibit intensified local velocity gradients, enhanced viscous dominance, weakened turbulence diffusion, and accelerated pressure attenuation. The vortex structures identified by the Q-criterion demonstrate increased fragmentation and reduced coherence at smaller scales. These findings provide theoretical support for engineering research on water entry of excessively scaled models, and offer a physical basis for evaluating similarity assumptions in cavity-driven hydrodynamic problems.