Numerical investigation of the hydrodynamic characteristics of a light high-speed amphibious vehicle in still water under oblique inflow conditions

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The unique structural configurations of amphibious vehicles, designed for dual land–water operations, pose significant challenges for hydrodynamic stability during water navigation. This study systematically investigated the hydrodynamic performance and motion response of a light high-speed amphibious vehicle (HSAV-II) under oblique inflow conditions. The working conditions of HSAV-II drift with five incoming flow angles (β) (0°, 5°, 10°, 15° and 20°) were considered. The computational fluid dynamics method, based on the steady Reynolds mean Navier–Stokes equation and the shear stress transport k-ω turbulence model, was used to simulate the viscous flow field. The computational domain was divided by a trim mesh, and the overset grid technique was used to analyze the coupled motion of the amphibious vehicle. Following verification of mesh independence and calculation method reliability, the flow field distributions were examined for a range of β. The results show that capsizing thresholds were identified through hydrodynamic analysis: heave motion transitioned to planing mode at Fr ≥ 0.711, whereas roll instability intensified abruptly beyond this speed. Asymmetric vortices and wave-breaking effects induced significant resistance amplification beyond β ≥ 10°, with transverse force stability limits exceeded at β > 15°. Pressure redistribution toward the bow coupled with lift effects triggered coupled instabilities. Free wave surface asymmetry and velocity contour interactions intensified above β = 15°, culminating in critical roll failure at β = 20° (Fr = 1.271). This study reveals the interrelation mechanisms among the pressure distribution, free wave surface, and velocity contour of the flow field during oblique navigation, providing theoretical guidance for amphibious vehicle stability enhancement under extreme maneuvers.