Formation mechanism of normal force of a vehicle during the oblique water entry based on multi-phase smoothed particle hydrodynamics

The oblique entry process of a vehicle not only generates strong axial forces, but also generates significant normal force due to the asymmetry of air and cavity flows, which poses a great threat to the local and overall strength of the vehicle. This paper employs a multiphase $\delta$-smoothed particle hydrodynamics ($\delta$-SPH) method to analyze the flow field evolution and pressure distribution on the vehicle during water entry. Firstly, the accuracy and convergency of numerical model are verified through an oblique water entry case. Furthermore, the normal force formation mechanism is investigated by capturing the pressure evolution on the vehicle. Finally, the influences of half-cone angle and water-entry angle on the normal force during water entry are discussed. The findings indicate that the formation of normal force can be attributed to the hydrodynamic pressure and the aerodynamic pressure difference, which will provide valuable insights for the designs of force reduction and structural safety.