Abstract: The mathematical model of the flow field of an amphibious vehicle is established with accounting free surface effort and the solving algorithm is explained by using the computational fluid dynamics (CFD) theory. The three-dimensional numerical simulation of the free surface flow is carried out by using FLUENT software based on RNG turbulence model, volume of fluid (VOF) method and pressure implicit with splitting of operators (PISO) method. The velocity, pressure, resistance and wave of the models are obtained, the computational results agree well with the experimental results. Then primary research is carried out on optimizing the geometrical characteristics of the amphibious vehicle model and analyzing the influence of its cut angle and the state of the wheel. The computational results show that the hydrodynamic characteristics of the modified model are better than those of the original model, which reduces resistance by 51.2% and provides an effective reference for the study on reducing resistance and raising speed.

Key words: Amphibious vehicle, Free surface, Numerical calculation, Shape optimization