Numerical research on the high-speed water entry trajectories of AUVs with asymmetric nose shapes

During the water entry process, autonomous underwater vehicles (AUVs) take a long time to reach a horizontal attitude. To reduce the time and distance required to adjust the attitude, an AUV with an asymmetric nose shape is proposed in this paper. A numerical model based on the volume of fluid (VOF) method is established to describe the cavity and trajectory characteristics of an AUV with a high-speed water entry. Since the velocity of the AUV impacting the water surface is greater than 0.3 Ma, the Tait equation is used to describe the compressibility effects in water, and the air phase is modelled as an ideal gas. The simulation results, such as cavitation shape and velocity, are compared with the experimental data from an earlier study. Good comparative results reveal the accuracy and performance of the employed numerical method. Subsequently, the computational fluid dynamics (CFD) code Fluent is used to simulate and analyse the variations in the trajectory characteristics with different water entry velocities, water entry angles, nose shapes and rudder deflection angles. The results obtained in this study can provide a good guideline for the trajectory control and nose shape design of an AUV.