Objective  To investigate the dynamic behavior and flow field characteristics of trans-medium submersibles during underwater straight-line navigation and turning maneuvers.

Method Computational fluid dynamics simulations were employed, using the VOF multiphase flow model and the SST k-ω turbulence model to establish a numerical model of the underwater navigation of the trans-medium submersibles. The accuracy of the numerical method was validated by comparing the experimental total drag data for the DARPA Suboff submarine model at various speeds with the numerical calculation results. On this basis, numerical simulations and analyses of underwater straight-line navigation and turning maneuvers of the trans-medium submersible were conducted, focusing on the effects of ducted propeller rotation speed and tail fin deflection angle on the underwater straight-line navigation and turning performance of the submersible.

Results The research results indicate that during straight-line underwater navigation, the forward speed of the trans-medium submersible exhibits an approximately linear relationship with the propeller's rotational speed. For instance, as the propeller speed increases from 600 r/min to 4800 r/min, the forward speed rises from 1.1 m/s to 8.1 m/s. At the same time, the pitch moment becomes less negative with increasing propeller speed (from −0.35 N·m to −0.17 N·m), indicating that the submersible remains stable in pitch during high-speed navigation. The propeller speed has little effect on the surface pressure distribution and the structure of the surrounding flow field. During underwater turning, the turning radius is mainly determined by the tail fin deflection angle and is largely unaffected by the propeller speed. The turning radius decreases with increasing tail fin deflection angle (from 3.35 times the submersible's body length to 0.75 times), though the rate of decrease diminishes. In contrast, the turning speed is affected by both the propeller speed and the tail fin deflection angle. The thrust generated by both propellers increases with higher propeller speeds and larger tail fin deflection angles. During turning, the thrust of the outer propeller consistently exceeds that of the inner propeller, and the thrust difference increases with greater tail fin deflection. Furthermore, tail fin deflection during turning leads to a significantly asymmetric surface pressure distribution on the submersible. This asymmetry becomes more pronounced with increasing tail fin deflection and is closely associated with the asymmetric flow characteristics of the surrounding flow field.

Conclusion This study provides a reference for the design and performance analysis of trans-medium submersible configurations.