Comparative study on the hydrodynamic flow characteristics around the BB2 submarine using RANS and PANS turbulence models under straight and drift conditions

This study presents a comparative computational analysis of the hydrodynamic flow characteristics around the Joubert BB2 submarine using Reynolds-Averaged Navier–Stokes (RANS) and Partially-Averaged Navier–Stokes (PANS) turbulence models. Simulations were performed under two representative operating conditions: straight-ahead motion and 10° drift. The numerical framework was validated against MARIN benchmark data, focusing on the total resistance and axial velocity distributions at the propeller plane. Comparative analyses demonstrated that the PANS model better captures the spatial development of turbulent kinetic energy, along with asymmetric wake features and intricate vortex interactions. The analysis included detailed comparisons of wall shear stress, axial velocity, vorticity, vortex structure and turbulent kinetic energy distributions. In particular, the PANS model demonstrated superior capability in capturing flow separation, vortex development, and wake evolution under asymmetric inflow conditions. Under both conditions, the PANS model captured more coherent vortex structures and more pronounced variations in velocity, while the RANS model exhibited overpredicted turbulence energy and more diffused wake characteristics. These findings suggest that the PANS model offers a physically consistent and computationally efficient alternative to RANS for simulating unsteady and asymmetric flows around submerged bodies, particularly in scenarios where wake dynamics critically influence propulsion and maneuvering performance.