Improved efficiency with concave cavities on S₃ surface of a rim-driven thruster

Rim-driven thrusters (RDT) are of great interest for the development of integrated electric motors for underwater vehicles. Gap flow is one of the most prominent flow characteristics and plays an important role in the hydrodynamic performance of RDT. In this study, the rim in a carefully designed RDT was modified with several concave cavities defined by four parameters, and their influence on hydrodynamics was carefully calculated and analyzed. The simulations were performed using the k-omega shear stress transport turbulence model by solving the unsteady Reynolds-averaged Navier-Stokes equations. The numerical method was verified using a popular combination. The numerical results showed that the concave cavities on the rim improve the propulsive efficiency of RDT by a maximum of 3.52%. The increase in the propulsive efficiency is directly associated with the parameters of the concave cavities. Nevertheless, the flow in the gap has a negligible effect on the main flow field through the RDT. According to the numerical analysis, the different pressure integrals at the front and back surfaces of the concave cavities are the main reason for the improvement of the propulsive efficiency. The modification of the rim is helpful and practical for the hydrodynamic optimization of the RDT.