Effects of transition turbulence modeling on the hydrodynamic performance prediction of a rim-driven thruster under different duct designs

Abstract

The rim-driven thruster (RDT) is an innovative marine propulsion device. During the design process, scale models of RDTs are frequently used and also smaller sized units used in Underwater Remotely Operated Vehicles (ROVs) or Autonomous Underwater Vehicles (AUVs) are often likely to operate under conditions where the boundary layer on the surface of the propeller makes a transition from a laminar to a turbulent regime. Accurately resolving this transitional boundary layer can help improve the performance prediction of RDTs. Studies addressing this are scarce and hence the present work investigates the influence of transition turbulence modeling on the hydrodynamic performance prediction of an RDT with different duct configurations by means of computational fluid dynamics (CFD). The turbulence models employed in this study are the two-equation SST k−ω model and the four-equation γ−Reθ transition model. For this purpose, three duct designs are considered, notably two modified 19A and 37 ducts, and one symmetric duct design often seen in RDT designs. Numerical calculations are performed using ANSYS Fluent 19.1 whilst a verification and validation study is firstly carried out to ensure the accuracy of the numerical model. The results demonstrate that the γ−Reθ transition model can better capture the transitional flow on the blade’s surface, and substantial discrepancies are observed between both turbulence models with regard to the streamline patterns near the blades on the one hand and skin friction profiles on the other. The torque calculated using the transition model better fits the experimental data, suggesting that it is more suitable to estimate the RDT performance. Three RDT duct designs are simulated which enable different ways to guide the incoming flow and it is shown that they have an important influence on the propeller performance. The results of the open water performance of the three different duct profiles are presented and compared, along with detailed analyses of the flow fields.