Simulation of Incompressible Viscous Flow Around a Tractor Thruster in Model and Full Scale

The incompressible viscous flow around a podded propulsor of tractor type is simulated by solving the RANS equations with the k-ε turbulence model. The FINFLO solver developed at Helsinki University of Technology is used in the calculations. This paper presents the results of computations performed for a tractor thruster in model and full scale. Grids of up to 7.5 million cells were built for the hydrodynamic analysis. No wall functions were used. The sliding mesh technique was employed for modeling the rotating and stationary parts of the propulsor unit. Circumferential averaging over the sliding surface was applied in order to reduce the unsteady problem to steady state, and consequently decrease the CPU time. The calculated flow patterns are illustrated and the forces on the different components of the tractor unit are shown in model and full scale. The effect of insufficient grid size on the flow patterns is shown in model scale. Comparison of the calculated forces with experiments in model scale is also provided for one advance number. Good correlation is obtained in terms of total efficiency of the thruster. The predictions of the force coefficients for the different components are moderately good. The results give valuable information on scaling effects and guidance for the hydrodynamic design. This work was made within the European Union OPTIPOD project.