RANSE-based simulation and analysis of scale effects on open-water performance of the PPTC-II benchmark propeller

•The scale effects on open water performance are numerically studied for a tip-rake propeller and its modified version by removing the tip rake.•The scale effect on thrust can be as important as that on the torque, which seems to be the result of reduced boundary layer thickness on full-scale blade surfaces.•Although the corrections for KT and KQ by the ITTC method differ largely from those by the RANS method, the corrections for η0 agree quite well at least in the cases of this paper. This paper presents our numerical study of the scale effects on a tip-rake propeller, the PPTC-II, based on the RANS simulations using software FLUENT 6.3. The low Re option in SST k–ω model is adopted at model scale, together with fine prism grids to resolve the viscous sub-layer. At full scale, standard wall function is adopted. The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method. To explain the CFD results, an analysis of sectional forces is performed. To investigate how the tip rake influences propeller scale effects, the geometry of PPTC-II is modified by removing the tip rake only, and the RANS-predicted scale effects for the modified propeller, PPTC-II-m, are compared with those for the PPTC-II. The study indicates that the scale effect on propeller thrust can be as important as that on the torque; somehow the RANS- and ITTC-based predictions for full-scale efficiency agree quite well; the tip-rake reduces tip loading and tip vortex strength, and brings about large differences in the scale effects as compared with the propeller without tip-rake.