A Numerical Study on Model Propeller Performance Prediction Including Transitional and Passively Controlled Boundary Layer Considerations

Viscous flow simulations, utilising Computational Fluid Dynamics (CFD), have increasingly become the standard approach in the design and optimisation processes for predicting propeller performance. This is primarily due to the significant influence of viscous effects on propeller performance, encompassing phenomena such as tip and hub vortices, tip vortex cavitation inception, flow separation, and the transition from laminar to turbulent boundary layers at model-scale. Numerous studies have demonstrated the necessity of incorporating transition modelling in CFD to accurately determine propeller performance at modelscale, whereas full-scale simulations can successfully rely on two-equation turbulence models.
However, despite these advancements in CFD, the industry continues to rely on a relatively simplistic procedures to scale model test results to full-scale in order to predict ship propeller performance. Generally, the conventional scaling procedures focus solely on reducing sectional drag between the model and full-scale propeller, assuming a partially laminar boundary layer at model-scale. Nevertheless, it is important to recognize that this approach oversimplifies the discrepancies between laminar and turbulent propeller boundary layers.
Therefore, the aim of this paper is to demonstrate that CFD, when employing the appropriate turbulence and transition models, can accurately predict propeller performance at model-scale, in scenarios involving partially laminar or fully turbulent boundary layers. Consequently, the findings provide additional insights on improving extrapolation methods through CFD simulations, particularly when model-scale considerations prioritize the accurate development of turbulent boundary layers.
A Reynolds averaged Navier-Stokes solver (RANS) was used in combination with the k-ω SST turbulence and ɣ-Reθtransition model for a modern designed MARIN stock propeller. The CFD results were compared to Experimental Fluid Dynamics (EFD) results, which involved propellers equipped with and without innovative turbulence stimulators, also known as turbulators. In addition comparing performance characteristics, the boundary layer flows regimes were also examined using EFD paint test results. Furthermore, full-scale Reynolds CFD simulations were conducted and compared to conventionally extrapolated EFD results. Excellent comparisons were achieved between EFD and CFD for model-scale Reynolds numbers, encompassing both uncontrolled and passively controlled boundary layers. A clear trend of Reynolds scaling was observed for propellers with a turbulent boundary layer at modelscale. However, this trend was not evident for propellers with laminar or partially laminar boundary layers at model-scale, demonstrating that the relevant boundary layer regimes should be modelled correctly.