Scale effects on open water characteristics of a controllable pitch propeller working within different duct designs

•Scale effects are comparable for a propeller working in different duct designs.•Duct thrust and propeller torque have most prominent scale effects.•Pitch ratio influences the magnitude of scale effects on propeller coefficients.•CFD calculations are done in model (k–ω–SST and transition models) and full scales.•Comparisons are made with open water tests and paint flow tests in model scale.

A detailed investigation of the scale effects on the open water characteristics of a moderately skewed 4-bladed controllable pitch propeller is presented in this paper. The influence of duct design on the flow characteristics, as well as the blade and duct forces in model and full scale conditions, has been studied using three ducts of different design- two standard ducts, Duct 19A and Duct 37, and an innovative duct concept InnoDuct10, which is proposed by Rolls-Royce and belongs to the group of so-called high-efficiency ducts. The scale effects have been estimated with the help of CFD calculations performed using the RANSE solver of STAR-CCM+ in both model and full-scale conditions. On the experimental side, open water tests were carried out to compare the force measurements with calculations in model scale, and paint flow tests were performed to visualize the flow patterns over propeller blades and duct at variable Reynolds number. It has been observed that scale effects on the integral open water characteristics are dependent on the blade pitch and thrust loading coefficient, while being essentially in the same range for all the duct designs.