Model testing and performance comparison of plastic and metal tidal turbine rotors

•Model testing of two metal and two plastic bi-directional tidal turbine rotors.•Testing apparatus, facility, calibration and measurement presented.•Hydrodynamic performance was measured and compared.•Nylon rotors had substantial hydrodynamic performance discrepancies.•Nylon rotor flexibility reduced blade pitch and hence much lower power production.

Experimental model tests were conducted to predict the performance of two sets of metal and plastic bi-directional tidal turbine rotors. This test programme aims to provide reliable and accurate measurement data as references for developers, designers and researchers on both model and full scale. The data set presented in this paper makes available the detailed geometry and motion parameters that are valuable for numerical tools validation. A rotor testing apparatus that was built using an off-the-shelf K&R propeller dynamometer, its configuration, testing set-up, calibration of the apparatus and data acquisition are described. Comparison analysis between the metal and plastic rotors hydrodynamic performance in terms of torque, drag and derived power and drag coefficients are also presented. The results show a substantial decrease in maximum power performance for the plastic rotors – about 40% decrease at a tip speed ratio of around 3.0, compared with rigid metal rotors. The plastic rotors have also a much higher cut-in speed. It showed that materials for rotor models with low rigidity such as polyamide (nylon) produced by selective laser sintering (SLS) systems may substantially under-predict power generation capacity. As a result, they are considered unsuitable for rotor model performance evaluation.