Model testing of a series of bi-directional tidal turbine rotors

•This is the first ever experimental work covers a series of bi-directional rotors (7 rotors).•Power and drag coefficients plus complete sets of geometry and motion parameters were obtained and presented.•Influences of Reynolds number, pitch ratio, pitch distribution and solidity on performance were found.•This is the tidal turbine model testing work focused on solidity and pitch optimization.•A solidity of 0.4 produced the highest power; most existing rotors has a solidity of about 0.2 or less.

A series of 7 bi-directional tidal turbine metal rotor models were manufactured and tested. A rotor testing apparatus was built using an off-the-shelf propeller dynamometer. Configuration, testing set-up, calibration of the apparatus and data acquisition details are described. Influences of Reynolds number, pitch ratio, pitch distribution and solidity, on hydrodynamic performance, were made and are presented. In addition to other findings, a rotor with a solidity of 0.4 produced the highest power output. The increase in power coefficient from a solidity of 0.2 to 0.4 and 0.6 to 0.4, is 14% and 16%, respectively. This indicates that for this kind of bi-directional turbine, a relatively larger solidity of about 0.4 than most installed turbine rotors maybe a better choice in terms of power output.