Experimental testing of bi-directional tidal turbine rotors

Performance characteristics of 7 bi-directional tidal turbine rotors were investigated in a circulating water channel (CWC). The effects of Reynolds number, pitch distribution, pitch ratio and solidity were evaluated and the influence of testing in turbulent flow discussed. An open boat assembly was used to house a Cussons dynamometer, to measure torque and thrust, and a Dunkermotor to control the shaft speed. The findings indicated that testing in the CWC, as opposed to a towing tank (TT), will produce a maximum power coefficient of approximately 50% less. This was attributed to the threedimensional turbulent flow of the CWC and the sensitivity of the performance characteristics of a horizontal axis tidal turbine (HATT) with respect to the inflow quality. Reynolds independence was reached at an inflow speed of 1.5 m/s; with maximum performance characteristics obtained by rotor 6, with a solidity ratio of 0.4. Further work to investigate rotor pitch can be carried out to optimise this type of rotor and complete a baseline data set necessary for organising full scale testing and analysis.