Design and testing of a contra-rotating tidal current turbine

A contra-rotating marine current turbine has a number of attractive features: near-zero reactive torque on the support structure, near-zero swirl in the wake, and high relative interrotor rotational speeds. Modified blade element modelling theory has been used to design and predict the characteristics of such a turbine, and a model turbine and test rig have been constructed. Tests in a towing tank demonstrated the feasibility of the concept. Power coefficients were very high for such a small model and in excellent agreement with predictions, confirming the accuracy of the computational modelling procedures. High-frequency blade loading data were obtained in the course of the experiments. These show the anticipated dynamic components for a contra-rotating machine. Flow visualisation of the wake verified the lack of swirl behind the turbine. A larger machine is presently under construction for sea trials.