Load alleviation technology for extending life in tidal turbines

The two main obstacles to the commercial deployment of tidal turbines are cost and reliability. Behind both of these lies the ability of a turbine to withstand the hostile marine environment for long periods without failure or costly maintenance. Unsteadiness in the incoming flow seen by a tidal turbine causes large fluctuations in thrust and torque, which generate fatigue loads on the blade and drivetrain respectively and thus significantly reduce turbine lifespan. This paper will present the development of flow control devices to keep thrust and torque constant despite changes in flow speed. In particular, it will be shown that torque can be controlled using a small trip near the leading edge of the blade, and that thrust can be controlled viaa flap at the trailing edge. Data from a small-scale turbine will be used to show the effectiveness of both devices, and a reduction in unsteady loading of up to 75% will be demonstrated. This could translate into an order of magnitude increase in fatigue life.