Morphing Blades for Tidal Turbines: a Theoretical Study

Tidal energy has the potential to significantly contribute to energy security by providing predictable renewable energy. New technology is needed to decrease the levelised cost of energy and to make this energy sector competitive in the energy market. A key area where technology can contribute to decrease costs is mitigating the hydrodynamic load fluctuations, and thus increasing the fatigue life of the turbine. Here, we formulate a passive morphing blade concept that aims to mitigate the unsteady thrust without affecting the mean torque and thus the harvested power.
We show that a blade with a trailing edge that deflects perfectly elastically can suppress virtually all fluctuations without varying the mean loads. The effect of the hydrodynamic and blade’s inertia, the material damping, and the radial shear stress, decrease the performances.
Using a low-order model of the blade, we show that when a gust occurs, the angle of attack experienced by a rigid blade increases, whilst that experienced by a well-designed morphing blade decreases. This counter-intuitive mechanism is what makes morphing blades highly effective. While blades that could pas- sively twist have previously been developed, this theoretical study suggests that chordwise flexibility is a suitable alternative that should be further explored. Keywords: unsteady load mitigation, passive load control, pitch control, morphing, fluid-structure interaction, tidal turbine