Model-scale experiments of passive pitch control for tidal turbines

TL;DR

This study experimentally demonstrates that passive morphing blades can significantly reduce load fluctuations in tidal turbines, improving their stability and performance in unsteady tidal currents.

Contribution

First experimental validation of passive morphing blades for tidal turbines, showing load fluctuation reduction and highlighting critical design considerations.

Findings

Fluctuations in root-bending moment, thrust, and torque are reduced across various tip-speed ratios.

Friction resistance can impair morphing blade effectiveness and must be minimized.

The work confirms the potential of morphing blades to enhance tidal turbine performance.

Abstract

Tidal currents are renewable and predictable energy sources that could prove fundamental to decrease dependency from fossil fuels. Tidal currents, however, are highly unsteady and non uniform, resulting in undesirable load fluctuations on the blades and the drive train of turbines. A passive morphing blade concept capable to reduce the load fluctuations without affecting the mean loads has recently been formulated and demonstrated with numerical simulations (Pisetta et al., 2022). In this paper, we present the first demonstration of this morphing blade concept, through experimental tests on a 1.2 m diameter turbine. We show that fluctuations in the root-bending moment, thrust and torque are consistently reduced over a broad range of tip-speed ratios. This work also highlights some critical design aspects of morphing blades. For instance, it is showed that the friction resistance can substantially decrease the effectiveness of the system and thus must be minimised by design. Overall this paper demonstrates for the first time the effectiveness of morphing blades for tidal turbines, paving the way to the future development of this technology.