Model-scale experiments of passive pitch control for tidal turbines

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.

Automated summary

Tidal currents are a renewable and predictable energy source that can reduce dependence on fossil fuels. However, they are highly unsteady and non-uniform, resulting in undesirable load fluctuations on turbine blades and the drive train. A passive morphing blade concept has been formulated to reduce these load fluctuations without affecting the mean loads, and its effectiveness has been demonstrated through experimental tests on a 1.2-m diameter turbine. This study also highlights critical design aspects, such as minimizing friction resistance, for the successful implementation of morphing blades in tidal turbines.