Passive Pitch Control in Marine Hydrokinetic Turbine Blades

Abstract

Green and renewable energy technologies are becoming more and more necessary as demand for energy grows exponentially around the world. Recently, there has been increased interest in using marine hydrokinetic turbines to generate energy from ocean currents and tidal flows. The blades of these turbines are slender and are subjected to large, dynamic fluid forces; for that reason they are typically constructed from fiber-reinforced composites. The bend-twist deformation coupling behavior of these materials can be hydroelastically tailored such that the pitch angle of the blades will passively change to adapt to the surrounding flow, creating an instantaneous reaction that can improve system performance over the expected life of the turbine. Potential benefits of this passive control mechanism include increased lifetime power generation, reduced hydrodynamic instabilities, and improved load shedding and structural performance. There are practical concerns, however, that increase the complexity of the design of these bend-twist coupled blades. Large inflow variations in viable locations for turbine implementation combined with system component limitations such as restrictions on the generator and maximum rotational speed require consideration of practical and site-specific constraints. Using a previously validated boundary element method-finite element method solver, this work presents a numerical investigation into the capabilities of passive pitch adaptation under both instantaneous and long-term variable amplitude loading to better describe potential benefits while considering practical design and operational restrictions.