Passive Pitch Control of Horizontal Axis Marine Hydrokinetic Turbine Blades

As the need for clean and renewable energy becomes greater, alternative energy technologies are becoming more and more prevalent. To that end, there has been a recent increase in research on marine hydrokinetic turbines to assess their potential as a reliable source of energy production and to expedite their implementation. These turbines are typically constructed from fiber reinforced composites and are subject to large, dynamic fluid forces. One of the benefits of composite materials is that the bend-twist deformation behavior can be hydroelastically tailored such that the blades are able to passively change their pitch to adapt to the surrounding flow, creating a nearly instantaneous control mechanism that can improve system performance over the expected range of operating conditions. These improvements include increasing energy capture, reducing instabilities, and improving structural performance. Practical constraints, however, lead to limitations in the scope of these performance enhancements and create tradeoffs between various benefits that can be achieved. This paper presents a numerical investigation into the capability of passive pitch control and combined active/passive pitch control to modify the performance of horizontal axis marine turbines with proper consideration of practical restrictions.