Adaptive Pitch Composite Blades for Axial-Flow Marine Hydrokinetic Turbines
Barber, Ramona Brockman
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Marine hydrokinetic (MHK) turbines are quickly becoming a viable and valuable method of generating renewable energy from ocean, tidal, and river currents. Modern MHK turbine blades are typically constructed from fiber reinforced polymer (FRP) composites, which provide superior strength- and stiffness-to-weight ratios and improved fatigue and corrosion resistance compared to traditional metallic alloys. Furthermore, it is possible to hydroelastically tailor the design of an FRP composite blade by manipulating the anisotropic nature of the material, creating a load-dependent adaptive pitch mechanism. With this strategy, the blade geometry is able to passively adjust to the instantaneous inflow, and system performance can be modified over the expected range of operating conditions. Adaptive blade designs have demonstrated the potential to increase performance, reduce hydrodynamic instabilities, and improve structural integrity in aerospace and other marine applications; however, previous research specific to adaptive MHK turbine blades has been preliminary. Further work is needed to better understand and model the behavior of these systems. To that end, the research presented here combines numerical and experimental modeling to develop greater insight into the potential benefits to be gained by the use of adaptive pitch MHK turbine blades. In this work, a well-validated boundary element method-finite element method solver is used to develop a numerical strategy for predicting the performance and structural response of adaptive turbine blades under a wide range of site-specific operating conditions. The behavior of adaptive MHK turbine blades under normal as well as cavitating conditions is analyzed; results suggest numerous advantages possible with the use of adaptive pitch blades. Following the numerical study, an experimental program is outlined in which a flume-scale turbine system is tested under steady and fluctuating inflow conditions. Loading and performance trends found in the experimental study agree well with numerical predictions. Finally, numerical and experimental results are synthesized into a complete analysis of the potential benefits to be gained with the use of adaptive blades in MHK turbine systems. Future research directions are identified with the goal of further evolving adaptive blade technology.
- Civil engineering