Space-time Loadings on Wind Turbine Blades driven by Atmospheric Boundary Layer Turbulence: Coupling LES and DES

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0933647BrasseurProject SummaryWind turbine downtime has been consistently higher than anticipated because of a lack of quantitative knowledge of the true space-time loadings along the span of the rotor blades that arise from the interactions between the rotor and the fluctuating wind field. The atmospheric surface layer (ASL) contains strongly inhomogeneous coherent turbulence structure that generates high variability in space-time wind vector orientation and magnitude relative to the rapidly rotating blades, creating non-steady spatially-dependent loadings. The non-steady forces and moments along the rotor blades underlie the vibrations, bending, and twisting of the blades, span-dependent non-steady boundary layer separations and dynamic stall, noise, trailing vortex formation, and blade pitch control. These loadings integrate to produce fluctuating forces on the drive shaft that are transferred to the gearbox, a hot point for failure. While field data cannot provide the needed wind data in full space-time, simulations have been limited by resolution, accuracy, and the lack of true space-time atmospheric wind inputs.Intellectual Merit: This project shall develop a sophisticated computational capability, well resolved in space-time that accurately predicts the details of rotor aerodynamics and loadings in response to true ASL turbulence structure over a wide range of atmospheric states. The computational facility will be applied to analyze the detailed dynamics underlying wind turbine loadings and fluctuating forces on the shaft and will also form the basis of a computational test-bed facility for validation of lower-order design models, for design and testing of control systems, and for studies of important related issues such as noise, downwind interactions, gearbox design, etc. The facility will be developed within the massively parallel framework of the NSF tera-grid by coupling two classes of simulation and code: (1) pseudo-spectral large-eddy simulation (LES) of the atmospheric boundary layer (ABL) over a wide range of atmospheric states, and (2) body-fitted aerodynamic simulations over individual rotor blades using a "detached eddy simulation" (DES) strategy. Broader Impacts: This research program could broadly impact wind turbine design by providing a high level resource within which low-order design tools can be developed and validated. It will initiate a long-term effort that we plan to grow to include a broad range of wind turbine design issues. The PIs shall contribute to the outreach efforts of the Penn State Institutes of Energy and the Environment (PSIEE) and Center for Sustainability (CfS) which works directly with undergraduate students through green energy projects. They will develop short lectures for undergraduate students involved in SfS projects and elsewhere. The focus will be "the need for high-level science and technology research related to wind power." They also plan to work with the Penn State Public Broadcasting Service (WPSU) to develop a web-based "digital learning object" directed at high school and undergraduate that shows the excitement of doing high-level scientific research in wind energy.