Nonlinear analysis of flow-induced instabilities of wind turbine blades using theoretical models and supported by experimental data

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Principal Investigator: Yahya Modarres-SadeghiNumber: 1437988 Title: Nonlinear analysis of flow-induced instabilities of wind turbine blades using theoretical models and supported by experimental dataInstitution: University of Massachusetts, AmherstIncreasingly, wind farms for the production electricity are being sited off shore to harvest this renewable energy resource. The available energy that individual wind turbines within the wind farm may extract is proportional to the swept area of the turbine rotor blades, creating a powerful incentive to design, manufacture, and commercially use longer and more slender blades. This trend is driven by economics - wind farm installation costs are substantially higher offshore than onshore, and so increased energy production per installed wind turbine is crucial for cost-effective offshore wind energy. However, as blades become longer and more slender, they become more susceptible to various flow induced instabilities. A particularly troublesome instability is the unwanted blade oscillations, or flutter, caused by the interaction of the blade with the wind. This unstable behavior can lead to catastrophic failure of the blades. This limitation poses a threat to the integrity of offshore wind turbines and their ability to reliably operate. In the current research, flow-induced instabilities of wind turbine blades will be studied using advanced computational models based on a technique called nonlinear analysis in order to better understand these instabilities and develop guidelines for the design of future wind turbine blades. As part of the proposed activities, the principal investigator will organize a session at the North American Wind Energy Academy (NAWEA) on Offshore Wind Energy, develop YouTube presentations on wind turbines targeted to middle and high school students, and give demonstrations to local high school students on the same topic. Technical DescriptionThe goal of this research is to develop a nonlinear, fully-coupled continuous fluid-structure interaction model for flexible and rotating wind turbine blades. This model will be used to study flow-induced instabilities for long and slender blades that are anticipated to be used in future shore wind turbines. A wind turbine blade is an inherently three-dimensional and nonlinear system. Nevertheless, current approaches for wind turbine blade instability analysis have modeled the blades as two-dimensional, linear systems in order to bypass the difficulties associated with three-dimensional, nonlinear system modeling. However, as blades become longer and more slender, the need for more comprehensive models is necessary. The proposed nonlinear model for flexible and rotating blades will account for varying blade shapes and cross-sections, as well as bending and torsional properties. Geometric, flow-related and fluid-structure interaction nonlinearities will be embedded into the model. A comprehensive series of wind tunnel experiments will be conducted to validate this model. The validated model will then be used to provide a fundamental understanding of flow-induced instabilities of wind turbine blades. This approach will also enable the study of nonlinear instability of flexible structures with non-uniform properties along their length under highly nonlinear interaction with flow, and thus provide a broader understanding of the physics underlying nonlinear fluid-structure interaction systems. With respect to education and broader impacts, the principal investigator will organize a session at the North American Wind Energy Academy (NAWEA) on Offshore Wind Energy. Outreach activities include development of YouTube presentations on wind turbines targeted to middle and high school students, and demonstrations to local high school students on the same topic.