Experimentally Observing Coupled-Mode Flutter

Presenter: Dominique Habchi

Faculty Sponsor: Yahya Modarres-Sadeghi

School: UMass Amherst

Research Area: Mechanical Engineering

Session: Poster Session 5, 3:15 PM - 4:00 PM, Concourse, B11

ABSTRACT

Wind energy has surged in popularity in the recent decade prompting research to be done to extend the lifecycle and increase the efficiency of wind turbines. One of the difficulties faced in turbine blade design is combatting wind instabilities as they can create strong vibrations that can shorten the lifespan of a blade. Coupled mode flutter is an aerodynamic instability that occurs when the first torsional mode and the third flapwise bending mode merge, causing a bending-twisting movement that over time will damage a wind turbine. This project explores the geometrical constraints of wind turbine spine and airfoil design. Four models of the NREL 5MW turbine blade have been experimentally observed in uniform flow with the intention of seeing coupled mode flutter. The initial model utilized a 40cm long rectangular spine lined with identical NACA 12 airfoils. After this model was tested and found to only display single-mode flutter, alterations were done in an attempt to create a more tip-driven blade susceptible to flutter. The second model utilized a 40cm long rectangular spine with NACA 12 airfoils tapering down the blade. The third model, 70cm long, was designed with a tapered blade, with a trapezoidal cutout in the center, lined with the same airfoil profiles as found on the original NREL 5MW blade. The last model, following the same blade shape and airfoil profiles as the one before, was 40cm long. Only single mode flutter has been achieved, suggesting a tapered spine will not increase the likelihood of coupled-mode flutter.

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