Structural Design and Analysis of a Segmented Ultralight Morphing Rotor (SUMR) for Extreme-Scale Wind Turbines

摘要

To alleviate the mass-scaling issues associated with conventional upwind rotors of extreme-scale wind turbines (≥ 10MW), a segmented ultralight morphing rotor (SUMR) concept was proposed by Loth et al. (2010, 2012). The concept employs a downwind rotor with segmented blades whose elements are stiff and whose joints can be unlocked to allow for moment-free downstream alignment. Aligning the combination of gravitational, centrifugal and thrust forces along the blade path reduces downwind cantilever loads, reducing to a primarily tensile loading. Herein, the SUMR concept is developed further by fixing the blade curvature and limiting morphing to a downwind coming angle through a single near-hub joint. Between cut-in and rated conditions, this downwind angle varies linearly between 0° (no alignment) to 24° (full alignment). Between rated conditions and cut-out conditions, the blade is fully-aligned, and this results in a decrease in coning angle to a value of 11° just before cut-out. To quantify mass savings, a 10 MW model (based on the NREL 5 MW reference turbine) was created for a conventional rotor blade and the SUMR blade. The morphing blade used an internal structure similar to the Sandia 100-m all-glass blade. The structural stresses were then predicted with a finite element method over a range of operating wind speeds and azimuthal angles. This leads to a net mass savings of 50% through decreased shell, spar, and shear web thicknesses. Furthermore, the ability to stow the morphing blades under extreme wind conditions with a pivot near the hub is found to substantially reduce the high wind constraint, as compared to that for conventional blades.