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Title: Downwind Pre-Aligned Rotor for a 13.2 MW Wind Turbine

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Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Wind and Water Technologies Office (EE-4W)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: AIAA SciTech: 33rd Wind Energy Symposium, 5-9 January 2015, Kissimmee, Florida
Country of Publication:
United States
17 WIND ENERGY; wind energy; wind turbine

Citation Formats

Loth, Eric, Ichter, Brian, Selig, Michael, and Moriarty, Patrick. Downwind Pre-Aligned Rotor for a 13.2 MW Wind Turbine. United States: N. p., 2015. Web. doi:10.2514/6.2015-1661.
Loth, Eric, Ichter, Brian, Selig, Michael, & Moriarty, Patrick. Downwind Pre-Aligned Rotor for a 13.2 MW Wind Turbine. United States. doi:10.2514/6.2015-1661.
Loth, Eric, Ichter, Brian, Selig, Michael, and Moriarty, Patrick. 2015. "Downwind Pre-Aligned Rotor for a 13.2 MW Wind Turbine". United States. doi:10.2514/6.2015-1661.
title = {Downwind Pre-Aligned Rotor for a 13.2 MW Wind Turbine},
author = {Loth, Eric and Ichter, Brian and Selig, Michael and Moriarty, Patrick},
abstractNote = {},
doi = {10.2514/6.2015-1661},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2015,
month = 1

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  • To alleviate the mass-scaling issues associated with conventional upwind rotors of extreme-scale wind turbines (>/=10 MW), a morphing downwind-aligned rotor (MoDaR) concept is proposed herein. The concept employs a downwind rotor with blades whose elements are stiff (no intentional flexibility) but with hub-joints that can be unlocked to allow for moment-free downwind alignment. Aligning the combination of gravitational, centrifugal and thrust forces along the blade path reduces downwind cantilever loads, resulting in primarily tensile loading. For control simplicity, the blade curvature can be fixed with a single morphing degree of freedom using a near-hub joint for coning angle: 22 degreesmore » at rated conditions. The conventional baseline was set as the 13.2-MW Sandia 100-m all glass blade in a three-bladed upwind configuration. To quantify potential mass savings, a downwind load-aligning, two-bladed rotor was designed. Because of the reduced number of blades, the MoDaR concept had a favorable 33% mass reduction. The blade reduction and coning led to a reduction in rated power, but morphing increased energy capture at lower speeds such that both the MoDaR and conventional rotors have the same average power: 5.4 MW. A finite element analysis showed that quasi-steady structural stresses could be reduced, over a range of operating wind speeds and azimuthal angles, despite the increases in loading per blade. However, the concept feasibility requires additional investigation of the mass, cost and complexity of the morphing hinge, the impact of unsteady aeroelastic influence because of turbulence and off-design conditions, along with system-level Levelized Cost of Energy analysis.« less
  • The potential of wind power to provide a fraction of US energy needs would be enhanced by a favorable environmental impact of wind turbines. One important factor in such an environmental impact is the aerodynamic noise generated by large wind turbines. This is especially true for a downwind rotor horizontal axis wind turbine. The flow field (wake) through which the rotor passes in a downwind horizontal axis configuration is quite complex. To delineate the noise sources resulting from a rotor interacting with the tower-wake requires a careful modelling of the phenomena experimentally and theoretically. This paper describes recent results obtainedmore » at MIT on the experimental and theoretical modelling of the aerodynamic noise generated by a downwind rotor horizontal axis wind turbine.« less
  • Tests have been conducted on a 38m diameter horizontal axis wind turbine, which had first a rotor downwind of the supporting truss tower and then upwind of the tower. Aside from the placement of the rotor and the direction of rotation of the drive train, the wind turbine was identical for both tests. Three aspects of the test results are compared: rotor blade bending loads, rotor teeter response, and nacelle yaw moments. As a result of the tests, it is shown that while mean flatwise bending moments were unaffected by the placement of the rotor, cyclic flatwise bending tended tomore » increase with wind speed for the downwind rotor while remaining somewhat uniform with wind speed for the upwind rotor, reflecting the effects of increased flow disturbance for a downwind rotor. Rotor teeter response was not significantly affected by the rotor location relative to the tower, but appears to reflect reduced teeter stability near rated wind speed for both configurations. Teeter stability appears to return above rated wind speed, however. Nacelle yaw moments are higher for the upwind rotor but do not indicate significant design problems for either configuration.« less
  • The wake of the MOD-0A1 wind turbine at Clayton, New Mexico has been measured using a vertical plane array of anemometers in a crosswind plane at a distance of two rotor diameters directly downwind of the turbine. Rotor blade vortices were well mixed into the wake turbulence and were not separately detectable. Wake swirl about the along-wind axis had a value not greater than 0.025 rad/s. Extra turbulence energy existed in the edge of the wake at a frequency of about n=0.025 Hz. The cross-wake plane analyses of wind speeds revealed a nearly circular inner portion and a strongly ellipticalmore » portion. The elliptical portion major axis was horizontal. An estimate of the average rate of reenergizing of the wake, using measurements of mean wind energy flow and turbine power, suggests that entrainment with ambient air may have been rapid. Some wake characteristics were compared with the corresponding ones for several simple wake models based upon concepts of mixing of ambient air into a wake or an equivalent coaxial jet. (LEW)« less