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RESEARCH PAPERS

Utility Scale Twist-Flap Coupled Blade Design

[+] Author and Article Information
Kyle K. Wetzel

 Wetzel Engineering, Inc., P.O. Box 4153, Lawrence, Kansas 66046-1153kyle.wetzel@kwetzel.com

J. Sol. Energy Eng 127(4), 529-537 (Jun 23, 2005) (9 pages) doi:10.1115/1.2037089 History: Received February 02, 2005; Revised June 21, 2005; Accepted June 23, 2005

This paper reports an investigation of the use of off-axis carbon fibers in the all-carbon spar cap of a 37-m wind turbine rotor blade to induce twist-flap coupling. Many studies have been published on the structure of wind turbine rotor blades incorporating off-axis fibers; none has studied optimizing the blade structure simultaneously considering the angle of off-axis material, the fraction of off-axis material, constraints on cross-fiber and in-plane shear strength, constraints on tip deflection, and blade cost. A parametric study has been conducted varying the angle of off-axis fibers from 5° to 25° and varying the volume fraction of off-axis fibers in the spar cap from 10% to 90%. In all configurations, the remainder of the spar cap material is 0° carbon fiber. The spar cap thickness has been adjusted in each blade to simultaneously minimize the weight of carbon material, and hence the blade cost, while satisfying constraints on carbon fiber strain and tip deflection. The study also examines the cross-fiber strain and stress and the in-plane shear stress in the 0° and off-axis carbon layers. The conclusion of this study is that the optimal angle for most cost-effectively achieving twist-flap coupling—considering constraints on fiber strain, cross-fiber strength, in-plane shear strength, and tip deflection—is closer to 7.5° than the 20° that has frequently been reported by prior researchers. As much as 90% of the spar cap carbon fibers can be rotated to 7.5° off-axis before in-plane shear strength is exceeded.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Planform and profile of the 37 m blade

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Figure 2

Twist-flap coupling as a function of the fraction of off-axis fibers in the spar cap

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Figure 3

Blade mass as a function of the fraction of off-axis fibers in the spar cap

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Figure 4

Relative blade cost as a function of the fraction of off-axis fibers in the spar cap

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Figure 5

Relative blade cost as a function of the twist-flap coupling

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Figure 6

Peak fiber strain in the off-axis fibers: (a) tension and (b) compression

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Figure 7

Decomposition of lamina stresses and strains in the presence of external loading (shown for the compression side of the blade)

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Figure 8

Peak cross-fiber (transverse) tensile strain: (a) 0° carbon layers and (b) off-axis carbon layers

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Figure 9

Peak cross-fiber (transverse) tensile stress: (a) 0° carbon layers and (b) off-axis carbon layers

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Figure 10

Peak in-plane shear stress as a function of the fraction of off-axis fibers: (a) 0° carbon layers and (b) off-axis carbon layers

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Figure 11

Peak in-plane shear stress as a function of twist-flap coupling: (a) 0° carbon layers and (b) off-axis carbon layers

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Figure 12

Maximum coupling achievable as a function of off-axis fiber angle

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