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Research Papers

Description and Computer Modeling of a Ball-and-Socket Hub That Enables Teetering for Three-Bladed Wind Turbines

[+] Author and Article Information
Arnold Ramsland

Ramsland Technology,
97533 Franklin Ridge,
Chapel Hill, NC 27517
e-mail: acrbjr@msn.com

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received May 20, 2014; final manuscript received February 4, 2015; published online March 12, 2015. Assoc. Editor: Yves Gagnon.

J. Sol. Energy Eng 137(3), 031019 (Jun 01, 2015) (12 pages) Paper No: SOL-14-1152; doi: 10.1115/1.4029813 History: Received May 20, 2014; Revised February 04, 2015; Online March 12, 2015

A horizontal axis wind turbine with a ball-and-socket hub is disclosed. The hub enables horizontal axis turbines with two or more blades to teeter in response to wind shear gradients. Computer modeling was done using existing and modified fast code in order to compare the new hub design with existing designs. Results show that a three-bladed turbine with the ball-and-socket hub provides very significant reductions in out-of-plane bending loads applied to the main shaft in comparison to a three-bladed turbine with a rigid hub. Results also show that the new hub design provides significant reductions in the out-of-plane loads applied to the blades. A blade fatigue study using a rainflow counting of multi-axial torque contributions at the blade root was performed in order to assess the impact of these reductions, and results show that the three-bladed turbine equipped with a ball-and-socket, teetering hub provides for very significant reductions in lifetime blade damage in comparison to existing wind turbine designs due to a combination of factors. The first factor is that teetering largely eliminates the cyclic variations in out-of-plane torque on the blades that are observed with rigid hubs. Here, the fatigue study shows that the three-bladed wind turbine with a teetering hub provides for an approximate sixfold reduction in lifetime blade damage in comparison to a three-bladed turbine with a rigid hub. The second factor is that the addition of a third blade reduces the load on each blade by one-third. Here, the fatigue study shows that a three-bladed turbine with a teetering hub provides for an approximate fourfold reduction in lifetime blade damage in comparison to a two-bladed turbine with a teetering hub.

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References

Figures

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Fig. 1

Wind Turbine undergoing teetering

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Fig. 2

Exploded view of ball-and-socket hub

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Fig. 3

Alternate main shaft ball with fitted transfer assembly

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Fig. 6

Main shaft ball showing teetering arc and teetering plane

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Fig. 7

Wind turbine with ball-and-socket hub protected by nose cone and back protector

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Fig. 8

Teetering and pitch axes of two-bladed wind turbine

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Fig. 9

Teetering and pitch axes of three-bladed wind turbine

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Fig. 10

Lifetime Weibull wind speed distribution

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Fig. 15

Rotating bending moment at LSS tip about ya axis with two-bladed hub (LSSTipMya)

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Fig. 14

Rotating bending moment at LSS tip about za axis with three-bladed hub (LSSTipMza)

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Fig. 13

Rotating bending moment at LSS tip about ya axis with three-bladed hub (LSSTipMya)

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Fig. 12

Blade 1 teetering profile with two-bladed hub

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Fig. 11

Blade 1 teetering profile with three-bladed hub

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Fig. 21

Out-of-plane bending moment at blade 1 root (RootMyc1)

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Fig. 20

In-plane bending moment at blade 1 root (RootMxc1)

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Fig. 19

Nonrotating low-speed shaft bending moment about zs axis at the shaft’s strain gage (LSSGagMzs)

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Fig. 18

Nonrotating low-speed shaft bending moment about ys axis at shaft’s strain gage (LSSGagMys)

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Fig. 17

Rotating bending moment at low-speed shaft tip about ya axis with three-bladed hub (LSSTipMya) showing spike with teetering hub

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Fig. 16

Rotating bending moment at LSS tip about za axis with two-bladed hub (LSSTipMza)

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