Research Papers

Comparison of Performance and Unsteady Loads of Multimegawatt Downwind and Upwind Turbines

[+] Author and Article Information
Edoardo Frau, Ndaona Chokani, Reza S. Abhari

Laboratory for Energy Conversion,
Department of Mechanical and
Process Engineering,
ETH Zurich,
Sonneggstrasse 3,
Zurich 8092, Switzerland

Christian Kress

Laboratory for Energy Conversion,
Department of Mechanical and
Process Engineering,
ETH Zurich,
Sonneggstrasse 3,
Zurich 8092, Switzerland
e-mail: kress@lec.mavt.ethz.ch

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 September 24, 2014; final manuscript received March 30, 2015; published online April 27, 2015. Assoc. Editor: Yves Gagnon.

J. Sol. Energy Eng 137(4), 041004 (Aug 01, 2015) (8 pages) Paper No: SOL-14-1278; doi: 10.1115/1.4030314 History: Received September 24, 2014; Revised March 30, 2015; Online April 27, 2015

The benefits and drawbacks of a multimegawatt downwind compared to upwind wind turbine are assessed using unsteady, three-dimensional (3D) computational fluid dynamics. For the same operating conditions, the downwind turbine has a 3% higher output power and a similar mean flapwise root bending moment. However, in comparison to the upwind turbine, the downwind turbine has a 3% higher thrust and a factor 3 larger peak-to-peak unsteady loading. These features arise due to higher flow incidences on the blade, higher axial velocities ahead of the rotor, and higher loading on the inboard span of the blade when the downwind turbine is compared to the upwind turbine. Overall, it is concluded that the downwind turbine configuration may be better suited for the design of multimegawatt offshore wind turbines.

Copyright © 2015 by ASME
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Fig. 1

Computational setup used in the simulations showing the spherical domain (a) and the cylindrical domain around the rotor and the hub (b)

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Fig. 2

Unstructured full-domain Delaunay-type volume mesh

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Fig. 3

Prism layers around the wind turbine blade at midspan

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Fig. 4

Normalized rotor power coefficient over one revolution

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Fig. 5

Normalized rotor thrust coefficient over one revolution

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Fig. 6

Normalized torque over one revolution

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Fig. 7

Normalized blade thrust over one revolution

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Fig. 8

Evolution of blade flapwise moment over one rotor revolution for upwind and downwind configurations. The moments are normalized relative to the mean moment of the downwind configuration.

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Fig. 9

Normalized blade circumferential force (a) and normalized blade torque over one revolution (b)

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Fig. 10

Vertical (a) and horizontal (b) lines used over the nacelle to measure the axial velocity. Drawing not to scale.

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Fig. 11

Axial velocity profile along line A at 0.15D upstream (a) and line B at 0.1D upstream (b) comparing downwind and upwind configuration. The zero is the hub center.

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Fig. 12

Axial velocity along line C at 10 m height (a) and line D at 3.5 m height (b) comparing downwind and upwind configurations. Flow left to right.

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Fig. 13

Contour of normalized axial velocity at 0.1D upstream of the hub for the downwind case (a) and the upwind case (b). The radial extent of the plot is 1D.

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Fig. 14

Contour of normalized axial velocity at 30% blade span below hub height at 180 deg azimuth angle for downwind (a) and upwind (b)

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Fig. 15

Incidences at 0 deg azimuth angle (a) and 180 deg azimuth angle (b) for downwind and upwind configuration

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Fig. 16

Incidences over one rotation at 30% blade span (a) and 75% blade span (b) for the upwind and downwind configuration




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