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Research Papers: Alternative Energy Sources

The Influence of Sea Waves on Offshore Wind Turbine Aerodynamics

[+] Author and Article Information
A. AlSam

Department of Energy Sciences,
P.O. Box 118,
Lund SE-221 00, Sweden
e-mail: ali.al_sam@energy.lth.se

R. Szasz

Department of Energy Sciences,
P.O. Box 118,
Lund SE-221 00, Sweden
e-mail: robert-zoltan.szasz@energy.lth.se

J. Revstedt

Professor
Department of Energy Sciences,
P.O. Box 118,
Lund SE-221 00, Sweden
e-mail: johan.revstedt@energy.lth.se

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received December 15, 2014; final manuscript received July 1, 2015; published online July 27, 2015. Assoc. Editor: Ryo Amano.

J. Energy Resour. Technol 137(5), 051209 (Jul 27, 2015) (10 pages) Paper No: JERT-14-1410; doi: 10.1115/1.4031005 History: Received December 15, 2014

The impacts of swells on the atmospheric boundary layer (ABL) flows and by this on the standalone offshore wind turbine (WT) performance are investigated by using large eddy simulations (LES) and actuator-line techniques. At high swell to wind speed ratio, the swell-induced stress reduces the total wind stress resulting in higher wind velocity, less wind shear, and lower turbulence intensity level. These effects increase by increasing swell to wind speed ratio (C/U) and/or swell steepness. Moreover, for the same hub-height wind speed (Uhub), the presence of swells increases the turbine power extraction rate by about 3% and 8.4% for C/Uhub = 1.53 and 2.17, respectively.

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Figures

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Fig. 1

The geometry and the mesh used to simulate the atmospheric boundary layer

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Fig. 3

Time- and space-averaged normalized streamwise velocity. From the left to the right, the cases are: (a) wave age (C/u*o = 45.0), (b) (C/u*o = 60.0), and (c) (C/u*o = 90.0). Solid lines are the flow over flat surface, the dotted lines are the flow over 0.1 wave steepness swell and dashed lines are the flow over 0.157 wave steepness swell.

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Fig. 7

The instantaneous normalized velocity (left), and the instantaneous vorticity magnitude (right). (a) The case of (C/u*o = 60.0) wave age and (b) the (C/u*o = 90.0) wave age case. Each swell case is shown with the counterpart flat surface case of the same driving pressure force underneath it.

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Fig. 2

Snapshots of the normalized resolved streamwise velocities (left) and the resolved vertical velocities (right) of 0.157 wave steepness swells and (a) (C/u*o = 45.0) wave age, (b) (C/u*o = 60.0) wave age, and (c) (C/u*o = 90.0) wave age. Each swell case is shown with the counterpart flat surface case of the same driving pressure force underneath it.

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Fig. 8

The time-averaged normalized streamwise velocity of x–z planes through the center of the WT. (a) The case of (C/u*o = 60.0) wave age and (b) the (C/u*o = 90.0) wave age case. Each swell case is shown with the counterpart flat surface case of the same driving pressure force underneath it.

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Fig. 9

The time-averaged normalized streamwise velocity of x–z planes through the center of the WT: (a) the case of (C/Uhub = 1.54) wave age and (b) is the (C/Uhub = 2.17) wave age case. Each swell case is shown with the counterpart flat surface case of the same hub-height wind speed.

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Fig. 10

Time-averaged profiles of normalized streamwise velocity in the plane through the rotor center at various distance downstream, the WT: (a) a vertical plane and (b) a horizontal plane. The dashed lines are swell case of 0.157 wave steepness and (C/Uhub = 2.17) wave age. The solid lines are the counterpart flat case of the same hub-height wind speed.

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Fig. 11

Time-averaged profiles of turbulence intensity in a vertical plane through the rotor center at various distance downstream, the WT. The cases and lines as in Fig. 10.

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Fig. 12

The instantaneous WT power production of two swell cases of 0.157 wave steepness: (a) C/Uhub = 1.54 wave age and (b) C/Uhub = 2.17 wave age

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Fig. 4

Time- and space-averaged normalized vertical shear stress. The cases and lines as in Fig. 3.

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Fig. 5

Time- and space-averaged turbulence intensity. The cases and lines as in Fig. 3.

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Fig. 6

Time- and space-averaged normalized streamwise velocity. From left to right: (a), wave age (C/Uhub = 1.20), (b) (C/Uhub = 1.54), and (c) (C/Uhub = 2.17). Solid lines are the flow over flat surface, and the dashed lines are the flow over 0.157 wave steepness swell.

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