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Research Papers: Alternative Energy Sources

Toward Identifying Aeroelastic Mechanisms in Near-Wake Instabilities of Floating Offshore Wind Turbines

[+] Author and Article Information
Steven N. Rodriguez

Department of Mechanical
Engineering and Mechanics,
Lehigh University,
Bethlehem, PA 18015
e-mail: snr214@lehigh.edu

Justin W. Jaworski

Assistant Professor
Department of Mechanical
Engineering and Mechanics,
Lehigh University,
Bethlehem, PA 18015
e-mail: jaworski@lehigh.edu

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received October 1, 2016; final manuscript received December 21, 2016; published online March 8, 2017. Assoc. Editor: Ryo Amano.

J. Energy Resour. Technol 139(5), 051203 (Mar 08, 2017) (16 pages) Paper No: JERT-16-1391; doi: 10.1115/1.4035753 History: Received October 01, 2016; Revised December 21, 2016

A free-vortex-wake aeroelastic framework evaluates the impact of blade elasticity on the near-wake formation and its linear stability for onshore and offshore configurations of the National Renewable Energy Laboratory (NREL) 5 MW reference wind turbine. Numerical results show that motion of the flexible rotor further destabilizes its tip-vortices through earlier onset of mutual inductance relative to the rigid rotor results for onshore and offshore turbines. The near-wake growth rate is demonstrated to depend on the azimuthal position of the rotor for all cases considered, which appears to not have been reported previously for wake stability analyses in the rotorcraft literature.

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References

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Figures

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Fig. 1

Aerodynamic states of a floating offshore wind turbine (left to right): (1) axial inflow, (2) initial rotor–wake interaction, (3) vortex-ring state, and (4) reversed axial inflow [8,9], where T is the rotor thrust

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Fig. 2

Example design configuration of the MIT/NREL floating offshore wind turbine concept [2]

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Fig. 3

MIT/NREL TLP synthetic rigid body motion

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Fig. 4

Illustration of a straight finite filament used in the Biot–Savart integral

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Fig. 5

Inertial coordinate system of FOWT and tip-vortex geometry

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Fig. 6

Schematic of the global reference frame used to compute blade dynamics and elasticity during rigid body motions

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Fig. 7

Blade deflection reference frame, parameters, and degrees-of-freedom

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Fig. 8

Damping decay rate of NREL blade first mode vibration

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Fig. 9

Illustration of blade deflection interaction with the vortex lattice shed into the wake

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Fig. 10

Transition of rotor blade displacements and fluid forces to steady-state: flapwise deflection (left) and rotor thrust (right)

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Fig. 11

Onshore flexible and rigid rotor stability trends for the maximum growth rate α (s−1) of each tip-vortex versus the perturbation wave number ω (rad−1)

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Fig. 12

Onshore flexible and rigid rotor near wake convection

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Fig. 13

Divergence rate fluctuation in time for both rigid and flexible rotors of the onshore base case at wavenumber ω = 1.5 (1/rad)

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Fig. 14

Offshore flexible and rigid rotor stability trends for the maximum growth rate α (s−1) of each tip-vortex versus the perturbation wave number ω (rad−1)

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Fig. 15

Divergence rate fluctuation in time for both rigid and flexible rotors of the MIT/NREL TLP system at wavenumber ω = 1.5 (1/rad)

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Fig. 16

Offshore flexible and rigid rotor near wake convection

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Fig. 17

Offshore and onshore flexible and rigid rotor stability trends at t = 16.67 s for the maximum growth rate α (s−1) of each tip-vortex versus the perturbation wave number ω (rad−1)

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Fig. 18

Divergence rate fluctuation in time for (a) rigid onshore and offshore rotors and (b) flexible onshore and offshore rotors at wave number ω = 1.5 (1/rad)

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Fig. 19

Wake geometry shed from a rigid rotor configuration, t = 16.67 s

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Fig. 20

Wake geometry shed from a flexible rotor configuration, t = 16.67 s

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