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Research Papers: Ocean Renewable Energy

Load Mitigation Using Slotted Flaps in Offshore Wind Turbines

[+] Author and Article Information
Shilpa Thakur

Department of Ocean Engineering,
Indian Institute of Technology—Madras,
Chennai 600 036, India
e-mail: thakur.iitm29@gmail.com

K. A. Abhinav

Department of Ocean Engineering,
Indian Institute of Technology—Madras,
Chennai 600 036, India
e-mail: abhinavka@gmail.com

Nilanjan Saha

Mem. ASME
Department of Ocean Engineering,
Indian Institute of Technology—Madras,
Chennai 600 036, India
e-mail: nilanjan@iitm.ac.in

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received October 24, 2017; final manuscript received May 2, 2018; published online June 13, 2018. Assoc. Editor: Qing Xiao.

J. Offshore Mech. Arct. Eng 140(6), 061901 (Jun 13, 2018) (10 pages) Paper No: OMAE-17-1196; doi: 10.1115/1.4040234 History: Received October 24, 2017; Revised May 02, 2018

This paper focuses on load mitigation by implementing controllable trailing-edge slotted flaps on the blades of an offshore wind turbine (OWT). The benchmark NREL 5 MW horizontal axis OWT is subjected to coupled stochastic aerodynamic-hydrodynamic analysis for obtaining the responses. The OWT is supported on three different fixed-bottom structures situated in various water depths. Blade element momentum (BEM) theory and Morison's equation are used to compute the aerodynamic and hydrodynamic loads, respectively. Presently, the load reduction obtained by means of the slotted flaps is regulated using an external dynamic link library considering the proportional-integral-derivative (PID) controller. BEM theory is presently modified to account for unsteady effects of flaps along the blade span. The present analysis results show reduction up to 20% in blade and tower loads for the turbine with different support structures on implementing controllable trailing edge flaps (TEFs). This study can form the basis for evaluating the performance of large-scale fixed OWT rotors.

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Figures

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Fig. 1

Aerodynamic power curve of NREL 5 MW wind turbine

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Fig. 2

Trailing edge flap—deflected and un-deflected positions

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Fig. 3

Flow through the slot

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Fig. 4

Comparison of numerical and experimental results forNACA64-618 airfoil section for the lift and drag coefficient value with respect to angle of attack: (a) Cl versus α and (b) Cd versus α

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Fig. 5

Lift coefficient Cl and drag coefficient Cd versus angle of attack α curves for different actuation angles: (a) Cl versus α and (b) Cd versus α

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Fig. 7

Blade azimuth angle

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Fig. 8

Support structures for offshore wind turbines

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Fig. 9

Comparison of the numerical programs USFOS and FAST

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Fig. 10

Model equipped with TEF with monopile support structure for all load cases: out-of-plane shear force at representative blade root (top); the flapwise moment at representative blade root (middle); and flapwise deflection at representative blade tip (bottom)

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Fig. 11

Model equipped with TEF with tripod support structure for all load cases: out-of-plane shear force at representative blade root (top); the flapwise moment at representative blade root (middle); and flapwise deflection at representative blade tip (bottom)

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Fig. 12

Model equipped with TEF with jacket support structure for all load cases: out-of-plane shear force at representative blade root (top); the flapwise moment at representative blade root (middle); and flapwise deflection at representative blade tip (bottom)

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Fig. 13

Aerodynamic coefficients for an airfoil section

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