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Research Papers

Hollow Blades for Small Wind Turbines Operating at High Altitudes

[+] Author and Article Information
Abolfazl Pourrajabian

Faculty of Aerospace Engineering,
K.N.Toosi University of Technology,
Tehran 16765-3381, Iran
e-mail: abolfazlp915@yahoo.com

Peyman Amir Nazmi Afshar

Department of Mechanical Engineering,
Sharif University of Technology,
Tehran 11365-11155, Iran
e-mail: peyman_nazmiafshar@yahoo.com

Masoud Mirzaei

Faculty of Aerospace Engineering,
K.N.Toosi University of Technology,
Tehran 16765-3381, Iran
e-mail: mirzaei@kntu.ac.ir

Reza Ebrahimi

Faculty of Aerospace Engineering,
K.N.Toosi University of Technology,
Tehran 16765-3381, Iran
e-mail: rebrahimi@kntu.ac.ir

David H. Wood

Department of Mechanical and
Manufacturing Engineering,
University of Calgary,
Calgary, AB T2N 1N4, Canada
e-mail: dhwood@ucalgary.ca

1Corresponding author.

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 August 4, 2015; final manuscript received July 3, 2016; published online September 2, 2016. Assoc. Editor: Yves Gagnon.

J. Sol. Energy Eng 138(6), 061001 (Sep 02, 2016) (8 pages) Paper No: SOL-15-1249; doi: 10.1115/1.4034333 History: Received August 04, 2015; Revised July 03, 2016

Since the air density reduces as altitude increases, operation of small wind turbines (SWTs), which usually have no pitch adjustment, remains challenging at high altitudes due largely to the reduction of starting aerodynamic torque. By reducing the moment of inertia through the use of hollow blades, this study aims to speed up the starting while maintaining the structural integrity of the blades and high output power. A horizontal axis turbine with hollow blades was designed for two sites in Iran with altitude of 500 m and 3000 m. The design variables are the distributions of the chord, twist, and shell thickness and the improvement of output power and starting are the design goals. Blade-element momentum (BEM) theory was employed to calculate these goals and beam theory was used for the structural analysis to investigate whether the hollow timber blades could withstand the aerodynamic and centrifugal forces. A combination of the goals formed the objective function and a genetic algorithm (GA) was used to find a blade whose output power at a predetermined tip speed ratio (TSR) and the starting performance were high while the stress limit was met. The results show that hollow blades have starting times shorter than solid ones by approximately 70%. However, in the presence of generator resistive torque, the algorithm could not find a blade for an altitude of 3000 m. To solve that problem, the tip speed ratio was added to other design variables and another optimization was done which led to the optimal blades for both altitudes.

FIGURES IN THIS ARTICLE
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Copyright © 2016 by ASME
Topics: Blades , Optimization , Torque
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Figures

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Fig. 1

Cross-sectional model of the hollow blade and its geometric properties

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Fig. 2

Aerodynamic forces together with the pitch moment (Mo) acting on the blade element

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Fig. 3

Substitution of the rectangle for the airfoil for the shear analysis

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Fig. 4

Chord distributions along the hollow blade for case study “A” for w = 0.7, 1 (Qr = 0 N m)

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Fig. 5

Twist distributions along the hollow blade for case study “A” for w = 0.7, 1 (Qr = 0 N m)

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Fig. 6

Flap-wise bending moment (M1) along the blade, blade redesign-1, Qr = 0 N m, w = 0.8

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Fig. 7

Equivalent stress along the blade, blade redesign-1, Qr = 0 N m, w = 0.8

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Fig. 8

Centrifugal force along the blade, blade redesign-1, Qr = 0 N m, w = 0.8

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Fig. 9

Pareto front for the optimized blades, blade redesign-1, case study “A,” ♦w = 0.7, ▴w = 0.8, ▪ w = 0.9,•w = 1

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