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Research Papers: Alternative Energy Sources

Power Properties of Two Interacting Wind Turbine Rotors

[+] Author and Article Information
Valery L. Okulov

Department of Wind Energy,
Technical University of Denmark,
Lyngby 2800, Denmark
e-mail: vaok@dtu.dk

Robert Mikkelsen

Department of Wind Energy,
Technical University of Denmark,
Lyngby 2800, Denmark
e-mail: rfmi@dtu.dk

Jens N. Sørensen

Department of Wind Energy,
Technical University of Denmark,
Lyngby 2800, Denmark
e-mail: jnso@dtu.dk

Igor V. Naumov

Institute of Thermophysics,
SB RAS,
Novosibirsk 630090, Russia
e-mail: naumov@itp.nsc.ru

Mikhail A. Tsoy

Institute of Thermophysics,
SB RAS,
Novosibirsk 630090, Russia
e-mail: miketsoy@gmail.com

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received October 17, 2016; final manuscript received March 2, 2017; published online March 30, 2017. Assoc. Editor: Ryo Amano.

J. Energy Resour. Technol 139(5), 051210 (Mar 30, 2017) (6 pages) Paper No: JERT-16-1410; doi: 10.1115/1.4036250 History: Received October 17, 2016; Revised March 02, 2017

In the current experiments, two identical wind turbine models were placed in uniform flow conditions in a water flume. The initial flow in the flume was subject to a very low turbulence level, limiting the influence of external disturbances on the development of the inherent wake instability. Both rotors are three-bladed and designed using blade element/lifting line (BE/LL) optimum theory at a tip-speed ratio, λ, of 5 with a constant design lift coefficient along the span, CL = 0.8. Measurements of the rotor characteristics were conducted by strain sensors installed in the rotor mounting. The resulting power capacity has been studied and analyzed at different rotor positions and a range of tip-speed ratios from 2 to 8, and a simple algebraic relationship between the velocity deficit in the wake of the front turbine and the power of the second turbine was found, when both rotors have the coaxial position.

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Figures

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Fig. 1

The rotor models in a flume

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Fig. 2

Sketches of the rotor positions: left—side view and right—top view

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Fig. 3

The dimensionless axial velocity U behind the single rotor on its axis as a function of the tip-speed ratio for different distances along the rotor axis x

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Fig. 4

Velocity profiles of the incident flow on the second rotor measured by LDA for different shifts S and fixed distance H = 6d between rotors

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Fig. 5

Power (a) and thrust (b) coefficients as a function of n2 of the second rotor under the fixed tip-speed ratio λ1 = 5 of the first rotor and at different axial distances H and without the axial shift S = 0 of both rotors

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Fig. 6

(a) Values of the dimensionless axial velocity squared (U/V0)2 behind the single rotor: crosses—measured by LDA, asterisk—data of Bartl et al. [14], and solid curve described by Eq. (4) as a function of the distance between both rotors, H/d. (b) The ratio of the maximum power coefficients CP2max/CP1opt of the two rotors for different shifts S between rotor axis: symbols—experimental data, dashed curves—approximation, asterisk—data of Bartl et al. [14], and solid curve—dimensionless axial velocity squared (4) as a function of the distance between both rotors, H/d.

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Fig. 7

Normalized CP2 and CT2 at λ2 = 5, as functions of λ1 for H/d = 4 (squares), 6 (circles), and 8 (triangles) and S/d = 0 (white), 0.5 (gray), and 1 (black)

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