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Research Papers: Alternative Energy Sources

Experimental Study and Simulation of a Small-Scale Horizontal-Axis Wind Turbine

[+] Author and Article Information
Randall S. Jackson

Mem. ASME
Department of Mechanical Engineering,
University of Wisconsin-Milwaukee,
225 Ridge Line Road,
Burlington, WI 53105
e-mail: rsjackson@wi.rr.com

Ryoichi Amano

Life ASME Fellow
Department of Mechanical Engineering,
University of Wisconsin-Milwaukee,
University Services and Research 201L,
115 East Reindl Way,
Glendale, WI 53212
e-mail: amano@uwm.edu

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received November 12, 2016; final manuscript received February 11, 2017; published online March 16, 2017. Assoc. Editor: Bengt Sunden.

J. Energy Resour. Technol 139(5), 051207 (Mar 16, 2017) (19 pages) Paper No: JERT-16-1455; doi: 10.1115/1.4036051 History: Received November 12, 2016; Revised February 11, 2017

The advancement of wind energy as an alternative source to hydrocarbons depends heavily on research activities in turbulence modeling and experimentation. The velocity deficit behind wind turbines affects the power output and efficiency of a wind farm. Being able to simulate the wake dynamics of a wind turbine effectively can result in optimum spacing, longer wind turbine life, and shorter payback on the wind farm investment. Two-equation turbulence closure models, such as k–ε and k–ω, are used extensively to predict wind turbine performance and velocity deficit profiles. The application of the Reynolds stress model (RSM) turbulence closure method has been limited to few studies where the rotor is modeled as an actuator disk (AD). The computational cost associated with RSM has made it challenging for simulations where the rotor is discretized directly; however, with advances in computer speed and power coupled with parallel computing architecture, RSM may be a better turbulence closure option. In this research, wind tunnel experiments were conducted, using hot-wire anemometry, to measure the velocity deficit profiles at different wake locations behind a small-scale, three-bladed, horizontal-axis wind turbine (HAWT). Experiments were also performed with two and three HAWTs in series to evaluate the change in velocity deficit and turbulence intensity (TI). High-speed imaging with an oil-based mist captured the vortices produced at the blade tips and showed the vortices dissipated approximately three rotor diameters downstream. Computational fluid dynamics (CFD) simulations were performed to predict the velocity deficit at wake locations matching the experiments. The Reynolds stress model was applied to a fully discretized rotor with a tower and nacelle included in the simulation. A steady-state moving reference frame (MRF) model was created with the computational domain subdivided into rotating and stationary domains. The MRF results were used as an initial condition for time-accurate rigid body motion (RBM) simulations. The RBM CFD simulations showed excellent agreement with experimental measurements for velocity deficit after properly accounting for experimental boundary effects. Isosurfaces of the Q-criterion highlighted the vortices produced at the blade tips and were consistent with high-speed images.

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References

Figures

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Fig. 1

Illustration of actuator disk (AD), actuator line (AL), and actuator surface (AS) methods for modeling a turbine [4]

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Fig. 2

Model wind turbine design

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Fig. 3

Model blade design

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Fig. 4

NACA4424 blade profile

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Fig. 5

Normalized standard deviation (error) of calibration at various yaw angles for flows ranging from 1.5 m/s to 21.5 m/s

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Fig. 6

Wake profiles of a horizontal-axis wind turbine [28]

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Fig. 7

Measurement plane locations for single turbine experiments

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Fig. 8

Velocity deficit profiles for three vertical measurement regions at locations shown in Fig. 7, U = 6.6 m/s: (a) is upstream corresponding to locations S0–S7, (b) is downstream corresponding to locations S8–S18 (x/Db < 2), and (c) is downstream corresponding to locations S19–S23 (x/Db > 2)

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Fig. 9

Downstream velocity deficit from vertical measurements at various y/r values, U = 6.6 m/s

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Fig. 10

Velocity deficit profiles for three horizontal measurement regions at locations shown in Fig. 7, U = 6.6 m/s: (a) is upstream corresponding to locations S0–S7, (b) is downstream corresponding to locations S8–S18 (x/Db < 2), and (c) is downstream corresponding to locations S19–S23 (x/Db > 2)

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Fig. 11

Turbulence intensity for two vertical measurement regions at locations shown in Fig. 7, U = 6.6 m/s: (a) is downstream corresponding to locations S8–S18 (x/Db < 2) and (b) is downstream corresponding to locations S19–S23 (x/Db > 2)

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Fig. 12

Downstream turbulence intensity from vertical measurements at various y/r values, U = 6.6 m/s

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Fig. 13

Measurement plane locations for dual turbine experiments

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Fig. 14

Velocity deficit profiles for three vertical measurement regions at locations shown in Fig. 13, U = 6.6 m/s: (a) is between first and second turbine corresponding to locations D8–D20, (b) is downstream of second turbine corresponding to locations D21–D32 (x/Db < 2), and (c) is downstream corresponding to locations D33–D43 (x/Db > 2)

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Fig. 15

Downstream velocity deficit from vertical measurements at various y/r values, U = 6.6 m/s

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Fig. 16

Velocity deficit profiles for three horizontal measurement regions at locations shown in Fig. 13, U = 6.6 m/s: (a) is between first and second turbine corresponding to locations D8–D20, (b) is downstream of second turbine corresponding to locations D21–D32 (x/Db < 2), and (c) is downstream corresponding to locations D33–D43 (x/Db > 2)

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Fig. 17

Turbulence intensity profiles for three vertical measurement regions at locations shown in Fig. 13, U = 6.6 m/s: (a) is between first and second turbine corresponding to locations D8–D20, (b) is downstream of second turbine corresponding to locations D21–D32 (x/Db < 2), and (c) is downstream corresponding to locations D33–D43 (x/Db > 2)

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Fig. 18

Downstream turbulence intensity from vertical measurements at various y/r values, U = 6.6 m/s

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Fig. 19

Measurement plane locations for experiments with three turbines

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Fig. 20

Velocity deficit profiles for three vertical measurement regions at locations shown in Fig. 19, U = 6.6 m/s: (a) is between first and second turbines corresponding to locations T8–T20, (b) is between second and third turbines corresponding to locations T21–T33, and (c) is downstream of third turbine corresponding to locations T34–T48

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Fig. 21

Downstream velocity deficit from vertical measurements at various y/r values, U = 6.6 m/s

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Fig. 22

Velocity deficit profiles for three horizontal measurement regions at locations shown in Fig. 19, U = 6.6 m/s: (a) is between first and second turbines corresponding to locations T8–T20, (b) is between second and third turbines corresponding to locations T21–T33, and (c) is downstream of third turbine corresponding to locations T34–T48

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Fig. 23

Turbulence intensity profiles for three horizontal measurement regions at locations shown in Fig. 19, U = 6.6 m/s: (a) is between first and second turbines corresponding to locations T8–T20, (b) is between second and third turbines corresponding to locations T21–T33, and (c) is downstream of third turbine corresponding to locations T34–T48

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Fig. 24

Comparison of velocity deficit with multiple turbines

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Fig. 25

Comparison of turbulence intensity with multiple turbines

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Fig. 26

High speed images showing wake vortices from a single turbine

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Fig. 27

Computational domain of direct rotor model with traverse arm located at x/Db ∼ 1

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Fig. 28

Computational domain of direct rotor model with traverse arm located at x/Db ∼ 3

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Fig. 29

Computational domain of direct rotor model with traverse arm located at x/Db ∼ 5

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Fig. 30

Computational domain of direct rotor model with traverse arm located at x/Db ∼ 8

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Fig. 31

Rotating subdomain using trimmed mesh model with prism layer meshing at rotor surfaces

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Fig. 32

Prism layer meshes at blade surface

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Fig. 33

Mesh at vertical midplane of computational domain with traverse arm at x/Db ∼ 5

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Fig. 34

Plan view of z-axis vorticity contour from RBM simulation with traverse located at x/Db ∼ 1

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Fig. 35

Plan view of z-axis vorticity contour from RBM simulation with traverse located at x/Db ∼ 3

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Fig. 36

Plan view of z-axis vorticity contour from RBM simulation with traverse located at x/Db ∼ 5

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Fig. 37

Comparison of velocity deficit to experimental data for the RBM method with the traverse arm positioned at (a) x/Db ∼ 1, (b) x/Db ∼ 3, and (c) x/Db ∼ 5; U = 6.60 m/s

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Fig. 38

Percent difference between simulation and experiment when accounting for the traverse location

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Fig. 39

Isosurface of Q-criterion, contoured by vorticity, from a transient RBM simulation

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