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Research Papers: Alternative Energy Sources

Time-Resolved Experimental Characterization of the Wakes Shed by H-Shaped and Troposkien Vertical Axis Wind Turbines

[+] Author and Article Information
Giacomo Persico

Laboratorio di Fluidodinamica delle Macchine,
Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
Milano I-20156, Italy
e-mail: giacomo.persico@polimi.it

Vincenzo Dossena, Berardo Paradiso

Laboratorio di Fluidodinamica delle Macchine,
Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
Milano I-20156, Italy

Lorenzo Battisti, Alessandra Brighenti, Enrico Benini

Laboratorio interdisciplinare
di Tecnologie Energetiche,
Dipartimento di Ingegneria Civile,
Ambientale e Meccanica,
Universitá degli Studi di Trento,
Via Mesiano 77,
Trento I-38123, Italy

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received March 30, 2016; final manuscript received January 10, 2017; published online February 24, 2017. Assoc. Editor: Ryo Amano.

J. Energy Resour. Technol 139(3), 031203 (Feb 24, 2017) (11 pages) Paper No: JERT-16-1153; doi: 10.1115/1.4035907 History: Received March 30, 2016; Revised January 10, 2017

In this paper, the aerodynamics of two vertical axis wind turbines (VAWTs) are discussed, on the basis of a wide set of experiments performed at Politecnico di Milano, Milan, Italy. A H-shaped and a Troposkien Darrieus turbine for microgeneration, featuring the same swept area and blade section, are tested at full-scale. Performance measurements show that the Troposkien rotor outperforms the H-shaped turbine, thanks to the larger midspan section of the Troposkien rotor and to the nonaerodynamic struts of the H-shaped rotor. These features are consistent with the character of the wakes shed by the turbines, measured by means of hot wire anemometry on several surfaces downstream of the models. The H-shape and Troposkien turbine wakes exhibit relevant differences in the three-dimensional morphology and unsteady evolution. In particular, large-scale vortices dominate the tip region of the wake shed by the H-shape turbine; these vortices pulsate significantly during the period, due to the periodic fluctuation of the blade aerodynamic loading. Conversely, the highly tapered shape of the Troposkien rotor not only prevents the onset of tip vortices, but also induces a dramatic spanwise reduction of tip speed ratio (TSR), promoting the onset of local dynamic stall marked by high periodic and turbulent unsteadiness in the tip region of the wake. The way in which these mechanisms affect the wake evolution and mixing process for the two classes of turbines is investigated for different tip speed ratios, highlighting some relevant implications in the framework of wind energy exploitation.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

H-shaped (left) and Troposkien (right) rotors

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Fig. 2

Turbine arrangement in the wind tunnel test section: (a) picture of the test section with Troposkien rotor and traversing and (b) sketch of the test section with turbine models

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Fig. 3

Aerodynamic power for the two turbines as a function of wind speed—the Pmax refers to the Troposkien rotor maximum data

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Fig. 4

Normalized aerodynamic power coefficient for the two turbines as a function of TSR—the CP, max refers to the Troposkien rotor maximum data

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Fig. 5

Measurement surfaces for the H-shaped turbine campaign

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Fig. 6

Time-mean and fluctuating velocity magnitude on the near MS for H-shaped rotor at high loading (TSR = 3.5 − V0=6.5 m/s)

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Fig. 7

Time-mean and fluctuating velocity magnitude on the near MS for H-shaped rotor at max CP (TSR = 2.5 − V0=9 m/s)

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Fig. 8

Time-mean and fluctuating velocity magnitude on the near MS for H-shaped rotor at low loading (TSR = 1.5 − V0=14.2 m/s)

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Fig. 9

Top: dynamic stall schematic with measurement traverses, adapted from Refs. [27] and [28]. Bottom: example of CFD calculation (from Ref. [14]) of VAWT midspan for TSR = 1.5.

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Fig. 10

Time-mean and fluctuating velocity magnitude in the far MS for H-shaped rotor at low loading (TSR = 1.5)

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Fig. 11

Flat and curved measurement surfaces for the Troposkien turbine campaign

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Fig. 12

Time-mean and fluctuating velocity on the curved MS for Troposkien rotor at high loading (TSR = 3.9 − V0=8.2 m/s)

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Fig. 13

Time-mean and fluctuating velocity on the curved MS for Troposkien rotor at maximum CP (TSR = 3.1 − V0=10.2 m/s)

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Fig. 14

Time-mean and fluctuating velocity on the curved MS for Troposkien rotor at low loading (TSR = 2.4 − V0=13.1 m/s)

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Fig. 15

Phase-resolved velocity field ((VTM+VPER)/V0) on the curved MS in the Troposkien turbine wake at low loading (TSR = 2.4 − V0=13.1 m/s). Blades are marked by bold lines on the revolution surface. The scales are the same of that of Fig.14. (a) t/BPP = 0.00, (b) t/BPP = 0.25, (c) t/BPP = 0.50, and (d) t/BPP = 0.75.

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Fig. 16

Phase-resolved turbulence field (ITU,PER) on the curved MS in the Troposkien turbine wake at low loading (TSR = 2.4 − V0=13.1 m/s). Blades are marked by bold lines on the revolution surface. The scales are the same of that of Fig. 14. (a) t/BPP = 0.00, (b) t/BPP = 0.25, (c) t/BPP = 0.50, and (d) t/BPP = 0.75.

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Fig. 17

Time-mean and fluctuating velocity magnitude for Troposkien rotor at maximum CP (TSR = 3.1) on the flat traverse

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