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Research Papers: Gas Turbines: Turbomachinery

Detailed Analysis of the Wake Structure of a Straight-Blade H-Darrieus Wind Turbine by Means of Wind Tunnel Experiments and Computational Fluid Dynamics Simulations

[+] Author and Article Information
Alessandro Bianchini

Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: bianchini@vega.de.unifi.it

Francesco Balduzzi

Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: balduzzi@vega.de.unifi.it

Giovanni Ferrara

Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: giovanni.ferrara@unifi.it

Lorenzo Ferrari

Department of Energy, Systems, Territory and
Construction Engineering,
University of Pisa,
Largo Lucio Lazzarino,
Pisa 56122, Italy
e-mail: lorenzo.ferrari@unipi.it

Giacomo Persico

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

Vincenzo Dossena

Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
Milano 20156, Italy
e-mail: vincenzo.dossena@polimi.it

Lorenzo Battisti

Department of Civil, Environmental and
Mechanical Engineering,
Università di Trento,
Via Mesiano 77,
Trento 38123, Italy
e-mail: lorenzo.battisti@unitn.it

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 5, 2017; final manuscript received July 19, 2017; published online October 17, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(3), 032604 (Oct 17, 2017) (9 pages) Paper No: GTP-17-1281; doi: 10.1115/1.4037906 History: Received July 05, 2017; Revised July 19, 2017

Darrieus vertical axis wind turbines (VAWTs) have been recently identified as the most promising solution for new types of applications, such as small-scale installations in complex terrains or offshore large floating platforms. To improve their efficiencies further and make them competitive with those of conventional horizontal axis wind turbines, a more in depth understanding of the physical phenomena that govern the aerodynamics past a rotating Darrieus turbine is needed. Within this context, computational fluid dynamics (CFD) can play a fundamental role, since it represents the only model able to provide a detailed and comprehensive representation of the flow. Due to the complexity of similar simulations, however, the possibility of having reliable and detailed experimental data to be used as validation test cases is pivotal to tune the numerical tools. In this study, a two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes (U-RANS) computational model was applied to analyze the wake characteristics on the midplane of a small-size H-shaped Darrieus VAWT. The turbine was tested in a large-scale, open-jet wind tunnel, including both performance and wake measurements. Thanks to the availability of such a unique set of experimental data, systematic comparisons between simulations and experiments were carried out for analyzing the structure of the wake and correlating the main macrostructures of the flow to the local aerodynamic features of the airfoils in cycloidal motion. In general, good agreement on the turbine performance estimation was constantly appreciated.

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Figures

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Fig. 1

Picture (a) and design sketch (b) of the tested H-Darrieus VAWT

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Fig. 2

Mesh refinement in the rotating region (a) and near the leading edge (b)

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Fig. 3

Power coefficient versus TSR: comparison between experiments [14] and simulations

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Fig. 4

Model for the calculation of the resistant torque of the struts

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Fig. 5

Signs and conventions for the analysis

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Fig. 6

Dimensionless velocity in the near traverse at TSR = 3.3: CFD versus experiments

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Fig. 7

Wake analysis in the near traverse at TSR = 1.5, TSR = 1.8, and TSR = 2.4. Right: comparison of computed mean wakes profiles—in terms of dimensionless velocity—between CFD and experiments. Left: instantaneous contour plots of dimensionless velocity in the same azimuthal position of the rotor.

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Fig. 8

Velocity distribution at TSR = 1.8 around θ = 270 deg (dimensionless velocity contours reported with the same scale ofFig. 7)

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Fig. 9

Contour plots of dimensionless vorticity around θ = 90 deg

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Fig. 10

Contour plots of dimensionless vorticity at θ = 220 deg (same scale of Fig. 9)

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Fig. 11

Mean wake profiles and periodic unsteadiness at TSR = 1.5: comparison between CFD and experiments

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Fig. 12

IPER values for three relevant TSRs: comparison between CFD and experiments

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