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Research Papers

Blade Design Criteria to Compensate the Flow Curvature Effects in H-Darrieus Wind Turbines

[+] Author and Article Information
Francesco Balduzzi

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

Alessandro Bianchini

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

Riccardo Maleci

Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: maleci@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

CNR-ICCOM,
National Research Council of Italy,
Via Madonna del Piano 10,
Sesto Fiorentino 50019, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 15, 2014; final manuscript received July 30, 2014; published online September 4, 2014. Editor: Ronald Bunker.

J. Turbomach 137(1), 011006 (Sep 04, 2014) (10 pages) Paper No: TURBO-14-1147; doi: 10.1115/1.4028245 History: Received July 15, 2014; Revised July 30, 2014

Darrieus wind turbines are experiencing a renewed interest in the wind energy scenario, in particular, whenever small and medium-size installations are considered. In these contexts, the average wind speeds are generally quite low due to scale effects and therefore the most exploited design choices for the turbines are the H-shape configuration, as the entire blade can take advantage of the maximum rotational radius, and high chord to radius ratios, in order to ensure suitable Reynolds numbers on the airfoils. By doing so, the aerodynamic effects induced by the motion of the airfoils in a curved flowpath become more evident and the airfoils themselves have to be designed to compensate these phenomena if conventional design tools based on the blade element momentum (BEM) theory are used. In this study, fully unsteady 2D simulations were exploited to analyze a three-bladed H-Darrieus wind turbine in order to define the real flow structure and its effects on the turbine performance; in detail, the influence of both the virtual camber and the virtual incidence were investigated. Computational fluid dynamics (CFD) results were supported by experimental data collected on full-scale models reproducing two different airfoil mountings. Finally, the proper design criteria to compensate these phenomena are proposed and their benefits on a conventional simulation with a BEM approach are discussed.

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Figures

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Fig. 1

Virtual camber effect

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Fig. 2

CFD domains and boundaries

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Fig. 3

Boundaries influence at 200 rpm: average torque of a blade over a revolution as a function of the domain length

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Fig. 4

Mesh sensitivity: instantaneous torque at 100 rpm

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Fig. 5

Mesh sensitivity at 100 rpm: average torque and coefficient of determination as a function of the elements number of the rotating region

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Fig. 6

Mesh G4: (a) rotating domain and (b) control circle region

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Fig. 7

Mesh G4: detail of the boundary layer discretization at the leading edge

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Fig. 8

Airfoil construction for virtual camber compensation

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Fig. 9

Torque curves with cambered-only airfoil: comparison between BEM predictions based on the NACA0018 airfoil's coefficients, CFD simulations and experiments

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Fig. 10

Torque profile over the revolution for the VC configuration at 150 rpm (CFD data)

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Fig. 11

Velocity contours and streamlines for a blade in the VC configuration at 150 rpm at different azimuthal angles (wind blowing from left to right of the figure)

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Fig. 12

Cp distributions at different revolution speeds: comparison between CFD results for the VC configuration, the geometric airfoil and the NACA0018 data

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Fig. 13

Airfoil pitching for virtual incidence compensation

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Fig. 14

Torque curves with cambered airfoil properly pitched to compensate the virtual incidence: comparison between BEM predictions with NACA0018 airfoil's coefficients, CFD simulations and experiments

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Fig. 15

Cp distributions at different revolution speeds: comparison between CFD results for the VC + VI configuration and the NACA0018 data at the theoretical flow incidence

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Fig. 16

Torque profiles comparison (VC versus VC + VI) over the revolution at 150 rpm (CFD data)

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Fig. 17

Vorticity comparison (VC versus VC + VI) at 150 rpm—ϑ = 105 deg

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Fig. 18

Torque profiles comparison (VC versus VC + VI) over the revolution at 200 rpm (CFD data)

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Fig. 19

Flow enthalpy comparison (VC versus VC + VI) at 200 rpm—ϑ = 337 deg

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