A better comprehension of the aerodynamic behavior of rotating airfoils in Darrieus vertical-axis wind turbines (VAWTs) is crucial both for the further development of these machines and for improvement of conventional design tools based on zero- or one-dimensional models (e.g., blade element momentum (BEM) models). When smaller rotors are designed with high chord-to-radius (c/R) ratios so as not to limit the blade Reynolds number, the performance of turbine blades has been suggested to be heavily impacted by a virtual camber effect imparted on the blades by the curvilinear flow they experience. To assess the impact of this virtual camber effect on blade and turbine performance, a standard NACA 0018 airfoil and a NACA 0018 conformally transformed such that the airfoil's chord line follows the arc of a circle, where the ratio of the airfoil's chord to the circle's radius is 0.25 were considered. For both airfoils, wind tunnel tests were carried out to assess their aerodynamic lift and drag coefficients for Reynolds numbers of interest for Darrieus VAWTs. Unsteady computational fluid dynamics (CFD) calculations have been then carried out to obtain curvilinear flow performance data for the same airfoils mounted on a Darrieus rotor with a c/R of 0.25. The blade incidence and lift and drag forces were extracted from the CFD output using a novel incidence angle deduction technique. According to virtual camber theory, the transformed airfoil in this curvilinear flow should be equivalent to the NACA 0018 in rectilinear flow, while the NACA0018 should be equivalent to the inverted transformed airfoil in rectilinear flow. Comparisons were made between these airfoil pairings using the CFD output and the rectilinear performance data obtained from the wind tunnel tests and xfoil output in the form of pressure distributions and lift and drag polars. Blade torque coefficients and turbine power coefficient are also presented for the CFD VAWT using both blade profiles.
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March 2016
Research-Article
An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines—Part I: Flow Curvature Effects
Alessandro Bianchini,
Alessandro Bianchini
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: bianchini@vega.de.unifi.it
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: bianchini@vega.de.unifi.it
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Francesco Balduzzi,
Francesco Balduzzi
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: balduzzi@vega.de.unifi.it
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: balduzzi@vega.de.unifi.it
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John M. Rainbird,
John M. Rainbird
Department of Aeronautical Engineering,
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.rainbird11@imperial.ac.uk
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.rainbird11@imperial.ac.uk
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Joaquim Peiro,
Joaquim Peiro
Department of Aeronautical Engineering,
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.peiro@imperial.ac.uk
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.peiro@imperial.ac.uk
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J. Michael R. Graham,
J. Michael R. Graham
Department of Aeronautical Engineering,
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: m.graham@imperial.ac.uk
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: m.graham@imperial.ac.uk
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Giovanni Ferrara,
Giovanni Ferrara
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: giovanni.ferrara@unifi.it
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: giovanni.ferrara@unifi.it
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Lorenzo Ferrari
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
National Research Council of Italy,
Via Madonna del Piano 10,
Sesto Fiorentino 50019, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it
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Alessandro Bianchini
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: bianchini@vega.de.unifi.it
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
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: balduzzi@vega.de.unifi.it
John M. Rainbird
Department of Aeronautical Engineering,
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.rainbird11@imperial.ac.uk
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.rainbird11@imperial.ac.uk
Joaquim Peiro
Department of Aeronautical Engineering,
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.peiro@imperial.ac.uk
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: j.peiro@imperial.ac.uk
J. Michael R. Graham
Department of Aeronautical Engineering,
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: m.graham@imperial.ac.uk
Imperial College,
South Kensington Campus,
London SW7 2AZ, UK
e-mail: m.graham@imperial.ac.uk
Giovanni Ferrara
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy
e-mail: giovanni.ferrara@unifi.it
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
National Research Council of Italy,
Via Madonna del Piano 10,
Sesto Fiorentino 50019, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it
Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 14, 2015; final manuscript received July 28, 2015; published online September 22, 2015. Editor: David Wisler.
J. Eng. Gas Turbines Power. Mar 2016, 138(3): 032602 (10 pages)
Published Online: September 22, 2015
Article history
Received:
July 14, 2015
Revised:
July 28, 2015
Connected Content
A companion article has been published:
An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines—Part II: Post-stall Data Extrapolation Methods
Citation
Bianchini, A., Balduzzi, F., Rainbird, J. M., Peiro, J., Graham, J. M. R., Ferrara, G., and Ferrari, L. (September 22, 2015). "An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines—Part I: Flow Curvature Effects." ASME. J. Eng. Gas Turbines Power. March 2016; 138(3): 032602. https://doi.org/10.1115/1.4031269
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