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Experimental Characterization of VAWT Airfoils Under Turbulent Flows

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Wind Energy Exploitation in Urban Environment (TUrbWind 2018)

Part of the book series: Research Topics in Wind Energy ((RTWE,volume 8))

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Abstract

Vertical-Axis Wind Turbines are receiving the attention of the wind energy community for urban wind harvesting. However, their practical application is still far from maturity, due to the lack of understanding of urban flows. High turbulence is one of the main characteristics of wind in complex environments, so special attention has been paid to modelling it inside wind tunnels for prototype testing. Previous experiments showed a considerable boost in VAWT performance when turbulence intensity increases, but the explanation of this increase still has to be determined. This study analyses the effect of turbulent flows on the performance of a NACA0018 airfoil, using a blade model provided with pressure tabs and a traverse system to analyze the wake. The model is subjected to the same angles of attack and Reynolds numbers that would be found in normal VAWT operation, while turbulence intensity and integral length scale are kept at levels similar to those found in urban environments. The effect of turbulence is evident as it considerably delays the stall angle of the blade. Using a Single Streamtube model, the results from this parametric study are compared with the overall turbine ratings, in order to find a way to optimize turbine blades using a simplified set-up.

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Abbreviations

b :

Grid bar width [m]

c :

Blade chord [m]

C D :

Drag coefficient [–]

C L :

Lift coefficient [–]

C N :

Normal force to the blade coefficient [–]

C p :

Pressure coefficient [–]

C P :

Turbine power coefficient [–]

C Psf :

Turbine power coefficient in smooth flow (low turbulence) [–]

d :

Distance to grid [–]

D :

Drag [N]

I u :

Turbulence intensity in the flow direction [%]

L ux :

Integral length scale of turbulence in the flow direction [m]

P :

Pressure [Pa]

Rec:

Chord Reynolds number [–]

u :

Local wind speed in the flow direction [m/s]

U :

Incident wind speed in the blade/turbine [m/s]

x :

Distance along the blade chord [m]

α :

Angle of attack [˚]

δ :

Uncertainty

λ :

Tip-speed ratio [–]

ρ :

Air density [kg/m3]

θ :

Azimuthal angle [˚]

HAWT :

Horizontal-Axis Wind Turbines

SST :

Single Streamtube

rms :

Root mean square

VAWT :

Vertical-Axis Wind Turbines

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Author information

Authors and Affiliations

  1. Department of Civil and Environmental Engineering, Università degli Studi di Firenze, Via di Santa Marta 3, 50139, Florence, Italy

    Andreu Carbó Molina & Gianni Bartoli

  2. Thermo and Fluid Dynamics (FLOW), Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium

    Andreu Carbó Molina, Sander Van de Maele, Tim De Troyer & Mark Runacres

Authors
  1. Andreu Carbó Molina
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  2. Sander Van de Maele
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  3. Gianni Bartoli
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  4. Tim De Troyer
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  5. Mark Runacres
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Corresponding author

Correspondence to Andreu Carbó Molina .

Editor information

Editors and Affiliations

  1. University of Trento, Trento, Italy

    Lorenzo Battisti

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Carbó Molina, A., Van de Maele, S., Bartoli, G., De Troyer, T., Runacres, M. (2019). Experimental Characterization of VAWT Airfoils Under Turbulent Flows. In: Battisti, L. (eds) Wind Energy Exploitation in Urban Environment. TUrbWind 2018. Research Topics in Wind Energy, vol 8. Springer, Cham. https://doi.org/10.1007/978-3-030-13531-7_2

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  • DOI: https://doi.org/10.1007/978-3-030-13531-7_2

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  • Publisher Name: Springer, Cham

  • Print ISBN: 978-3-030-13530-0

  • Online ISBN: 978-3-030-13531-7

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