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Research Papers: Gas Turbines: Turbomachinery

Effects of Airfoil's Polar Data in the Stall Region on the Estimation of Darrieus Wind Turbine Performance

[+] Author and Article Information
David Marten

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: david.marten@tu-berlin.de

Alessandro Bianchini

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

Georgios Pechlivanoglou

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: george@pechlivanoglou.com

Francesco Balduzzi

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

Christian Navid Nayeri

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: christian.nayeri@tu-berlin.de

Giovanni Ferrara

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

Christian Oliver Paschereit

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: oliver.paschereit@tu-berlin.de

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 Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2016; final manuscript received July 4, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 022606 (Sep 13, 2016) (9 pages) Paper No: GTP-16-1286; doi: 10.1115/1.4034326 History: Received June 28, 2016; Revised July 04, 2016

Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 1990s, in favor of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the blade element momentum theory for HAWTs' applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the double multiple streamtubes (DMS) theory, based on momentum balances, and the lifting line theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition toward the “thin plate like” behavior has a large effect on simulation results. This paper will demonstrate the importance of stall and poststall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of poststall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna–Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both the simulation methods is highlighted and discussed.

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References

Figures

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Fig. 1

Comparison between wind tunnel experiments and CFD simulations for the study turbine

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Fig. 2

Power curve of a single blade as a function of the TSR (simulated with CFD)

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Fig. 3

Comparison of lift curves at Re = 150,000: experiments [13] versus XFoil simulations plus Viterna–Corrigan extrapolation

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Fig. 4

Power coefficient versus TSR for the analyzed single-blade rotor: CFD versus predictions with BEM and LLT models using either experimental polars or XFoil + Viterna

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Fig. 5

Torque coefficient versus azimuthal angle at TSR = 2.2 for the analyzed single-blade rotor: CFD versus predictions with BEM and LLT models using either experimental polars or XFoil + Viterna

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Fig. 6

Torque coefficient versus azimuthal angle at TSR = 3.9 for the analyzed single-blade rotor: CFD versus predictions with BEM and LLT models using either experimental polars or XFoil + Viterna

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Fig. 7

AoA and lift coefficient versus azimuthal angle at TSR = 2.2 for the analyzed single-blade rotor: BEM model using either experimental polars or XFoil + Viterna

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Fig. 8

AoA and lift coefficient versus azimuthal angle at TSR = 3.9 for the analyzed single-blade rotor: BEM model using either experimental polars OR XFoil + Viterna

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Fig. 9

Smoothed lift curves used in the analysis for some relevant Reynolds numbers

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Fig. 10

Power coefficient versus TSR for the analyzed single-blade rotor: CFD versus predictions with BEM and LLT models using experimental polars smoothed with the Viterna–Corrigan model after stall

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Fig. 11

Torque coefficient versus azimuthal angle at TSR = 2.8 for the analyzed single-blade rotor: CFD versus predictions with LLT using experimental, XFoil, and smoothed experimental polars

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Fig. 12

Power coefficient versus TSR for the analyzed single-blade rotor: CFD versus predictions with BEM and LLT models using smoothed experimental polars (with dynamic stall submodels enabled)

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Fig. 13

Torque coefficient versus azimuthal angle at TSR = 2.8 (single-blade rotor): CFD versus BEM and LLT models using smoothed experimental polars

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Fig. 14

Torque coefficient versus azimuthal angle at TSR = 2.8 (single-blade rotor): CFD versus BEM and LLT models (with dynamic stall) using smoothed experimental polars

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