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Research Papers: Alternative Energy Sources

Aerodynamic Measurements on a Vertical Axis Wind Turbine in a Large Scale Wind Tunnel

[+] Author and Article Information
L. Battisti

DIMS, Faculty of Engineering,  Università degli Studi di Trento, Via Mesiano 77, I-38050 Povo (TN), Italylorenzo.battisti@ing.unitn.it

L. Zanne, S. Dell’Anna

DIMS, Faculty of Engineering,  Università degli Studi di Trento, Via Mesiano 77, I-38050 Povo (TN), Italy

V. Dossena

Laboratorio di Fluidodinamica delle Macchine, Dipartimento di Energia,  Politecnico di Milano, Via Lambruschini 4, I-20158, Milano, Italyvincenzo.dossena@polimi.it

G. Persico, B. Paradiso

Laboratorio di Fluidodinamica delle Macchine, Dipartimento di Energia,  Politecnico di Milano, Via Lambruschini 4, I-20158, Milano, Italy

J. Energy Resour. Technol 133(3), 031201 (Jul 22, 2011) (9 pages) doi:10.1115/1.4004360 History: Received September 09, 2010; Revised May 13, 2011; Published July 22, 2011; Online July 22, 2011

This paper presents the first results of a wide experimental investigation on the aerodynamics of a vertical axis wind turbine. Vertical axis wind turbines have recently received particular attention, as interesting alternative for small and micro generation applications. However, the complex fluid dynamic mechanisms occurring in these machines make the aerodynamic optimization of the rotors still an open issue and detailed experimental analyses are now highly recommended to convert improved flow field comprehensions into novel design techniques. The experiments were performed in the large-scale wind tunnel of the Politecnico di Milano (Italy), where real-scale wind turbines for micro generation can be tested in full similarity conditions. Open and closed wind tunnel configurations are considered in such a way to quantify the influence of model blockage for several operational conditions. Integral torque and thrust measurements, as well as detailed aerodynamic measurements were carried out to characterize the 3D flow field downstream of the turbine. The local unsteady flow field and the streamwise turbulent component, both resolved in phase with the rotor position, were derived by hot wire measurements. The paper critically analyses the models and the correlations usually applied to correct the wind tunnel blockage effects. Results highlight that the presently available theoretical correction models do not provide accurate estimates of the blockage effect in the case of vertical axis wind turbines. The tip aerodynamic phenomena, in particular, seem to play a key role for the prediction of the turbine performance; large-scale unsteadiness is observed in that region and a simple flow model is used here to explain the different flow features with respect to horizontal axis wind turbines.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental set-up. The measuring section is located 1.5 D downstream of the rotor axis

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Figure 2

Picture of the wind turbine and traversing system in the open tunnel configuration

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Figure 3

Contours of non dimensional velocity V/V0 on the measurement plane at λ = 1.6 for open and closed configurations

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Figure 4

Contours of non dimensional velocity V/V0 on the measurement plane at λ = 2.5 for open and closed configurations

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Figure 5

Simplified flow field model upstream and downstream of a wind turbine

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Figure 6

Wake shape in terms of Cpt distribution at different spanwise locations (test closed, 3D, λ = 2.5)

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Figure 7

Comparison of the wake shape at rotor midspan in closed and open tunnel tests at λ = 1.6 (2D and 3D tests)

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Figure 8

Comparison of thrust coefficients CT obtained by strain gauge measurement and by aerodynamic measurement data reduction for the open and closed configurations

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Figure 9

Wind speed correction factors as function of the thrust coefficient. Experiments and theoretical predictions with the Glauert, Maskell, and M-W (Merker-Wiedemann) methods

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Figure 10

(a) Phase-resolved velocity magnitude at λ = 2.5, midspan, (b) Phase-resolved turbulence intensity at λ = 2.5, midspan, (c) Phase-resolved velocity magnitude at λ = 2.5, Z/H = 1.1, and (d) Phase-resolved turbulence intensity at λ = 2.5, Z/H = 1.1

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Figure 11

Schematic of the vortex structures released by the blades at mispan and tip sections of the turbine

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