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Research Papers

Effect of Blade Inclination Angle on a Darrieus Wind Turbine

[+] Author and Article Information
Marco Raciti Castelli

Department of Mechanical Engineering, University of Padova, Via Venezia, 1-35131 Padova, Italymarco.raciticastelli@unipd.it

Ernesto Benini

Department of Mechanical Engineering, University of Padova, Via Venezia, 1-35131 Padova, Italyernesto.benini@unipd.it

J. Turbomach 134(3), 031016 (Jul 15, 2011) (10 pages) doi:10.1115/1.4003212 History: Received September 03, 2010; Revised September 04, 2010; Published July 15, 2011; Online July 15, 2011

This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0 deg, 30 deg, 60 deg, 90 deg, and 120 deg for a rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall rotor torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.

Copyright © 2012 by American Society of Mechanical Engineers
Topics: Rotors , Blades , Torque
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References

Figures

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Figure 1

Exemplification of a helical blade developing on the surface of a cylinder

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Figure 2

Comparison between Model 0, Model 60, and Model 120 blade

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Figure 3

Azimuthal coordinate

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Figure 4

Schematic of the survey methodology

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Figure 5

Computational domain (validation model)

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Figure 6

Rotor sub-grid mesh (validation model)

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Figure 7

Control cylinder (validation model)

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Figure 8

Blade size functions

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Figure 9

Improved mesh regularity after conversion into polyhedra 1

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Figure 10

Improved mesh regularity after conversion into polyhedra 2

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Figure 11

Effect of grid resolution on the instantaneous torque for a single-bladed rotor (turbulence model: k-ω SST)

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Figure 12

Effect of turbulence model on the instantaneous torque for a three-bladed rotor (mod A mesh)

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Figure 13

Blade subdivision into 20 zones, numbered from 1 to 20 from top downward

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Figure 14

Computational domain and relative mesh (computational model, 1)

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Figure 15

Computational domain and relative mesh (computational model, 2)

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Figure 16

Rotor sub-grid mesh for Model 0 (computational model)

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Numerical problems caused by parallel to principal flow direction interfaces and problem solution using extended rotating mesh 1

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Figure 18

Numerical problems caused by parallel to principal flow direction interfaces and problem solution using extended rotating mesh 2

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Figure 19

Power curves for the five models

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Figure 20

Instantaneous torque coefficient as a function of azimuthal coordinate

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Figure 21

Contribution of instantaneous torque in each blade zone for Model 0 and Model 120 (azimuthal coordinate 92 deg)

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Figure 22

Contribution of instantaneous torque in each blade zone for Model 0 and Model 120 (azimuthal coordinate 276 deg)

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Figure 23

Contribution of instantaneous torque in each blade zone for Model 0 and Model 120 (azimuthal coordinate 48 deg)

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Figure 24

Average torque for each blade zone for Model 0 and Model 1200

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Figure 25

Instantaneous torque coefficient values as a function of azimuthal position for Model 0 and Model 120 (zone 1)

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Figure 26

Instantaneous torque coefficient values as a function of azimuthal position for Model 00 and Model 120 (zone 20)

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Figure 27

Velocity vectors visualization for upper and lower blade tip zones (1)

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Figure 28

Velocity vectors visualization for upper and lower blade tip zones (2)

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Figure 29

Model 00, zone 10: streamlines are parallel to the horizontal plane

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Figure 30

Model 0, zone 10: streamlines deviate upward

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Figure 31

Streamlines deviation in a direction perpendicular to the leading edge

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Figure 32

Horizontal cut on the top of helical blades

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Figure 33

Blade section interacting with the flow field (dark blue) compared with the original NACA 0021 horizontal section (light blue) for phase shift angle of 120 deg

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Figure 34

Blade section distortion (dark blue) for phase shift angle of 60 deg and 120 deg, compared with the original NACA 0021 section (light blue)

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Figure 35

Axial forces acting on Model 0 and Model 60 blades for a tip speed ratio of 3.36

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