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Research Papers

On the Use of Velocity Data for Load Estimation of a VAWT in Dynamic Stall

[+] Author and Article Information
Carlos J. Simão Ferreira, Gerard J. W. van Bussel, Gijs A. M. van Kuik

DUWIND—Wind Energy Section, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlandsc.j.simaoferreira@tudelft.nl

Fulvio Scarano

Aerodynamics Section, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlandsf.scarano@tudelft.nl

Further details on the experimental setup and the effect of blockage can be found in these two references.

In the simulation, the loads are obtained by integrating the pressure and friction loads over the aerofoil surface.

The occurrence of dynamic stall implies a condition of stall, significant loss of lift, when conditions of the hysteresis of the flow are present due to unsteady effects. The operation at angles of attack past the static stall angle is not the only condition when dynamic stall is observed. In particular, for the VAWT, blade-vortex interaction is an equally important source of the occurrence of dynamic stall.

J. Sol. Energy Eng. 133(1), 011006 (Jan 28, 2011) (8 pages) doi:10.1115/1.4003182 History: Received November 15, 2008; Revised October 04, 2010; Published January 28, 2011; Online January 28, 2011

This paper focuses on evaluating the feasibility of estimating loads on vertical axis wind turbine blades in dynamic stall with velocity data acquired with Particle Image Velocimetry. The study uses numerical simulation data of a 2D Vertical Axis Wind Turbine in dynamic stall to verify sources of error and uncertainty and estimate the accuracy of the method. The integration of the forces from the velocity field overcomes the difficulties and limitations presented by pressure sensors for estimating the local section loads, but adds the difficulty in determining the correct velocity field and its time and spatial derivatives. The analysis also evaluates the use of phase-locked average data as an estimator of average loads.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Scheme of the rotation of a VAWT at eight azimuthal positions; the scheme represents the effective velocity Ueff perceived by the blade at θ=0 deg, 90 deg, 180 deg, and 270 deg, and the resultant orientation of the lift and drag forces and their decomposition in normal FN and tangential FT forces

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Figure 2

Shed vorticity at θ=127 deg and θ=163 deg for λ=3

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Figure 3

Shed vorticity at θ=127 deg and θ=163 deg for λ=4

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Figure 4

Representation of the control volume bounded by the outer contour S and the body contour Sb

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Figure 5

Vorticity field for θ=90 deg and θ=120 deg, simulation with detached eddy simulation

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Figure 6

Pressure result from CFD simulation and estimated (integration of the velocity data) over contour B (Fig. 7)

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Figure 7

Location of volume contours A, B, C, and D when θ=40 deg. Results of the integration of the forces around these contours are presented in Table 1.

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Figure 8

Effect of the resolution of the velocity field (Δgrid/c). Comparison of CFD results for normal and tangential force coefficients CN and CT and the estimates from the integration of the velocity fields CNest and CTest (pressure formulation).

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Figure 9

Effect of the size of time/phase step Δt for estimation of the velocity time derivatives (flux formulation). Comparison of CFD results for normal and tangential force coefficients CN and CT, and the estimates from integration of the velocity fields CNest and CTest, for different Δt.

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Figure 10

Comparison of CFD results for normal and tangential force coefficients CN and CT and the estimates from integration of the velocity fields CNest and CTest for θ=0–150 (flux formulation)

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Figure 11

Effect of varying σV uncertainty on the estimation of Fy

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Figure 12

Effect of a σV=0.01 uncertainty on the estimation of Fy for varying radius of the integration contour

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Figure 13

Representation of the two flow field regions (A and B), divided by dashed line

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Figure 14

Variation in the normal load as a function of error in the overlap in tangential and normal directions to the chord of the blade

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Figure 15

Variation in the tangential load as a function of error in the overlap in the tangential and normal directions to the chord of the blade

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