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Ocean Engineering

Three-Dimensional Numerical Modeling of the Transient Fluid-Structural Interaction Response of Tidal Turbines

[+] Author and Article Information
Yin L. Young1

Department of Naval Architecture and Marine Engineering, University of Michigan, Ann Arbor, MI 48109ylyoung@umich.edu

Michael R. Motley

Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544

Ronald W. Yeung

Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA, 94720

1

Corresponding author.

J. Offshore Mech. Arct. Eng 132(1), 011101 (Dec 21, 2009) (12 pages) doi:10.1115/1.3160536 History: Received March 04, 2009; Revised April 12, 2009; Published December 21, 2009; Online December 21, 2009

The objective of this work is to develop and validate a coupled boundary element method-finite element method to simulate the transient fluid-structure interaction response of tidal turbines subject to spatially varying inflow. The focus is on tidal turbines, although the methodology is also applicable for the analysis and design of wind turbines. An overview of the formulation for both the fluid and solid domains, and the fluid-structure interaction algorithms, is presented. The model is validated by comparing the predicted thrust and power measurements, as well as cavitation patterns, with experimental measurements and observations for an 800 mm marine current turbine presented in the work of Bahaj (2007, “Power and Thrust Measurements of Marine Current Turbines Under Various Hydrodynamic Flow Conditions in a Cavitation Tunnel and a Towing Tank,” Renewable Energy, 32, pp. 407–426). Additional numerical results are shown for the same turbine, but scaled up to 20 m in diameter, operating in a tidal boundary layer flow with a water depth of 30 m. The results show that transient cavitation will develop near the blade tip when the blades are near the free surface at highly-loaded off-design conditions, and the blades will undergo excessive deformation because of the high fluid loading and slender blade profile. The results also show that the natural frequencies of the blades are significantly reduced when operating in water, as compared with when operating in air, because of added-mass effects. In addition to demonstrating the need for proper consideration for fluid cavitation and structural response, current design challenges for both wind and tidal turbines are discussed.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of a wind or tidal turbine subject to a spatially varying wake

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Figure 2

Discretized turbine geometry and blade section profiles

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Figure 3

Comparison of the predicted and measured thrust coefficients (CT) for varying tip speed ratio. The experimental results (“EXP”) are obtained from Ref. 42.

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Figure 4

Comparison of the predicted and measured power coefficients (Cpow) for varying tip speed ratio. The experimental results (EXP) are obtained from Ref. 42.

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Figure 5

Predicted wetted pressure distribution (left), cavitation patterns and cavitation pressure distribution (right) for a turbine with hub pitch angle of 25 deg at TSR=7.5

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Figure 6

Comparison of power and thrust coefficients in fully wetted and cavitating (σn=3.9) conditions. The experimental results (EXP) are obtained from Ref. 42.

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Figure 7

Normalized axial velocity distribution for a 20 m diameter turbine in 30 m depth of water

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Figure 8

Predicted in-air (fdry) and in-water (fwet) frequencies and in-water mode shapes for the 20 m diameter turbine

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Figure 9

Predicted pressure coefficients at various blade angles for the 20 m diameter turbine subject to boundary layer flow at the design flow condition. V=2.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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Figure 10

Predicted variations in thrust and power coefficients for each blade and the total thrust and power transferred to the shaft at the design flow condition. V=2.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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Figure 11

Predicted variations in horizontal and vertical force coefficients for each blade and for the shaft (total) at the design flow condition. V=2.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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Figure 12

Predicted variations in horizontal and vertical moment coefficients for each blade and for the shaft (total) at the design flow condition. V=2.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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Figure 13

Predicted pressure coefficients at various blade angles for the 20 m diameter turbine subject to boundary layer flow under highly-loaded off-design flow conditions. V=3.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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Figure 14

Predicted cavity planforms at various blade angles for the 20 m diameter turbine subject to boundary layer flow under highly-loaded off-design flow conditions. V=3.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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Figure 15

Predicted bending stress contours (top) and maximum displacement and maximum von mises stress (bottom) for the 20 m diameter turbine under highly-loaded off-design flow conditions. V=3.5 m/s, n=14.32 rpm, Fn=0.12, and σn=21.47.

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