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Flows in Complex Systems

Three-Dimensional Effects on an Oscillating-Foil Hydrokinetic Turbine

[+] Author and Article Information
Thomas Kinsey1

Guy Dumas

Laboratoire de Mécanique des Fluides Numérique,Department of Mechanical Engineering,  Laval University, Quebec City, QC, G1V 0A6, Canadagdumas@gmc.ulaval.ca

1

Corresponding author.

J. Fluids Eng 134(7), 071105 (Jun 22, 2012) (11 pages) doi:10.1115/1.4006914 History: Received January 18, 2012; Revised May 23, 2012; Published June 22, 2012; Online June 22, 2012

Three-dimensional hydrodynamic losses are assessed in this investigation for a foil oscillating sinusoidally in a combined heave and pitch motion with large amplitudes. Simulations are performed using a unsteady Reynolds-Averaged-Navier-Stokes (URANS) solver on an oscillating foil in a power-extraction mode; thus acting as a hydrokinetic turbine at high Reynolds number. Foils of various aspect ratios (span to chord length ratio) are considered, both with and without endplates for one representative operation point. Hydrodynamic forces and extracted power are compared with results from the equivalent two-dimensional (2D) computations. It is found that the relative drop of performance (cycle-averaged power extracted) due to 3D hydrodynamic losses can be limited to 10% of the 2D prediction when endplates are used on a foil of aspect ratio greater than ten. The practical consideration of an oscillating-foil hydrokinetic turbine operating in an imperfectly-aligned upstream water flow is also addressed with simulations considering an upstream flow at a yaw angle up to 30° with respect to the foil chord line. Effects on performance are found to be proportional to the projected kinetic energy flux.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D foil parameters

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Figure 2

Domain size and boundary condition types for a 3D foil simulated in its heaving reference frame (adapted from Ref. [23])

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Figure 3

3D mesh details: (a) nonconformal sliding interface, and (b) spanwise discretization for the AR=5 hydrofoil with endplates

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Figure 4

Endplate geometry relative to the chord length

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Figure 5

Comparison between hydrodynamic efficiencies predicted from 3D URANS simulations and experiment [3,23]

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Figure 6

Comparison of instantaneous forces, moment and power coefficients between 2D and 3D simulations with no endplates and different aspect ratios. Re  500,000, f*  0.14, θ0  75  deg, H0  c.

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Figure 7

Comparison between 2D and 3D (AR  7, no endplates) predictions at two instants during the cyclic motion of the foil. Flow structures are visualized using slices of Z-vorticity at every half-chord length distance along the foil span (blue for negative vorticity, red for positive). Pressure coefficient distributions along the chord line are provided and compared to 2D results for two stations along the span; one at midspan (z  3.5c) and one at only 0.5c away from the wingtip.

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Figure 8

Comparison of instantaneous forces, moment and power coefficients between 2D and 3D simulations with endplates and different aspect ratios. Re  500,000, f*  0.14, θ0  75  deg, H0  c.

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Figure 9

Comparison between 2D and 3D (AR  7, with endplates). See caption of Fig. 7.

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Figure 10

Comparison of instantaneous forces, moment and power coefficients between 3D simulations associated to upstream-velocity yaw angles of 0, 15 and 30  deg. Re  500,000, f*=0.14, θ0  75  deg, H0  c, AR  7, with endplates.

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