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Ocean Engineering

The Effect of Boundary Proximity Upon the Wake Structure of Horizontal Axis Marine Current Turbines

[+] Author and Article Information
A. S. Bahaj, L. E. Myers

Sustainable Energy Research Group, School of Civil Engineering and the Environment,  University of Southampton, Southampton, SO171BJ United Kingdom

R. I. Rawlinson-Smith, M. Thomson

Garrad Hassan and Partners Limited, St. Vincent’s Works, Silverthorne Lane, Bristol, BS2 0QD, United Kingdom

J. Offshore Mech. Arct. Eng 134(2), 021104 (Dec 06, 2011) (8 pages) doi:10.1115/1.4004523 History: Received October 04, 2010; Revised March 06, 2011; Published December 06, 2011; Online December 06, 2011

An experimental and theoretical investigation of the flow field around small-scale mesh disk rotor simulators is presented. The downstream wake flow field of the rotor simulators has been observed and measured in the 21m tilting flume at the Chilworth hydraulics laboratory, University of Southampton. The focus of this work is the proximity of flow boundaries (sea bed and surface) to the rotor disks and the constrained nature of the flow. A three-dimensional Eddy-viscosity numerical model based on an established wind turbine wake model has been modified to account for the change in fluid and the presence of a bounding free surface. This work has shown that previous axi-symmetric modeling approaches may not hold for marine current energy technology and a novel approach is required for simulation of the downstream flow field. Such modeling solutions are discussed and resultant simulation results are given. In addition, the presented work has been conducted as part of a UK Government funded project to develop validated numerical modeling tools which can predict the flow onto a marine current turbine within an array. The work feeds into the marine energy program at Southampton to assist developers with layout designs of arrays which are optimally spaced and arranged to achieve the maximum possible energy yield at a given tidal energy site.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Some variables that will affect device performance and wake structure

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Figure 2

Theoretical and measured tidal current boundary layer profiles

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Figure 3

Installed experiment at Chilworth flume (left), close up of mesh disk pivot unit (right)

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Figure 4

Regions of flow mapped in results section of this paper. Center plane vertical slice (left) and centerline (right)

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Figure 5

Center plane velocity deficits for varying disk submersion depths. Disk center at 0.75d (a), 0.66d (b), 0.33d (c)

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Figure 6

Centreline wake velocity deficits downstream of 4 disks at varying distances from the bed

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Figure 7

Center plane vertical slices of Reynolds stress of a disk with increasing downstream distance (disk vertically centered at 0.33d from bed)

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Figure 8

Center plane vertical slices of normalized TKE at 4D downstream for disk at varying depths

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Figure 9

Wake profile used in the eddy viscosity model

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Figure 10

Wake profile used in the eddy viscosity model Reynolds stress normalized to the inflow profile (U(z) [2]). Disk Ct = 0.86.

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Figure 11

Measured ambient eddy-viscosity profiles

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Figure 12

Comparison of wake model with experimental data: Ct = 0.86; Initial deficit = 0.55; Amb Eddy = 0.01. K1 = 0.004

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Figure 13

Centerline comparison of wake model with experimental data: hh = 0.33d; Initial deficit = 0.55; Amb Eddy: top = 0.009, bottom = 0.011, lateral = 0.01. K1 = 0.004

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Figure 14

Measured shape factor

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Figure 15

Comparison of model centerline vertical profiles (disk Ct = 0.86)

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Figure 16

Comparison of model centerline lateral profiles (disk Ct = 0.86)

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