Numerical Study of Island Wake in Deep Water

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Numerical Study of Island Wakein Deep Water

• Changming (Charles) Dong
• James McWilliams
• Alexander Shchepetkin
• IGPP/UCLA, Los Angels,USA

Acknowledgements J. Molemaker, C. Zhang, M. Blass
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• Introduction
• Model Configuration
• Basic Experiment
• Sensitivity Tests
• Summary

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Introduction
1. Observational and numerical evidence
2. Wake Classic Fluid Dynamics
3. Wake in geophysical fluid dynamics
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a) no separation, laminar boundary layer b)
vortex pair with central return flow c) wake
formation with wave disturbances along the
current/wake interface d) von Karman vortex
street

(From M. Tomczak, 2000)
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Two Categories (Tomczak,1988)

• Shallow water
• Wolanski (1984)
• Signell and Geyer (1991)
• Davies (1995)
• Deep water
• Heywood et al (1996)
• Coutis and Middleton (2002)

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Basic Experiment Rectangular Domain 180km x
80km , Water Depth 500m Island Diameter D
10km Spatial Resolution DX 500 m
(160 x 360 x20)
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• Boundary Condition
• a). Upstream BC (incident flow)
• b). Downstream BC
• c). BC neighboring the island

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• Downstream BC
• Modified Orlanski radiation
• (Marchesiello et al , 2001)
• 2. Specified BC with sponge layer

Island BC Non-slippery with mask
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Strouhal Number StnD/U0.207
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Time Series of Lateral Boundary Layer
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• Sensitivity Tests
• Reynolds number
• Rotation
• Island Scale
• Vertical Shear
• Stratification

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• Background Horizontal Viscosity µ
• Grid Reynolds Number
• RedxU/µ
• Implicit diffusion associated with
  upstream-biased advection scheme
• If Regt 10, scheme diffusion dominates
• If Relt10, physical diffusion dominates

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Unknown Re
Re200
Re100
Re25
Re10
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• Sensitivity Tests
• 1. Reynolds Number
• 2. Rotation
• 3. Island Scale
• 4. Vertical Shear
• 5. Stratification
• 6. Grid size

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• Sensitivity Tests
• 1. Reynolds
• 2. Rotation
• 3. Island Scale
• 4. Vertical Shear
• 5. Stratification

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St0.18
St 0.20
St0.23
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• Sensitivity Tests
• 1. Reynolds
• 2. Rotation
• 3. Island Scale
• 4. Vertical Shear
• 5. Stratification

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Basic Case
Weaker Shear
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Weaker Shear
Basic Case
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• Sensitivity Tests
• 1. Reynolds
• 2. Rotation
• 3. Island Scale
• 4. Vertical Shear
• 5. Stratification

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Weaker Stratification
Basic Case
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Weaker Stratification
Basic Case
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• Summary
• ROMS is applied to study the ideal island wake
• in the dynamically deep water with rotation
  and
• stratification.
• 2. Background eddy viscosity should be chosen
  appropriately
• higher spatial resolution show finer
  structure of eddy
• activities in the wake.
• 3. Rotation, island scale, vertical shear and
  stratification
• affect the wake structure.

The work is still in progress!