Numerical Study of Island Wake in Deep Water
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Transcript of Numerical Study of Island Wake in Deep Water
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
• Introduction
• Model Configuration
• Basic Experiment
• Sensitivity Tests
• Summary
Introduction
2. Wake Classic Fluid Dynamics
3. Wake in geophysical fluid dynamics
1. Observational and numerical evidence
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)
1. Shallow water
Wolanski (1984) Signell and Geyer (1991) Davies (1995)
2. Deep water
Heywood et al (1996) Coutis and Middleton (2002)
Two Categories (Tomczak,1988)
Basic Experiment Rectangular Domain: 180km x 80km , Water Depth : 500m
Island Diameter D= 10km
Spatial Resolution : DX = 500 m (160 x 360 x20)
Boundary Condition
a). Upstream BC (incident flow)
b). Downstream BC
c). BC neighboring the island
Downstream BC:
1. Modified Orlanski radiation (Marchesiello et al , 2001)
2. Specified BC with sponge layer
Island BC: Non-slippery with mask
Strouhal Number: St=nD/U=0.207
Time Series of Lateral Boundary Layer
Sensitivity Tests
1. Reynolds number
2. Rotation
3. Island Scale
4. Vertical Shear
5. Stratification
Background Horizontal Viscosity μ
Grid Reynolds Number
Re=dx*U/μ
• Implicit diffusion associated with upstream-biased advection scheme
• If Re> 10, scheme diffusion dominates
• If Re<=10, physical diffusion dominates
Re=200
Re=100
Re=25
Re=10
Unknown Re
Sensitivity Tests
1. Reynolds Number
2. Rotation
3. Island Scale
4. Vertical Shear
5. Stratification
6. Grid size
Sensitivity Tests
1. Reynolds
2. Rotation
3. Island Scale
4. Vertical Shear
5. Stratification
St=0.18 St = 0.20 St=0.23
Sensitivity Tests
1. Reynolds
2. Rotation
3. Island Scale
4. Vertical Shear
5. Stratification
Basic Case Weaker Shear
Weaker ShearBasic Case
Sensitivity Tests
1. Reynolds
2. Rotation
3. Island Scale
4. Vertical Shear
5. Stratification
Weaker StratificationBasic Case
Weaker StratificationBasic Case
Summary
1. 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!