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Numerical Study of Island Wake in Deep Water

Numerical Study of Island Wake in 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

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Numerical Study of Island Wake in Deep Water

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  1. 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

  2. Introduction • Model Configuration • Basic Experiment • Sensitivity Tests • Summary

  3. Introduction 1. Observational and numerical evidence 2. Wake Classic Fluid Dynamics 3. Wake in geophysical fluid dynamics

  4. 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)

  5. Two Categories (Tomczak,1988) • Shallow water • Wolanski (1984) • Signell and Geyer (1991) • Davies (1995) • Deep water • Heywood et al (1996) • Coutis and Middleton (2002)

  6. Basic Experiment Rectangular Domain: 180km x 80km , Water Depth : 500m Island Diameter D= 10km Spatial Resolution : DX = 500 m (160 x 360 x20)

  7. Boundary Condition • a). Upstream BC (incident flow) • b). Downstream BC • c). BC neighboring the island

  8. Downstream BC: • Modified Orlanski radiation • (Marchesiello et al , 2001) • 2. Specified BC with sponge layer Island BC: Non-slippery with mask

  9. Strouhal Number: St=nD/U=0.207

  10. Time Series of Lateral Boundary Layer

  11. Sensitivity Tests • Reynolds number • Rotation • Island Scale • Vertical Shear • Stratification

  12. 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

  13. Unknown Re Re=200 Re=100 Re=25 Re=10

  14. Sensitivity Tests • 1. Reynolds Number • 2. Rotation • 3. Island Scale • 4. Vertical Shear • 5. Stratification • 6. Grid size

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

  16. St=0.18 St = 0.20 St=0.23

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

  18. Basic Case Weaker Shear

  19. Basic Case Weaker Shear

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

  21. Basic Case Weaker Stratification

  22. Basic Case Weaker Stratification

  23. 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!

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