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Direct numerical simulations of convective flows Oceanography - Gas Transfer Sam Fredriksson, University of Gothenburg Outline of this presentation Aim with this presentation Background Route forward Work so far Carbon Cycle


  1. Direct numerical simulations of convective flows Oceanography - Gas Transfer Sam Fredriksson, University of Gothenburg

  2. Outline of this presentation • Aim with this presentation • Background • Route forward • Work so far Carbon Cycle – IPCC (2007)

  3. How are CO 2 fluxes determined? Typically: 1.CO 2 concentration in surface water (pCO 2 ) 2.Flux model: F = k ( C aq – C eq ) 3.Piston velocity/gas transfer koefficient ( k ) calculated from average wind speed at 10 m height.

  4. D. Bade 2009, Encycl. of Inland Waters

  5. Surfactant influence of flow field and gas transfer Clean Oley alcohol II k as a funct. of time Surface velocity (surfactant concentration cholesterol) Surface vorticity Surface divergence McKenna 2000

  6. Gas exchange research strategy Forming a group of researchers Gas exchange and concentration measurements Wind measurements Turbulence measurements Infrared camera recording Numerical modeling

  7. Route forward numerical simulations General • DNS (Direct Numerial Simulations) with OpenFoam • DNS with convection • DNS with surface shear • DNS with surfactant • LES (Large Eddy Simulations) • Waves …

  8. Route forward numerical simulations Lars Davidsson et al. ”DNS of plane vertical channel with and without buoyancy”, Turbulence, Heat and General Mass Transfer, 2003 • DNS with OpenFoam 1.4 1.2 • DNS with convection 1 0.8 • DNS with surface shear Umean/Ubar Umean 0.6 _Lada/Ubar • DNS with surfactant 0.4 0.2 • LES/DNS moving surface 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 • Waves … 0.2 0.18 0.16 0.14 0.12 urms/Ubar vrms/Ubar 0.1 wrms/Ubar urms_Lada/Ubar 0.08 urms_Lada/Ubar wrms_Lada/Ubar 0.06 0.04 0.02 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

  9. Route forward numerical simulations General Robert Handler: ”Direct numerical simulations of free convection • DNS with OpenFoam beneath an air-water interface at low • DNS with convection Rayleigh numbers”, Physics of Fluids, 2003 • DNS with surface shear • DNS with surfactant • LES/DNS moving surface • Waves …

  10. Computational domain Evaporation

  11. Boussinesq formulation Momentum and Continuity �� �� � U ∙ � U � � 1 �� � ν � � � � �� � � � � � � � � ∙ U � 0 Linear approximation of density � �� � � � � � 1 � � � � � � , � � � �� � � � � Temperature field is governed by a convection-diffusion equation given by �� �� � U ∙ � T � � � � T � S

  12. Temperature field, Ra q ≈ 5x10 6 0.076 m Played 10 times real time

  13. IR-measurements at Bornö L z = 0.122 (Side = 0.17 m) Ra ~ QL z 4 ≈ 1 m Magnus Gålfalk

  14. Surfactant - Finite Area Method - fam

  15. Areas for investigation Analysis • Mesh convergence – it seems that there is a need for finer meshes with present formulation compared to Handler et al. • Size of computational box and mesh resolution • More thorough analysis and comparison against experiments etc. • Surfactant formulation, cyclic boundaries for fam • Find correlation between IR and gas transfer • Find a good measure/representation of the temperature field (rms, skewness, flatness, divergence etc.) • Waves etc.

  16. Thank you

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