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MODELLING OF MULTIPHASE FLOWS OVER SURFACE WITH PENETRABLE ROUGH RELIEF

MODELLING OF MULTIPHASE FLOWS OVER SURFACE WITH PENETRABLE ROUGH RELIEF. Yevgeniy A. Shkvar National Aviation University, Kyiv, Ukraine e-mail: shkvar@ukrpost.net. Several kinds of turbulent flows associated with this investigation. Object of investigation is.

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MODELLING OF MULTIPHASE FLOWS OVER SURFACE WITH PENETRABLE ROUGH RELIEF

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  1. MODELLING OF MULTIPHASE FLOWS OVER SURFACE WITH PENETRABLE ROUGH RELIEF Yevgeniy A. Shkvar National Aviation University, Kyiv, Ukraine e-mail: shkvar@ukrpost.net

  2. Several kinds of turbulent flows associated with this investigation

  3. Object of investigation is a boundary layer developing under conditions close to atmospheric (over rough surface and with presence of additive phase) Background of the problem Brief information about typical dimensions and scales The atmosphere from space (source NASA)

  4. Atmosphere, its structure and phenomena • The troposphere is a region of mixing, containing: • the largest percentage of the mass of the total atmosphere; • 99 % of the water vapor in the atmosphere. • All weather phenomena occur within the troposphere. Natural convective processes in the neighborhood of the land

  5. Surface relief (roughness and penetrable roughness) • There are many practically interested cases, • when relief elements like • Land cover irregularities; • Forests; • Urban relief (buildings, streets, etc.) • may be considered as a special kind of roughness distributed • in the neighborhood of land and having penetrable effect

  6. Sources of Air Pollution: • Smoke; • Naturalairpollution; • Enterprise emissions; • Exhaust gas emissions; • Forest fires; • Radiation, chemical accidents. The atmosphere “lives” under strong influence of pollutions with different nature

  7. Accounting factors: Surface is covered by rough relief with penetrable structure; Flow can be heterogeneous; Atmospheric pollutants have properties of scalar passive additives. Negligible factors: Land Curvature; Earth rotation, Coriolis effects; Air compressibility; Air stratification; Radiation; Heating; Chemical and mechanical phase interaction Goal of the researchConstruct the simple model of the atmospheric boundary layer that will be able to account a rough relief influence on flow properties and pollution diffusion

  8. Flow direction Streamlined surface Penetrable rough elements Investigated geometries of surface relief

  9. Governing equations Continuity equation: (1) Momentum equation in projections on x and y axes: (2) (3) Transfer equation of scalar additive concentration : (4) Here - the effective fluid volume,

  10. Turbulence modelingDifferential k-e approach (5) (6) DIFFUSIVE COEFFICIENTS & DENSITY DETERMINATION (7)

  11. Model details The set of model coefficients с=0,09; с1=1,45; с2=1,92; k=1; =1,3 Near-wall modifications (8) Source modifications (9) - T. Maryuama

  12. Smooth surface U+ lny Turbulence modeling Algebraic approach , (10) - V. Movchan’ formula , , (11) , , (12) ; Here: - the model’s coefficients

  13. Boundary conditions Streamlined surface: Initial cross-section (input boundary): Output boundaries of computational domain: , Numerical Method Grid– nonuniform orthogonal staggered; Method– SIMPLE + Leonard’, Zijlema’ 3-rd order schemes; Calculation procedure– Thomas algorithm.

  14. Testing of elaborated models Predictions of flow properties for several geometries of rough relief and their comparison with the experimental data

  15. Flow behind penetrable obstacles Experimental data source: P. H. A. Barbosa; M. Cataldi; A. P. S. Freire, “Wind tunnel simulation of atmospheric boundary layer flows” J. Braz. Soc. Mech. Sci. vol.24 no.3 Rio de Janeiro July 2002 Flow phenomena: This flow was artificially thickened for making its parameters to be similar for typical atmospheric flows

  16. Velocity profiles comparison in semi-logarithmic coordinatesInvestigated case: Flow behind rods array with 160 mm ,U∞=3 m/s a) Experiments P. H. A. Barbosa; M. Cataldi; A. P. S. Freire (Brazil, 2002); b) Predictions on the base of this model

  17. Skin friction coefficient vs. Reδ**Investigated case: Flow behind rods array with 160 mm ,U∞=3 m/s Experiments P. H. A. Barbosa; M. Cataldi; A. P. S. Freire (Brazil, 2002);

  18. Cf δ* H=δ*/δ** Flow over penetrable rough relief (short rough zone Lrough=0.5m, ρrough=0.25)

  19. U, C k ε νt Flow over penetrable rough relief (short rough zone Lrough=0.5m , ρrough=0.25)

  20. Cf δ* H=δ*/δ** Flow over penetrable rough relief(continuous rough zone Lrough=6.5m, ρrough=0.25)

  21. U, C k ε νt Flow over penetrable rough relief(continuous rough zone Lrough=6.5m , ρrough=0.25)

  22. Cf δ* H=δ*/δ** Flow over penetrable rough relief(rough array Lrough=4x0.5m, ρrough=0.25)

  23. U, C k ε νt Flow over penetrable rough relief(rough array Lrough=4x0.5m , ρrough=0.25)

  24. Conclusion • Presented model is able to account an influence of penetrable roughness on the turbulent flow properties; • This model predicts an influence of rough relief on a scalar additive transfer; • Algebraic approach to turbulence modeling is acceptable for this kind of viscous flows; • Penetrable roughness can be used as an effective tool of air protection.

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