Advertisement

Boundary-Layer Meteorology

, Volume 104, Issue 2, pp 229–259 | Cite as

Near Wall Flow over Urban-like Roughness

  • Hong Cheng
  • Ian P. Castro
Article

Abstract

In this study, comprehensive measurements over a number of urban-type surfaces with the same area density of 25% have been performed in a wind tunnel. The experiments were conducted at a free stream velocity of 10 m s-1 and the main instrumentation was 120 ° x-wire anemometry, but measurement accuracy was checked using laser Doppler anemometry.The results haveconfirmed the strong three-dimensionalityof the turbulent flow inthe roughness sublayer and the depths of the inertial sublayer (log-law region) and roughness sublayer for each surface have been determined. Spatial averaging has been used to remove the variability of the flow in the roughness sublayer due to individual obstacles and it is shown that the spatially averaged mean velocity in the inertial sublayer and roughness sublayer can,together, be described by a single log-law with a mean zero-plane displacement and roughness length for the surface, provided that the proper surface stress is known. The spatially averaged shear stresses in the inertial sublayer and roughness sublayer are compared with the surface stress deduced from form drag measurements on the roughness elements themselves.

The dispersive stress arising from the spatial inhomogeneity in the mean flow profiles was deduced from the data and is shown to be negligible compared with the usual Reynolds stresses in the roughness sublayer. Comparisons have been made between a homogeneous (regular element array) surface and one consisting of random height elements of the same total volume. Although the upper limits of the inertial sublayer for both surfaces were almost identical at equivalent fetch, the roughness sublayer was much thicker for the random surface than for the uniform surface, the friction velocity and the roughness length were significantly larger and the `roughness efficiency' was greater. It is argued that the inertial sublayer may not exist at all in some of the more extreme rough urban areas. These results will provide fundamental information for modelling urban air quality and forecasting urban wind climates.

Form drag Roughness sublayer Spatial average Urban random surface Wind tunnel 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Böhm, M., Finnigan, J. J., and Raupach, M. R.: 2000, 'Dispersive Fluxes and Canopy Flows: Just how Important Are They?', in American Meteorology Society, 24th Conference on Agricultural and Forest Meteorology, 14—18 August 2000, University of California, Davis, CA, pp. 106–107.Google Scholar
  2. Cheng, H. and Castro, I.: 2002, 'Near-Wall Flow Development after a Step Change in Surface Roughness', Boundary-Layer Meteorol., in press.Google Scholar
  3. Garratt, J. R.: 1980, 'Surface Influence upon Vertical Profiles in the Atmospheric Near-Surface Layer', Quart. J. Roy. Meteorol. Soc. 106, 803–819.Google Scholar
  4. Grimmond, C. S. B. and Oke, T. R.: 1999, 'Aerodynamics Properties of Urban Areas Derived from Analysis of Surface Form', J. Appl. Meteorol. 38, 1262–1292.Google Scholar
  5. Jackson, P. S.: 1981, 'On the Displacement Height in the Logarithmic Velocity Profile', J. Fluid Mech. 111, 15–25Google Scholar
  6. Kaimal, J. C. and Finnigan, J. J.: 1994, Atmospheric Boundary Layer Flows: Their Structure and Measurement, Oxford University Press, ISBN 0-19-506239-6.Google Scholar
  7. Macdonald, R. W.: 2000, 'Modelling the Mean Velocity Profile in the Urban Canopy Layer', Boundary-Layer Meteorol. 97, 25–45.Google Scholar
  8. Macdonald, R. W., Carter, S., and Slawson, P. R.: 2000, Measurements of Mean Velocity and Turbulence Statistics in Simple Obstacle Arrays at 1:200 Scale, Thermal Fluids Report 2000-1, University of Waterloo, Canada.Google Scholar
  9. Modi, V. J. and Deshpande, V. S.: 2001, 'Fluid Dynamics of a Cubic Structure as Affected by Momentum Injection and Height', J. Wind Eng. And Ind. Aero. 89, 445–470.Google Scholar
  10. Mulhearn, P. J. and Finnigan, J. J.: 1978, 'Turbulent Flow over a Very Rough, Random Surface', Boundary-Layer Meteorol. 15, 109–132.Google Scholar
  11. Perry, A. E., Henbest, S., and Chong, M. S.: 1986, 'A Theoretical and Experimental Study of Wall Turbulence', J. Fluid Mech. 165, 163–199.Google Scholar
  12. Perry, A. E., Lim, K. L., and Henbest, S. M.: 1987, 'An Experimental Study of the Turbulence Structure in Smooth and Rough Wall Turbulent Boundary Layer', J. Fluid Mech. 177, 437–466.Google Scholar
  13. Plate, E. J.: 1995, 'Urban Climates and Urban Climate Modelling: An Introduction', in J. E. Cermak et al. (eds.), Wind Climate in Cities, Kluwer Academic Publishers, Dordrecht, Boston, pp. 23–39.Google Scholar
  14. Plate, E. J. (ed.): 1982, Engineering Meteorology: Studies in Wind Engineering and Industrial Aerodynamics, Vol. 1, Elsevier Scientific Publishing Company, Amsterdam, New York.Google Scholar
  15. Ploss, A., Castro, I., and Cheng. H.: 2000, 'The Surface Region of Rough-Wall Boundary Layers', in C. Dopazo (ed.), Advances in Turbulence VIII, CIMNE, pp. 455–459.Google Scholar
  16. Ranga Raju, K. G., Loeser, J., and Plate, E. J.: 1976, 'Velocity Profiles and Fence Drag for a Turbulent Boundary Layer along Smooth and Rough Flat Plates', J. Fluid Mech. 76, 383–399.Google Scholar
  17. Raupach, M. R., Antonia, R. A., and Rajagopalan, S.: 1991, 'Rough-Wall Turbulent Boundary Layers', Appl. Mech, Rev. 44, 1–25.Google Scholar
  18. Raupach, M. R., Coppin, P. A., and Legg, B. J.: 1986, 'Experiments on Scalar Dispersion within a Model Plant Canopy Part I: The Turbulence Structure', Boundary-Layer Meteorol. 35, 21–52.Google Scholar
  19. Raupach M. R., Finnigan, J. J., and Brunet, Y.: 1996, 'Coherent Eddies and Turbulence in Vegetation Canopies: The Mixing — Layer Analogy', Boundary-Layer Meteorol. 78, 351–382.Google Scholar
  20. Raupach, M. R., Thom, A. S., and Edwards, I.: 1980, 'AWind Tunnel Study of Turbulent Flow Close to Regularly Arrayed Rough Surfaces', Boundary-Layer Meteorol. 18, 373–397.Google Scholar
  21. Rotach, M. W.: 1993a, 'Turbulence Close to a Rough Urban Surface, Part I: Reynolds Stress', Boundary-Layer Meteorol. 65, 1–28.Google Scholar
  22. Rotach, M. W.: 1993b, 'Turbulence Close to a Rough Urban Surface, Part II: Variances and Gradients', Boundary-Layer Meteorol. 66, 75–92.Google Scholar
  23. Rotach, M. W.: 1995, 'Profiles of Turbulence Statistics above an Urban Street Canyon', Atmos. Environ. 29, 1473–1486.Google Scholar
  24. Roth, M.: 2000, 'Review of Atmospheric Turbulence over Cities', Quart. J. Roy. Meteorol. Soc. 146, 941–990.Google Scholar
  25. Roth, M. and Oke, T. R.: 1993, 'Turbulent Transfer Relationships over an Urban Surface. I: Spectral Characteristics', Quart. J. Roy. Meteorol. Soc. 119, 1071–1104.Google Scholar
  26. Smalley, R. J., Anotnia, R. A., and Djenidi, L.: 2001, 'Self-Preservation of Rough-Wall Turbulent Boundary Layer', Eur. J. Mech. B(Fluids) 20, 591–602.Google Scholar
  27. Snyder, W. H. and Castro, I. P.: 2002, 'The Critical Reynolds Number for Rough-Wall Boundary Layers', J. Wind Eng. Ind. Aero. 90, 41–54.Google Scholar
  28. Stull, R. B.: 1988, An Introduction to Boundary Layer Meteorology, Kluwer Academic Publishers, Dordrecht, 666 pp.Google Scholar
  29. Thom, A. S.: 1971, 'Momentum Absorption by Vegetation', Quart. J. Roy. Meteorol. Soc. 97, 414–428.Google Scholar
  30. Tutu, N. K. and Chevray R.: 1975, 'Cross-Wire Anemometry in High Intensity Turbulence', J. Fluid Mech. 71, 785–800.Google Scholar
  31. Wood, N. and Mason, P.: 1993, 'The Pressure Force Induced by Neutral Turbulent Flow over Hills', Quart. J. Roy. Meteorol. Soc. 119, 1233–1267.Google Scholar

Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Hong Cheng
    • 1
  • Ian P. Castro
    • 2
  1. 1.EnFlo, School of EngineeringUniversity of SurreyGuildfordU.K
  2. 2.School of Engineering SciencesUniversity of SouthamptonSouthamptonU.K

Personalised recommendations