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Structure of turbulent flow over regular arrays of cubical roughness.

By O. Coceal, A. Dobre, T.G. Thomas and S.E. Belcher

Abstract

The structure of turbulent flow over large roughness consisting of regular arrays of cubical obstacles is investigated numerically under constant pressure gradient conditions. Results are analysed in terms of first- and second-order statistics, by visualization of instantaneous flow fields and by conditional averaging. The accuracy of the simulations is established by detailed comparisons of first- and second-order statistics with wind-tunnel measurements. Coherent structures in the log region are investigated. Structure angles are computed from two-point correlations, and quadrant analysis is performed to determine the relative importance of Q2 and Q4 events (ejections and sweeps) as a function of height above the roughness. Flow visualization shows the existence of low-momentum regions (LMRs) as well as vortical structures throughout the log layer. Filtering techniques are used to reveal instantaneous examples of the association of the vortices with the LMRs, and linear stochastic estimation and conditional averaging are employed to deduce their statistical properties. The conditional averaging results reveal the presence of LMRs and regions of Q2 and Q4 events that appear to be associated with hairpin-like vortices, but a quantitative correspondence between the sizes of the vortices and those of the LMRs is difficult to establish; a simple estimate of the ratio of the vortex width to the LMR width gives a value that is several times larger than the corresponding ratio over smooth walls. The shape and inclination of the vortices and their spatial organization are compared to recent findings over smooth walls. Characteristic length scales are shown to scale linearly with height in the log region. Whilst there are striking qualitative similarities with smooth walls, there are also important differences in detail regarding: (i) structure angles and sizes and their dependence on distance from the rough surface; (ii) the flow structure close to the roughness; (iii) the roles of inflows into and outflows from cavities within the roughness; (iv) larger vortices on the rough wall compared to the smooth wall; (v) the effect of the different generation mechanism at the wall in setting the scales of structures.<br/

Topics: QC
Year: 2007
OAI identifier: oai:eprints.soton.ac.uk:64317
Provided by: e-Prints Soton

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  1. (2000). A d r i a n ,R .J . ,M e i n h a r t ,C .D .&T o m k i n s
  2. (1986). A theoretical and experimental study of wall turbulence.
  3. (1995). A wall-wake model for the turbulence structure of boundary layers. Part 1. Extension of the attached eddy hypothesis.
  4. (2005). An experimental and numerical study of channel flow with rough walls.
  5. (1954). Characteristics of turbulence in a boundary layer with zero pressure gradient.
  6. (1991). Coherent motions in the turbulent boundary layer.
  7. (1993). Common vortical structure of turbulent flows over smooth and rough boundaries.
  8. (1981). Conditional statistics of Reynolds stress in rough-wall and smooth-wall turbulent boundary layers.
  9. (2001). Direct numerical simulation of turbulent flow over a rectangular trailing edge.
  10. (2003). Direct numerical simulations of turbulent channel flow with transverse square bars on one wall.
  11. (1988). Direct simulation of a turbulent boundary layer up to Rθ =1410.
  12. (2001). DNS of a fully developed turbulent channel flow with respect to the Reynolds number dependence.
  13. e n i d i ,L . ,E l a v a r a s a n ,R .&A n t o n i a ,R .A .1999 The turbulent boundary layer over transverse square cavities.
  14. (2000). F i n n i g a n
  15. (2000). Flow Control. Passive, Active and Reactive Flow Management.
  16. (1995). H a m i l t o n
  17. (1992). K r o g s t a d ,P .A . ,A n t o n i a ,R .A .&B r o w n e
  18. (1998). M o i n ,P .&M a h e s h ,K
  19. (2006). Mean flow and turbulence statistics over groups of urban-like cubical obstacles.
  20. (1999). Mechanisms for generating coherent packets of hairpin vortices in channel flow.
  21. (1971). Momentum absorption by vegetation.
  22. (2002). Near wall flow over urban-like roughness. Boundary-Layer Met.
  23. (2004). Numerical study of vortical structures around a wall-mounted cubic obstacle in channel flow.
  24. (1974). On density effects and large structure in turbulent mixing layers.
  25. (2006). On the definition of the s h e a rv e l o c i t yi nr o u g hb e do p e nc h a n n e lfl o w s
  26. (1981). On the displacement height in the logarithmic profile.
  27. (1995). On the identification of a vortex.
  28. (2001). On the role of large-scale structures in wall turbulence.
  29. (2005). On the structure of turbulence in the bottom boundary layer of the coastal ocean.
  30. (1981). Organized motion in turbulent flow.
  31. (2001). Overview of the self-sustaining mechanisms of wall turbulence.
  32. (2002). Packet structure of surface eddies in the atmospheric boundary layer.
  33. (1996). R a u p a c h ,M .R . ,F i n n i g a n
  34. R o t a c h ,M .W .1993 Turbulence close to a rough urban surface, Part I: Reynolds stress.
  35. (1989). Relation between outer structures and wall-layer events in boundary layers with and without manipulation.
  36. (1991). Rough-wall turbulent boundary layers.
  37. (2003). Spanwise structure and scale growth in turbulent boundary layers.
  38. (1971). Structural features of turbulent flow over smooth and rough boundaries.
  39. (1994). Structure of turbulent boundary layers on smooth and rough walls.
  40. (1965). Structure of turbulent velocity and scalar fields at large wave numbers.
  41. (1999). Surface roughness effects in turbulent boundary layers.
  42. (1972). T e n n e k e s ,H .&L u m l e y
  43. (1999). The autonomous cycle of near-wall turbulence.
  44. (1998). The dynamics of coherent structures in the wall region of a turbulent boundary layer.
  45. (2005). The generation of streaks and hairpin vortices from a localized vortex disturbance embedded in unbounded uniform shear flow.
  46. (1971). The production of turbulence near a smooth wall in a turbulent boundary layer.
  47. (1967). The structure of turbulent boundary layers.
  48. (1976). The Structure of Turbulent Shear Flow.
  49. (1992). The three-dimensional evolution of a plane mixing layer: the Kelvin-Helmholz rollup.
  50. (1972). The wall region in turbulent shear flow.
  51. (2000). Turbulence in plant canopies.
  52. (2006). Turbulence over urban-type roughness: deductions from wind tunnel measurements.
  53. (1987). Turbulence statistics in fully devloped channel flow at low Reynolds number.
  54. (2004). Turbulent flows over rough walls.
  55. (2000). Turbulent Flows.
  56. (1991). Vortical structures and coherent motion in turbulent flow over smooth and rough boundaries.

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