Environmental Fluid Mechanics

, Volume 5, Issue 5, pp 393–413 | Cite as

Upstream Turbulence Effect on Pollution Dispersion

  • Ijaz M. Khan
  • Richard R. Simons
  • Anthony J. Grass
Article

Abstract

Experiments have been carried out to investigate turbulence at and above roof-level in an urban environment, and to predict the behaviour of street pollution from experiments using dye dispersion, for different roughness conditions and bed geometries. The flow in the boundary layer above an idealised urban environment has been simulated in a laboratory water flume. Comparisons have been made for the same model street canyon with and without the presence of upstream roughness. In the tests reported here, model street canyons were aligned perpendicular to the flow direction, and velocity measurements made within and above the model street canyons using a laser Doppler velocimeter (LDV). Flow visualisation techniques have also been used to confirm the gross flow features from streak images. Turbulence generated from the upstream roughness has a significant effect on the turbulence production and dispersion behaviour of the dye simulating pollution in street canyons.

Keywords

flow pattern internal boundary layer pollution dispersion sudden change in bed roughness surface roughness turbulence 

Nomeclature

Bu

height of upstream slat of the immediate large scale roughness

Bd

height of downstream slat of the immediate large scale roughness

D

flow depth in the water flume

H

hyperbolic hole

Hu

height of upstream slat of the model street canyon

Hd

height of tall downstream slat of the model street canyon

k

roughness element height

Pu

gap distance between immediate large scale roughness slats

Pd

gap distance between roughness slats of immediate large scale roughness and model street canyon

s

gap distance between the roughness slats of model street canyon

U(=u+u′)

instantaneous stream wise velocity

u

fluctuating stream wise velocity component

\(\sqrt{\overline{u^{\prime2}}}\)

root mean square value for U

u

local mean stream wise velocity

u*

bed shear velocity

W(=w+w′)

instantaneous vertical velocity

w

fluctuating vertical velocity component

\(\sqrt{\overline{w^{\prime2}}} \)

root mean square value for W

w

local mean vertical velocity

z

vertical distance from the roof level of roughness element for various positions where LDV measurements were made

z′′

vertical distance from the wall to the roof level of the roughness element for various positions where LDV measurements were made

zo

roughness length scale

z

vertical distance from the effective origin of mean velocity profile

\(-\rho\overline{{u}'w^{\prime}}\)

Reynolds stress

χ

stream wise position at roof-level between the roughness elements

ɛ

origin correction shift

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Copyright information

© Springer 2006

Authors and Affiliations

  • Ijaz M. Khan
    • 1
  • Richard R. Simons
    • 2
  • Anthony J. Grass
    • 2
  1. 1.Department of Chemical EngineeringThe University of BirminghamEdgbastonUK
  2. 2.Civil and Environmental Engineering DepartmentUniversity College LondonLondonUK

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