Model for the Mean Wind and Turbulence Within and Above an Urban Canopy Part I: Theory and Numerical Implementation


  1. Yee, E.
  2. Wilson, J.D.
Corporate Authors
Defence Research Establishment Suffield, Ralston ALTA (CAN);Alberta Univ, Edmonton ALTA (CAN)
In this paper, a three-dimensional (3-D) model for the disturbed mean wind flow and turbulence in an urban canopy composed of an extensive array of obstacles is developed. The context of this work is the provision of a computational tool for the rapid diagnosis of transport and dispersion of toxic contaminants (e.g., chemical and biological warfare agents) over a relatively homogeneous urban area. A variant of the K proportional to Lambda k 1/2 first-order closure (where K is the eddy viscosity, k is the turbulence kinetic energy (TKE) calculated from its simplified governing differential equation and Lambda is an algebraically specified turbulence length scale) is studied and used to close the mean momentum equations and the TKE transport equation. The turbulence length scale Lambda has been designed to reproduce the known characteristics of the length scale in a canopy; namely, recognition of the limitation imposed on eddy size by proximity to the ground, the constant length scale across much of the upper canopy that is intimately connected to the canopy shear length scale (vorticity thickness) and the displacement of the equilibrium flow structure above the canopy due to the presence of the canopy. A method for the partitioning of the TKE into its component normal Reynolds stresses is obtained. TRUNCATED
Chemical warfare agents;Dispersion;Air flow;Air pollution;Outdoor environments;Urban Flow Modelling;Turbulence Modelling in Urban Canopies;CFD (Computational Fluid Dynamics);Numerical simulation
Report Number
DRES-TR-2000-020 — Technical Report (Final Report)
Date of publication
01 Jun 2000
Number of Pages
Hardcopy;Document Image stored on Optical Disk

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