Dispersion models require as input various geometrical parameters to calculate the flow field and dispersion characteristics in the urban environment. As a result of recent advances in digital photogrammetry and remote sensing, databases of the actual 3-D geometry of city centre areas are now increasingly available. In this work we outline a procedure to reduce this large amount of data to a structured input for urban pollution dispersion models, i.e. to extract the important flow and dispersion parameters from the urban databases. Based on a review of the scientific literature, we have identified a number of parameters relevant to the modelling of pollution dispersion and atmospheric flows in urban areas. These parameters are: the plan and frontal area densities, the plan and frontal area density as a function of height, the distribution of heights, their standard deviation, the aerodynamic roughness length and the sky view factor.These parameters are obtained by analysing urban Digital Elevation Models (DEMs) which are regularly spaced grids of elevation values. Examples of the parameters calculated from high-resolution databases (with pixel size of about 1 m) for three European (London, Toulouse and Berlin) and two North American (Salt Lake City and Los Angeles) cities are presented and discussed. The calculated aerodynamic roughness length was smaller for the European cities than for the North American ones. A multiplicative correction factor κ to the aerodynamic roughness length is proposed to include the effect of the variability of the building heights.

The effect of roughness obstacles on flow and dispersion in urban and industrial areas

Analysis of 3-D Urban Databases with Respect to Pollution Dispersion for a Number of European and American Cities

This paper presents the design, construction, and preliminary characterization of the atmospheric boundary layer wind tunnel facility for environmental flow studies at Assiut University. The wind tunnel is a low speed-open loop and driven by a 2 kW, 4 m3/s, axial flow fan. The main core of the designed wind tunnel is the long section (3.5 m length) devoted to produce and simulate the atmospheric boundary layer (ABL) for various environmental flow studies. The simulation of the ABL can be achieved for different earth surface conditions by inserting of well designed spires arrangement and arrays of roughness elements. The design procedure and the construction steps for the main components of the wind tunnel are summarized. The experimental results of the mean axial velocity profiles for different fan speeds are presented and discussed for the preliminary characterization of the wind tunnel. The results show that the present wind tunnel is capable to maintain long run steady flow characteristics and reproducible flow patterns. The use of designed triangular spires and cube roughness elements is successful in simulating real ABL of thickness up to 600 m corresponding to urban area.

http://www.aun.edu.eg/journal_files/28_J_3220.pdf

The effect of roughness obstacles on flow and dispersion in urban and industrial areas

Citations

Analysis of 3-D Urban Databases with Respect to Pollution Dispersion for a Number of European and American Cities

Design and construction of a wind tunnel for environmental flow studies

Related Papers (5)

The effect of urban obstacles on the flow distribution at pedestrian area

Spatially-varying surface roughness and ground-level air quality in an operational dispersion model.

Flow and pollutant dispersion in urban areas

Extension of an operational short-range dispersion model for applications in an urban environment

Analysis of 3-D Urban Databases with Respect to Pollution Dispersion for a Number of European and American Cities