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Theoretical Concepts and Wind Tunnel Model Experiments with Prismatic Building Shapes

Gas diffusion from a source near a building cannot be predicted with conventional diffusion formulas because the mean flow field near the building is distorted, and the turbulence is highly nonisotropic and non-homogeneous. However, wind tunnel model experiments have shown that recognizable concentration patterns do occur, and may be described by isopleths of a non-dimensional concentration coefficient. Typical 3-dimensional isopleth surfaces around characteristic building configurations are presented, together with a method for using the isopleths to predict gas concentrations around full-size buildings. The usefulness of the isopleths in other configurations requires an understanding of flow patterns around sharp-edged buildings. An extended theoretical section is included to show the nature of these patterns, and to give the reader not having a background in turbulent diffusion an acquaintance with its physical concepts and mathematical terminology.