Wind tunnel investigation of the effects of a rectangular-shaped building on dispersion of effluents from short adjacent stacks

Abstract In a wind tunnel study, the influence of the highly turbulent region found in the lee of a model building upon plumes emitted from short stacks was examined through smoke visualization and tracer gas concentration mappings. A thick, simulated atmospheric boundary layer was used to provide background dispersion. A rectangular-shaped building with its length equal to twice its height and width was oriented with the long side perpendicular to the approaching wind. The stack was placed midway along the lee side of the building. In all phases of the study, each smoke or tracer release from the stack was repeated with the building removed. This allowed for a simple demonstration of the building wake effects. A simple mathematical model was developed that provided good estimates of concentrations in the building wake. The building influence was found to be reduced with increases in the effective source height. Application of the “2.5 times rule”, i.e. an effective source height at 2.5 times the height of the building, resulted in maximum ground-level concentration in the wake being approximately 20 per cent higher than found in the absence of the building. A stack 1.5 times the height of the building resulted in maximum ground-level concentrations in the wake being 250 per cent higher, a far more significant effect.