Numerical simulation of wind-induced dispersion of emissions from rooftop stacks

The precise prediction of plume concentration distribution on or near buildings is very important for building engineers to design proper exhaust stacks and set proper air intakes to avoid adverse air quality impacts. The present study simulates the dispersion of emissions from stacks in the neutrally stable atmospheric boundary layer (ABL) by FLUENT 6.1, a commercial computational fluid dynamics (CFD) code. Three case studies have been conducted. The first case involves a simulation of plume dispersion from one isolated stack. The second case is concerned with a simulation of plume dispersion from a flush stack located at the roof center of a cubic building. The third case involves a simulation of plume dispersion from a short stack located on the rooftop of a rectangular building with some rooftop structures. Numerical results are compared with some empirical formulae, such as the Gaussian model and ASHRAE model, and validated with some experimental data. The effects of the momentum ratio, the stack height, and the turbulent characteristics caused by the building on the plume behavior are discussed. Some numerical parametric studies have been carried out.