Using CFD and mathematical optimization to investigate air pollution due to stacks

This paper describes the use of Computational Fluid Dynamics (CFD) and mathematical optimization techniques to minimize pollution due to industrial sources like stacks. The optimum placement of a new pollutant source (e.g. a new power plant with its stacks) depends on many parameters. These include stack height, stack distance from surrounding populated areas, barriers, local meteorological conditions, etc. As an experimental approach is both time-consuming and costly, use is made of numerical techniques. Using CFD without optimization on a trial-and-error basis, however, does not guarantee optimal solutions. A better approach, that until recently has been too expensive, is to combine CFD with mathematical optimization techniques, thereby incorporating the inßuence of the variables automatically. The current study investigates a simpliÞed two-dimensional case of the minimisation of pollutant stack distance to a street canyon with or without barrier for a given maximum ground-level concentration of pollutants in a street canyon. Two to Þve design variables are considered. The CFD simulation uses the STAR-CD code with RNG kÐe turbulence model. Making use of initial Þeld restarts drastically reduces CFD solution time. The optimization is carried out by means of SnymanÕs DYNAMIC-Q method, which is speciÞcally designed to handle constrained problems where the objective or constraint functions are expensive to evaluate. The paper illustrates how the parameters considered inßuence the stack placement and how these techniques can be used by the environmental engineer to perform impact studies of new pollutant sources. Copyright