Example Application of CFD Simulations for Short-Range Atmospheric Dispersion over the Open Fields ofProject Prairie Grass

摘要

Computational Fluid Dynamics (CFD) techniques are increasingly being applied to airquality modeling of short-range dispersion, especially the flow and dispersion aroundbuildings and other geometrically complex structures. The proper application andaccuracy of such CFD techniques needs to be assessed. The first step in such anassessment is to examine the ability to simulate atmospheric-like boundary layer flow inabsence of buildings and plume dispersion over open fields.Case studies based on the Project Prairie Grass field program were used to develop andevaluate CFD simulation of plume dispersion over an open field. A commercial CFDcode, FLUENT has been used in this study. For a given ground roughness height andfriction velocity, a 2D CFD simulation was first developed to generate an atmospherelikeboundary layer. The simulated mean velocity profile matched field measurements.This atmosphere-like boundary layer was then applied as a boundary condition in the 3DCFD simulation of each dispersion case study. The simulated profiles of mean velocity,turbulent kinetic energy and turbulent dissipation rate were maintained within thedownwind domain for the CFD simulation.The steady-state CFD simulation was used to model the time-averaged plume byapplying wind direction temporal data to account for variations in wind direction. Resultsfor field runs characterized by near thermally neutral stability conditions were evaluatedthoroughly in comparison with the field-measured plume from point source release of atracer gas. The CFD model performed well as demonstrated by the reported performancemetrics, based on comparisons with not only the measured centerline concentrations butalso the full lateral and vertical profiles.