Accidental releases of toxic airborne pollutants in the urban environment and the threat of urban chemical and biological warfare have become urgent concerns in recent years. For risk analysis purposes it is important to know, based on where a contaminant source is released in an urban setting, the extent of the downwind area that will be affected and may need to be evacuated.

This poster briefly outlines a series of reduced-scale experiments that were conducted in a water flume in order to evaluate the importance of several factors on flow and dispersion in regular obstacle arrays. Flow visualization studies and measurements of mean velocity and turbulence profiles, as well as mean concentration measurements, were made in several obstacle arrays with various packing densities, obstacle type, array configuration (square vs. staggered), upstream conditions, and release location. It was found that upstream conditions and obstacle type can significantly affect the dispersion, while other factors such as packing density and array geometry do not have as much influence in arrays of simple geometry.

This study was sponsored as part of the CHARM (Coordinated Hazardous Atmospheric Release Modelling) program at George Mason University. The information gathered is currently being provided for computer simulations of flow and dispersion in obstacle arrays and a comprehensive velocity data set has already been used to test computational fluid dynamics (CFD) codes for urban flow fields.