An evaluation of downwash under low windspeed conditions

The primary purpose of this research effort was to examine the building effects on the ground level concentration field in the immediate vicinity of the Jersey City, New Jersey Total Energy (TE) Demonstration Plant by means of a full-scale field study. Trends exhibited by the collected data were evaluated in terms of the general diffusion parameters (i.e., emission strength, Q, windspeed, u, and concentration, x) and the data were compared to mathematical modeling procedures developed by Briggs.

In the case studied, concentrations in the cavity were found to be dependent on fractional plume entrapment which was best described as an exponential function of windspeed. This empirically developed relationship between plume entrapment and windspeed was used to alter the Briggs model to allow prediction of ground level concentrations in the cavity region north of the Central Equipment Building (CEB) at the TE Demonstration Plant.

It was also speculated, based on the data trends, that the extent of the cavity zone north of the CEB was approximately 2.5 building heights downwind.