1University of Regina, Regina, Saskatchewan, Canada
2University of Western Ontario, London, Ontario, Canada
Issues of concern in environmental flows, such as flammability, malodor and toxicity, generally require a specification of the probability density function of contaminant concentration. It would appear that the overall shape of the PDF can be reconstructed from some few, low-order moments. A simple model, which describes the distributed moments of the PDF in terms of two functions of downstream distance in a steady flow, has received widespread experimental verification. Calculations of the second moment, taking advantage of this model and using a physically plausible and greatly simplified closure scheme, has provided reasonable comparison with the limited amount of available experimental data. Experimental evidence from plume experiments in grid turbulence suggest that one of the two functions in the simple model depends slightly on moment order and this slight dependence is significant in reconstructiong the PDF. In this paper the third moment is calculated and compared with the measured wind-tunnel plume results.