Experimental Measurements of Expected Mass Fraction in a Contaminant Plume |
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| Authors: | Partha Sarathi Roi Gurka Paul J Sullivan Gregory A Kopp |
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| Institution: | (1) Swiss Federal Institute of Technology Lausanne (EPFL), CH-1015, Lausanne, Switzerland; |
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| Abstract: | The sudden release of a quantity of gas into the atmospheric boundary layer produces a contaminant cloud. The expected mass
fraction function provides a relatively simple measure of the contaminant concentration values found within the cloud and
represents the ensemble-averaged fraction of the conserved release mass found at the different contaminant concentration intervals
as the cloud evolves. The plume generated by a line source in grid turbulence is used to investigate the expected mass fraction
function as it applies to scalar concentration values found on a typical line normal to the plume axis. Simultaneous particle
image velocimetry and planar laser induced fluorescence are used to measure velocity and concentration fields, respectively.
The measured expected mass fraction functions are observed to be approximately self-similar when concentration values are
normalized by the centreline mean concentration. The moments of the expected mass fraction function are observed to be simply
related to the centreline moments of the probability density function of scalar concentration. Arguments based on a source
fluid, non-source fluid decomposition of the scalar probability density function are used to explain these observations. The
results are compared with the theoretical and experimental results established for a line source of scalar in grid turbulence. |
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