A Simple Model of Concentration Fluctuations in Neutrally Buoyant Clouds |
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| Authors: | D M Lewis |
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| Institution: | (1) Department of Mathematics, School of Mathematics, Actuarial Science and Statistics, City University, Northampton Square, London, EC1V 0HB, U.K. |
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| Abstract: | This paper presents a new model of concentration fluctuations for neutrally buoyant gas clouds dispersing in a wind tunnel. It is derived from a series of exact results, which apply in the hypothetical case when there is no molecular diffusion, coupled with a probability density function model previously used to describe steady releases of contaminant. A simple self-similar relationship between the evolution of the concentration intensity and mean is established. As a first step the time independent variant of the model, applicable to a continuous plume, is tested against some previously published experimental data for steady wind-tunnel releases. Comparisons of experimental results and model predictions at different downwind positions, heights and source geometry are presented. Then, the results for the time dependent model, applicable to instantaneous releases, are discussed. The experimental evidence presented here supports the self-similar relationship established earlier. The implications for modelling higher moments of concentration and the fixed point probability density function are investigated. |
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| Keywords: | Concentration fluctuations Plumes Probability density function |
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