The Dispersion of Slightly Dense Contaminants
Existing theoretical models of dense gas dispersion vary greatly in degree of complexity from simple layer averaged (integral equation) approaches to the use of complex turbulence models, the latter usually employing some form of eddy diffusivity closure approximation. However there remain several aspects of the problem which are poorly understood, and may therefore not be adequately modelled. For example the question of how “entrainment” (however it may be defined) or eddy diffusivities can be related to stability. Evidently a careful look at the dynamics of dense contaminant dispersion is called for. Our research, which we review here, is an attempt to study in some detail one aspect of the dispersion dynamics in particular, namely the effects of stable stratification, which may be set up in dispersing plumes or clouds, on the turbulence. We shall describe three approaches to the problem. Firstly, the use of Rapid Distortion Theory to investigate structural changes to homogeneous turbulence with varying degrees of stable stratification in the presence of a mean velocity gradient. Secondly, a Lagrangian dynamical model of fluid element motions (as previously employed in studies of mixing in homogeneous stratified turbulence) is introduced in the context of the present problem. Finally, an experimental program is described.
KeywordsInternal Wave Fluid Element Stable Stratification Inertial Subrange Bulk Richardson Number
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