INSTABILITIES IN VARIABLE-DENSITY FLOWS - STABILITY AND SENSITIVITY ANALYSES FOR HOMOGENEOUS AND HETEROGENEOUS MEDIA

This study improves our understanding of instability phenomena that ma y accompany the transport of dense plumes of dissolved contaminants. O ne major objective is to test how well analytic stability theory devel oped by List [1965] applies to the transport of dense plumes in both h omogeneous and heterogeneous media. The data to test the prediction co me from numerical model experiments in which instability growth is gen erated by perturbing the interface between fluids of differing density . Stability criteria, as determined by the transverse Rayleigh number, the ratio of transverse to longitudinal Rayleigh numbers, and the non dimensional wave number compare very well with results observed in the numerical experiments for isotropic media. Comparisons involving corr elated random fields were much less successful because plume stability is determined on a local basis as a function of the changing permeabi lity field. Instabilities tend to dissipate in zones of lower permeabi lity and grow in zones of higher permeability. Another objective of th e study is to determine the factors that contribute to stability and i nstability in homogeneous aad heterogeneous systems. Sensitivity analy ses using a transport model within the framework of List's stability t heory show that stability is promoted by low medium permeability, smal l density differences; and significant dispersion. In heterogeneous me dia, stability is promoted by increased correlation length scales and increased log permeability variance. Furthermore, the simulations illu strate the intimate relationship that exists between instability growt h and decay and the heterogeneous nature df the permeability field. Th us stability criteria that do not incorporate characteristics of the p ermeability field will not be suitable for natural or field-scale poro us media.