Interfacial mixing in stratified flows

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Abstract
In this paper the phenomenon of turbulent mixing at a density interface is studied. Based on a unified view of the mixing processes, quantitative laws are sought, which would be generally valid in flows with mean motion in at least one of the layers. Re-examination of available experimental data from four types of stratified flow, supplemented by theoretical considerations, leads to the identification of four such governing laws, all of a power form, applicable in different ranges of the overall Richardson number, Ri 0. Two of these laws refer to supercritical and subcritical conditions and are considered as fundamental, being related to qualitatively different mechanisms of interfacial mixing. An intermediate law applies around the critical Ri 0 value of unity, while an asymptotic law corresponds to the limit of homogeneous flow as Ri 0 tends to zero. All the above laws are given by simple expressions in terms of the mean flow characteristics, allowing their straightforward application for the quantification of interfacial mixing in a variety of flows.