密度成層流の界面安定性に対するRichardson数及びReynolds数の影響

概要

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For the design of the functional systems such as smoke control of marine fire and purging of gases in a tank, it is often required to solve the problem of two-layer horizontal flows with different densities. The efficiency of the gas control in an enclosed space may vary seriously with the development of the mixture of the flows. An extensive knowledge on stability of such stratified flow, therefore, is needed for a successful design. In this paper, the instability of a stratified shear layer is investigated both experimentally and numerically. The experiment is carried out in a small tank containing two layers of fluid, in which the upper fluid (fresh water) is flowing over a steady heavier lower fluid (salt water). The flow velocity is otained by a method of digital image processing of visualized flow patterns. In the numerical simulation, the time-dependent, incompressible two-dimensional Navier-Stokes equations under the Boussinesq approximation are calculated using the SIMPLE procedure. The development of the Kelvin-Helmholtz instability and mixing of the stratified shear layers is simulated characteristically. The unstable region of the stratified flow, which is governed by Richardson number and Reynolds number, is presented from the experimental and numerical results.
1999-03-29