High-Azimuthal Number Axisymmetry-Breaking Convective Instabilities in Axisymmetric Freezing of Ice
by
A.Yu. Gelfgat
Technion - Israel Institute of Technology
Coauthors: P.Z. Bar-Yoseph, A. Solan, T.A. Kowalewski

We consider natural convection of water without and with phase change in a vertical cylinder cooled from the top. The top wall made of metal is assumed to be isothermal. The cavity is immersed in an external water bath kept at the higher temperature. The non-adiabatic side and bottom walls are made of glass. They allow a heat flux from the external bath. The steady flow configuration consists of a single jet of cold liquid flowing downwards along the cylinder axis and a reverse flow along side wall. In the experiments performed it was found that despite the cylindrical symmetry, a star like structure may apear underneath the lid. For the pure convection the temperature field visualized for the horizontal plane close to the top shows 16-18characteristic spikes running radially from the lid centre. If ice is growing from the top, star-like grooves can be seen at its surface.

The present work is devoted to numerical analysis of this axisymmetry-breaking problem. A combined numerical approach based on the finite volume and global Galerkin methods was developed to describe the experimentally observed instabilities. It was shown that the axisymmetry-breaking instability can set in due to a set of three-dimensional perturbations with a relatively high azimuthal wavenumber k (k>=8). It is shown that the instability is caused by the Rayleigh-Benard mechanism and number of the azimuthal structures is defined by the depth of the temperature boundary layer attached to the cold cover of the container.

Date received: March 24, 1999

Copyright © 1999 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caco-23.