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Contribution to the theory of cellular thermal convection

Published online by Cambridge University Press:  28 March 2006

Enok Palm  and
Henry Øiann
Enok Palm
Affiliation:
Institute of Mechanics, The Technical University of Norway, Trondheim Now at Institute of Mechanics, University of Oslo.
Henry Øiann
Affiliation:
Institute of Mechanics, The Technical University of Norway, Trondheim
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Abstract

In a previous paper on cellular thermal convection (Palm 1960) the importance of the effect caused by temperature variation of kinematic viscosity was pointed out. It was demonstrated that this effect would, owing to non-linear interactions, lead to a tendency towards hexagonal cells. For mathematical simplicity, only the interaction of two wave-components was taken into account.

Segel & Stuart (1962), working with the same equations, have examined the stability of the various equilibrium solutions. They arrive at the important conclusion that a necessary condition for the solution corresponding to hexagons to be stable is that the variation of viscosity with temperature be sufficiently great.

In the present paper the problem is discussed from a somewhat more general point of view. First it is shown that, when the variation of viscosity with temperature is sufficiently great, the solution corresponding to hexagons is the only stable one if only two wave-components are taken into account. To examine if this result is also true when the motion consists of an arbitrary number of wave-components, the case of three wave-components is studied. It turns out that in this case also the only possible mode is the pattern consisting of hexagons. The validity of this result is easily extended to a more general class of wave-components. It is shown that the solution corresponding to hexagons is stable for all small disturbances which can possibly occur. To prove this it is necessary to take into account non-linear disturbance theory.

A reasonable conclusion from the paper by Segel & Stuart and the present paper is that a hexagonal pattern is observed only when a condition of the form (6.9) is fulfilled. Experiments concerning this problem are, however, lacking.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 19 , Issue 3 , July 1964 , pp. 353 - 365
Copyright
© 1964 Cambridge University Press

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References

Chandrasekhar, C. 1961 Hydrodynamic and Hydromagnetic Stability. Oxford: Clarendon Press.
Gantmacher, F. R. 1959 Applications for the Theory of Matrices, English edn, trans. by J. L. Brenner, D. W. Bushaw & S. Evanusa. New York: Interscience.
La Salla, J. & Lefschetz, S. 1961 Stability by Liapunov's Direct Method. New York: Academic Press.
Palm, E. 1960 J. Fluid Mech. 8, 183.
Segel, L. A. & Stuart, J. T. 1962 J. Fluid Mech. 13, 289.