Thermoconvective instabilities in a vertical cylinder of water with maximum density effects part 1. Experiments

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Abstract
Thermoconvective instabilities were investigated in cylindrical water layers under a 0-4° C vertical temperature gradient. For aspect ratios (height/diameter) ranging from 0.3 to 5.7. angular flow patterns were deduced from thermocouple measurements. The first two diametrically antisymmetrical modes (n=l,2) were detected in the steady and unsteady regime. Slow oscillatory motions with a characteristic time of severals hours were found for aspect ratios (height/diameter) larger than 2. The Fourier analysis of the angular temperature distribution at regular time intervals yields the result that the vertical nodal planes rotate around the cylinder axis in the oscillatory regime. A physical mechanism is suggested to explain the occurrence of such oscillatory instability.