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Thermal Sciences 2004. Proceedings of the ASME - ZSIS International Thermal Science Seminar II
June, 13-16, 2004, Bled, Slovenia

DOI: 10.1615/ICHMT.2004.IntThermSciSemin


ISBN Print: 978-9-61913-930-1

Double-diffusive Finger Convection near Neutral Buoyancy

pages 307-313
DOI: 10.1615/ICHMT.2004.IntThermSciSemin.330
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RÉSUMÉ

This is a numerical study of double-diffusive finger convection at a density interface in the thermo-haline system for which the ratio of salt to heat diffusivity is 1/100. The initial configuration of the system is such that a uniformly salty and warm fluid lies above a reservoir of cold and fresh fluid. Specifically, the issue concerning the value of the heat-to-salt flux ratio is addressed. We systematically decreased the solute concentration and thus the Salinity Rayleigh number while keeping the density stability ratio, Rρ, fixed to 1.001 (line corresponding to Rρ = 1 is neutral buoyancy line). Four cases were calculated for the thermal Rayleigh numbers, RaT, of 106, 105, 104 and 103 all at fixed Rρ and aspect ratio. Across the 4 runs conducted, the convective motion shows considerable variation in both structure and time scale. In the range of parameters used, the ratio of the flux of density due to heat to that salt, Rf, varies from 0.82 to 0.27 as the Rayleigh number is decreased from 106 to 103 at constant Rρ. Finger system never reaches equilibrium in any of the four cases. High RaT system exhibits strong convection due to high driving force amassed in the salinity field. Fingers transport substantial amount of heat and salinity across the reservoir resulting in high Rf. Low RaT system exhibits strong diffusion of heat due to sluggish penetration of fingers into the opposite reservoir and the consequence is low Rf. Value of flux ratio reported here shows that the disagreement can be traced to the hypothesis of maximum flux and growth rate as the Rρ approaches 1.

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