Article

Sur la convection de Rayleigh-Bénard turbulente: Caractérisation dynamique par PIV

Ecole Nationale Supérieure d'Ingénieurs du Mans, 72085, Le Mans cedex 9, France; LET, UMR 6608 CNRS, Ecole Nationale Supérieure de Mécanique et d'Aérotechnique, Poitiers, France
01/2006; 9:4-341.

ABSTRACT le 22 Novembre 2006 -accepté le 20 Décembre 2006) Résumé -Ce travail expérimental s'intéresse à la caractérisation dynamique par PIV de la convection de Rayleigh-Bénard turbulente dans une cavité parallélépipédique, remplie d'air et de rapport de forme (L H) égal à 4. L'analyse des résultats obtenus, pour des valeurs du nombre de Rayleigh H Ra (basé sur la hauteur H de la cavité) variant entre 10 8 et 4,23×10 8 , montre surtout que les fluctuations de vitesse sont importantes et au moins du même ordre de grandeur que les vitesses moyennes. Par ailleurs, même à des valeurs très éloignées de la valeur critique du nombre de Rayleigh (facteur 10 3), une structuration très cohérente et organisée autour de trois rouleaux contra-rotatifs est particulièrement bien visible sur les valeurs moyennes. D'autre part, une investigation dans la troisième direction a permis de quantifier l'énergie cinétique turbulente 3D et des effets tridimensionnels secondaires qui n'avaient pas été quantifiés auparavant. Enfin, l'effet d'une infime perturbation sur le sens de rotation des rouleaux de Rayleigh-Bénard a été également examiné. Abstract -This experimental work is focused on the dynamic characterization by PIV of the turbulent Rayleigh-Bénard convection in an air filled parallelepipedal cavity of aspect ratio (L H) equal to 4. The analysis of the results obtained, for values of the Rayleigh number H Ra (based on the height H of the cavity) variable between 10 8 and 4.23×10 8 , shows especially that the fluctuations of velocity are important and at least of the same order of magnitude as the mean velocities. In addition, even with values very far away from the critical value of Rayleigh number (factor 10 3), a very coherent structure, organized around three contra-rotating rollers, is particularly quite visible on the mean values. In addition, an investigation in the third direction made it possible to quantify the turbulent kinetic energy 3D and the secondary three-dimensional effects which had not been quantified before. Lastly, the effect of a negligible disturbance on the direction of rotation of the Rayleigh-Bénard rollers was also examined. Mots clés: Convection naturelle de Rayleigh-Bénard -Cavité parallélépipédique -Instabilités -Instationnarités -Chaos -Turbulence -Nombre de Rayleigh critique -Etude expérimentale -PIV-2D.

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