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International Heat Transfer Conference 11

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

THERMAL INFLUENCE ON THE BEHAVIOUR OF VERTICAL PLANE JETS AT LOW REYNOLDS NUMBERS: STABILITY ANALYSIS AND DIRECT NUMERICAL SIMULATION

Franqois Penot
LET, CNRS, UMR 6608, ENSMA, 1 Avenue Clément Ader, 86961 Futuroscope, France

E. Alvinerie
Laboratoire d'Etudes Thermiques UMR CNRS 6608 ENSMA BP 109 - Chasseneuil du Poitou 86960 Futuroscope cedex France

DOI: 10.1615/IHTC11.2300
pages 485-490

Résumé

This paper is concerned with the loss of stability of jets at moderate Reynolds numbers, flowing at a temperature different from the ambient one. The influence of the buoyancy forces is analysed with the help of linear stability analysis, solving the Orr-Sommerfeld equations and with computational direct simulation. The characteristic Reynolds number varies in the range 0<Re<104, and the Froude number in the range 3 < Fr < ∞.
The linear theory indicates lower critical Reynolds numbers in the case of mixed convection than in the case of forced convection. This was evident in the case of opposing mixed convection, but it was a surprising result in the case of aiding mixed convection.
The direct numerical simulation agrees with the linear theory and it is shown that the amplification of the perturbations depends on the shear induced by the mean velocity profile of the jet. The aiding mixed convection leads to smaller critical values but with lower amplification rates of perturbation, than in the case of isothermal jets.

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