On the effect of the Prandtl number on the onset of Bénard convection

J. L. Lage, A. Bejan, J. Georgiadis

Research output: Contribution to journalArticlepeer-review


This note summarizes the results of a numerical study designed to question (i.e., refute or validate) Chao et al.'s1 and Bertin and Ozoe's2 conclusion that the critical Rayleigh number increases substantially as the Prandtl number becomes very small. The numerical method is based on the finite-difference control volume formulation and the complete equations for two-dimensional (2-D) time-dependent flow. The present results show that the lowest attainable Rayleigh number for numerically simulated convection increases as Pr decreases below 0.1. These results also extend the Prandtl number domain of the observations down to Pr=10-4 and indicate that the natural shape of a single roll in this Pr range is approximately square. The discrepancy between these observations and the constant Rac=1,707.8 of the linear stability analysis is attributed to the extrapolation method on which the numerical convection-onset Ra data1,2 were based. It is shown that the numerical results agree with the linear stability constant Rac=1,707.8 and Schlüter et al.'s9 small amplitude perturbation analysis.

Original languageEnglish (US)
Pages (from-to)184-188
Number of pages5
JournalInternational Journal of Heat and Fluid Flow
Issue number2
StatePublished - Jun 1991
Externally publishedYes


  • Bénard convection
  • critical Rayleigh number
  • Prandtl number effect

ASJC Scopus subject areas

  • Fluid Flow and Transfer Processes
  • Mechanical Engineering


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