2007/07/31 by K. Sugiyama, Kazuyasu Sugiyama, Enrico Calzavarini +5 · 56 citations
Chemical Engineering · Computer Science · Engineering · Physics and Astronomy · #Convection #Flow (mathematics) #Natural convection #Nonlinear Dynamics and Pattern Formation #Nusselt number #Phase Equilibria and Thermodynamics #Rayleigh number #Rayleigh scattering #Rheology and Fluid Dynamics Studies #Thermal #Viscosity #physics.flu-dyn
paper · pdf · doi:10.1209/0295-5075/80/34002
published in Europhysics Letters (EPL) 80(3), 34002 (Institute of Physics) · 6 pages, 7 figures
openalex publication_date 2007/09/28 · arxiv created 2007/10/02 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We numerically analyze Non–Oberbeck-Boussinesq (NOB) effects in two-dimensional Rayleigh-Bénard flow in glycerol, which shows a dramatic change in the viscosity with temperature. The results are presented both as functions of the Rayleigh number Ra up to 10 8 (for fixed temperature difference Δ between the top and bottom plates) and as functions of Δ ("non-Oberbeck-Boussinesqness" or "NOBness") up to 50 K (for fixed Ra ). For this large NOBness the center temperature T c is more than 5 K larger than the arithmetic mean temperature T m between top and bottom plate and only weakly depends on Ra . To physically account for the NOB deviations of the Nusselt numbers from its Oberbeck-Boussinesq values, we apply the decomposition of Nu NOB / Nu OB into the product of two effects, namely first the change in the sum of the top and bottom thermal BL thicknesses, and second the shift of the center temperature T c as compared to T m . While for water the origin of the Nu deviation is totally dominated by the second effect (cf. Ahlers G. et al ., J. Fluid Mech. , 569 (2006) 409) for glycerol the first effect is dominating, in spite of the large increase of T c as compared to T m .