Numerical study of subcritical Rayleigh–Bénard convection rolls in strongly shear-thinning Carreau fluids
| Autor: | Emmanuel Plaut, Antoine Briard, Mathieu Jenny |
|---|---|
| Přispěvatelé: | Laboratoire Énergies et Mécanique Théorique et Appliquée (LEMTA ), Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Institut Jean le Rond d'Alembert (DALEMBERT), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS) |
| Rok vydání: | 2015 |
| Předmět: |
Convection
Shear thinning Materials science Applied Mathematics Mechanical Engineering General Chemical Engineering Thermodynamics Rayleigh number Mechanics Condensed Matter Physics Nusselt number Non-Newtonian fluid Condensed Matter::Soft Condensed Matter Physics::Fluid Dynamics [SPI]Engineering Sciences [physics] Viscosity Newtonian fluid General Materials Science Rayleigh–Bénard convection |
| Zdroj: | Journal of Non-Newtonian Fluid Mechanics Journal of Non-Newtonian Fluid Mechanics, 2015, 219, pp.19-34. ⟨10.1016/j.jnnfm.2015.03.002⟩ Journal of Non-Newtonian Fluid Mechanics, Elsevier, 2015, 219, pp.19-34. ⟨10.1016/j.jnnfm.2015.03.002⟩ |
| ISSN: | 0377-0257 |
| DOI: | 10.1016/j.jnnfm.2015.03.002 |
| Popis: | International audience; Abstract The Rayleigh–Bénard thermoconvection of Newtonian fluids has been extensively studied. The transition from the conductive, static state to thermoconvection flows corresponds in this case to a supercritical bifurcation. In shear-thinning fluids, on the contrary, recent weakly nonlinear studies have shown that the transition may become subcritical. Using a custom numerical code developed with Freefem++ to compute bidimensional, fully nonlinear roll solutions in Carreau fluids, for a large range of rheological parameters, and more particularly for strongly shear-thinning fluids, approaching power-law fluids, we confirm this result. A simple expression of the value of the Rayleigh number at which subcritical convection rolls appear is proposed. This law suggests to reconsider the choice of the reference viscosity for shear-thinning fluids. Indeed, when the shear-thinning effects increase, the critical Rayleigh number increases or decreases depending on the choice of the reference viscosity. The ‘neutral’ or ‘effective’ viscosity, which gives a constant value of the Rayleigh number at the onset of subcritical convection rolls, is close to the bulk average viscosity. In addition, a correlation is proposed to estimate the Nusselt number of subcritical rolls. |
| Databáze: | OpenAIRE |
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