Heat transport and coupling modes in Rayleigh–Bénard convection occurring between two layers with largely different viscosities
A high-resolution numerical simulation model in two-dimensional cylindrical geometry was used to discuss the heat transport and coupling modes in two-layer Rayleigh-Bénard convection with a high Rayleigh number (up to the order of 109), an infinite Prandtl number, and large viscosity contrasts (up t...
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Veröffentlicht in: | Physics of fluids (1994) 2017-09, Vol.29 (9) |
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Sprache: | eng |
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Zusammenfassung: | A high-resolution numerical simulation model in two-dimensional cylindrical geometry was
used to discuss the heat transport and coupling modes in two-layer Rayleigh-Bénard
convection with a high Rayleigh number (up to the order of 109), an infinite
Prandtl number, and large viscosity contrasts (up to 10−3) between an outer,
highly viscous layer (HVL) and an inner, low-viscosity layer (LVL). In addition to
mechanical and thermal interaction across the HVL-LVL interface, which has been
investigated by Yoshida and Hamano [“Numerical studies on the dynamics of two-layer
Rayleigh-Bénard convection with an infinite Prandtl number and large viscosity contrasts,”
Phys. Fluids 28(11), 116601 (2016)], the spatiotemporal analysis in this
study provides new insights into (1) heat transport over the entire system between the
bottom of the LVL and the top of the HVL, in particular that associated with thermal
plumes, and (2) the convection regime and coupling mode of the two layers, including the
transition mechanism between the mechanical coupling mode at relatively low viscosity
contrasts and the thermal coupling mode at higher viscosity contrasts. Although flow in
the LVL is highly time-dependent, it shares the spatially opposite/same flow pattern
synchronized to the nearly stationary upwelling and downwelling plumes in the HVL,
corresponding to the mechanical/thermal coupling mode. In the transitional regime between
the mechanical and thermal coupling modes, the LVL exhibits periodical switching between
the two phases (i.e., the mechanical and thermal coupling phases) with a stagnant period.
A detailed inspection revealed that the switching was initiated by the instability in the
uppermost boundary layer of the LVL. These results suggest that convection in the highly
viscous mantle of the Earth controls that of the extremely low-viscosity outer core in a
top-down manner under the thermal coupling mode, which may support a scenario of top-down
hemispherical dynamics proposed by the recent geochemical study. |
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ISSN: | 1070-6631 1089-7666 |
DOI: | 10.1063/1.4989592 |