Laboratory-numerical models of rapidly rotating convection in planetary cores

Cheng, Jonathan; Stellmach, Stephan; Ribeiro, Adolfo; Grannan, A. M.; King, E. M.; Aurnou, J. M.

doi:10.1093/gji/ggu480

Cited by 108 publications

(238 citation statements)

References 95 publications

(146 reference statements)

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“…This further implies that knowledge of RBC convective scaling behavior is necessary to understand the behaviors of the MC and RC systems. A similar result exists for rotating convective heat transfer in moderate P r fluids, such as water [13]. Thus, the import of understanding RBC as the essential basis for more complicated convection systems holds broadly.…”

Section: Compilation Of Heat Transfer Measurementssupporting

confidence: 54%

“…In moderate Prandtl number convection (P r 1), studies often find the heat transfer is controlled by boundary layer physics resulting in α values between 2/7 and 1/3 [13,16,36,41,42]. The α 1/3 law is predicted to arise under the following when vigorous convective mixing creates a nearly isothermal fluid bulk (P e c 1).…”

Section: Essential Theorymentioning

confidence: 99%

“…This ordering implies that the characteristic length and time scales of the magnetic fields will tend to exceed those of the thermal structures, which will again exceed the characteristic scales of the underlying flow fields, e.g., [10]). Indeed, energy is expected to be injected at small-scales via buoyancy-driven convection processes in natural dynamo systems ( [11][12][13]; Figure 1c), and is likely to then cascade upscale to larger scales [14], where we hypothesize that dynamo action likely occurs more efficiently [15] and where large-scale magnetic structures are likely formed. Thus, a detailed understanding of turbulent convection processes in metals is essential for the development of broadly accurate models of geophysical and astrophysical dynamo processes.…”

Section: Introductionmentioning

confidence: 99%

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Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals

Ribeiro¹,

Fabre²,

Guermond³

et al. 2015

Metals

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Planets and stars are often capable of generating their own magnetic fields. This occurs through dynamo processes occurring via turbulent convective stirring of their respective molten metal-rich cores and plasma-based convection zones. Present-day numerical models of planetary and stellar dynamo action are not carried out using fluids properties that mimic the essential properties of liquid metals and plasmas (e.g., using fluids with thermal Prandtl numbers P r < 1 and magnetic Prandtl numbers P m 1). Metal dynamo simulations should become possible, though, within the next decade. In order then to understand the turbulent convection phenomena occurring in geophysical or astrophysical fluids and next-generation numerical models thereof, we present here canonical, end-member examples of thermally-driven convection in liquid gallium, first with no magnetic field or rotation present, then with the inclusion of a background magnetic field and then in a rotating system (without an imposed magnetic field). In doing so, we demonstrate the essential behaviors of convecting liquid metals that are necessary for building, as well as benchmarking, accurate, robust models of magnetohydrodynamic processes in P m P r < 1 geophysical and astrophysical systems. Our study results also show strong agreement between laboratory and numerical experiments, demonstrating that high resolution numerical simulations can be made capable of modeling the liquid metal convective turbulence needed in accurate next-generation dynamo models.

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Section: Compilation Of Heat Transfer Measurementssupporting

confidence: 54%

Section: Essential Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals

Ribeiro¹,

Fabre²,

Guermond³

et al. 2015

Metals

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“…Beyond this transition, a much slower growth of Nu withR is observed. Unfortunately, laboratory experiments have yet to reach small enoughR at low E to investigate this regime change [2][3][4]. The experimental data presented here are no exception (cf.…”

Section: Prl 113 254501 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 83%

“…While experiments easily reach high levels of turbulence, they struggle to ensure that Coriolis forces remain dominant in the force balance [2][3][4]. Numerical simulations suffer from the enormous range of spatial and temporal scales that need to be resolved.…”

mentioning

confidence: 99%

Approaching the Asymptotic Regime of Rapidly Rotating Convection: Boundary Layers versus Interior Dynamics

et al. 2014

Self Cite

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Rapidly rotating Rayleigh-Bénard convection is studied by combining results from direct numerical simulations (DNS), laboratory experiments and asymptotic modeling. The asymptotic theory is shown to provide a good description of the bulk dynamics at low, but finite Rossby number. However, large deviations from the asymptotically predicted heat transfer scaling are found, with laboratory experiments and DNS consistently yielding much larger Nusselt numbers than expected. These deviations are traced down to dynamically active Ekman boundary layers, which are shown to play an integral part in controlling heat transfer even for Ekman numbers as small as 10 −7 . By adding an analytical parameterization of the Ekman transport to simulations using stress-free boundary conditions, we demonstrate that the heat transfer jumps from values broadly compatible with the asymptotic theory to states of strongly increased heat transfer, in good quantitative agreement with no-slip DNS and compatible with the experimental data. Finally, similarly to non-rotating convection, we find no single scaling behavior, but instead that multiple well-defined dynamical regimes exist in rapidly-rotating convection systems.

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Testing the dynamic coupling of the core‐mantle and inner core boundaries

Driscoll

2015

JGR Solid Earth

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The proposal that the seismically observed hemispherical asymmetry of Earth's inner core is controlled by the heat flux structure imposed on the outer core by the lower mantle is tested with numerical dynamo models driven by mixed thermochemical convection. We find that models driven by a single core-mantle boundary (CMB) spherical harmonic of degree and mode 2, the dominant mode in lower mantle seismic shear velocity tomography, produce a similar structure at the inner core boundary (ICB) shifted 30 ∘ westward. The sensitivity of the ICB to the CMB is further tested by increasing the CMB heterogeneity amplitude. In addition, two seismic tomographic models are tested: first with CMB resolution up to degree and order 4, and second with resolution up to degree and order 8. We find time-averaged ICB heat flux in these cases to be similar at large scale, with small-scale differences due to higher CMB harmonics (above degree 4). The tomographic models produce "Earth-like" magnetic fields, while similar models with twice the CMB heat flow amplitudes produce less Earth-like fields, implying that increasing CMB heterogeneity forces the model out of an Earth-like regime. The dynamic ICB heat fluxes are compared to the proposed translation mode of the inner core to test whether the CMB controls inner core growth and structure. This test indicates that, although CMB tomography is unlikely to be driving inner core translation, the ICB heat flux response is weak enough to not interfere with the most unstable translation mode, if it is occurring.

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Laboratory-numerical models of rapidly rotating convection in planetary cores

Cited by 108 publications

References 95 publications

Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals

Canonical Models of Geophysical and Astrophysical Flows: Turbulent Convection Experiments in Liquid Metals

Approaching the Asymptotic Regime of Rapidly Rotating Convection: Boundary Layers versus Interior Dynamics

Testing the dynamic coupling of the core‐mantle and inner core boundaries

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