Experimental study of global-scale turbulence in a librating ellipsoid

Grannan, A. M.; Bars, Michaël Le; Cébron, David; Aurnou, J. M.

doi:10.1063/1.4903003

Cited by 24 publications

(80 citation statements)

References 63 publications

(91 reference statements)

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“…As shown here, the fundamental quantity to be considered is, therefore, the ratio between geostrophic flows and 3D modes, which depends on the specifics of the considered system and has been mostly neglected when comparing different rotating turbulence configurations. In previous experiments and simulations in spherical or ellipsoidal geometries, the geostrophic modes resulting from the nonlinear interactions of inertial waves manifest themselves as zonal flows, i.e., mean steady axisymmetric flows pervading the fluid interior [16,17,[51][52][53] (see [54], however). Their amplitudes tend to be proportional to β 2 E −α , with α ranging from 0 to 2 [52,55,56], depending on the excitation frequency.…”

Section: -2mentioning

confidence: 99%

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Inertial Wave Turbulence Driven by Elliptical Instability

et al. 2017

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The combination of elliptical deformation of streamlines and vorticity can lead to the destabilization of any rotating flow via the elliptical instability. Such a mechanism has been invoked as a possible source of turbulence in planetary cores subject to tidal deformations. The saturation of the elliptical instability has been shown to generate turbulence composed of nonlinearly interacting waves and strong columnar vortices with varying respective amplitudes, depending on the control parameters and geometry. In this Letter, we present a suite of numerical simulations to investigate the saturation and the transition from vortex-dominated to wave-dominated regimes. This is achieved by simulating the growth and saturation of the elliptical instability in an idealized triply periodic domain, adding a frictional damping to the geostrophic component only, to mimic its interaction with boundaries. We reproduce several experimental observations within one idealized local model and complement them by reaching more extreme flow parameters. In particular, a wave-dominated regime that exhibits many signatures of inertial wave turbulence is characterized for the first time. This regime is expected in planetary interiors.

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Section: -2mentioning

confidence: 99%

“…The saturation of the instability can lead to either sustained flows [15][16][17] or cyclic behaviors between laminar and turbulent states [12,[18][19][20], reminiscent of the "resonant collapse" of inertial waves observed by McEwan [21]. The presence or absence of geostrophic modes appears to be important, but the diversity remains to be explained in detail.…”

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confidence: 99%

Inertial Wave Turbulence Driven by Elliptical Instability

et al. 2017

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“…Our paper builds upon the recent laboratory experimental work by Grannan et al,22 where quantitative measurements were only available for the horizontal flow in the equatorial plane. We therefore complement their experimental results with high-resolution direct numerical simulations (DNS), from which a complete three-dimensional description of the flow is available.…”

Section: Introductionmentioning

confidence: 99%

“…[13][14][15][16][17] as in axisymmetric cases, but also of a topographic nature. Although librational forcing cannot directly excite eigenmodes of the system through a direct resonance in the inviscid case, 18,19 it has been shown that three-dimensional flows can be driven by the resonance of two inertial modes with an elliptically deformed base flow, 4,[20][21][22] the so-called libration-driven elliptical instability (LDEI). More generally, the elliptical instability 23 is a resonance mechanism between a pair of normal modes of the system and the underlying strain field associated with regions of two-dimensional, elliptical streamlines.…”

Section: Introductionmentioning

confidence: 99%

Generation and maintenance of bulk turbulence by libration-driven elliptical instability

et al. 2015

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Longitudinal libration corresponds to the periodic oscillation of a body’s rotation rate and is, along with precessional and tidal forcings, a possible source of mechanically-driven turbulence in the fluid interior of satellites and planets. In this study, we present a combination of direct numerical simulations and laboratory experiments, modeling this geophysically relevant mechanical forcing. We investigate the fluid motions inside a longitudinally librating ellipsoidal container filled with an incompressible fluid. The elliptical instability, which is a triadic resonance between two inertial modes and the oscillating base flow with elliptical streamlines, is observed both numerically and experimentally. The large-scale inertial modes eventually lead to small-scale turbulence, provided that the Ekman number is small enough. We characterize this transition to turbulence as additional triadic resonances develop while also investigating the properties of the turbulent flow that displays both intermittent and sustained regimes. These turbulent flows may play an important role in the thermal and magnetic evolution of bodies subject to mechanical forcing, which is not considered in standard models of convectively driven magnetic field generation.

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“…This suggests an alternative way to break TPT. The Coriolis force can supply the restoring force that supports so-called inertial oscillations and waves in rotating fluids [79][80][81][82]. These inertial flows allow for an oscillatory-style of rotating columnar-style convection, which is typically more easily excited in low P r fluids than the steady form of convection.…”

Section: Essential Theorymentioning

confidence: 99%

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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Experimental study of global-scale turbulence in a librating ellipsoid

Cited by 24 publications

References 63 publications

Inertial Wave Turbulence Driven by Elliptical Instability

Inertial Wave Turbulence Driven by Elliptical Instability

Generation and maintenance of bulk turbulence by libration-driven elliptical instability

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

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