Basile Gallet

Basile Gallet
Atomic Energy and Alternative Energies Commission | CEA · Service de Physique de l'Etat Condensé

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74
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947
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Publications

Publications (74)
Article
Three-dimensional convection driven by internal heat sources and sinks (CISS) leads to experimental and numerical scaling laws compatible with a mixing-length—or ‘ultimate’—scaling regime N u ∼ R a . However, asymptotic analytic solutions and idealized two-dimensional simulations have shown that laminar flow solutions can transport heat even more e...
Preprint
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The competition between turbulent convection and global rotation in planetary and stellar interiors governs the transport of heat and tracers, as well as magnetic-field generation. These objects operate in dynamical regimes ranging from weakly rotating convection to the `geostrophic turbulence' regime of rapidly rotating convection. However, the la...
Preprint
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Despite the increasing sophistication of numerical models of hot Jupiter atmospheres, the large time-scale separation required in simulating the wide range in electrical conductivity between the dayside and nightside has made it difficult to run fully consistent magnetohydrodynamic (MHD) models. This has led to many studies that resort to drag para...
Preprint
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We numerically and theoretically investigate the Boussinesq Eady model, where a rapidly rotating density-stratified layer of fluid is subject to a meridional temperature gradient in thermal wind balance with a uniform vertically sheared zonal flow. Through a suite of numerical simulations, we show that the transport properties of the resulting turb...
Article
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Astrophysical flows are often subject to both rotation and large-scale background magnetic fields. Individually, each is known to two-dimensionalize the flow in the perpendicular plane. In realistic settings, both of these effects are simultaneously present and, importantly, need not be aligned. In this work, we numerically investigate three-dimens...
Preprint
We address magnetic-field generation by dynamo action in systems with inhomogeneous electrical conductivity and magnetic permeability. More specifically, we first show that the Taylor-Couette kinematic dynamo undergoes a drastic reduction of its stability threshold when a (zero-mean) modulation of the fluid's electrical conductivity or magnetic per...
Article
The competition between turbulent convection and global rotation in planetary and stellar interiors governs the transport of heat and tracers, as well as magnetic field generation. These objects operate in dynamical regimes ranging from weakly rotating convection to the “geostrophic turbulence” regime of rapidly rotating convection. However, the la...
Preprint
Full-text available
The meridional temperature profile of the upper layers of planetary atmospheres is set through a balance between differential radiative heating by a nearby star, or by intrinsic heat fluxes emanating from the deep interior, and the redistribution of that heat across latitudes by turbulent flows. These flows spontaneously arise through baroclinic in...
Article
Full-text available
We report hot-wire measurements performed in two very different, co- and counterrotating flows, in normal and superfluid helium at 1.6K, 2K, and 2.3K. As recently reported, the power spectrum of the hot-wire signal in superfluid flows exhibits a significant bump at high frequency [Diribarne et al., Phys. Rev. B 103, 144509 (2021)]. We confirm that...
Article
Full-text available
The meridional temperature profile of the upper layers of planetary atmospheres is set through a balance between differential radiative heating by a nearby star, or by intrinsic heat fluxes emanating from the deep interior, and the redistribution of that heat across latitudes by turbulent flows. These flows spontaneously arise through baroclinic in...
Article
Full-text available
We address magnetic-field generation by dynamo action in systems with inhomogeneous electrical conductivity and magnetic permeability. More specifically, we first show that the Taylor-Couette kinematic dynamo undergoes a drastic reduction of its stability threshold when a (zero-mean) modulation of the fluid's electrical conductivity or magnetic per...
Article
Full-text available
Velocity measurements in turbulent superfluid helium between co-rotating propellers are reported. The parameters are chosen such that the flow is fully turbulent, and its dissipative scales are partly resolved by the velocity sensors. This allows for the first experimental comparison of spectra in quantum versus classical turbulence where dissipati...
Preprint
Full-text available
We report hot-wire measurements performed in two very different, co- and counter-rotating flows, in normal and superfluid helium at 1.6 K, 2 K, and 2.3 K. As recently reported, the power spectrum of the hot-wire signal in superfluid flow exhibits a significant bump at high frequency. We confirm that the bump frequency does not depend significantly...
Preprint
Full-text available
Astrophysical plasmas are often subject to both rotation and large-scale background magnetic fields. Individually, each is known to two-dimensionalize the flow in the perpendicular plane. In realistic flows, both of these effects are simultaneously present and, importantly, need not be aligned. In this work, we numerically investigate three-dimensi...
Article
Between 5 and 25% of the total momentum transferred between the atmosphere and ocean is transmitted via the growth of long surface gravity waves called ‘swell’. In this paper, we use large eddy simulations to show that swell-transmitted momentum excites near-inertial waves and drives turbulent mixing that deepens a rotating, stratified, turbulent o...
Preprint
The absorption of light or radiation drives turbulent convection inside stars, supernovae, frozen lakes and the Earth's mantle. In these contexts, the goal of laboratory and numerical studies is to determine the relation between the internal temperature gradients and the heat flux transported by the turbulent flow. This is the constitutive law of t...
Article
Full-text available
We report the quantitative experimental observation of the weak inertial-wave turbulence regime of rotating turbulence. We produce a statistically steady homogeneous turbulent flow that consists of nonlinearly interacting inertial waves, using rough top and bottom boundaries to prevent the emergence of a geostrophic flow. As the forcing amplitude i...
Preprint
Full-text available
We report the quantitative experimental observation of the weak inertial-wave turbulence regime of rotating turbulence. We produce a statistically steady homogeneous turbulent flow that consists of nonlinearly interacting inertial waves, using rough top and bottom boundaries to prevent the emergence of a geostrophic flow. As the forcing amplitude i...
Article
Onset of three-dimensionality in rapidly rotating turbulent flows - Volume 901 - Kannabiran Seshasayanan, Basile Gallet
Preprint
Thermal convection driven by internal heat sources and sinks was recently shown experimentally to exhibit the mixing-length, or "ultimate", scaling-regime: the Nusselt number $Nu$ (dimensionless heat flux) increases as the square-root of the Rayleigh-number $Ra$ (dimensionless internal temperature difference). While for standard Rayleigh-B\'enard c...
Preprint
We report on the transition between two regimes of heat transport in a radiatively driven convection experiment, where a fluid gets heated up within a tunable heating length $\ell$ in the vicinity of the bottom of the tank. The first regime is similar to the one observed in standard Rayleigh-B\'enard experiments, the Nusselt number $Nu$ being relat...
Preprint
The mean state of the atmosphere and ocean is set through a balance between external forcing (winds, radiation, heat and freshwater fluxes) and the emergent turbulence, which transfers energy to dissipative structures. The forcing gives rise to jets in the atmosphere and currents in the ocean, which spontaneously develop turbulent eddies through th...
Article
On the role of the Prandtl number in convection driven by heat sources and sinks - Volume 900 - Benjamin Miquel, Vincent Bouillaut, Sébastien Aumaître, Basile Gallet
Article
Full-text available
Near-resonant instability of geostrophic modes: beyond Greenspan's theorem - Volume 900 - T. Le Reun, B. Gallet, B. Favier, M. Le Bars
Preprint
Turbulent flows driven by a vertically invariant body force were proven to become exactly two-dimensional above a critical rotation rate, using upper bound theory. This transition in dimensionality of a turbulent flow has key consequences for the energy dissipation rate. However, its location in parameter space is not provided by the bounding proce...
Preprint
We report on a numerical study of turbulent convection driven by a combination of internal heat sources and sinks. Motivated by a recent experimental realisation (Lepot et al. 2018), we focus on the situation where the cooling is uniform, while the internal heating is localised near the bottom boundary, over approximately one tenth of the domain he...
Article
We report on laboratory experiments of wave-driven rotating turbulence. A set of wave makers produces inertial-wave beams that interact nonlinearly in the central region of a water tank mounted on a rotating platform. The forcing thus injects energy into inertial waves only. For moderate forcing amplitude, part of the energy of the forced inertial...
Preprint
We report on laboratory experiments of wave-driven rotating turbulence. A set of wavemakers produces inertial-wave beams that interact nonlinearly in the central region of a water tank mounted on a rotating platform. The forcing thus injects energy into inertial waves only. For moderate forcing amplitude, part of the energy of the forced inertial w...
Preprint
We explore the near-resonant interaction of inertial waves with geostrophic modes in rotating fluids via numerical and theoretical analysis. When a single inertial wave is imposed, we find that some geostrophic modes are unstable provided that the wave amplitude, or Rossby number $Ro$, is sufficiently large. We show this instability to be caused by...
Article
The mean state of the atmosphere and ocean is set through a balance between external forcing (radiation, winds, heat and freshwater fluxes) and the emergent turbulence, which transfers energy to dissipative structures. The forcing gives rise to jets in the atmosphere and currents in the ocean, which spontaneously develop turbulent eddies through th...
Article
Thermal convection driven by internal heat sources and sinks was recently shown experimentally to exhibit the mixing-length or “ultimate” scaling-regime: The Nusselt number Nu (dimensionless heat flux) increases as the square-root of the Rayleigh-number Ra (dimensionless internal temperature difference). While for standard Rayleigh-Bénard convectio...
Article
We report on an instability arising when surface gravity waves propagate in a rotating frame. The Stokes drift associated to the uniform wave field, together with global rotation, drives a mean flow in the form of a horizontally invariant Ekman-Stokes spiral. We show that the latter can be subject to an instability that triggers the appearance of a...
Preprint
We report on an instability arising when surface gravity waves propagate in a rotating frame. The Stokes drift associated to the uniform wave field, together with global rotation, drives a mean flow in the form of a horizontally invariant Ekman-Stokes spiral. We show that the latter can be subject to an instability that triggers the appearance of a...
Article
We present analytical examples of fluid dynamos that saturate through the action of the Coriolis and inertial terms of the Navier–Stokes equation. The flow is driven by a body force and is subject to global rotation and uniform sweeping velocity. The model can be studied down to arbitrarily low viscosity and naturally leads to the strong-field scal...
Article
We report on the transition between two regimes of heat transport in a radiatively driven convection experiment, where a fluid gets heated up within a tunable heating length $\ell$ in the vicinity of the bottom of the tank. The first regime is similar to that observed in standard Rayleigh–Bénard experiments, the Nusselt number $Nu$ being related to...
Preprint
We present analytical examples of fluid dynamos that saturate through the action of the Coriolis and inertial terms of the Navier-Stokes equation. The flow is driven by a body force and is subject to global rotation and uniform sweeping velocity. The model can be studied down to arbitrarily low viscosity and naturally leads to the strong-field scal...
Article
The absorption of light or radiation drives turbulent convection inside stars, supernovae, frozen lakes, and Earth's mantle. In these contexts, the goal of laboratory and numerical studies is to determine the relation between the internal temperature gradients and the heat flux transported by the turbulent flow. This is the constitutive law of turb...
Article
Full-text available
While the saturated magnetic energy is independent of viscosity in dynamo experiments, it remains viscosity dependent in state-of-the-art 3D direct numerical simulations (DNS). Extrapolating such viscous scaling laws to realistic parameter values leads to an underestimation of the magnetic energy by several orders of magnitude. The origin of this d...
Article
Full-text available
We introduce a velocimetry technique based on the Doppler-shift of surface waves propagating between an emitter and a receiver. In the limit of scale separation between the wavelength and the scale of the flow, we derive the direct connection between the subsurface flow and the measured phase shift between emitter and receiver. Because of its ease...
Article
Full-text available
When a vortex refracts surface waves, the momentum flux carried by the waves changes direction and the waves induce a reaction force on the vortex. We study experimentally the resulting vortex distortion. Incoming surface gravity waves impinge on a steady vortex of velocity U0 driven magnetohydrodynamically at the bottom of a fluid layer. The waves...
Article
We study the statistics of the power P dissipated by waves propagating in a one-dimensional disordered medium with damping coefficient ν. An operator imposes the wave amplitude at one end, therefore injecting a power P that balances dissipation. The typical realization of P vanishes for ν→0: Disorder leads to localization and total reflection of th...
Article
Full-text available
What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at a constant angular velocity ${\it\omega}$ in a water tank mounted on a platform rotating at a rate ${\it\Omega}$ . We report a dramatic reduction in drag...
Article
Full-text available
Recently, CEA Grenoble SBT has designed, built and tested three liquid helium facilities dedicated to turbulence studies. All these experiments can operate either in HeI or HeII within the same campaign. The three facilities utilize moving parts inside liquid helium. The SHREK experiment is a von Kármán swirling flow between 0.72 m diameter counter...
Article
One-dimensional patterns generated by the Faraday instability at the surface of a vertically vibrated fluid are investigated when the reflection symmetry in the direction of the pattern is broken. For large symmetry breaking, the stationary instability turns into a Hopf bifurcation at a codimension-2 point. This Hopf bifurcation amounts to a period...
Article
We consider the flow of a Newtonian fluid in a three-dimensional domain, rotating about a vertical axis and driven by a vertically invariant horizontal body-force. This system admits vertically invariant solutions that satisfy the 2D Navier-Stokes equation. At high Reynolds number and without global rotation, such solutions are usually unstable to...
Article
Full-text available
This work addresses the question of the stability of stratified, spatially periodic shear flows at low P\'eclet number but high Reynolds number. This little-studied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of "low-P\'eclet-number equations" proposed...
Article
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We investigate the behavior of flows, including turbulent flows, driven by a horizontal body-force and subject to a vertical magnetic field, with the following question in mind: for very strong applied magnetic field, is the flow mostly two-dimensional, with remaining weak three-dimensional fluctuations, or does it become exactly 2D, with no depend...
Article
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In field theory, particles are waves or excitations that propagate on the fundamental state. In experiments or cosmological models one typically wants to compute the out-of-equilibrium evolution of a given initial distribution of such waves. Wave Turbulence deals with out-of-equilibrium ensembles of weakly nonlinear waves, and is therefore well-sui...
Article
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We present a spatio-temporal analysis of a statistically stationary rotating turbulence experiment, aiming to extract a signature of inertial waves, and to determine the scales and frequencies at which they can be detected. The analysis uses two-point spatial correlations of the temporal Fourier transform of velocity fields obtained from time-resol...
Article
Full-text available
We present experimental evidence for a double cascade of kinetic energy in a statistically stationary rotating turbulence experiment. Turbulence is generated by a set of vertical flaps, which continuously injects velocity fluctuations towards the center of a rotating water tank. The energy transfers are evaluated from two-point third-order three-co...
Article
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Using recordings of swell from pitch-and-roll buoys, we have reproduced the classic observations of long-range surface wave propagation originally made by Munk et al. (1963) using a triangular array of bottom pressure measurements. In the modern data, the direction of the incoming swell fluctuates by about $\pm 10^\circ$ on a time scale of one hour...
Article
Full-text available
We characterize the statistical and geometrical properties of the cyclone-anticyclone asymmetry in a statistically-steady forced rotating turbulence experiment. Turbulence is generated by a set of vertical flaps which continuously inject velocity fluctuations towards the center of a tank mounted on a rotating platform. We first characterize the cyc...
Article
We investigate dynamo action for a parallel flow of an electrically conducting fluid located over a boundary with spatially varying magnetic permeability. We first compute the dynamo threshold numerically. Then we perform an asymptotic expansion in the limit of small permeability modulation, which gives accurate results even for moderate modulation...
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We investigate solutions of the two-dimensional Navier–Stokes equation in a square box with stress-free boundary conditions. The flow is steadily forced by the addition of a source to the vorticity equation; attention is restricted to even so that the forcing has zero integral. Numerical solutions with and show that at high Reynolds numbers the sol...
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We report the first experimental observation of a spatially localized dynamo magnetic field, a common feature of astrophysical dynamos and convective dynamo simulations. When the two propellers of the von Kármán sodium experiment are driven at frequencies that differ by 15%, the mean magnetic field's energy measured close to the slower disk is near...
Article
We show that a simple flow of an electrically conducting fluid along a boundary with variable magnetic permeability can generate a magnetic field. An analytic study in the limit of weak permeability modulation allows to understand the mechanism of this dynamo and predicts scaling laws for the threshold. We discuss the possible contribution of this...
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Full-text available
The Von Karman Sodium experiment displays a magnetic field generated by dynamo action in a fully turbulent flow of liquid sodium. The magnetic field can be either statistically stationary, oscillatory, or bistable between these two states. For other values of the control parameters, it displays random reversals similar to the ones observed in palae...
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We present a study of several systems in which a large scale field is generated over a turbulent background. These large scale fields usually break a symmetry of the forcing by selecting a direction. Under certain conditions, the large scale field displays reversals so that the symmetry of the forcing is recovered statistically. We present examples...
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In a mixture of two species of grains of equal size but different mass, placed in a vertically vibrated shallow box, there is spontaneous segregation. Once the system is at least partly segregated and clusters of the heavy particles have formed, there are sudden peaks of the horizontal kinetic energy of the heavy particles, that is otherwise small....
Article
Full-text available
In a mixture of two species of grains of equal size but differing by their mass, placed in a vertically vibrated shallow box, there is spontaneous segregation. Once the system is at least partly segregated, energy bursts take place: the horizontal kinetic energy of the heavy particles, that normally is small, suddenly increases. An explanation is p...
Article
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The Von Kármán Sodium experiment yields a variety of dynamo regimes, when asymmetry is imparted to the flow by rotating impellers at different speed F 1 and F 2. We show that as the intensity of forcing, measured as F 1+F 2, is increased, the transition to a self-sustained magnetic field is always observed via a supercritical bifurcation to a stati...
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We report the first experimental observation of a bistable dynamo regime. A turbulent flow of liquid sodium is generated between two disks in the von ar an geometry (VKS experiment). When one disk is kept at rest, bistability is observed between a stationary and an oscillatory magnetic field. The stationary and oscillatory branches occur in the vic...
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We consider the effect of radial fluid injection and suction on Taylor-Couette flow. Injection at the outer cylinder and suction at the inner cylinder generally results in a linearly unstable steady spiralling flow, even for cylindrical shears that are linearly stable in the absence of a radial flux. We study nonlinear aspects of the unstable motio...
Article
We present an instability occuring in a turbulent flow containing grains that interact via a dipole-dipole force. Above a critical intensity of the interaction, the local density of grains displays a noisy oscillation. This instability takes place in a spatially and temporally fluctuating medium. We identify the control parameter of the instability...
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We show that hemispherical dynamos can result from weak equatorial symmetry breaking of the flow in the interior of planets and stars. Using a model of spherical dynamo, we observe that the interaction between a dipolar and a quadrupolar mode can localize the magnetic field in only one hemisphere when the equatorial symmetry is broken. This process...
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We report an experimental investigation on the influence of an external magnetic field on forced 3D turbulence of liquid gallium in a closed vessel. We observe an exponential damping of the turbulent velocity fluctuations as a function of the interaction parameter N (ratio of Lorentz force over inertial terms of the Navier-Stokes equation). The flo...
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The magnetic field of planets or stars is generated by the motion of a conducting fluid through a dynamo instability. The saturation of the magnetic field occurs through the reaction of the Lorentz force on the flow. In relation to this phenomenon, we study the effect of a magnetic field on a turbulent flow of liquid gallium. The measurement of ele...