Article
Mechanics
J. Pratt, A. Busse, W-C Mueller
Summary: This study investigates the influence of a magnetic field on anisotropic magnetohydrodynamic (MHD) turbulence using direct numerical simulations. The results show that the diffusion curves of single particles exhibit mildly superdiffusive behaviors in different directions. The dispersion of particle pairs is affected by competing alignment processes, especially at the beginning of the inertial subrange. The observed scaling for relative dispersion is steeper than the Richardson prediction, particularly at larger Reynolds numbers.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Astronomy & Astrophysics
Nikos Sioulas, Marco Velli, Zesen Huang, Chen Shi, Trevor A. A. Bowen, B. D. G. Chandran, Ioannis Liodis, Nooshin Davis, Stuart D. D. Bale, T. S. Horbury, Thierry Dudok de Wit, Davin Larson, Michael L. L. Stevens, Justin Kasper, Christopher J. J. Owen, Anthony Case, Marc Pulupa, David M. M. Malaspina, Roberto Livi, Keith Goetz, Peter R. R. Harvey, Robert J. J. MacDowall, John W. W. Bonnell
Summary: In this study, a merged data set from Parker Solar Probe (PSP) and Solar Orbiter (SO) was analyzed to investigate the radial evolution of power and spectral index anisotropy in the wavevector space of solar wind turbulence. The results show that the anisotropic signatures of turbulence display a distinct radial evolution when considering fast and slow wind streams. The findings provide strong observational constraints for anisotropic theories of MHD turbulence in the solar wind.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
N. Andres, R. Bandyopadhyay, D. J. McComas, J. R. Szalay, F. Allegrini, R. W. Ebert, D. J. Gershman, J. E. P. Connerney, S. J. Bolton
Summary: In this study, the first estimation of the energy cascade rate in Jupiter's magnetosheath is presented. In situ observations and compressible models are used to investigate the cascade rate in the magnetohydrodynamic scales. The study finds that while there are high levels of compressible density fluctuations in Jupiter's magnetosheath, there is a constant energy flux in the magnetohydrodynamic range. The energy cascade rate in Jupiter's magnetosheath is at least two orders of magnitude smaller than the typical value in Earth's magnetosheath.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Tommaso Alberti, Simone Benella, Giuseppe Consolini, Mirko Stumpo, Roberto Benzi
Summary: The Parker Solar Probe mission presents a unique opportunity to study the characteristics of the solar wind. Recent research has revealed changes in the magnetic and velocity field fluctuations when moving away from the Sun, likely due to the effects of magnetic field fluctuations and plasma thermal expansion.
ASTROPHYSICAL JOURNAL LETTERS
(2022)
Article
Physics, Fluids & Plasmas
Peter H. Yoon, Gwangson Choe
Summary: This paper revisits the weak turbulence formalism of incompressible MHD turbulence under the assumption of zero residual energy, revealing the steady-state turbulent spectrum obtained when turbulence is assumed to occur in a two-dimensional plane.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
Arijit Halder, Supratik Banerjee, Anando G. Chatterjee, Manohar K. Sharma
Summary: A detailed study on small-scale Hall magnetohydrodynamic dynamos has been conducted, combining analytical and numerical methods. By assuming separate magnetic field and current fields, the contribution of the Hall term has been divided into two parts and studied individually. The calculated scale-separated transfer rates show that small-scale current fields play a primary role in sustaining large-scale magnetic fields. Moreover, the nature of scale-to-scale fluxes is found to be globally intact with the ion inertial scale.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Physics, Multidisciplinary
David N. Hosking, Alexander A. Schekochihin
Summary: The article introduces a new theoretical picture of magnetically dominated, decaying turbulence, demonstrating through numerical simulations that the rate of turbulent decay is controlled by magnetic reconnection. Predictions for turbulence decay on reconnection timescales are obtained, while verifying the conservation of certain integral invariants in numerical simulations.
Article
Astronomy & Astrophysics
N. S. Dzhalilov, R. Ismayilli
Summary: The linear magnetohydrodynamic Kelvin-Helmholtz instability in an anisotropic plasma is investigated using the governing equations derived from the 16 moments of Boltzmann-Vlasov kinetic equations. The study finds that quasi-transverse modes grow faster in the case of tangential discontinuity between supersonic flows along the magnetic field. Dispersion equations for these modes considering the finite width of the transition zone are derived. Analytical solutions are obtained, which aid in verifying numerical simulations. In addition, the study shows that the fundamental plasma instabilities arising from the transition zone's finite width can modify and enhance the Kelvin-Helmholtz instability.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Mechanics
X. Shao, J. Fang, L. Fang
Summary: The existence of a large-scale non-equilibrium dissipation law has been confirmed through experiments on grid-generated turbulent wake flows. Previous studies have shown the coexistence of a rapid non-equilibrium dissipation law before the large-scale counterpart in homogeneous isotropic turbulence. In this paper, a simplified minimal two-scale wake model is introduced, which confirms the coexistence of both dissipation laws similar to previous studies.
Article
Astronomy & Astrophysics
F. Pugliese, M. Brodiano, N. Andres, P. Dmitruk
Summary: This study uses direct numerical simulations to investigate the relationship between wave modes and coherent structures in three-dimensional compressible magnetohydrodynamic turbulence, and the resulting energization of test particles. The main mechanism of particle energization is found to be through structures rather than resonance with wave modes.
ASTROPHYSICAL JOURNAL
(2023)
Article
Mathematics, Applied
Haifeng Shang, Yaru Zhai
Summary: This paper focuses on the stability problem and large time behavior of solutions to the three-dimensional anisotropic magnetohydrodynamic equations. By fully exploiting the structure of the system and using energy methods and the method of bootstrapping arguments, the global stability of solutions with small initial data in H-3(R-3) is proven. Furthermore, for global solutions with large initial data in H-4(R-3), a global H-4(R-3) bound which is independent of time is obtained. Moreover, the optimal decay rates of these global solutions and their first-order derivatives are established.
ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND PHYSIK
(2022)
Article
Mechanics
Brodie C. Pearson, Jenna L. Pearson, Baylor Fox-Kemper
Summary: The study proposes new relations to diagnose energy and enstrophy dissipation rates in anisotropic two-dimensional turbulence, using second-order advective structure functions. These new relations show improvement over existing methods through increased accuracy, insensitivity to sampling direction, and lower temporal and spatial variability. Advective structure functions have benefits under weakly anisotropic conditions, becoming increasingly important as third-order structure functions become inappropriate.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Krzysztof A. Mizerski
Summary: The magnetohydrodynamic (MHD) turbulence is present in both engineering laboratory flows and natural systems. It has the ability to generate and sustain large-scale and small-scale magnetic fields, playing a crucial role in processes such as nuclear fusion energy production. The turbulence also enhances large-scale diffusion and affects the energy and helicity spectra of strongly turbulent flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Astronomy & Astrophysics
Loren E. Held, Henrik N. Latter
Summary: Research shows that convection and the magnetorotational instability interact significantly in angular momentum transport, resulting in different flow characteristics in different phases. Convection forms large-scale and oscillatory convective cells in the nonlinear phase, helping the MRI persist to lower Rm values.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Alfred Mallet, Jonathan Squire, Benjamin D. G. Chandran, Trevor Bowen, Stuart D. Bale
Summary: This study examines the dynamics of large-amplitude Alfven waves in the expanding solar wind, making predictions about the occurrence and characteristics of switchbacks observed by the Parker Solar Probe. The expansion of plasma generates compressive components in the wave's evolution, affecting the magnetic field strength and gradient of switchbacks. The findings suggest that observed switchbacks may result from the nonlinear evolution of initially small-amplitude Alfven waves.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Sebastien Galtier
Summary: This paper presents a derivation of the kinetic equation for capillary wave turbulence, focusing on the absence of gravity and the approximation of deep water. The use of directional polarities for three-wave interactions leads to a compact form of the equation that is fully compatible with previous work. Additionally, exact solutions are derived using the Zakharov transformation applied to wavenumbers, and experimental and numerical works from recent decades are reviewed.
GEOPHYSICAL AND ASTROPHYSICAL FLUID DYNAMICS
(2021)
Article
Physics, Fluids & Plasmas
Sebastien Galtier, Vincent David
PHYSICAL REVIEW FLUIDS
(2020)
Article
Astronomy & Astrophysics
S. Y. Huang, F. Sahraoui, N. Andres, L. Z. Hadid, Z. G. Yuan, J. S. He, J. S. Zhao, S. Galtier, J. Zhang, X. H. Deng, K. Jiang, L. Yu, S. B. Xu, Q. Y. Xiong, Y. Y. Wei, T. Dudok de Wit, S. D. Bale, J. C. Kasper
Summary: The study shows an inverse correlation between power amplitude and spectral steepness at sub-ion scales in solar wind turbulence, as well as a similar trend between steep spectra and increasing normalized cross helicity. It also discusses the ubiquitous nature of the ion transition range in the inner heliosphere.
ASTROPHYSICAL JOURNAL LETTERS
(2021)
Article
Physics, Fluids & Plasmas
Renaud Ferrand, Sebastien Galtier, Fouad Sahraoui
Summary: A compact exact law for isothermal compressible Hall magnetohydrodynamic turbulence has been derived using mixed second-order structure functions, making it suitable for analyzing numerical simulations and in situ data from space plasmas, particularly when only single-spacecraft data is available.
JOURNAL OF PLASMA PHYSICS
(2021)
Article
Astronomy & Astrophysics
N. Andres, F. Sahraoui, L. Z. Hadid, S. Y. Huang, N. Romanelli, S. Galtier, G. DiBraccio, J. Halekas
Summary: The compressible energy transfer rate from different heliocentric distances was calculated using PSP, THEMIS, and MAVEN observations, showing moderate increases with respect to the incompressible cascade rate. The impact of plasma compressibility on the total cascade rate was demonstrated, and the results were connected with local ion temperature and solar wind heating.
ASTROPHYSICAL JOURNAL
(2021)
Article
Physics, Multidisciplinary
Sebastien Galtier, Sergey Nazarenko
Summary: The study conducts the first direct numerical simulation of gravitational wave turbulence under the constraints of weak gravitational waves and freely decaying turbulence. It reveals a dual cascade of energy and wave action, as well as selective amplification of wave fluctuations during the inverse cascade process.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
R. Ferrand, F. Sahraoui, D. Laveder, T. Passot, P. L. Sulem, S. Galtier
Summary: This study calculates the energy cascade rate in incompressible Hall magnetohydrodynamics turbulence using an exact law and shows the role of Landau damping in dissipating energy at all scales. It provides new prospects for analyzing dissipation in kinetic simulations and spacecraft observations, as well as new insights into theoretical description of collisionless magnetized plasmas.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
N. Andres, F. Sahraoui, S. Huang, L. Z. Hadid, S. Galtier
Summary: This study investigates the isotropy and anisotropy energy cascade rates in solar wind turbulence using more than two years of Parker Solar Probe (PSP) observations. The results show a dominance of perpendicular cascades over parallel cascades, and a dominant 2D cascade and/or geometry over the slab component in the largest MHD scales.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
R. Ferrand, F. Sahraoui, S. Galtier, N. Andres, P. Mininni, P. Dmitruk
Summary: Various exact laws governing compressible magnetohydrodynamic and compressible Hall-MHD turbulence have been derived in recent years. These laws not only have fundamental theoretical significance, but also can be used to estimate energy dissipation rate from spacecraft observations to address various problems related to solar wind and magnetospheric plasmas. In this study, numerical simulation data is used to analyze two of these laws, and the results show the equivalence of these laws in the inertial range, and reveal the relationship between the strength of the Hall effect and the amplitude of the cascade rate at sub-ion scales.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
V David, S. Galtier, F. Sahraoui, L. Z. Hadid
Summary: In this study, a new method based on inertial dissipation is introduced to estimate the energy transfer rate in the solar wind. The presence of discontinuities near the Sun is found to lead to a strong energy transfer. Switchbacks exhibit a different scaling behavior compared to classical discontinuities.
ASTROPHYSICAL JOURNAL
(2022)
Article
Physics, Fluids & Plasmas
Vincent David, Sebastien Galtier
Summary: A wave turbulence theory is developed for inertial electron magnetohydrodynamics (IEMHD) in the presence of a relatively strong and uniform external magnetic field. The study shows that the transfer of energy and momentum in this regime is anisotropic with a direct cascade mainly in the direction perpendicular to the external magnetic field. The exact stationary solutions and the Kolmogorov constant are obtained, and the application of the theory to space plasmas is discussed.
JOURNAL OF PLASMA PHYSICS
(2022)
Article
Mechanics
Vincent David, Sebastien Galtier
Summary: Using the wave turbulence theory for rotating incompressible fluids proposed by Galtier in 2003, we have determined the local conditions that the solutions of the kinetic equation must satisfy. We have shown that the exact anisotropic Kolmogorov-Zakharov spectrum satisfies these conditions, confirming the existence of a constant positive energy flux solution. Our numerical results indicate that while a direct cascade is expected in both transverse and parallel directions to the rotation axis, some triadic interactions in the latter direction can contribute negatively to the energy flux. By neglecting the parallel energy flux, we have obtained an estimation of the Kolmogorov constant to be approximately 0.749. These findings provide theoretical support for recent numerical and experimental studies.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Nuclear Science & Technology
Thomas Schiano, Barbara Bigot, Jean-Francois Haquet, Pierre Saramito, Claude Smutek
Summary: A viscoplastic model for lava is proposed in this paper, which is applied to the spreading of corium with dimensionless numbers. The model considers the tridimensional flow as non-Newtonian and non-isothermal. Simulations are conducted using an adaptive finite element method based on C++ library Rheolef, and the results are compared with the VEU7 corium spreading test. A sensitivity analysis is also performed on the viscoplastic parameters of corium. The tridimensional solution is computed from the bidimensional height-averaged solution.
NUCLEAR ENGINEERING AND DESIGN
(2023)
Article
Physics, Fluids & Plasmas
Sebastien Galtier
Summary: An analytical theory of wave turbulence is developed for pure compressible magnetohydrodynamics in the small limit. The theory is applicable to fast magneto-acoustic waves and uses the compressible Elsasser fields as canonical variables. The theory provides a plausible explanation for observed isotropic spectra with a power-law index of -3/2.
JOURNAL OF PLASMA PHYSICS
(2023)
Article
Physics, Fluids & Plasmas
Vincent David, Sebastien Galtier
Summary: This study examines weak solutions of one-dimensional compressible magnetohydrodynamics, demonstrating that lack of smoothness in fields introduces inertial dissipation named inertial dissipation and proposing exact solutions assuming equal kinematic viscosity and magnetic diffusivity. In the limit of small viscosity, inertial dissipation is shown to be positive and equal on average to mean viscous dissipation rate, validating the conjecture of the zeroth law of turbulence and the presence of anomalous dissipation. The findings suggest collisionless shocks could be a primary source of heating in the outer solar wind, with a heating rate significantly higher than that obtained from turbulent fluctuations.
