Calibrating passive scalar transport in shear-flow turbulence

Madarassy, Eniko J. M.; Brandenburg, Axel

doi:10.1103/physreve.82.016304

Cited by 20 publications

(27 citation statements)

References 31 publications

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“…Our present study is based on a previously developed numerical solution of the GPE [26][27][28][29], which was obtained using the Crank-Nicholson method in combination with Cayley's formula [34], in the presence of an isotropic trapping potential (for a numerical investigation of BECs in the presence of anisotropic traps see [35,36].) In particular, the use of Cayley's formula ensures that the numerical solution remains stable, and the unitarity of the wavefunction is maintained.…”

Section: The Numerical Codementioning

confidence: 99%

“…In the present paper, we investigate the stability of self-gravitating BECs using numerical software code that was originally developed to study two-dimensional condensates in the laboratory [26][27][28][29]. The code was later extended to study three-dimensional self-gravitating condensates [30] and further refined to eliminate instabilities due to the choice of the initial condensate profile [25].…”

Section: Arxiv:14127152v1 [Hep-ph] 22 Dec 2014mentioning

confidence: 99%

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Evolution and dynamical properties of Bose-Einstein condensate dark matter stars

Madarassy

Toth

2015

Phys. Rev. D

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Using recently developed nonrelativistic numerical simulation code, we investigate the stability properties of compact astrophysical objects that may be formed due to the Bose-Einstein condensation of dark matter. Once the temperature of a boson gas is less than the critical temperature, a Bose-Einstein condensation process can always take place during the cosmic history of the universe. Due to dark matter accretion, a Bose-Einstein condensed core can also be formed inside massive astrophysical objects such as neutron stars or white dwarfs, for example.Numerically solving the Gross-Pitaevskii-Poisson system of coupled differential equations, we demonstrate, with longer simulation runs, that within the computational limits of the simulation the objects we investigate are stable. Physical properties of a self-gravitating Bose-Einstein condensate are examined both in non-rotating and rotating cases.

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Section: The Numerical Codementioning

confidence: 99%

Section: Arxiv:14127152v1 [Hep-ph] 22 Dec 2014mentioning

confidence: 99%

Evolution and dynamical properties of Bose-Einstein condensate dark matter stars

Madarassy

Toth

2015

Phys. Rev. D

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“…These coefficients depend on time and one spatial coordinate, but because of stationarity and approximate homogeneity of the turbulence intensity, we present in the following temporal and spatial averages of these coefficients. The test scalar method has been used previously to quantify mixing in turbulence in the presence of rotation and magnetic fields (Brandenburg et al 2009), shear (Madarassy & Brandenburg 2010), as well as isothermal density stratification (Brandenburg et al 2012). However, unlike those earlier works, the entropy equation is here included and a nonisothermal equation of state for a perfect monatomic gas is used with γ = 5/3.…”

Section: Direct Numerical Simulationsmentioning

confidence: 99%

Transport of angular momentum and chemical species by anisotropic mixing in stellar radiative interiors

Kitchatinov

Brandenburg

2012

Astron Nachr

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Small levels of turbulence can be present in stellar radiative interiors due to, e.g., the instability of rotational shear. In this paper we estimate turbulent transport coefficients for stably stratified rotating stellar radiation zones. Stable stratification induces strong anisotropy with a very small ratio of radial-to-horizontal turbulence intensities. Angular momentum is transported mainly due to the correlation between azimuthal and radial turbulent motions induced by the Coriolis force. This non-diffusive transport known as the Λ-effect has outward direction in radius and is much more efficient compared to the effect of radial eddy viscosity. Chemical species are transported by small radial diffusion only. This result is confirmed using direct numerical simulations combined with the test-scalar method. As a consequence of the non-diffusive transport of angular momentum, the estimated characteristic time of rotational coupling ( < ∼ 100 Myr) between radiative core and convective envelope in young solar-type stars is much shorter compared to the time-scale of Lithium depletion (∼1 Gyr).

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“…In the passive scalar case, test scalars are used to determine the transport coefficients. Results have been obtained for anisotropic flows in the presence of rotation or strong magnetic fields ), linear shear (Madarassy & Brandenburg 2010), and for irrotational flows (Rädler et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Mean-field transport in stratified and/or rotating turbulence

Brandenburg

Rädler

Kemel

2012

A&A

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Context. The large-scale magnetic fields of stars and galaxies are often described in the framework of mean-field dynamo theory. At moderate magnetic Reynolds numbers, the transport coefficients defining the mean electromotive force can be determined from simulations. This applies analogously also to passive scalar transport. Aims. We investigate the mean electromotive force in the kinematic framework, that is, ignoring the back-reaction of the magnetic field on the fluid velocity, under the assumption of axisymmetric turbulence determined by the presence of either rotation, density stratification, or both. We use an analogous approach for the mean passive scalar flux. As an alternative to convection, we consider forced turbulence in an isothermal layer. When using standard ansatzes, the mean magnetic transport is then determined by nine, and the mean passive scalar transport by four coefficients. We give results for all these transport coefficients. Methods. We use the test-field method and the test-scalar method, where transport coefficients are determined by solving sets of equations with properly chosen mean magnetic fields or mean scalars. These methods are adapted to mean fields which may depend on all three space coordinates. Results. We find the anisotropy of turbulent diffusion to be moderate in spite of rapid rotation or strong density stratification. Contributions to the mean electromotive force determined by the symmetric part of the gradient tensor of the mean magnetic field, which were ignored in several earlier investigations, turn out to be important. In stratified rotating turbulence, the α effect is strongly anisotropic, suppressed along the rotation axis on large length scales, but strongly enhanced at intermediate length scales. Also the Ω × J effect is enhanced at intermediate length scales. The turbulent passive scalar diffusivity is typically almost twice as large as the turbulent magnetic diffusivity. Both magnetic and passive scalar diffusion are slightly enhanced along the rotation axis, but decreased if there is gravity. Conclusions. The test-field and test-scalar methods provide powerful tools for analyzing transport properties of axisymmetric turbulence. Future applications are proposed ranging from anisotropic turbulence due to the presence of a uniform magnetic field to inhomogeneous turbulence where the specific entropy is nonuniform, for example. Some of the contributions to the mean electromotive force which have been ignored in several earlier investigations, in particular those given by the symmetric part of the gradient tensor of the mean magnetic field, turn out to be of significant magnitude.

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Calibrating passive scalar transport in shear-flow turbulence

Cited by 20 publications

References 31 publications

Evolution and dynamical properties of Bose-Einstein condensate dark matter stars

Evolution and dynamical properties of Bose-Einstein condensate dark matter stars

Transport of angular momentum and chemical species by anisotropic mixing in stellar radiative interiors

Mean-field transport in stratified and/or rotating turbulence

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