Fluctuation dynamo amplified by intermittent shear bursts in convectively driven magnetohydrodynamic turbulence

Pratt, J.; Busse, Angela; Müller, Wolf-Christian

doi:10.1051/0004-6361/201321613

Cited by 23 publications

(17 citation statements)

References 35 publications

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“…Remarkably, we obtain from DNS the same scaling, γ(S) ∝ |S| 2/3 , for SSD growth rate as was theoretically predicted by Kolokolov et al (2011) for a given velocity field. Interestingly, the occurrences of intermittent shear bursts were found to amplify the growth of the SSD in turbulent magnetoconvection (Pratt et al 2013).…”

Section: Discussionmentioning

confidence: 99%

Enhancement of Small-scale Turbulent Dynamo by Large-scale Shear

Singh¹,

Brandenburg²

2017

ApJL

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Small-scale dynamos are ubiquitous in a broad range of turbulent flows with large-scale shear, ranging from solar and galactic magnetism to accretion disks, cosmology and structure formation. Using high-resolution direct numerical simulations we show that in non-helically forced turbulence with zero mean magnetic field, large-scale shear supports small-scale dynamo action, i.e., the dynamo growth rate increases with shear and shear enhances or even produces turbulence, which, in turn, further increases the dynamo growth rate. When the production rates of turbulent kinetic energy due to shear and forcing are comparable, we find scalings for the growth rate γ of the small-scale dynamo and the turbulent velocity u rms with shear rate S that are independent of the magnetic Prandtl number: γ ∝ |S| and u rms ∝ |S| 2/3 . For large fluid and magnetic Reynolds numbers, γ, normalized by its shear-free value, depends only on shear. Having compensated for shear-induced effects on turbulent velocity, we find that the normalized growth rate of the small-scale dynamo exhibits the scaling, γ ∝ |S| 2/3 , arising solely from the induction equation for a given velocity field.

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Section: Discussionmentioning

confidence: 99%

Enhancement of Small-scale Turbulent Dynamo by Large-scale Shear

Singh¹,

Brandenburg²

2017

ApJL

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“…We investigate three different types of turbulent systems: forced homogeneous isotropic Navier-Stokes turbulence (simulation NST) [43], Boussinesq convection in a neutral fluid (simulation HC), and Boussinesq convection in an electrically conducting fluid (simulation MC) [12,44]. These simulations are not designed for close comparison, but produced for a broad exploration of the convex hull analysis.…”

Section: Simulationsmentioning

confidence: 99%

“…However, in astrophysical environments where the effects of magnetic fields, rotation, or gravity are often significant, the more complex nature of statistically anisotropic or even inhomogenous nonlinear dynamics warrants additional examination. Dispersion in dynamically anisotropic systems such as vigorously convecting flows [12][13][14][15][16] where preferred directions exist and spatially coherent, persistent structures like convective plumes can form, motivates the present consideration of a complementary diagnostic based on a different Lagrangian concept: the convex hull [17] of a n-particle group (n 4  ). The convex hull is the smallest convex polygon that encloses a group of particles; two dimensional convex hulls are pictured in figure 1.…”

Section: Introductionmentioning

confidence: 99%

Extreme-value statistics from Lagrangian convex hull analysis for homogeneous turbulent Boussinesq convection and MHD convection

et al. 2017

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We investigate the utility of the convex hull of many Lagrangian tracers to analyze transport properties of turbulent flows with different anisotropy. In direct numerical simulations of statistically homogeneous and stationary Navier-Stokes turbulence, neutral fluid Boussinesq convection, and MHD Boussinesq convection a comparison with Lagrangian pair dispersion shows that convex hull statistics capture the asymptotic dispersive behavior of a large group of passive tracer particles. Moreover, convex hull analysis provides additional information on the sub-ensemble of tracers that on average disperse most efficiently in the form of extreme value statistics and flow anisotropy via the geometric properties of the convex hulls. We use the convex hull surface geometry to examine the anisotropy that occurs in turbulent convection. Applying extreme value theory, we show that the maximal square extensions of convex hull vertices are well described by a classic extreme value distribution, the Gumbel distribution. During turbulent convection, intermittent convective plumes grow and accelerate the dispersion of Lagrangian tracers. Convex hull analysis yields information that supplements standard Lagrangian analysis of coherent turbulent structures and their influence on the global statistics of the flow.

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“…In this paper, we consider the following 2D incompressible Boussinesq equations for magnetohydrodynamics (MHD) convection with stratification effects [5,6,48]:              ∂ t θ + u · ∇θ − div(κ(θ)∇θ)) = −u 2 T ′ 0 (x 2 ), ∂ t u + u · ∇u − div(µ(θ)∇u) + ∇Π = θe 2 + J B ⊥ , ∂ t B + u · ∇B − ∇ ⊥ (σ(θ)J) = B · ∇u, divu = div B = 0.…”

Section: Introduction and Main Resultsmentioning

confidence: 99%

Initial-boundary value problem to 2D Boussinesq equations for MHD convection with stratification effects

Bian

Liu

2017

Journal of Differential Equations

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Abstract. This paper is concerned with the initial-boundary value problem to 2D magnetohydrodynamics-Boussinesq system with the temperature-dependent viscosity, thermal diffusivity and electrical conductivity. First, we establish the global weak solutions under the minimal initial assumption. Then by imposing higher regularity assumption on the initial data, we obtain the global strong solution with uniqueness. Moreover, the exponential decay estimate of the solution is obtained.

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Fluctuation dynamo amplified by intermittent shear bursts in convectively driven magnetohydrodynamic turbulence

Cited by 23 publications

References 35 publications

Enhancement of Small-scale Turbulent Dynamo by Large-scale Shear

Enhancement of Small-scale Turbulent Dynamo by Large-scale Shear

Extreme-value statistics from Lagrangian convex hull analysis for homogeneous turbulent Boussinesq convection and MHD convection

Initial-boundary value problem to 2D Boussinesq equations for MHD convection with stratification effects

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