Zero Net Flux MRI Turbulence in Disks: Sustenance Scheme and Magnetic Prandtl Number Dependence
Research output: Contribution to journal › Journal article › Research › peer-review
Standard
Zero Net Flux MRI Turbulence in Disks : Sustenance Scheme and Magnetic Prandtl Number Dependence. / Mamatsashvili, George; Chagelishvili, George; Pessah, Martin E.; Stefani, Frank; Bodo, Gianluigi.
In: Astrophysical Journal, Vol. 904, No. 1, 47, 20.11.2020.Research output: Contribution to journal › Journal article › Research › peer-review
Harvard
APA
Vancouver
Author
Bibtex
}
RIS
TY - JOUR
T1 - Zero Net Flux MRI Turbulence in Disks
T2 - Sustenance Scheme and Magnetic Prandtl Number Dependence
AU - Mamatsashvili, George
AU - Chagelishvili, George
AU - Pessah, Martin E.
AU - Stefani, Frank
AU - Bodo, Gianluigi
PY - 2020/11/20
Y1 - 2020/11/20
N2 - We investigate sustenance and dependence on magnetic Prandtl number (Pm) for magnetorotational instability (MRI)-driven turbulence in Keplerian disks with zero net magnetic flux using standard shearing box simulations. We focus on the turbulence dynamics in Fourier space, capturing specific/noncanonical anisotropy of nonlinear processes due to disk flow shear. This is a new type of nonlinear redistribution of modes over wavevector orientations in Fourier space-the nonlinear transverse cascade-which is generic to shear flows and fundamentally different from the usual direct/inverse cascade. The zero flux MRI has no exponentially growing modes, so its growth is transient, or nonmodal. Turbulence self-sustenance is governed by constructive cooperation of the transient growth of MRI and the nonlinear transverse cascade. This cooperation takes place at small wavenumbers (on the flow size scales) referred to as the vital area in Fourier space. The direct cascade transfers mode energy from the vital area to larger wavenumbers. At large Pm, the transverse cascade prevails over the direct one, keeping most of modes' energy contained in small wavenumbers. With decreasing Pm, however, the action of the transverse cascade weakens and can no longer oppose the action of the direct cascade, which more efficiently transfers energy to higher wavenumbers, leading to increased resistive dissipation. This undermines the sustenance scheme, resulting in the turbulence decay. Thus, the decay of zero net flux MRI turbulence with decreasing Pm is attributed to the topological rearrangement of the nonlinear processes when the direct cascade begins to prevail over the transverse cascade.
AB - We investigate sustenance and dependence on magnetic Prandtl number (Pm) for magnetorotational instability (MRI)-driven turbulence in Keplerian disks with zero net magnetic flux using standard shearing box simulations. We focus on the turbulence dynamics in Fourier space, capturing specific/noncanonical anisotropy of nonlinear processes due to disk flow shear. This is a new type of nonlinear redistribution of modes over wavevector orientations in Fourier space-the nonlinear transverse cascade-which is generic to shear flows and fundamentally different from the usual direct/inverse cascade. The zero flux MRI has no exponentially growing modes, so its growth is transient, or nonmodal. Turbulence self-sustenance is governed by constructive cooperation of the transient growth of MRI and the nonlinear transverse cascade. This cooperation takes place at small wavenumbers (on the flow size scales) referred to as the vital area in Fourier space. The direct cascade transfers mode energy from the vital area to larger wavenumbers. At large Pm, the transverse cascade prevails over the direct one, keeping most of modes' energy contained in small wavenumbers. With decreasing Pm, however, the action of the transverse cascade weakens and can no longer oppose the action of the direct cascade, which more efficiently transfers energy to higher wavenumbers, leading to increased resistive dissipation. This undermines the sustenance scheme, resulting in the turbulence decay. Thus, the decay of zero net flux MRI turbulence with decreasing Pm is attributed to the topological rearrangement of the nonlinear processes when the direct cascade begins to prevail over the transverse cascade.
KW - Stellar accretion disks
KW - Magnetohydrodynamics
KW - Plasma astrophysics
KW - High energy astrophysics
KW - Protoplanetary disks
KW - Magnetic fields
KW - Interplanetary turbulence
KW - ANGULAR-MOMENTUM TRANSPORT
KW - LOCAL SHEAR INSTABILITY
KW - MAGNETOROTATIONAL INSTABILITY
KW - TRANSIENT GROWTH
KW - ACCRETION DISKS
KW - MHD SIMULATIONS
KW - FLOWS
KW - SATURATION
KW - BOX
KW - PERTURBATIONS
U2 - 10.3847/1538-4357/abbd42
DO - 10.3847/1538-4357/abbd42
M3 - Journal article
VL - 904
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 47
ER -
ID: 252877825