Mechanism for Sequestering Magnetic Energy at Large Scales in Shear-Flow Turbulence
arXiv:2205.01298 · doi:10.1063/5.0096886
Abstract
Straining of magnetic fields by large-scale shear flow, generally assumed to lead to intensification and generation of small scales, is re-examined in light of the persistent observation of large-scale magnetic fields in astrophysics. It is shown that, in magnetohydrodynamic turbulence, unstable shear flows have the unexpected effect of sequestering magnetic energy at large scales, due to counteracting straining motion of nonlinearly excited large-scale stable eigenmodes. This effect is quantified via dissipation rates, energy transfer rates, and visualizations of magnetic field evolution by artificially removing the stable modes. These analyses show that predictions based upon physics of the linear instability alone miss substantial dynamics, including those of magnetic fluctuations.
arXiv commentAccepted for publication in Physics of Plasmas as a Letter; A simulation movie embedded in Fig. 4
References in corpus (15)
- Astrophysical magnetic fields and nonlinear dynamo theory
- Evidence for strong extragalactic magnetic fields from Fermi observations of TeV blazars
- Dedalus: A Flexible Framework for Numerical Simulations with Spectral Methods
- Slowing the Spins of Stellar Cores
- Energy transfer from large to small scales in turbulence by multi-scale nonlinear strain and vorticity interactions
- The small-scale structure of magnetohydrodynamic turbulence with large magnetic Prandtl numbers
- Statistics of an Unstable Barotropic Jet from a Cumulant Expansion
- Forecasting Fluid Flows Using the Geometry of Turbulence
- The signature of the magnetorotational instability in the Reynolds and Maxwell stress tensors in accretion discs
- Generation of large-scale magnetic fields by small-scale dynamo in shear flows
- Role of stable modes in driven shear-flow turbulence
- Dimensional Reduction of Direct Statistical Simulation
- Coupling of Damped and Growing Modes in Unstable Shear Flow
- Near-cancellation of up- and down-gradient momentum transport in forced magnetized shear-flow turbulence
- The impact of magnetic fields on momentum transport and saturation of shear-flow instability by stable modes