Subgrid scale and backscatter model for magnetohydrodynamic turbulence based on closure theory: theoretical...

Area of Science:

• Fluid Dynamics
• Plasma Physics
• Magnetohydrodynamics (MHD)

Background:

• Magnetohydrodynamics (MHD) describes fluid dynamics of electrically conducting fluids.
• Turbulence in MHD involves complex interactions between velocity and magnetic fields.
• Subgrid-scale (SGS) modeling is crucial for large-eddy simulations (LES) of turbulent flows.

Purpose of the Study:

• To construct spectral eddy and backscatter viscosity and resistivity for incompressible, 3D, isotropic, nonhelical MHD turbulence.
• To extend existing fluid turbulence closure models to MHD turbulence.
• To provide improved SGS parametrizations for MHD turbulence LES.

Main Methods:

• Utilized the eddy-damped quasinormal Markovian (EDQNM) statistical closure model.
• Extended Leslie and Quarini's methodology for fluid turbulence to MHD.
• Numerically calculated eddy and backscatter coefficients using assumed kinetic and magnetic energy spectra for different Alfvén ratios (r(A)).

Main Results:

• Demonstrated that unresolved scales induce eddy damping and backscatter on resolved scales in MHD turbulence.
• Showed that eddy and backscatter viscosity/resistivity depend on k/k(c) similarly to Navier-Stokes turbulence.
• Quantified these effects for r(A)=1 and r(A)=1/2.

Conclusions:

• The derived eddy and backscatter viscosity and resistivity are essential for accurate MHD turbulence modeling.
• These coefficients can enhance SGS parametrizations in spectral large-eddy simulations of homogeneous MHD turbulence.
• The study provides a foundation for more precise simulations of astrophysical and geophysical MHD phenomena.