Magnetohydrodynamic turbulence via the alpha model

P.D. MININNI, D.C. MONTGOMERY, Y A. POUQUET

Seattle, Estados Unidos

Congreso; 57th Annual Meeting of the Division of Fluid Mechanics, American Physical Society; 2004

APS

Incompressible magnetohydrodynamic (MHD) turbulent computations require a large range of spatial resolution when either or both of the Reynolds numbers are large. The present set of computations explores the ability of the Holm "alpha model'' to reproduce the large scales in homogeneous MHD turbulence by systematically suppressing the small scales. We compute three well-established effects in two-dimensional MHD turbulence both with full DNS and with the alpha model, starting from identical initial conditions in regimes where fully-resolved MHD DNS is possible. Large-scale spectral components are well reproduced by the alpha model at greatly reduced resolution. But individual phase-dependent features, such as the spatial locations of long-lived structures in configuration space, do not track well. We also present the results of a direct cascade simulation that lies outside presently-resolvable regimes for full MHD to see what power laws will result for the energy spectra. Finally, some three-dimensional comparisons between DNS and alpha-model MHD are exhibited.