Turbulence Numerics Team, IMAGe (NCAR)
Tuesday, January 20, 2009
Center Green Laboratory 1, Room 2126
Lecture 2:00 pm
Comparison of Three Classes of Symmetric MHD Decay Flow Simulations with High Resolution DNS
Three different MHD decay flows displaying Taylor-Green-type symmetries are computed at high resolution using an efficient, parallel, spectral code customized to exploit the flow symmetries without loss of accuracy. Different phenomenological behavior is identified for the three classes of flows, where the occurrence of Alfven waves, micro-instabilities, and dynamic alignment are found to be dependent on initial conditions and Reynolds numbers, which determine characteristic time scales, such as the Alfven and eddy turnover times. All of the flows are three-dimensional and deliberately quasi-isotropic to better understand small-scale behavior in the absence of a mean magnetic field. Strong background magnetic fields, common in geophysical and astrophysical plasma environments, are known to suppress energy transfer in the parallel direction and therefore may limit the dynamical possibilities of MHD. In this study, both isotropic and anisotropic tools are used to assess and interpret the physics of the flows, which are postulated to be unchanged by the symmetries implemented in the code.