Turbulence Science
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This figure is a close-up view
of a magnetic current sheet in an MHD computation done on a grid of
15363 points. Current sheets are numerous in the earth's
magnetosphere and in the solar corona, and their instability is poorly
understood. The figure shows current sheet roll-up seen in nature and
similar to the Kelvin-Helmoltz instability of classical fluids;
turbulence science studies are designed to help us understand the
factors causing such instability. |
The Turbulence Numerics Team (TNT) investigates homogeneous and
isotropic turbulence at high Reynolds numbers, incorporating new
phenomena:
advection-diffusion with
condensation and dispersion in midlatitude troposphere,
bounds on energy and
enstrophy dissipation,
instability domain
in shear stratified fluids, intermittency in
models of turbulent flows,
and rotation (first with periodic boundary conditions). A striking
result concerns the determination of
nonlocality of nonlinear
transfer, i.e. the relative importance of interactions between
widely separated scales.
TNT's FY 2006 work in magnetohydrodynamics (MHD) pursued the search for
threshold for dynamo action
in fluids at low magnetic Prandtl numbers PM for a variety of
flows, and the instability was detected down to PM~0.005;
inverse cascade of magnetic
helicity and Hall MHD as relevant to the magnetosphere are also
investigated. We also began exploring
turbulent flows with boundaries
but at moderate Reynolds numbers. Furthermore, code was developed to
achieve a computation at NCAR of decaying MHD turbulence on a grid of
1,5363 points,
self-similar growth of current maxima was detected, and roll-up of current
sheets in a turbulent environment was observed for the first time
(see figure).
This work will be pursued further in FY 2007, and we will also
explore turbulent flows in two dimensions with
adaptive codes and
multiresolution analysis.
More information about this work appears in the
CISL Research Catalog.
TNT research supports NCAR's strategic priorities "Conducting research
in computer science, applied mathematics, statistics, and numerical
models" and "Creating a conceptual framework for integrating research
across time and space scales to aid decision makers and enrich
understanding of processes across scales." TNT is sponsored by NSF
Core funds and partially by NSF grant CMG-0327888.
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