IFIBA   22255
INSTITUTO DE FISICA DE BUENOS AIRES
Unidad Ejecutora - UE
artículos
Título:
Structures in magnetohydrodynamic turbulence: Detection and scaling
Autor/es:
V.M. URITSKY; A. POUQUET; D. ROSENBERG; P.D. MININNI; E.F. DONOVAN
Revista:
PHYSICAL REVIEW E
Editorial:
AMER PHYSICAL SOC
Referencias:
Año: 2010 vol. 82 p. 5632601 - 5632615
ISSN:
1539-3755
Resumen:
We present a systematic analysis of statistical properties of turbulent
current and vorticity structures at a given time using cluster analysis.
The data stem from numerical simulations of decaying three-dimensional
magnetohydrodynamic turbulence in the absence of an imposed uniform
magnetic field; the magnetic Prandtl number is taken equal to unity, and
we use a periodic box with grids of up to 15363 points and
with Taylor Reynolds numbers up to 1100. The initial conditions are
either an X -point configuration embedded in three dimensions, the
so-called Orszag-Tang vortex, or an Arnold-Beltrami-Childress
configuration with a fully helical velocity and magnetic field. In each
case two snapshots are analyzed, separated by one turn-over time,
starting just after the peak of dissipation. We show that the algorithm
is able to select a large number of structures (in excess of 8000) for
each snapshot and that the statistical properties of these clusters are
remarkably similar for the two snapshots as well as for the two flows
under study in terms of scaling laws for the cluster characteristics,
with the structures in the vorticity and in the current behaving in the
same way. We also study the effect of Reynolds number on cluster
statistics, and we finally analyze the properties of these clusters in
terms of their velocity-magnetic-field correlation. Self-organized
criticality features have been identified in the dissipative range of
scales. A different scaling arises in the inertial range, which cannot
be identified for the moment with a known self-organized criticality
class consistent with magnetohydrodynamics. We suggest that this range
can be governed by turbulence dynamics as opposed to criticality and
propose an interpretation of intermittency in terms of propagation of
local instabilities.