11,209 research outputs found
Global instability of low-density jets
The global stability of laminar axisymmetric low-density jets is investigated
in the low Mach number approximation. The linear modal dynamics is found to be
characterised by two features: a stable arc branch of eigenmodes and an
isolated eigenmode. Both features are studied in detail, revealing that,
whereas the former is highly sensitive to numerical domain size and its
existence can be linked to spurious feedback from the outflow boundary, the
latter is the physical eigenmode that is responsible for the appearance of
self-sustained oscillations in low-density jets observed in experiments at low
Mach numbers. In contrast to previous local spatio-temporal stability analyses,
the present global analysis permits, for the first time, the determination of
the critical conditions for the onset of global instability, as well the
frequency of the associated oscillations, without additional hypotheses,
yielding predictions in fair agreement with previous experimental observations.
It is shown that under the conditions of those experiments, viscosity variation
with composition, as well as buoyancy, only have a small effect on the onset of
instability
The structure of the ICM from High Resolution SPH simulations
We present results from a set of high (512^3 effective resolution), and
ultra-high (1024^3) SPH adiabatic cosmological simulations of cluster formation
aimed at studying the internal structure of the intracluster medium (ICM). We
derive a self-consistent analytical model of the structure of the intracluster
medium (ICM). We discuss the radial structure and scaling relations expected
from purely gravitational collapse, and show that the choice of a particular
halo model can have important consequences on the interpretation of
observational data. The validity of the approximations of hydrostatic
equilibrium and a polytropic equation of state are checked against results of
our simulations. The properties of the ICM are fully specified when a
'universal' profile is assumed for either the dark or the baryonic component.
We also show the first results from an unprecedented large-scale simulation of
500 Mpc/h and 2 times 512^3 gas and dark matter particles. This experiment will
make possible a detailed study of the large-scale distribution of clusters as a
function of their X-ray properties.Comment: 5 pages, 3 figures, to appear in the Proceedings of IAU Colloquium
195: "Outskirts of Galaxy Clusters: intense life in the suburbs", Torino
Italy, March 200
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