50,791 research outputs found
Spinodal decomposition of off-critical quenches with a viscous phase using dissipative particle dynamics in two and three spatial dimensions
We investigate the domain growth and phase separation of
hydrodynamically-correct binary immiscible fluids of differing viscosity as a
function of minority phase concentration in both two and three spatial
dimensions using dissipative particle dynamics. We also examine the behavior of
equal-viscosity fluids and compare our results to similar lattice-gas
simulations in two dimensions.Comment: 34 pages (11 figures); accepted for publication in Phys. Rev.
Simulating Three-Dimensional Hydrodynamics on a Cellular-Automata Machine
We demonstrate how three-dimensional fluid flow simulations can be carried
out on the Cellular Automata Machine 8 (CAM-8), a special-purpose computer for
cellular-automata computations. The principal algorithmic innovation is the use
of a lattice-gas model with a 16-bit collision operator that is specially
adapted to the machine architecture. It is shown how the collision rules can be
optimized to obtain a low viscosity of the fluid. Predictions of the viscosity
based on a Boltzmann approximation agree well with measurements of the
viscosity made on CAM-8. Several test simulations of flows in simple geometries
-- channels, pipes, and a cubic array of spheres -- are carried out.
Measurements of average flux in these geometries compare well with theoretical
predictions.Comment: 19 pages, REVTeX and epsf macros require
Thermal photons in QGP and non-ideal effects
We investigate the thermal photon production-rates using one dimensional
boost-invariant second order relativistic hydrodynamics to find proper time
evolution of the energy density and the temperature. The effect of
bulk-viscosity and non-ideal equation of state are taken into account in a
manner consistent with recent lattice QCD estimates. It is shown that the
\textit{non-ideal} gas equation of state i.e behaviour
of the expanding plasma, which is important near the phase-transition point,
can significantly slow down the hydrodynamic expansion and thereby increase the
photon production-rates. Inclusion of the bulk viscosity may also have similar
effect on the hydrodynamic evolution. However the effect of bulk viscosity is
shown to be significantly lower than the \textit{non-ideal} gas equation of
state. We also analyze the interesting phenomenon of bulk viscosity induced
cavitation making the hydrodynamical description invalid. We include the
viscous corrections to the distribution functions while calculating the photon
spectra. It is shown that ignoring the cavitation phenomenon can lead to
erroneous estimation of the photon flux.Comment: 11 pages, 13 figures; accepted for publication in JHE
Effect of bulk viscosity on Elliptic Flow near QCD phase transition
Effects of the bulk viscosity on the elliptic flow are studied. To introduce
a realistic equation of state and transport coefficients, we apply the results
of the lattice QCD and hadron resonance gas calculations for these quantities.
We found that the bulk viscosity acts in a non trivial manner on the elliptic
flow . The reduction of is more effective at low
compared to the case of shear viscosity, whereas at high , the situation
is reversed, leading to enhancement. We argue that this is caused by
the competition of the critical behaviors of the equation of state and the
transport coefficients. We further found that Grad's method with the 14 moments
approximation is not applicable to estimate the viscous effects for the
one-particle distribution function at the freeze out.Comment: 14 pages, 12 figure
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