6,726 research outputs found
Modelling the Interfacial Flow of Two Immiscible Liquids in Mixing Processes
This paper presents an interface tracking method for modelling the flow of immiscible metallic liquids in mixing processes. The methodology can provide an insight into mixing processes for studying the fundamental morphology development mechanisms for immiscible interfaces. The volume-of-fluid (VOF) method is adopted in the present study, following a review of various modelling approaches for immiscible fluid systems. The VOF method employed here utilises the piecewise linear for interface construction scheme as well as the continuum surface force algorithm for surface force modelling. A model coupling numerical and experimental data is established. The main flow features in the mixing process are investigated. It is observed that the mixing of immiscible metallic liquids is strongly influenced by the viscosity of the system, shear forces and turbulence. The numerical results show good qualitative agreement with experimental results, and are useful for optimisating the design of mixing casting processes
The dynamics of dissipative multi-fluid neutron star cores
We present a Newtonian multi-fluid formalism for superfluid neutron star
cores, focussing on the additional dissipative terms that arise when one takes
into account the individual dynamical degrees of freedom associated with the
coupled "fluids". The problem is of direct astrophysical interest as the nature
of the dissipative terms can have significant impact on the damping of the
various oscillation modes of the star and the associated gravitational-wave
signatures. A particularly interesting application concerns the
gravitational-wave driven instability of f- and r-modes. We apply the developed
formalism to two specific three-fluid systems: (i) a hyperon core in which both
Lambda and Sigma^- hyperons are present, and (ii) a core of deconfined quarks
in the colour-flavour-locked phase in which a population of neutral K^0 kaons
is present. The formalism is, however, general and can be applied to other
problems in neutron-star dynamics (such as the effect of thermal excitations
close to the superfluid transition temperature) as well as laboratory
multi-fluid systems.Comment: RevTex, no figure
Relativistic hydrodynamics in heavy-ion collisions: general aspects and recent developments
Relativistic hydrodynamics has been quite successful in explaining the
collective behaviour of the QCD matter produced in high energy heavy-ion
collisions at RHIC and LHC. We briefly review the latest developments in the
hydrodynamical modeling of relativistic heavy-ion collisions. Essential
ingredients of the model such as the hydrodynamic evolution equations,
dissipation, initial conditions, equation of state, and freeze-out process are
reviewed. We discuss observable quantities such as particle spectra and
anisotropic flow and effect of viscosity on these observables. Recent
developments such as event-by-event fluctuations, flow in small systems
(proton-proton and proton-nucleus collisions), flow in ultra central
collisions, longitudinal fluctuations and correlations and flow in intense
magnetic field are also discussed.Comment: 36 pages, 16 figures, invited review, published versio
A covariant action principle for dissipative fluid dynamics: From formalism to fundamental physics
We present a new variational framework for dissipative general relativistic
fluid dynamics. The model extends the convective variational principle for
multi-fluid systems to account for a range of dissipation channels. The key
ingredients in the construction are i) the use of a lower dimensional matter
space for each fluid component, and ii) an extended functional dependence for
the associated volume forms. In an effort to make the concepts clear, the
formalism is developed in steps with the model example of matter coupled to
heat considered at each level. Thus we discuss a model for heat flow, derive
the relativistic Navier-Stokes equations and discuss why the individual
dissipative stress tensors need not be spacetime symmetric. We argue that the
new formalism, which notably does not involve an expansion away from an assumed
equilibrium state, provides a conceptual breakthrough in this area of research
and provide an ambitious list of directions in which one may want to extend it
in the future. This involves an exciting set of problems, relating to both
applications and foundational issues.Comment: 21 pages RevTex, 3 pdf figures, matches the published version. arXiv
admin note: text overlap with arXiv:1107.1005 by other author
Towards dense, realistic granular media in 2D
The development of an applicable theory for granular matter - with both qualitative and quantitative value - is a challenging prospect, given the multitude of states, phases and (industrial) situations it has to cover. Given the general balance equations for mass, momentum and energy, the limiting case of dilute and almost elastic granular gases, where kinetic theory works perfectly well, is the starting point.\ud
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In most systems, low density co-exists with very high density, where the latter is an open problem for kinetic theory. Furthermore, many additional nonlinear phenomena and material properties are important in realistic granular media, involving, e.g.:\ud
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(i) multi-particle interactions and elasticity\ud
(ii) strong dissipation,\ud
(iii) friction,\ud
(iv) long-range forces and wet contacts,\ud
(v) wide particle size distributions and\ud
(vi) various particle shapes.\ud
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Note that, while some of these issues are more relevant for high density, others are important for both low and high densities; some of them can be dealt with by means of kinetic theory, some cannot.\ud
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This paper is a review of recent progress towards more realistic models for dense granular media in 2D, even though most of the observations, conclusions and corrections given are qualitatively true also in 3D.\ud
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Starting from an elastic, frictionless and monodisperse hard sphere gas, the (continuum) balance equations of mass, momentum and energy are given. The equation of state, the (Navier–Stokes level) transport coefficients and the energy-density dissipation rate are considered. Several corrections are applied to those constitutive material laws - one by one - in order to account for the realistic physical effects and properties listed above
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