1,885 research outputs found
Numerical simulation of single droplet dynamics in three-phase flows using ISPH
In this study, a new surface tension formulation for modeling incompressible, immiscible three-phase fluid flows in the context of incompressible smoothed particle hydrodynamics (ISPH) in two dimensions has been proposed. A continuum surface force model is employed to transform local surface tension force to a volumetric force while physical surface tension coefficients are expressed as the sum of phase specific surface tension coefficients, facilitating the implementation of the proposed method at triple junctions where all three phases are present. Smoothed color functions at fluid interfaces along with artificial particle displacement throughout the computational domain are combined to increase accuracy and robustness of the model. In order to illustrate the effectiveness of the proposed method, several numerical simulations have been carried out and results are compared to analytical data available in literature. Results obtained by simulations are compatible with analytical data, demonstrating that the ISPH scheme proposed here is capable of handling three-phase flows accurately
Comparison of multiphase SPH and LBM approaches for the simulation of intermittent flows
Smoothed Particle Hydrodynamics (SPH) and Lattice Boltzmann Method (LBM) are
increasingly popular and attractive methods that propose efficient multiphase
formulations, each one with its own strengths and weaknesses. In this context,
when it comes to study a given multi-fluid problem, it is helpful to rely on a
quantitative comparison to decide which approach should be used and in which
context. In particular, the simulation of intermittent two-phase flows in pipes
such as slug flows is a complex problem involving moving and intersecting
interfaces for which both SPH and LBM could be considered. It is a problem of
interest in petroleum applications since the formation of slug flows that can
occur in submarine pipelines connecting the wells to the production facility
can cause undesired behaviors with hazardous consequences. In this work, we
compare SPH and LBM multiphase formulations where surface tension effects are
modeled respectively using the continuum surface force and the color gradient
approaches on a collection of standard test cases, and on the simulation of
intermittent flows in 2D. This paper aims to highlight the contributions and
limitations of SPH and LBM when applied to these problems. First, we compare
our implementations on static bubble problems with different density and
viscosity ratios. Then, we focus on gravity driven simulations of slug flows in
pipes for several Reynolds numbers. Finally, we conclude with simulations of
slug flows with inlet/outlet boundary conditions. According to the results
presented in this study, we confirm that the SPH approach is more robust and
versatile whereas the LBM formulation is more accurate and faster
Multiphase smoothed-particle hydrodynamics
We adapt the smoothed-particle hydrodynamics (SPH) technique to allow a multiphase fluid in which SPH particles of widely differing density may be freely intermixed. Applications include modelling of galaxy formation and cooling flows
Modelling discontinuities and Kelvin-Helmholtz instabilities in SPH
In this paper we discuss the treatment of discontinuities in Smoothed
Particle Hydrodynamics (SPH) simulations. In particular we discuss the
difference between integral and differential representations of the fluid
equations in an SPH context and how this relates to the formulation of dissip
ative terms for the capture of shocks and other discontinuities.
This has important implications for many problems, in particular related to
recently highlighted problems in treating Kelvin-Helmholtz instabilities across
entropy gradients in SPH. The specific problems pointed out by Agertz et al.
(2007) are shown to be related in particular to the (lack of) treatment of
contact discontinuities in standard SPH formulations which can be cured by the
simple application of an artificial thermal conductivity term. We propose a new
formulation of artificial thermal conductivity in SPH which minimises
dissipation away from discontinuities and can therefore be applied quite
generally in SPH calculations.Comment: 31 pages, 10 figures, submitted to J. Comp. Phys. Movies + hires
version available at http://www.astro.ex.ac.uk/people/dprice/pubs/kh/ . v3:
modified as per referee's comments - comparison with Ritchie & Thomas
formulation added, quite a few typos fixed. No major change in metho
Galaxy Mergers with Adaptive Mesh Refinement: Star Formation and Hot Gas Outflow
In hierarchical structure formation, merging of galaxies is frequent and
known to dramatically affect their properties. To comprehend these interactions
high-resolution simulations are indispensable because of the nonlinear coupling
between pc and Mpc scales. To this end, we present the first adaptive mesh
refinement (AMR) simulation of two merging, low mass, initially gas-rich
galaxies (1.8e10 Ms each), including star formation and feedback. With galaxies
resolved by ~2e7 total computational elements, we achieve unprecedented
resolution of the multiphase interstellar medium, finding a widespread
starburst in the merging galaxies via shock-induced star formation. The high
dynamic range of AMR also allows us to follow the interplay between the
galaxies and their embedding medium depicting how galactic outflows and a hot
metal-rich halo form. These results demonstrate that AMR provides a powerful
tool in understanding interacting galaxies.Comment: 4 pages, 5 figures, Accepted for publication in the Astrophysical
Journal Letters, Image resolution greatly reduced, High-resolution version of
this article and movies are available at
http://www.jihoonkim.org/index/research.html#merge
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