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Three-dimensional micro-droplet collision simulation using the Lattice Boltzmann method
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The modelling of binary droplet collisions has important applications in many engineering problems, including spray coating and fuel injection. The Lattice Boltzmann method (LBM) is a well established technique for modelling multiphase fluids, and does so without the difficulties of explicit interface tracking found in other CFD methods. However, simulating droplet collisions under realistic conditions remains a complex problem. Challenges include reproducing the different collision outcomes observed experimentally (Qian and Law, 1997), and maintaining a stable simulation at sufficiently high Reynolds and Weber numbers, and with a high density ratio between the liquid and gas phases. Although previous studies have achieved these goals individually, they have not been successfully combined to simulate droplet collisions with realistic physical parameters. A number of different methods for extending the LBM for multiphase flow exist, with the Shan-Chen interparticle potential method (Shan and Chen, 1993) being the basic model used here. Many extensions to improve the original Shan-Chen method have been proposed, to improve achievable Reynolds number and density ratio. Using combinations of these, both coalescence and separation of two-dimensional droplets were successfully simulated at density ratios of order 1000, and high Weber numbers (Lycett-Brown et al., 2011). In this study, the developed methodologies in Lycett-Brown et al. (2011) are extended to simulate three dimensional micro-droplet collisions by making use of the LBM’s excellent scalability on massively parallel computers. These high-resolution simulations are also compared with low-resolution three-dimensional simulations using a multiple-relaxation-time LBM approach (Monaco and Luo, 2008).This study is funded by the Engineering and Physical Sciences Research Council for Grant No. EP/I000801/1 and a HEC Studentship
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
Droplet collision simulation by multi-speed lattice Boltzmann method
Realization of the Shan-Chen multiphase flow lattice Boltzmann model is considered in the framework of the higher-order Galilean invariant lattices. The present multiphase lattice Boltzmann model is used in two dimensional simulation of droplet collisions at high Weber numbers. Results are found to be in a good agreement with experimental findings
Generalized Lattice Boltzmann Method with multi-range pseudo-potential
The physical behaviour of a class of mesoscopic models for multiphase flows
is analyzed in details near interfaces. In particular, an extended
pseudo-potential method is developed, which permits to tune the equation of
state and surface tension independently of each other. The spurious velocity
contributions of this extended model are shown to vanish in the limit of high
grid refinement and/or high order isotropy. Higher order schemes to implement
self-consistent forcings are rigorously computed for 2d and 3d models. The
extended scenario developed in this work clarifies the theoretical foundations
of the Shan-Chen methodology for the lattice Boltzmann method and enhances its
applicability and flexibility to the simulation of multiphase flows to density
ratios up to O(100)
Mesoscopic model for soft flowing systems with tunable viscosity ratio
We propose a mesoscopic model of binary fluid mixtures with tunable viscosity
ratio based on the two-range pseudo-potential lattice Boltzmann method, for the
simulation of soft flowing systems. In addition to the short range repulsive
interaction between species in the classical single-range model, a competing
mechanism between the short range attractive and mid-range repulsive
interactions is imposed within each species. Besides extending the range of
attainable surface tension as compared with the single-range model, the
proposed scheme is also shown to achieve a positive disjoining pressure,
independently of the viscosity ratio. The latter property is crucial for many
microfluidic applications involving a collection of disperse droplets with a
different viscosity from the continuum phase. As a preliminary application, the
relative effective viscosity of a pressure-driven emulsion in a planar channel
is computed.Comment: 14page
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