3,172 research outputs found
Modeling incompressible thermal flows using a central-moment-based lattice Boltzmann method
In this paper, a central-moment-based lattice Boltzmann (CLB) method for
incompressible thermal flows is proposed. In the method, the incompressible
Navier-Stokes equations and the convection-diffusion equation for the
temperature field are sloved separately by two different CLB equations. Through
the Chapman-Enskog analysis, the macroscopic governing equations for
incompressible thermal flows can be reproduced. For the flow field, the tedious
implementation for CLB method is simplified by using the shift matrix with a
simplified central-moment set, and the consistent forcing scheme is adopted to
incorporate forcing effects. Compared with several D2Q5
multiple-relaxation-time (MRT) lattice Boltzmann methods for the temperature
equation, the proposed method is shown to be better Galilean invariant through
measuring the thermal diffusivities on a moving reference frame. Thus a higher
Mach number can be used for convection flows, which decreases the computational
load significantly. Numerical simulations for several typical problems confirm
the accuracy, efficiency, and stability of the present method. The grid
convergence tests indicate that the proposed CLB method for incompressible
thermal flows is of second-order accuracy in space
Three-Dimensional Multi-Relaxation Time (MRT) Lattice-Boltzmann Models for Multiphase Flow
In this paper, three-dimensional (3D) multi-relaxation time (MRT)
lattice-Boltzmann (LB) models for multiphase flow are presented. In contrast to
the Bhatnagar-Gross-Krook (BGK) model, a widely employed kinetic model, in MRT
models the rates of relaxation processes owing to collisions of particle
populations may be independently adjusted. As a result, the MRT models offer a
significant improvement in numerical stability of the LB method for simulating
fluids with lower viscosities. We show through the Chapman-Enskog multiscale
analysis that the continuum limit behavior of 3D MRT LB models corresponds to
that of the macroscopic dynamical equations for multiphase flow. We extend the
3D MRT LB models developed to represent multiphase flow with reduced
compressibility effects. The multiphase models are evaluated by verifying the
Laplace-Young relation for static drops and the frequency of oscillations of
drops. The results show satisfactory agreement with available data and
significant gains in numerical stability.Comment: Accepted for publication in the Journal of Computational Physic
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