2,319 research outputs found
A unified operator splitting approach for multi-scale fluid-particle coupling in the lattice Boltzmann method
A unified framework to derive discrete time-marching schemes for coupling of
immersed solid and elastic objects to the lattice Boltzmann method is
presented. Based on operator splitting for the discrete Boltzmann equation,
second-order time-accurate schemes for the immersed boundary method, viscous
force coupling and external boundary force are derived. Furthermore, a modified
formulation of the external boundary force is introduced that leads to a more
accurate no-slip boundary condition. The derivation also reveals that the
coupling methods can be cast into a unified form, and that the immersed
boundary method can be interpreted as the limit of force coupling for vanishing
particle mass. In practice, the ratio between fluid and particle mass
determines the strength of the force transfer in the coupling. The integration
schemes formally improve the accuracy of first-order algorithms that are
commonly employed when coupling immersed objects to a lattice Boltzmann fluid.
It is anticipated that they will also lead to superior long-time stability in
simulations of complex fluids with multiple scales
Liquid-gas-solid flows with lattice Boltzmann: Simulation of floating bodies
This paper presents a model for the simulation of liquid-gas-solid flows by
means of the lattice Boltzmann method. The approach is built upon previous
works for the simulation of liquid-solid particle suspensions on the one hand,
and on a liquid-gas free surface model on the other. We show how the two
approaches can be unified by a novel set of dynamic cell conversion rules. For
evaluation, we concentrate on the rotational stability of non-spherical rigid
bodies floating on a plane water surface - a classical hydrostatic problem
known from naval architecture. We show the consistency of our method in this
kind of flows and obtain convergence towards the ideal solution for the
measured heeling stability of a floating box.Comment: 22 pages, Preprint submitted to Computers and Mathematics with
Applications Special Issue ICMMES 2011, Proceedings of the Eighth
International Conference for Mesoscopic Methods in Engineering and Scienc
Simulation of immiscible two-phase flows based on a kinetic diffuse interface approach
International audienceA direct numerical simulation (DNS) code is developed to simulate immiscible two-phase flows based on the recently developed discrete unified gas-kinetic scheme (DUGKS). This scheme simulates hydrodynamic equations of the quasi-incompressible Cahn-Hilliard-Navier-Stokes system by the use of two mesoscopic distributions and the proper design of their equilibrium distributions and source terms. Several immiscible two-phase flows are used to validate the scheme in both 2D and 3D, including a stationary droplet in 2D and 3D, the Rayleigh-Taylor flows, and two-phase homogeneous isotropic decaying turbulence. The results obtained by DUGKS are compared carefully to these from the literature and the ARCHER code, i.e., a Coupled Level Set-Volume of Fluid (CLSVOF) method. The comparisons indicate that DUGKS is a promising scheme for direct numerical simulations of immiscible two-phase flows
A conservative coupling algorithm between a compressible flow and a rigid body using an Embedded Boundary method
This paper deals with a new solid-fluid coupling algorithm between a rigid
body and an unsteady compressible fluid flow, using an Embedded Boundary
method. The coupling with a rigid body is a first step towards the coupling
with a Discrete Element method. The flow is computed using a Finite Volume
approach on a Cartesian grid. The expression of numerical fluxes does not
affect the general coupling algorithm and we use a one-step high-order scheme
proposed by Daru and Tenaud [Daru V,Tenaud C., J. Comput. Phys. 2004]. The
Embedded Boundary method is used to integrate the presence of a solid boundary
in the fluid. The coupling algorithm is totally explicit and ensures exact mass
conservation and a balance of momentum and energy between the fluid and the
solid. It is shown that the scheme preserves uniform movement of both fluid and
solid and introduces no numerical boundary roughness. The effciency of the
method is demonstrated on challenging one- and two-dimensional benchmarks
A gas-surface interaction algorithm for discrete velocity methods in predicting rarefied and multi-scale flows
The rarefied flow and multi-scale flow are crucial for the aerodynamic design
of spacecraft, ultra-low orbital vehicles and plumes. By introducing a discrete
velocity space, the discrete velocity method (DVM) and unified methods can
capture complex and non-equilibrium distribution functions and describe flow
behaviors exactly. The unified methods predict flows from continuum to rarefied
regimes by adopting unified modeling, and they can be further applied to other
multi-scale physics such as radiation heat transfer, phonon heat transfer and
plasma. In the flow field, the concrete dynamic process needs to describe the
gas-gas interaction and gas-surface interaction (GSI). However, in both DVM and
unified methods, only a simple but not accurate GSI is used, which can be
regarded as a Maxwell GSI with a fixed accommodation coefficient of 1 (full
accommodation) at the present stage. To overcome the bottleneck in extending
DVM and unified methods to the numerical experiment and investigate real
multi-scale flow physics, this paper realizes precise GSI in the DVM framework
by constructing the boundary conditions of a concrete Maxwell GSI with an
adjustable accommodation coefficient. In the constructing process, the problems
of macro-conservation and micro-consistency in the DVS at the boundary are well
solved by reflected macroscopic flux and interpolation distribution function
and interpolation error correction, respectively. Meanwhile, considering that
the multi-scale flows in the background of aeronautics and aerospace are often
at supersonic and hypersonic speeds, the unstructured velocity space (UVS) is
essential. From the perspective of generality, the GSI is forced on UVS.
Besides, by combined with the unified method (the unified gas-kinetic scheme in
the paper), the effectiveness and validity of the present GSI on the DVM
framework are verified by a series of simulations
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