PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00063/1470
Lattice Boltzmann Methods
David R. Rector, Bruce J. Palmer, Brian Wood
Computational fluid dynamics simulations employ lattice Boltzmann equations for modeling multiphase flows in many
practical areas of environmental, energy, and chemical processing research. This project develops new lattice Boltzmann
equations for thermal and multiphase flow simulations.
Project Description
Lattice Boltzmann simulations have emerged as a
promising method for simulating fluid flow in several
regimes where traditional computational fluid dynamics
simulations are inadequate or fail altogether. These
include flows in topologically complex geometries such
as those encountered in porous media and multiphase
flows. Flows of these types are important in
environmental, energy, and processing applications. Over
the last several years, the Laboratory has made extensive
progress in extending and refining the capabilities of the
lattice Boltzmann technique for calculating flow and
transport behavior.
Although the original lattice Boltzmann (scalar) code was
suitable for simulating small systems and for
demonstrating the capabilities of the algorithms,
simulations of more complicated systems required code
and algorithm enhancements. The target application of
these capabilities is the simulation of microbial transport
through porous media. These enhancements include
implementing the algorithm on a parallel computer,
beginning work on an adaptive mesh refinement
capability, developing surface boundary conditions to
reflect microbe-wall interactions, and demonstrating these
capabilities by simulating transport through complex
porous media.
Results and Accomplishments
A major strength of the lattice Boltzmann simulation
method is that it is inherently parallelizable. We
parallelized the lattice Boltzmann program by performing
a block domain decomposition using the Global Array
tools developed at the Laboratory. The program shows
near linear speedup on both the Silicon Graphics, Inc.,
Power Challenge and the EMSL IBM SP computers for
typical porous media simulations.
136 FY 2000 Laboratory Directed Research and Development Annual Report
Another method of increasing the accuracy of the lattice
Boltzmann method is to embed a more detailed lattice
grid in those regions where more resolution is required.
For example, multiphase systems typically only require
greater resolution in the regions surrounding the interface.
A significant portion of this work is the passing of
information between the lattice subgrid and the primary
lattice through interpolation.
In FY 2000, we evaluated methods for incorporating
lattice subgrids into the lattice Boltzmann program. An
initial implementation of an adaptive mesh algorithm was
achieved using an adaptive mesh toolkit developed at
NASA, in Gaithersburg. In FY 2001, we plan to
investigate if adaptive mesh refinement routines in
NWGrid (grid generation software) can be used to get
improved results.
We have evaluated methods for generating porous media
geometries using experimental data and simulation. A
simulation method was established for generating model
porous geometries using randomly places spheres. A
three-dimensional image of a soil sample was obtained
using nuclear magnetic resonance imaging capabilities in
the EMSL, which were converted into a lattice Boltzmann
grid. Lattice Boltzmann simulations were performed on
both types of geometries to determine flow as a function
of applied pressure drop to determine permeability.
Figure 1 shows the x-direction velocity through a y-z
plane for a computer-generated model geometry.
For the upscaling portion of this research, the primary
accomplishment has been the development of an effective
reaction rate model for the process of microbial
attachment/detachment on mineral surfaces. The
effective model was developed by integrating a general
(Smoluchowski) transport equation that includes the
effects of cell-surface interaction forces. The new model
illustrates how fundamental physical properties (such as
the local diffusivity and the interaction force) can be used