|Phone:||+49 711 685-67652|
|Fax:||+49 711 685-63658|
|Email:||Thomas.Zauner _at_ icp.uni-stuttgart.de|
Institute for Computational Physics
The general field of my research is the computational investigations of natural porous media. A typical example of such a porous medium is sandstone. It consists of very small consolidated grains that form a solid backbone but, due to the space between individual grains, is permeable for many fluids. Insight into physical transport phenomena of natural porous media, such as flow rates, trapping behavior and prediction of effective transport coefficients, has always been of great practical interest for the oil and gas industry and has currently drawn public attention in the context of CO2 sequestration. Porous materials are also used for many industrial applications for example in filtration processes, as catalyst in chemical reactions or building materials with specially physical properties (insulating material).
Two scientific problems that I address in my work are:
- Developing algorithms that generate realistic and macroscopic computer models for granular porous media.These models will be made of many hundred millions of individual grains whose positions and orientations must fulfill certain correlations and restrictions. This large computational demand requires highly efficient parallelized computer algorithms.
- Evaluating numerical methods to allow accurate and predictive calculations of physical transport properties. These calculations usually require numerically solving partial differential equations within a chosen discretization scheme and at a specific resolution or order of accuracy.
Realistic computer models for granular porous media
In the reconstruction procedure a dense packing of possibly polydisperse spheres is created. The packing must fulfill some given restrictions such as density, overlap and size distribution and more. The spheres are subsequentially substituted by more complex geometrical objects determined by the shapes of the grains used in the specific model. One option is to use polyhedrons as grain shape. The resulting model then is a continuum model in the sense that the microgeometry is defined by a points in the continuum and polyhedrons with analytical defined shapes and orientations. An example of such a model for Fountainebleau sandstone is shown in image 1. This continuous computer model can then be discretized at any desired resolution for further analysis and computer simulations, see image 2.
A porous mediums permeability is an example of a effective transport parameter. It describes the mediums ability to transmit fluid flow through it. Using Darcy's law the permeability of a porous medium can be calculated from the velocity and corresponding pressure field on the porescale. These fields are solution of hydrodynamic partial differential equations describing fluid flow on the porescale. Many different numerical methods that solve different hydrodynamic equations can be used to obtain the velocity and pressure field. Possibilities are Navier-Stokes simulations or Lattice-Boltzmann simulations. Our Lattice-Boltzmann implementation, for example, numerically solves the Boltzmann equation using a transient explicit finite-difference scheme. The simulation is then carried out long enough to obtain a stationary solution. From this stationary solution the hydrodynamic fields can be calculated.
 A. Narvaez, T. Zauner, F. Raischel, R. Hilfer, J. Harting, “Quantitative analysis of numerical estimates for the permeability of porous media from lattice-Boltzmann simulations”, Journal of Statistical Mechanics, P11026, 2010, Preprint
 S. Grottel, G. Reina, T. Zauner, R. Hilfer, T. Ertl, "Particle-based Rendering for Porous Media", SIGRAD, 2010, Preprint
 J. Harting, T. Zauner, R. Weeber, and R. Hilfer Numerical modeling of fluid flow in porous media and in driven colloidal suspensions in High Performance Computing in Science and Engineering '08, edited by W. Nagel, D. Kröner, M. Resch, Springer ,2008. Preprint