Contributions to the large-scale Simulation of Flow and Transport in Heterogeneous Porous Media

Powerful software tools for the sequential and parallel simulation of water and solute transport in strongly heterogeneous porous media are developed based on an extensive discussion of the involved processes, as well as of numerical and implementation aspects. The tools are applied to study problems involving parameter estimation in heterogeneous porous media, virtual soil systems and dynamic effects in heterogeneous soils. The excelent scalability of the numerical solver for both water as well as solute transport is investigated on BlueGene/P and /Q type supercomputers. As file transfer can be a bottleneck for large-scale simulations it is analysed carefully, obtaining near optimal data transfer rates with data sets of up to 17.5 Terabyte

Coupled transport in natural porous media

As the interactions between transport processes are important for a number of interesting systems, a set of partial differential equations and appropriate parameter functions for the study of coupled water, heat, gas and solute transport was formulated and a state of the art computer model for the numerical solution of the equation system was created. A new phase pressure/partial pressure formulation for the coupled transport of liquid and gas phase was developed. The model was used to simulate the water and energy dynamics of a permafrost soil. A good qualitative agreement was achieved. Differences between modeled and measured data could be explained with heterogeneity in combination with the model's sensitivity to a change in hydraulic parameters. Water vapor and solute transport had no effect on the simulation result but transport of liquid water proved to be an important heat transfer process near 0 °C. The impact of the chosen parameterization and model on the simulation of a multistep outflow experiment was analyzed. Differences between a model based on Richards' equation and a twophase model only occurred when the Brooks-Corey parameterization was used. The results of the twophase model showed a retarded drainage and a hysteresis during imbibation which is in good agreement with experimental results

Numerical simulation of growth of Escherichia coli in unsaturated porous media

A model for the aerobic and anaerobic growth of Escherichia coli (HB101 K12 pGLO) depending on the concentration of oxygen and DOC as substrate has been developed based on laboratory batch experiments. Using inverse modelling to obtain optimal sets of parameters, it could be shown that a model based on a modified double Contois kinetic can predict cell densities, organic carbon utilisation, oxygen transfer and utilisation rates for a large number of experiments under aerobic and anaerobic conditions with a single unique set of parameters. The model was extended to describe growth of E. coli in unsaturated porous media, combining diffusion, phase exchange and microbiological growth. Experiments in a Hele-Shaw cell, filled with quartz sand, were conducted to study bacterial growth in the capillary fringe above a saturated porous medium. Cell density profiles in the Hele-Shaw cell were predicted with the growth model and the parameters from the batch experiments without any further calibration. They showed a very good qualitative and quantitative agreement with cell densities determined from samples taken from the Hele-Shaw cell by re-suspension and subsequent counting. Thus it could be shown, that it is possible to successfully transfer growth parameters from batch experiments to porous media for both aerobic and anaerobic conditions.Comment: Minor changes in conclusions, results unchange

Multi-step and two-step experiments in heterogeneous porous media to evaluate the relevance of dynamic effects

International audienceThe determination of hydraulic properties in non-stationary experiments is suspected to be affected by dynamic effects. This is based on thermodynamic considerations on the pore scale displacement of wetting and non-wetting phase. But also macroscopic heterogeneities at the continuum scale may influence the dynamics of water during drainage and wetting. In this paper we investigate both aspects. Firstly, we present the results of typical multi-step outflow experiments in heterogeneous sand columns which are compared with twostep outflow experiments covering the same pressure range. The discrepancies caused by pressure steps of different size reveal the impact of dynamic effects due to the non-stationarity of the experiments. Secondly, the influence of macroscopic heterogeneities is investigated based on two-dimensional heterogeneous parameter fields where we compare static hydraulic properties with those obtained from simulated dynamic experiments. These analyses are restricted to numerical experiments because the focus is on the effect of heterogeneities and not on the validity of the applied model (i.e. Richards equation). We found that dynamic effects are not critical neither during the non-stationary experiments nor for heterogeneous parameter fields. This is a positive message for the usage of multi-step outflow experiments to estimate hydraulic parameters. A prerequisite for this clear statement was the introduction of a highly flexible parametrization of the pressure-saturation relation psi(teta) which has the only physical constraint to be monotone