Development of flow and transport models and effective parameters for flow with dynamic boundary conditions
Zusammenfassung der Projektergebnisse
In our project we investigated flow and transport in media with time dependent boundary conditions, in particular with changing flow directions. We used numerical simulations and physical experiments to validate our numerical experiments. We also studied infiltration into dry soils. We evaluated physical laboratory experiments on unstable infiltration into dry porous media counducted during our last project phase. We evaluated finger properties that are commonly used to characterize instable flow such as the finger width, velocity and penetration depth. Our analysis of macroscopically homogeneous experiments, where either glass beads or sand with very similar grain size distribution were used as porous medium, showed very different results regarding finger properties. We were able to illustrate that besides hydraulic conductivity, grain shape of the porous material has a substantial influence on the finger properties. We also analyzed infiltration experiments where heterogeneity was induced by block-shaped inclusions. We found that heterogeneity did not stabilize flow. Fingers commonly impinged on an inclusion, filled it and then left the inclusion with unchanged width. Fingers touching inclusions continued with a decreased speed. The data gathered during our analysis will be made publicly availiable and can be used to test extended Richards models. We investigated the influence of dynamic boundary conditions on flow and transport in heterogeneous porous media by analyzing numerical simulations, where cyclic inilftration and evaporation with different rates and durations was applied to the surface of a heterogeneous porous medium. We found that dynamic boundary conditions can have a strong effect on solute transport and could induce entirely different transport mechanisms. We were able to distinguish three general transport regimes, quantified by structure of the heterogeneity, unsaturated hydraulic conductivity curves of the materials, infiltration rates and evaporation length. From this we can conclude that it is necessary to explicitly consider dynamic boundary conditions to estimate transport of dissolved substances instead of applying a net averaged temporally constant infiltration, which is frequently done. With the insights obtained from our detailed 2d numerical simulations, we developed an upscaled model with effective parameters that can be solved semi-analytically and is able to reproduce solute breakthrough curves of the detailed model well. Parameters could be estimated based on material parameters, length scales of structures and infiltration and evaporation rates and duration. To validate the models, we carried out physical laboratory experiments under dynamic boundary conditions. Water contents were measured via X-ray radiography and solute transport was evaluated qualitatively via use of multiple dye tracers and image analysis. First results from our physical experiments confirm the lateral transport mechanisms that are crucial for the distinction of different transport regimes. Additionally to the studies on flow and transport with changing boundary conditions, we developed an upscaled model for a statistical interface growth model (bridging from the pore to the continuum scale). Although the upscaled model could reproduce the averaged interfaces, it is not locally mass conservative and has therefore not the fundamental properties of a continuum scale flow model. This limits the use of statistical interface models to describe fluid-fluid displacement processes in porous media.
Projektbezogene Publikationen (Auswahl)
- (2016): Experimental and numerical analysis of air trapping in a porous medium with coarse textured inclusions, Acta Geophysica 64, 2487-2509
P. Szymanska, A. Szymkiewikc, C. Schuetz, W. Tisler, I. Neuweiler and R. Helmig
(Siehe online unter https://doi.org/10.1515/acgeo-2016-0095) - (2016): Noise-Driven Interfaces and Their Macroscopic Representation, Physical Review E 94, 052802
Dentz, M., I. Neuweiler, Y. Méheust and D. M. Tartakovsky
(Siehe online unter https://doi.org/10.1103/PhysRevE.94.052802) - (2016): Solute Transport in Heterogeneous Soil with Time-Dependent Boundary Conditions, Vadose Zone Journal 15 (6)
Cremer, C.J.M., I. Neuweiler, M. Bechtold, J. Vanderborght
(Siehe online unter https://doi.org/10.2136/vzj2015.11.0144)
