Research Project A02

Exchange processes across a porous-medium free-flow interface occur in a wide range of environmental, technical and bio-mechanical systems. The primary objectives of this project are to (i) analyse and improve the theory, as well as (ii) offer solution methods for non-isothermal, multi-phase, multi-component flow and transport processes at a porous-medium free-flow interface and (iii) investigate the influence of these processes on both the porous medium and free-flow region for various application scales.

The challenge of including scale-dependent, interface-driven processes into mathematical and numerical models for systems of coupled free flow and porous-medium flow is the primary object of research of project A02. We found that existing models usually operate on either the pore scale or on the REV scale which has the following drawbacks: pore-scale models provide a detailed physical insight into various types of processes but their prohibitively high computational demand makes them only applicable to relatively small domains. On the other hand, the higher degree of computational efficiency provided by REV-scale models comes at the price of losing potentially process-relevant sub-scale information. In addition, several assumptions and simplifications commonly involved in REV-scale modelling can only be justified for a limited range of applications and flow conditions.

Our main goal is the development of new model concepts combining the strengths of both pore-scale and REV-scale approaches.

One focus point is the numerical investigation of interface exchange processes on the pore scale for highly resolved porous geometries and how characteristics of the pore geometry contribute to macro-scale quantities. This can then be integrated into the second focus point, the incorporation of pore-scale effects into REV-scale modelling approaches. This aims to improve the sometimes oversimplified interface conditions on REV-scale models. One of the key goals is the development of an interface-region approach where a pore-network model is used to couple a free-flow domain and a bulk porous region.

Extension of the hybrid approach and development of new multi-scale model concepts that allow to accurately describe interface processes. A special focus is to analyse the influence of surface roughness, surface topology and soil heterogeneities on mass, momentum and energy transfer across the interface for single-phase and multi-phase systems. Such analyses can be systematically performed on different scales using appropriate numerical models, i.e. pore-scale and macro-scale models, and validated with experimental data.

Utrecht University

Our collaboration partners at Utrecht University provide us with pore-scale experimental data based on micro-particle image velocimetry (µPIV) for the development and validation of our numerical models. Profiting from a fully-equipped lab and years of experience with microfluidic experuments, we study free flow adjacent to porous media using micro models made of Polydimethylsiloxane (PDMS) and confocal laser scanning microscopy.

In cooperation with our partner, we first considered single-phase free flow above an array of regular square obstacles. In a next step, the data acquisition and evaluation procedure was further developed and automated to a large extend and we were able to reconstruct  three-dimensional flow fields.

Regarding two phases, the physics of a droplet of immiscible liquid pinned to a solid wall adjacent to free-flow was investigated in a µPIV experiment and recalculated successfully using the volume of fluids method (VOF).

We are currently working on a micromodel experiment with single-phase free flow above a porous domain featuring two phases.Using tracer particles in both fluid phases,the interphasial momentum transfer can be assessed which is essential for the extension of the widely-used Beavers-Joseph condition for modelling two-phase flow on the REV scale.

University of Pittsburgh / KTH Royal Institute of Technology

We developed a novel mortar coupling approach  which guarantees flux conservation in cooperation with our international partners (More information can be found under the internal project I-01). We envisage to extend and further develop these concepts.

University of Bergamo

The external partners provide expert knowledge for the detailed measurement of complex pore structures and XRCT which allow the accurate three-dimensional mapping of solid bodies. Pore-network models (PNM) can be extracted from XRCT volume data sets.