InterPore2025

Multiscale Analysis of Coupled Free-Flow and Porous Media Systems: Structured and Random Configurations

22 May 2025, 10:20

15m

Oral Presentation (MS11) Microfluidics and nanofluidics in porous systems MS11

Speaker

Mario Del Mastro

Description

This study initially undertakes a detailed experimental two-dimensional analysis of vector fields in both structured and random porous media configurations. Structured media are examined at porosities of 55%, 75%, and 85%, while random media are analysed at 75% porosity. As shown in Figure 1, both the axial and transverse velocity fields are significantly influenced by the geometry of the porous material, despite having the same porosity. This demonstrates that the pore arrangement at the interface profoundly impacts the flow behaviour at the boundary between the two domains. The more structured the pore configuration, the more the flow aligns axially, resulting in higher slip velocities. A detailed study is then dedicated to the analysis of the domain at the mesoscale. To develop appropriate tools for identifying this scale, a thorough analysis is performed to determine the optimal size of the representative elementary volume (REV) for studying the system, as reported by Figure 2. For systems with well-structured porous materials, the REV scale exhibits geometric characteristics, where the optimal length associated with the unit volume is l_opt≈l_t+l_p. In contrast, for systems with random porous materials, a method based on a deviation tolerance is employed. The study highlights the critical impact of inadequately calibrated REV scales on the accuracy of experimentally derived coefficients, such as the Beaver and Joseph slip velocity coefficient and the Whitaker stress jump coefficient. It demonstrates that improper calibration leads to significant inaccuracies, rendering these coefficients unreliable for practical applications and theoretical modelling.
To address this issue, the research concludes with the development of an analytical model grounded in a single-domain approach, employing the Darcy-Brinkman framework to describe the axial component of the coupled system. Particular attention is given to the interface at the mesoscale, where the coupling between free-flow and porous regions is most pronounced. This model provides a refined and consistent representation of flow dynamics across the interface, offering improved reliability for macroscopic modelling and a deeper understanding of the mesoscale phenomena that govern flow behaviour in coupled systems for microfluidic applications.