Marco De Paoli, assistant professor at the Institute of Fluid Mechanics and Heat Transfer of the Technical University Vienna (Austria), will give the Pretty Porous Science Lecture #79 on the topic "Convective mixing in porous media: from exact theoretical predictions to geophysical applications".
Date: 30 July 2026
Time: 3 pm
Title: "Convective mixing in porous media: from exact theoretical predictions to geophysical applications"
Speaker: Univ. Ass. MSc PhD Marco De Paoli, Institute of Fluid Mechanics and Heat Transfer, TU Wien (Austria)
Location: Multi Media Lab, University of Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart
Abstract
Buoyancy-driven mixing in porous media is central to a range of geophysical and engineering processes, from subsurface carbon dioxide (CO2) storage to latent heat thermal energy storage systems. Despite decades of study, accurate predictions of transport rates remain challenging due to the interplay of nonlinear fluid properties, complex boundary conditions, dispersive effects, and finite-size effects.
In this talk, I will present a unified perspective on convective mixing in porous media. I will begin by addressing the sensitivity of mixing predictions to modelling assumptions in geophysically relevant settings. High-resolution simulations at Rayleigh-Darcy numbers of order 10,000 reveal that the choice of density-concentration relationship (linear, nonlinear, or non-monotonic) and boundary conditions (fixed or free interface) can alter predicted mixing rates by up to one order of magnitude. Across all configurations, the mean scalar dissipation emerges as a robust and unifying metric for quantifying convective-diffusive interactions.
I will then discuss the role of hydrodynamic dispersion, modeled through an anisotropic Fickian dispersion tensor, demonstrating that while molecular diffusion remains the leading-order mechanism, dispersion introduces second-order corrections that modulate mixing efficiency during intermediate flow regimes. This theoretical framework, validated against pore-scale simulations and bead-pack experiments, offers a pathway to improve current dispersion models and obtain more reliable estimates of solute transport in buoyancy-driven subsurface flows.
Finally, starting from exact time-dependent budget identities for Rayleigh-Taylor-Darcy flow, I will show how transport, flow intensity, and scalar dissipation are rigorously linked. A minimal one-parameter eddy-diffusivity closure yields self-similar mean profiles, universal second-order statistics, and a linear mixing-layer growth law. The theoretical findings are confirmed by high-resolution direct numerical simulations.
About Marco De Paoli
Marco De Paoli obtained his PhD from the University of Udine in 2017. He worked as a postdoc at TU Wien (Austria) until 2022. Later, he joined the University of Twente (the Netherlands) first as Erwin Schrödinger Fellow (2022-2023) and then as Marie Sklodowska-Curie fellow (2023-2025). He is currently Assistant Professor at TU Wien. He is Associate Editor of The European Physical Journal E and full member of the Wolfgang Pauli Institute of Vienna. He received a Starting Grant from the European Research Council on “flow in porous media with morphology modifications”, where experiments, simulations and modelling are combined to predict the transport properties of such systems. Current research interests also include heat and mass transport in environmental flows and dispersion of microplastics in turbulence.