| Date | Event | Place | resource |
|---|---|---|---|
| 14/03/24 | Invited talk at the Lab. Fluid Mech. Lille | Lille (France) | ppt |
| 12/03/24 | Invited talk at the Lab. of Complex Fluids | Anglet (France) | ppt |
| 19/12/23 | Paper Highlighted by Eur. Phys. J. E | link | |
| 16/12/23 | Paper published in Eur. Phys. J. E | ||
| 20/11/23 | Presentation at APS-DFD | Washington | ppt |
| 16/11/23 | Presentation at the Fluid Dynamics Meeting | Philadelphia | ppt |
| 14/11/23 | Invited talk at the PoreLab Lecture Series | Oslo (online) | recording, ppt |
| 27/10/23 | Presentation at JMBC Contact Group “Turbulence” | Delft | ppt |
| 13/9/23 | Presentation at 10th GACM colloquium | Vienna | ppt |
| 13/9/23 | Organisation of Symposium at 10th GACM Colloquium | Vienna | |
| 10/9/23 | Co-chair of 10th GACM colloquium | Vienna | |
| 9/9/23 | Paper selected by AIPP for Kudos Showcase | ||
| 7/9/23 | Paper published in Rev. Sci. Instrum. | paper | |
| 29/8/23 | Participation to IJMF 50 | Vienna | |
| 31/5/23 | Participation to Burgers Symposium 2023 | Lunteren | |
| 22/5/23 | Presentation at InterPore 2023 | Edinburgh | ppt |
| 1/1/23 | Appointed Associate Editor of EPJ – E |
Review paper published in The European Physical Journal E
Can we predict the formation of sea ice? And the dissolution of CO2 in geological reservoirs? These phenomena are controlled by convective motions in a porous medium. In this review article fresh off the presses, published in The European Physical Journal E, I present recent advances on convection in porous media, a paramount topic for climate change and energy transition. The paper (Open Access) is freely available for download at here.
When a porous medium is filled with two fluid layers of different density, with the heavier fluid sitting on top of the lighter one, the system may become unstable. Due to the vertical density contrast, convective finger-like structures can form and accelerate fluid mixing. This configuration is representative of a variety of systems of practical interest, particularly in geophysical processes.
The regular polygonally patterned ridges observed in dry salty lakes are the surface signature of the convective transport of salt in the subsurface porous soil, a fundamental process in arid regions. Formation of sea ice or solidification of multicomponent alloys may originate mushy layers, which consist of porous media filled by a multicomponent fluid subject to density gradients. It follows that the consequent convective motions control the solidification dynamics. The long-term storage of carbon dioxide in underground geological formations is also driven by convection. These examples are representative of why understanding convective mixing in porous media is crucial, for instance, to tackle grand societal challenges like energy transition, or to predict how environmental systems respond to climate change.
The fluid mechanics underlying porous media convection is made complex by the multiscale and multiphase character of the flow. As a result, a combination of different complementary approaches has been deployed to elucidate the intricate physics of convection in porous media. This work reviews recent numerical, experimental, and theoretical findings, discusses their limits of applicability, and highlights possible future research directions.
How to study the behaviour of microplastics?
Microplastics are plastic fragments smaller than 5 mm originated from human activities, and have been found everywhere, also in the remotest places of the Earth. Measuring their position and velocity in turbulent flows, such as ocean, rivers and lakes, is crucial to better understand their behaviour and make physical models that describe their paths. To this aim, we designed a new facility, the TU Wien turbulent Water Channel, which we recently presented in paper published on Review in Scientific Instrument. This project is funded by FWF (Austrian Science Fund).
The TU Wien Turbulent Water Channel is a 3000 litres volume and 10 meters long flow loop designed for 3D and time-resolved measurements of anisotropic particles dynamics. We developed a novel approach to track microplastics, since they are usually anisotropic and techniques developed for spherical particles are not suitable to track such objects. In addition, in this work, we provide guidelines to design turbulent water ducts, and we also compare against existing facilities.
The data and the paper (Open Access) are freely available for download.
Would you like to perform experiments in the TU Wien Turbulent Water Channel? Contact us!
This work has been selected for the Kudos Research Showcase.
Experiments on convection in porous media
Solute transport and dispersion in underground geological formations play a key role in hydrology and geophysics, from carbon sequestration to water contamination. Understanding the underlying fluid dynamics is crucial to make reliable long-term predictions of the evolution of these systems. In this work, published on Physical Review Fluids and partially funded by the Austrian Science Fund (FWF), we investigate experimentally the role of convection on solute transport in confined porous media.
We assess experimentally the existence of a superlinear scaling for the growth of the mixing region in a confined porous medium. We employ an optical method to obtain high-resolution measurements of the density fields in Hele-Shaw flows, and we perform experiments for large values of the Rayleigh-Darcy number. We can confirm that the growth of the mixing length during the convection-dominated phase follows the scaling predicted by previous two-dimensional simulations.
Thank you Diego Perissutti (visiting Master student at TU Wien at the time of the experiments, now PhD candidate at the University of Udine), Cristian Marchioli (University of Udine) and Alfredo Soldati (TU Wien and University of Udine) for the collaboration. This work has been partially performed at the University of Twente, Physics of Fluids Group.
In the movie, you can see the evolution of the finger number for one of the experiments considered. Article, visualizations, and data about this work are available here:
[1] De Paoli et al., arXiv:2206.13363 (2022), https://arxiv.org/abs/2206.13363
[2] De Paoli et al., Phys. Rev. Fluids 7, 093503 (2022), https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.7.093503
[3] De Paoli et al., Data and figures in MatLab format, https://doi.org/10.6084/m9.figshare.19761766.v3
[4] Movie 1 https://youtu.be/njuebV7mLxw
[5] Movie 2 https://youtu.be/lC8Xbfal4J0
What is the flow topology of a convective porous media flow?
What is the minimum domain size we need to simulate to capture the large-scale flow structures?
We have addressed these questions in our recent work published on Journal of Fluid Mechanics. With the aid of massively parallelized numerical simulations, we show that the near-wall, large-scale temperature patterns (supercells) represent the footprint of the flow structure in the core of the domain (megaplumes). We have also analyzed the effect of the domain size (aspect ratio, AR), on the resulting flow topology.
Why teapots always drip
There is an age-old question: How can the so-called “teapot effect” be explained? Our demonstrative experiments illustrating this phenomenon have been discussed in quiz shows by BBC and Servus TV (available from Germany and Austria).
The “teapot effect” has been threatening spotless white tablecloths for ages: if a liquid is poured out of a teapot too slowly, then the flow of liquid sometimes does not detach itself from the teapot, finding its way into the cup, but dribbles down at the outside of the teapot.
This phenomenon has been studied scientifically for decades – now a research team at TU Wien has succeeded in describing the “teapot effect” completely and in detail with an elaborate theoretical analysis and numerous experiments: An interplay of different forces keeps a tiny amount of liquid directly at the edge, and this is sufficient to redirect the flow of liquid under certain conditions.
News by TU Wien and full movie available on YouTube.
Paper published on J. Fluid Mech.
“INFLUENCE OF REYNOLDS NUMBER ON THE DYNAMICS OF RIGID, SLENDER AND NON-AXISYMMETRIC FIBRES IN CHANNEL FLOW TURBULENCE”
Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720. The paper is open access and available here. This article follows our previous work on the reconstruction and tracking on anisotropic particles in channel flow turbulence.
In this work, we investigate experimentally the dynamics of non-axisymmetric fibres in channel flow turbulence, focusing specifically on the importance of the fibres size relative to the flow scales. To this aim, we maintain the same physical size of the fibres and we increase the shear Reynolds number. Experiments are performed in the TU Wien Turbulent Water Channel for three values of shear Reynolds number, namely 180, 360 and 720.
Fibres are slender – length to diameter ratio of 120 -, rigid, curved and neutrally buoyant particles and their shape ranges from low curvature – almost straight fibres – to moderate curvature. In all cases, fibres size remains small compared to the channel height (1.5%). Three-dimensional and time-resolved recordings of the laser-illuminated measurement region are obtained from four high-speed cameras and used to infer fibres dynamics. With the aid of multiplicative algebraic reconstruction techniques, fibres position, orientation, velocity and rotation rates are determined. Our measurements span over half channel height, from wall to center, and allow a complete characterization of the fibres dynamics in all the regions of the flow. Specifically, we measure fibre preferential distribution and orientation. We observe that the fibres dynamics is always influenced by their curvature. Through a comparison between measurements of near-wall dynamics of fibres and near-wall dynamics of flow, we identify a causal relationship between fibre velocity and orientation, and the near-wall turbulence dynamics. Finally, we have been able to provide original measurements of the tumbling rate of the fibres, for which we report the influence of fibres curvature. We underline that our measurements confirm previous findings obtained in numerical and experimental works.
Summer School on Porous Media
Udine, JULY 11, 2022 to JULY 15, 2022
26TH CISM-IUTAM INTERNATIONAL SUMMER SCHOOL ON “CONVECTION AND DEFORMATION IN POROUS MEDIA: GEOPHYSICAL AND BIOLOGICAL FLOWS”
This course is organised at CISM (Udine, Italy) and coordinated by Prof. Chris. MacMinn (University of Oxford) and me. All the details about the course are available here. You can download the flyer here.
Flow and transport in porous media are relevant for many geophysical, industrial, and biological applications, including carbon sequestration, glacial drainage, papermaking, transport across vascular walls, and bacteria motility. Predicting the evolution of these systems is difficult because of the interplay between different physical features, such as complex flow patterns, convection and reaction, and transformation of the porous matrix through deformation and phase change. In addition, flow and transport in porous media are governed by physical processes that span a wide range of length and time scales. Rapidly increasing computational power has recently enabled threedimensional, high-resolution and time-dependent simulations of these flows at both the pore-scale and the Darcy-scale, producing an entire branch of flourishing research into multiphase flow in porous media. Experimental progress has also been substantial, thanks to improved measurement techniques inboth 2D and 3D. Therefore, it is now useful to review the many studies on the subject to provide an overview of the current state of the art, and to put future research paths in perspective.
This course will provide an overview of the most up-to-date modelling approaches, numerical simulations, and experimental methods used to study the dynamics and properties of porous media flows characterized by convection and deformation.
Fundamentals of transport in porous media will be presented, including upscaling techniques, thermodynamics of two-phase mixtures, Lagrangian interpretations, fractional diffusion, non-locality and memory.
Time-dependent evolution of convection-driven flows in different configurations will be analyzed, with reference to geophysical and industrial applications and with particular attention to the dynamics and structures of convection, effect of porous media properties on convection and transition from 2D to 3D convection. An overview of experimental and numerical techniques for convective flows in porous media will be presented and reviewed.
Principles of the coupling between flow, transport, and deformation in porous media will be presented. The small-deformation limit and classical linear poroelasticity will be discussed in the context of subsurface flows. Large-deformation poromechanics will be discussed in the context of polymeric hydrogels (including swelling and drying phenomena), paper-pulp suspensions (including viscoelasticity and plasticity), and granular media (including friction and rearrangement).
The implications of deformation for the dispersion and mixing of solutes will be considered. Two-phase flows will be considered, including capillary and wettability effects. Phase-field approaches will be introduced in the context of multiphase solidification problems (including ice, methane clathrates, and lava) and applied to the growth and migration of gas bubbles in soft porous media.
The course is addressed to graduate students and researchers in applied mathematics, physics and chemical/mechanical engineering.
The advanced topics and the presentation of current progress in this very active field will also be of considerable interest to senior researchers and industrial practitioners having a strong interest in understanding the multiscale complex behavior of such multiphase flows.
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Marco De Paoli 