Flow kinematic in 3D porous media

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INRAE presentation

The French National Research Institute for Agriculture, Food, and Environment (INRAE) is a major player in research and innovation. It is a community of 12,000 people with 272 research, experimental research, and support units located in 18 regional centres throughout France. Internationally, INRAE is among the top research organisations in the agricultural and food sciences, plant and animal sciences, as well as in ecology and environmental science. It is the world’s leading research organisation specialising in agriculture, food and the environment. INRAE’s goal is to be a key player in the transitions necessary to address major global challenges. Faced with a growing world population, climate change, resource scarcity, and declining biodiversity, the Institute has a major role to play in building solutions and supporting the necessary acceleration of agricultural, food and environmental transitions.

Work environment, missions and activities

Context and problematic

Geomaterial are complex porous material presenting a wide diversity of structures that set the flow kinematic of any fluids through it. When rainwater flows through rocks, or when expansive resin is injected to stabilize a soil and reinforce its mechanical properties to prevent crack, the way the injected solute is dispersed and homogenized in the surrounding media is directly driven by the local microstructure and the pore network. The presence of local heterogeneities such as a crack, the progressive development of an erosion channel, or the clogging of pores, will strongly affect the dispersion and mixing processes. These transport processes are characterized by investigating the velocity fields and relating the local pore scale processes to the macroscale behaviour of the porous material. The understanding of the small scale mechanisms thus allows to predict and control the macroscale dispersion and mixing process. This is of crucial importance for a broad range of applications, such as contaminant transport in soils and aquifers, drug delivery and nutrient transport in brain or plant tissues, heat exchangers, filters and catalytic processes in chemical or energy industry, biocalcification and soil reinforcement of hydraulic structures such as dam and dikes.

Because of the opaque nature of porous media, the characterization of the velocity fields within a porous media is particularly challenging in three-dimensional (3-D) porous media. However, recent development of experimental techniques including index matching [5], allow to use transparent porous media (fluid and grains with the same optical refractive index) to perform direct visualization of the flow in artificial porous media [6]. These promising techniques allow to provide highly resolved experimental reconstruction of the 3-D Eulerian fluid velocity field. Such approach have already been successfully implemented to study porous media composed of randomly packed solid monodisperse spheres, and to investigate how a blob of injected dye stretches and get mixed.

Experimental methodology

This thesis project plans to characterize the effect of the microstructure over the flow kinematic within porous media, by developping experimental techniques to perform direct visualization in 3D artificial porous media. The porous media will be made transparent by use of iso-optical index matching techniques, with a progressively increasing microstructure complexity. The porous media will be composed of a solid matrix made of randomly packed beads of transparent material, see Figure 1a. A fluid of corresponding optical refractive index will then be injected within the interstitial pores. Using velocimetry techniques (PIV/PTV), successive scans of the velocity field will be measured and used to reconstruct the 3D velocity field in the bulk of the porous media.

Starting with investigating the effect of polydispersity over the flow kinematic, the complexity of the artificial porous media will be progressively increased, and several configurations will be explored such as porous media presenting cracks, or within which some pores could get eroded, transporting fine particles which may eventually clog downstream pores.

In particular, we will focus on investigating how the velocity distribution of the interstitial fluid can be related to the microstructure, and on the effect of local heterogeneities over the macroscale transport processes. Furthermore, with the ongoing development of numerical methods to simulate the flow within complex 3D porous media, there is nowadays a strong need for benchmark datas set for testing and validation. Providing reliable three-dimensional high resolution experimental velocity fields datas sets therefore represents a very innovative work lacking to this day from the scientific bibliography, and the datas sets will be used for scientific collaborations with local colleague researchers to feed DEM (Direct Element Method) simulations.

Framework

The doctoral student will be registered at the doctoral school of Aix-Marseille University (ED 353, Engineer Science : Mechanics, Physics, Micro and Nano Electronics) and will be based in the RECOVER unit of INRAE PACA. This research unit is equipped with experimental benches and technical means for the characterization and study of porous material and their mechanical properties. RECOVER is an active research team composed of more than 75 permanent staff (researchers, engineers, and professors) and about 40 non-permanent scholars (PhD students, post-docs and technical support staff). The lab is located in Le Tholonet, few kilometers from Aix-en-Provence and close to Marseille (south of France).
The PhD is scheduled to start in October 2026 (with some flexibility) for a period of 36 months. Depending on the work progress, a master student may be recruited and supervised by the PhD candidate during the course of the PhD. The PhD will also benefit from a good quality of life, enriching interactions in an international environment, with a working site in an outstanding natural setting and a quality company restaurant.

Training and skills

We are looking for a candidate with a master of research or graduate in mechanics – fluid mechanics – geotechnical engineering. The candidate is expected to have a potent inclination for experiments and strong knowledge in fluid mechanics. A training course in mixing, transport processes or a past experience in laboratory work will be profitable. The PhD student will be involved at all stages of the project : experimental setup design, sample preparation, and numerical image analysis (PIV, particle tracking, 3D reconstruction).

Expected skills : motivation for research work, faculty for working independently and in a team, capability to formulate concepts, curiosity, constructive criticism, perseverance and scientific rigour. A good level in English is mandatory.

INRAE's life quality

By joining our teams, you benefit from (depending on the type of contract and its duration):

- up to 30 days of annual leave + 15 days "Reduction of Working Time" (for a full time);
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.

How to apply

I send my CV and my motivation letter