General information
Offer title : PhD in Hydrodynamics (M/F) France-Argentine PhD (H/F)
Reference : UMR7057-CARPHI-027
Number of position : 1
Workplace : PARIS 13
Date of publication : 16 July 2024
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2024
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Section(s) CN : Fluid and reactive environments: transport, transfer, transformation processes
Description of the thesis topic
Permafrost covers one-fifth of the planet’s land surface. It consists of a first layer a few meters below the surface, known as active permafrost, which freezes in winter and thaws in summer, situated above a thicker layer of ground that is constantly below freezing. The presence and displacement of a solidification front in a soil can cause underground water flows and structural changes, leading to the emergence of surprising shapes on the surface, some examples of which are illustrated in the figure below. With global warming and the melting of permafrost, this type of event is likely to become increasingly frequent, altering landscapes and their ecosystems and infrastructures.
All these behaviours are still poorly understood. Indeed, the associated physical mechanisms are still unclear, and we lack coherent predictive models for heat transport, phase change dynamics and induced groundwater flows in these complex environments. The aim of this work is therefore to gain a better understanding of solidification in porous media and the flows generated. To this end, we propose to carry out an experimental study of freezing dynamics in two model porous media soaked in water: a granular medium and a hollow solid matrix.
We propose to begin by studying solidification dynamics in a water-soaked grain stack. This stack could be placed between two plates, more or less close together, or in a tube. The propagation dynamics of the gel front will be studied, paying particular attention to the coupling between the movement of the front, the liquid flows generated and the movement of the grains. Grain size, initial compaction, thermal parameters and Young’s modulus (from undeformable to deformable) will be varied. We will use model grains (ceramic and glass beads, etc.) and grains from real soils (clay, silt, sand). The structure of the granular medium when frozen, and after several freeze-thaw cycles, will be studied and interpreted.
In the course of the thesis, we will also study the solidification dynamics in a two-dimensional, transparent, Hele-Shaw-type model system consisting of a few interconnected microchannels. We will study the influence of the channel network on the propagation of the ice front. The flow generated will be quantified. We’ll make the structure of this porous medium more complex by adding microchannels and increasing the porosity, tortuosity and disorder of its network. The thermal parameters of the solid and its Young’s modulus will be varied. We will study the influence of the transition to three dimensions by controlling the structure of the porous medium.
This work will enable us to improve our understanding of the mechanisms associated with soil freezing and thawing, and thus be able to predict the consequences, ranging from the destruction of pavements to the overall behavior of permafrost over the coming decades.
Work Context
The PhD will be carried out between the international laboratory (IRL) Institut Franco-Argentin de Dynamique des Fluides pour l’Environnement (IFADyFE) in Buenos Aires (Argentina) and the Matière et Systèmes Complexes (MSC) laboratory in Paris (France). It will be supervised by Thomas SĂ©on (IFADyFE – CNRS) and Axel Huerre (MSC – CNRS), in collaboration with M. VerĂłnica D’Angelo (CONICET & UBA) of the Porous Media Group at the University of Buenos Aires and Christophe Josserand (Ecole polytechnique & CNRS) of LadHyX in Palaiseau (France).
The 3-year doctoral contract is part of the 2023 edition of the CNRS international thesis program. Part of the thesis will be carried out at the IFADyFE IRL in Buenos Aires. The thesis will be attached to Sorbonne University’s SMAER doctoral school. The position will be filled between October 1, 2024 and March 1, 2025.
Additional Information
The candidate should have an engineering degree and/or a master’s degree in physics or engineering. The thesis requires a sound knowledge of fluid mechanics and a strong interest in model experiments and scaling laws. We are looking for a young, curious and autonomous researcher.
Applications should include a detailed CV, at least two references (persons likely to be contacted), a one-page cover letter, a one-page summary of the Master’s thesis and grades from Master 1 or 2 or engineering school. Selected candidates will be contacted for an interview. The selection process will end as soon as one candidate has been selected for the position.
