Phd student in thermal plasma process (M/F)

This Work will take place in Institute for Research on Ceramics (IRCER UMR CNRS 7315).
Plasma spraying of suspensions allows to obtain coatings with fine and varied microstructures answering applications which emerge at the industrial level as for example, thermal barriers of new generation for aeronautics. In this process, the liquid suspension containing the submicronic particles of the material to be deposited is injected into a thermal plasma jet to be fragmented, evaporated releasing the submicronic particles which are then accelerated and melted and will impact and spread on the part to be coated to form the deposit. The control of the process requires the understanding of the mechanisms that govern the treatment of the suspension and the construction of the coating. This understanding requires the simulation of the process from the generation of the plasma jet, its interaction with the suspension, the impact of the particles/droplets on the substrate and the construction of the deposit. The IRCER and TREFLE laboratories of I2M have joined together to advance this issue, which is of great interest to Safran and Oerlikon, international leaders in the production of coatings for aeronautical parts and in the manufacture of spraying equipment. Modeling work on the plasma jet generation, its turbulent development and the construction of the deposit has begun. The work of this PhD will consist in modeling the hydrodynamic fragmentation of the suspension by shearing by the gas flow as well as the behavior of the fine particles within a drop of suspension whose carrier liquid evaporates, deforms and recirculates by taking into account the diffusion and the forces on/between particles, so as to make it possible to predict the number of particles resulting, their size and even their shape, a drop possibly leading to the birth of several aggregates.

Modelling the physical mechanisms in suspension plasma processing
The proposed study is linked to the Selenite project co-financed by the CNRS. Selenite project is led by IRCER, the Institute of Mechanics and Engineering (I2M) of Bordeaux, the companies Safran (2nd aeronautical equipment manufacturer, leader for the realization of deposits on aeronautical parts) and Oerlikon (first world manufacturer of plasma torches and integrated industrial projection systems).

The Selenite project will focus on the modeling of the plasma jet generation by the electric arc by a MagnetoHydoDynamic approach in the Sinplex projection torch developed by the Oerlikon company (Code_Saturne), the development of the turbulent jet in ambient air, the primary and secondary fragmentation of the suspension by the plasma jet, its kinematic, thermal and physical treatment by a global approach (evaporation, 1 drop 1 agglomerated particle) are in progress at IrCer with the Ansys_Fluent code. The I2M models the formation of the deposit on the substrate from the results of the previous models with the Notus code. These codes will be partly common to the Selenetine (CNRS) and Aventurine projects.

Description of the work: The work of the PhD student will focus on a detailed description of the plasma-liquid input interactions. This description is essential to obtain a reliable simulation of the treatment of a suspension in plasma. It aims at understanding and modeling the thermal, hydrodynamic and physical treatment of suspension drops. The developed model will have to take into account:
• the hydrodynamic fragmentation of the suspension by shearing by the gas flow ;
• the behavior of fine particles within a suspension drop whose carrier liquid evaporates, deforms and recirculates, taking into account the diffusion and the forces on/between particles.
This will allow to predict, depending on the operating conditions and thus on the treatment of the suspension within the plasma jet, the shape and morphology of the solid phase resulting from this evaporation, its size and eventually the particle size distribution; a drop can lead to several solid particles resulting from the agglomeration of submicronic particles. The developed model should allow to establish a law of evaporation of the drops of suspensions in a plasma environment as a function of the original load in solid particles and their size. The results of the model will eventually be integrated into the Ansys-Fluent fluid mechanics code which allows to simulate the behavior of a large number of drops injected into a plasma jet with different temperatures and velocities taking into account the modification of the plasma gas properties by the evaporation of the liquid.

This thesis, co-supervised by IRCER and I2M, will take place mainly at IRCER and in close collaboration with i) IRCER researchers who are working on the experimental observation of the treatment of suspensions in the plasma jet and ii) people from SAFRAN and Oerlikon who are industrializing the process of plasma projection of suspensions and iii) the docotrant and post doc of the Aventurine project The TREFLE department of the I2M will bring its expertise in terms of modeling of the physical phenomena and their numerical aspects and will ensure the adequacy of the results with the model of construction of the deposit which it develops.

Role and skills of the PhD student
• Develop and implement numerical models to represent the physics governing the interactions between the suspension drop and the plasma: Eulerian two-phase approach (gas/liquid), Lagrangian approach (behavior of the particles in suspension in the drop),
• Implement numerical schemes adapted to these models.
• To feed the database developed in the IRCER/Oerlikon project and to ensure a harmonious exchange of data flows with the other calculation codes used in this project (Fluent and Notus).
Knowledge and experience in modeling, numerical methods, programming and physics, good physical sense, ability to communicate with partners