Abstract:
Suspension plasma spraying can be used to produce coatings with a variety of fine microstructures to meet the demanding requirements of emerging industrial applications, such as new-generation thermal barriers for the aerospace industry. In this process, the liquid suspension containing submicron particles of the material to be deposited is injected into a thermal plasma jet to be fragmented and evaporated, releasing individual or agglomerated submicron particles which are then accelerated and melted, impacting and spreading out on the part to be coated to form the coating. Mastering the process requires an understanding of the complex, interdependent mechanisms governing suspension processing and coating construction.
This understanding requires simulation of the process as a function of its operating parameters by a digital twin, from plasma jet generation to deposit construction. The IRCER and TREFLE laboratories at I2M have joined forces to make progress on this issue, which is of great interest to Safran, the international leader in the production of coatings for aeronautical parts. This modeling work on plasma jet formation, turbulent development, suspension treatment and deposit construction gave rise to an initial project, which is continuing with support from Safran and the Nouvelle-Aquitaine region.
The work of this PhD will consist of continuing to model the development of the unsteady turbulent plasma jet (LES/U-RANS) in the presence of a moving substrate with the Ansys_Fluent CFD Code, optimizing numerical methods to increase the robustness of simulations and reduce their duration, and modeling the atomization then secondary fragmentation of the suspension jet and its physical treatment in interaction with another PhD student from the project.
Context:
Plasma spray coating allows for the creation of coatings with fine and varied microstructures (columnar, dense, etc.) that meet the requirements of emerging industrial applications, such as new-generation thermal barriers for aeronautics or solid electrolytes for fuel cells.
In this process, the liquid suspension containing the submicron particles of the material to be deposited is injected into a thermal plasma jet to be fragmented and evaporated, releasing individual or agglomerated submicron particles that are then accelerated and melted and will impact and spread over the part to be coated to form a deposit. Its microstructure, and therefore its usage properties, depend on a large number of operating parameters relating to the plasma torch, the suspension, the substrate, and the torch-substrate kinematics.
The complexity of this process requires numerous tests to achieve a coating with controlled properties on a complex-shaped part, which slows down its adoption by manufacturers. Mastering the process requires an understanding of the complex and interdependent mechanisms that govern the treatment of the suspension and the construction of the coating. This understanding requires simulation of the process using a digital twin, including the generation of the plasma jet using a magnetohydrodynamic (MHD) approach (1), the turbulent development of the jet with the injection and hydrodynamic fragmentation of the suspension (2), the treatment of the suspension droplets by the plasma (3), the impact of molten particles on the substrate, and the construction of the deposit (4) according to its operating parameters.
The proposed study is part of the Azurite project co-financed by the region, IRCER, and Safran. This digital twin project is led by IRCER, the Institute of Mechanics and Engineering (I2M) in Bordeaux, and Safran (the second largest aerospace equipment manufacturer and leader in the production of deposits on aerospace parts). This study consists of continuing the modeling work begun as part of a previous project, which laid the foundations for models 1 to 4 and developed model 2 in particular, for which the modeling of turbulent free flow using an LES approach and its chaining with model 1 is well advanced.Objectives:
The ultimate objective of this thesis is to develop a robust and predictive model implemented in the Ansys_Fluent CFD code, enabling the simulation of the treatment of the suspension in the plasma jet interacting with a moving substrate (2). This objective involves the following sub-objectives:
- Predictively simulate the development of the turbulent plasma jet in kinematic and thermal interaction with a moving substrate flow fields
- Simulate the atomization and secondary fragmentation of the suspension during its interaction with the plasma flow distribution of droplet sizes, positions, velocities, and trajectories
- Simulate the physical treatment of a large number of droplets in the simulated unsteady plasma flow fields: i) first using a simplified approach (multi-component approach) ii) by integrating the predictive model (subsystem 3) developed by another doctoral student on the project as it is developed distribution of particle size, position, velocity, and temperature just before impact in order to feed subsystem 4
Methodology/proposed work:
The study timeline will follow the successive objectives defined above in conjunction with the progress made by the postdoctoral/doctoral students responsible for models 1 and 3 in particular, taking care at each stage to validate the calculations through measurements (PIV, in-flight material collection, etc.) carried out in collaboration with IRCER experimenters.
At the same time, work will need to be done on initializing the calculations and optimizing the numerical methods to facilitate and accelerate convergence and chaining/coupling between models, as well as to reduce CPU costs (U-RANS vs. LES?).Conditions de déroulement de la thèse/Collaborations :
Cette thèse co-encadrée par l’IRCER et l’I2M, se déroulera en grande partie à l’IRCER et en étroite collaboration i) avec les chercheurs de l’IRCER qui travaillent sur l’observation expérimentale du traitement des suspensions dans le jet de plasma et ii) les personnes de SAFRAN qui industrialisent le procédé de projection plasma de suspension et iii) les doctorants et post doc du projet Azurite. Le département TREFLE de l’I2M apportera son expertise en termes de modélisation des phénomènes physiques et leurs aspects numériques et veillera à l’adéquation des résultats avec le modèle de construction du dépôt qu’il développe.
Conditions matérielles :
Salaire : Net mensuel : 1 768 €, origine : 50% Safran, 50% AAP recherche Région NA 2025 Azurite
Candidate profile: CFD, mathematical engineering, modeling engineering
Knowledge and initial experience essential in modeling, numerical methods, programming and physics, good physical sense, ability to communicate with partners.
Activities/Skills of the PhD student :
- Develop a CFD model, implement model 3 with the appropriate numerical schemes in the Ansys_Fluent code environment using user functions, create meshes with Icem and manage moving meshes.
- Master two-phase fluid approaches.
- Develop data processing programs in Python.
- Interact with laboratory researchers to validate the model and with PhD students in stages 1 and 3.
To apply: https://adum.fr/as/ed/proposition.pl
