Filters
Results 1 - 1 of 1
Results 1 - 1 of 1.
Search took: 0.02 seconds
AbstractAbstract
[en] The space propulsion has been a political issue in the midst of the Cold War and remains nowadays a strategic and industrial issue. The chemical propulsion on rocket engines is limited by its ejection velocity and its lifetime. Electric propulsion and more particularly Hall effect thrusters appear then as the most powerful and used technology for space satellite operation. The physics inside a thruster is complex because of the electromagnetic fields and important collision processes. Therefore, all specificities of the engine operation are not perfectly understood. After hundreds of hours of tests, thruster walls are curiously eroded and electromagnetic instabilities are developing within the ionization chamber. The measured electron mobility is in contradiction with the analytical models and raises issues on the plasma behavior inside the discharge chamber. As a result, the AVIP code was developed to provide a massively parallel and unstructured 3D code to Safran Aircraft Engines modeling unsteady plasma inside the thruster. Lagrangian and Eulerian methods are used and integrated in the solver and my work has focused on the development of a fluid model which is faster and therefore better suited to industrial conception. The model is based on a set of equations for neutrals, ions and electrons without drift-diffusion hypothesis, combined with a Poisson equation to describe the electric potential. A rigorous expression of collision terms and a precise description of the boundary conditions for sheaths have been established. This model has been implemented numerically in an unstructured formalism and optimized to obtain good performances on new computing architectures. The model and the numerical implementation allow us to perform a real Hall effect thruster simulation. Overall operating properties such as the acceleration of the ions or the location of the ionization zone are captured. Finally, a second application has successfully reproduced azimuthal instabilities in the Hall thruster with the fluid model and justified the role of these instabilities in the anomalous electron transport and in the erosion of the walls. (author)
[fr]
L'etude du transfert de matiere entre deux phases immiscibles, l'une etant dispersee dans l'autre,constitue une etape cle dans le developpement et l'optimisation des procedes d'extraction par solvant. Le caractere multiphasique et multi-echelles de ces procedes rend souvent leur etude tres complexe. Aussi, une description fine a l'echelle d'une goutte isolee est un prealable indispensable a la comprehension du comportement des procedes mettant en jeu des nuages ou des populations de gouttes (de formes et tailles variees). Ce travail est consacre particulierement a l'etude par simulation numerique directe de l'hydrodynamique et du transfert de matiere couples a travers l'interface d'une goutte spherique, placee dans une autre phase immiscible en ecoulement uniforme. Les equations completes de Navier-Stokes et de transport de la concentration du solute sont pour cela resolues, en coordonnees curvilignes orthogonales, par une methode de volumes finis. Une attention particuliere est portee a l'implementation des conditions a l'interface liquide-liquide afin de correctement representer le couplage des phenomenes internes et externes a la goutte. On s'interesse dans cette etude au transfert sans reaction chimique d'un solute extractible, de la goutte vers la phase continue. Nous avons conduit une etude de sensibilite parametrique couvrant une large gamme de conditions operatoires (rapport de densite, viscosite, et diffusivite, coefficient de partage de solute) sur la variation du nombre de Sherwood. Les resultats montrent que la structure du champ de vitesse depend fortement du nombre de Reynolds et du rapport de viscosite. L'evolution du nombre de Sherwood revele en outre une forte influence du coefficient de partage et du rapport de diffusivite, tant sur son evolution temporelle que sur sa valeur asymptotique. L'ensemble des configurations etudiees a permis de relier le nombre Sherwood global aux valeurs representatives des problemes de transfert interne et externe. Les resultats numeriques montrent que le comportement axisymetrique typique des configurations a Reynolds interne/externe modere (Re ≤ 100), n'est plus valable au dela de Re=300. Dans ces conditions, les simulations mettent en evidence des bifurcations tridimensionnelles internes du champ de vitesse ce qui impacte fortement la distribution spatiale de la concentration et ainsi la physique et la rapidite du transfert. (auteur)Original Title
Etude numerique du transfert de matiere a travers l'interface d'une goutte spherique en mouvement: mise en evidence des effets 3D
Primary Subject
Source
9 Apr 2019; 207 p; 86 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Dynamique des Fluides
Record Type
Report
Literature Type
Thesis/Dissertation
Report Number
Country of publication
Reference NumberReference Number
INIS VolumeINIS Volume
INIS IssueINIS Issue