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Development of subgrid models for a periodic circulating fluidized bed

21 juillet 2017

Development of subgrid models for a periodic circulating fluidized bed
of binary mixture of particles

Soutenance de Thèse Solène Chevrier

Mardi 11 juillet à 10 h 00 - Amphithéâtre Nougaro

Abstract :

Detailed sensitivity numerical studies have shown that the mesh cell-size may have a drastic effect on the modelling of circulating fluidized bed with small particles. Typically, the cell-size must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Hence, the Euler-Euler numerical simulations of industrial processes are generally performed with grids too coarse to allow the prediction of the local segregation effects. Appropriate modelling, which takes into account the influence of unresolved structures, have been already proposed for monodisperse simulations. In this work, the influence of unresolved structures on a binary mixture of particles is investi gated and models are proposed to account for those effect on bidisperse simulations of bidisperse gas-solid fluidized bed. To achieve this goal, Euler-Euler reference simulations are performed with grid refinement up to reach a mesh independent solution. Such kind of numerical simulation is very expensive and is restricted to very simple configurations. In this work, the configuration consists of a 3D periodical circulating fluidized bed, that could represent the established zone of an industrial circulating fluidized bed. In parallel, a filtered approach is developed where the unknown terms, called sub-grid contributions, appear. They correspond to the difference between filtered terms, which are calculated with the reference results then filtered, and resolved contributions, calculated with the filtered fields. Then spatial filters can be applied to reference simulation results to measure each sub-grid contribution appearing in the theoretical filtered approach. A budget analysis is carried out to understand and model the sub-grid term. The analysis of the filtered momentum equation shows that the resolved fluid-particle drag and inter-particle collision are overestimating the momentum transfer effects. The analysis of the budget of the filtered random kinetic energy shows that the resolved production by the mean shear and by the mean particle relative motion are underestimating the filtered ones. Functional models are proposed for the subgrid contributions of the drag and the inter-particle collision.


  • Simon SCHNEIDERBAUER Chargé de Recherche Membre du Jury
  • Juray DE WILDE Professeur Membre du Jury
  • Shahriar AMINI Maitre de conférences Membre du Jury
  • Rim BRAHEM Ingénieur de recherche Membre du Jury
  • Louis JESTIN Professeur Membre du Jury
  • Olivier SIMONIN Professeur Directeur de thèse
  • Pascal FEDE Maitre de conférences Co-Directeur de thèse