Chevrier, Solène. Development of subgrid models for a periodic circulating fluidized bed of binary mixture of particles. PhD, Dynamique des fluides, Institut National Polytechnique de Toulouse, 2017

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Abstract
Detailed sensitivity numerical studies have shown that the mesh cellsize may have a drastic effect on the modelling of circulating fluidized bed with small particles. Typically, the cellsize must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Hence, the EulerEuler 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 investigated and models are proposed to account for those effect on bidisperse simulations of bidisperse gassolid fluidized bed. To achieve this goal, EulerEuler 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 subgrid 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 subgrid contribution appearing in the theoretical filtered approach. A budget analysis is carried out to understand and model the subgrid term. The analysis of the filtered momentum equation shows that the resolved fluidparticle drag and interparticle 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 interparticle collision.
Item Type:  PhD Thesis 

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Institution:  Université de Toulouse > Institut National Polytechnique de Toulouse  Toulouse INP (FRANCE) 
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Research Director:  Simonin, Olivier and Fede, Pascal 
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Deposited On:  26 Apr 2018 09:22 
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