(716g) Verification Study of Anisotropic Filtered Two Fluid Model Closures

Fundamental modelling of fluidized bed reactors is generally done via the two fluid model (TFM) approach where the effects of non-resolved particle motions and collisions is modelled by the kinetic theory of granular flows (KTGF). This approach has been developed to a high level of maturity over the past three decades, but is generally impractical for large-scale 3D simulations of fluidized bed reactors. TFM simulations generally require very fine grid sizes to capture the dynamics of small particle clusters and/or gas bubbles that form in a fluidized bed. If these structures are not adequately resolved, large prediction errors can occur because all transport phenomena in a fluidized bed reactor are directly influenced by cluster/bubble dynamics.

One promising approach for computationally affordable simulations of large scale fluidized bed reactors is the filtered TFM (fTFM) approach. This multiscale modelling approach uses a large set of resolved TFM simulation data to derive closures for the effect of particle structures on transport phenomena in the bed. These filtered closures can then be implemented in a large-scale 3D simulation using a coarse computational grid that cannot directly resolve particle structures.

Recent work has identified a large degree of anisotropy in the filtered data from highly resolved 2D TFM simulations. In comparison to state of the art isotropic fTFM closures, anisotropic fTFM closures have been quantitatively shown to explain a much larger amount of the variance in the filtered data. These anisotropic closures can therefore be expected to improve the performance of fTFM simulations carried out on coarse grids.

This work will present a verification study comparing the performance of newly derived anisotropic fTFM closures to isotropic closures derived according to the current state of the art. Simulations will include models for drag, stresses, reactions and species diffusion in order to simulate a reactive fluidized bed. fTFM model predictions will be compared to highly computationally expensive resolved simulations covering three different fluidization regimes in order to assess model generality. The effect of anisotropic fTFM closures on model performance will therefore be directly assessed to quantify the importance of accounting for anisotropy.