Searching for a mesh-independent sub-grid model for CFD simulation of gas-solid riser flows |
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Authors: | Bona Lu Wei Wang Jinghai Li |
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Affiliation: | a State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China b Graduate University of Chinese Academy of Science, Beijing 100049, China |
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Abstract: | This work aims to examine the effects of grid size in applying the two-fluid model (TFM), and thereby attempts to search for a mesh-independent sub-grid model for simulating gas-solid riser flows. To this end, we performed a series of TFM simulations over a periodic domain with various grid resolutions and drag closures. Of these drag models, EMMS/matrix model in its simplified version was chosen to be the focus of discussion. It was found that TFM simulation with a homogeneous drag model reaches its numerically asymptotic solution when the grid scale is as small as 10 times the particle diameter, but it still fails to capture the characteristic S-shaped axial voidage profile and highly over-predicts the solids flux. By comparison, EMMS/matrix model seems to reach a mesh-independent solution of the effect of sub-grid structures on the drag force, and predict successfully the axial voidage profile and the solids flux with even coarse grid. Therefore, the fine-grid TFM simulation is inadequate for gas-solid riser flows. We need sub-grid modeling of the heterogeneous structure. |
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Keywords: | Sub-grid Structure Multiscale Momentum transfer Multiphase flow Simulation Fluidization |
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