Coarse-grid simulations of full-loop gas-solid flows using a hybrid drag model: Investigations on turbulence models

The effect of fluid turbulence models on the coarse-grid simulation for the mesoscale gas-solid flow system is not as clear as that for gas-liquid/single flows. In this study, the effect of different turbulence models on predictions of riser-only, turbulent and bubbling flow hydrodynamics is quantified. Then the selected turbulence models are examined by coarse-grid simulations in a full-loop circulating fluidized bed (CFB) with a proposed hybrid drag model which integrates two SGMs and Hulin-Gidaspow model. Results show that the standard k-epsilon and k-omega models fail to capture a correct fluidization pattern in riser. Meanwhile, the RNG and realizable k-epsilon models and SST k-omega model enable satisfactory predictions which are highly comparable to discrete model predictions and experiments over different flow regimes. However, the realizable k-epsilon model produces more pronounced flow fluctuations causing computational instability. Using superior turbulence closures, full-loop simulations with the proposed hybrid model can predict desirable hydrodynamics. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found that the impact of different turbulence models on predictions of fluidization processes in the mesoscale gas-solid flow system varies. By utilizing a hybrid model and different turbulence closure models in a circulating fluidized bed CFB, more accurate predictions of flow characteristics can be achieved.