Improvement of unresolved CFD-DEM by velocity field reconstruction on unstructured grids

For conventional unresolved CFD-DEM, the accurate Lagrangian tracking of the dispersed particles requires the interpolation of cell-centered fluid velocity to the particle position instead of equally treating every particle in the same cell. However, the interpolation on unstructured grids and the systematic investigations about the influence of interpolation on the simulation results are rarely reported. This study adopted gradient-based interpolation to reconstruct the velocity field on unstructured grids considering efficiency and precision. Three gradient limit strategies were introduced into the unresolved CFD-DEM to constrain the gradient determined by the weighted least-square method because gradient-based interpolation may bring about unwanted extrema that will distort the results. The influence of gradient-based interpolation, as well as three gradient limit strategies on the simulation results, were estimated by comparing the simulation results with experimental measurements in a spouted bed with a conical base. The bubble behaviors demonstrated that the reconstruction of the velocity field was of crucial significance to the improvement of unresolved CFD-DEM. Besides, the pressure drops of experiments coincided with that of simulations except for the case using the limit strategy that constrained the extrema at face centroids. Considering the bubble behaviors and pressure drops, the limit strategy that constrained the extrema at grid vertices was the most recommended.