A general grid refinement rule for near-wall regions in coarse-grid simulations of gas-solid fluidized beds

Coarse-grid methods, commonly used in large-scale fluidized bed simulations, encounter challenges in accurately capturing the flow characteristics in the near-wall regions due to the complex inhomogeneous structure. Given that finer grids can better resolve the structures near the wall, this study aims to develop a general grid refinement rule suitable for both laboratory- and industrial-scale fluidized beds. The rule seeks to balance the computational resource usage and the accuracy in resolving flow features near the wall. Recommendations for grid refinement strategies for different fluidized bed sizes are provided. Using a fine grid in the near-wall region is necessary, and as the size of the fluidized bed increases, the proportion of the fine-grid region gradually decreases to maintain an acceptable simulation accuracy. The rule is comprehensively evaluated through a series of a posteriori validations through coarse-grid two-fluid model simulations, demonstrating its effectiveness.