Unified gas-kinetic wave-particle method for three-dimensional simulation of gas-particle fluidized bed

The gas–solid particle two-phase flow in a fluidized bed shows complex physics. The multi-scale algorithm composed of the coupled gas-kinetic scheme (GKS) for the gas phase and unified gas-kinetic wave-particle method (UGKWP) for the solid particle phase is developed for three-dimensional fluidized bed study. For the solid-particle phase, different from the widely-used Eulerian and Lagrangian approaches, the UGKWP unifies the wave (dense particle region) and discrete particle (dilute particle region) formulation seamlessly according to a continuous variation of particle cell’s Knudsen number (Kn). The GKS-UGKWP for the coupled gas-particle evolution system can automatically become an Eulerian–Eulerian (EE) method in the high particle collision regime and Eulerian–Lagrangian (EL) formulation in the collisionless particle regime. In the transition regime, the UGKWP can achieve a smooth transition between the Eulerian and Lagrangian limiting formulation. More importantly, the weights of mass distributions from analytical wave and discrete particle are related to the local Kn by (1−exp(−1/Kn)) for wave and exp(−1/Kn) for discrete particle. The UGKWP provides an optimal modeling in capturing the particle phase in difference regimes with the full consideration of physical accuracy and numerical efficiency. In the numerical simulation, the UGKWP does not need any prior division of dilute/dense regions, which makes it suitable for the fluidized bed problem, where the dilute/transition/dense regions instantaneously coexist and are dynamically interconvertible. In this paper, based on the GKS-UGKWP formulation two lab-scale fluidization cases, i.e., one turbulent fluidized bed and one circulating fluidized bed, are simulated in 3D and the simulation results are compared with the experimental measurements. The typical heterogeneous flow features of the fluidized bed are well captured and the statistics are in good agreement with experiment data.