An improved computational fluid dynamics-discrete bubble model for multiphase bubble flow simulation with a wide grid/bubble size ratio

The Euler–Lagrange method is a great way for multiphase bubble flow simulation, the detailed information of bubbles can be effortlessly obtained, and it is helpful for the efficiency and safety of different industry processes. Traditionally, the computational fluid dynamics-discrete bubble model (CFD-DBM) method has always been used to simulate this flow process. Nevertheless, the ability of the traditional CFD-DBM method is significantly limited in terms of the size ratio between the grid and bubble, where the grid size must be larger than the bubble size. In reality, the bubble may be larger than the grid and the grid/bubble size ratio can be very large due to the effects of complex bubble dynamics (such as the bubble breakup and coalescence) and complex internal flows. To address this issue, an improved CFD-DBM method is proposed in this study, which can be used for the simulation with a wide grid/bubble size ratio in gas–liquid–bubble multiphase simulation, and the volume of fluid (VOF) method is applied to capture the interface between gas and liquid phases. A gradient-based interpolation method is employed to reconstruct the liquid velocity around the target bubble when the grid size is much larger than the bubble size. If the bubble size is comparable with or larger than the grid size, the interphase force correction and the field smoothing will be carried out within a spherical support area. Subsequently, the proposed model is validated by the comparison with a bubble column experiment, in terms of the bubble size distribution and bubble vertical velocity. The results demonstrate the high accuracy of the new method. Finally, the influence of different parameters including normal spring stiffness, critical Weber number, and the range of the spherical support area on the bubble flow is investigated.