Simulation of single ellipsoidal bubble dynamics for pool scrubbing

Okagaki, Yuria  ; Motegi, Kosuke  ; Abe, Satoshi*  

Our future research strategy is to apply the three-dimensional (3D) Computer Fluid Dynamics (CFD) approach to understand the detailed bubble internal flow effect for aerosol particle transportation, which is difficult to be assessed experimentally. This study focused on the flow behavior within a single buoyant rising elliptical bubble in a quiescent liquid. Based on previous studies, a solver based on the Simple Coupled Volume Of Fluid with Level Set (S-CLSVOF) method was applied for OpenFOAM to capture the gas-liquid interface. Simulations were performed for an initial bubble diameter of 4 mm in full 3D geometry models in addition to quarter symmetry (quarter structure with symmetry boundaries) 3D geometry models. This is because the bubble rise behavior becomes unstable for bubble diameters larger than 4 mm and the bubble wake loses its axisymmetry, as is well known. We revealed the difference in the simulation results between the quarter symmetry and full 3D geometry models in this study. Moreover, the Adaptive Mesh Refinement (AMR) method was applied to investigate the accuracy of the calculation with limited computational resources, and the results were compared with those obtained with equally spaced fine meshes. As a result, to accurately predict the internal flow, it was not sufficient to subdivide the inside of the bubble with the AMR mesh in full 3D geometry, and it was necessary to subdivide the mesh of the bubble inside and the bubble wake side. The terminal velocity might approach closest to the empirical correlations by subdividing the bubble inside and bubble wake side meshes. The knowledge obtained is expected to play an important role in developing and evaluating the constitutive equations in the stand-alone pool scrubbing code.