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This study compares three interface capturing schemes (ICSs) – PLIC, original THINC, and THINC/WLIC – for bubble volume conservation in multiphase flow simulations, relevant to void fraction prediction in boiling water reactors. Simulations of bubbly flows revealed that THINC/WLIC causes significant VOF diffusion in relatively coarse grid resolution, leading to dissipation of bubble volume evaluated as the volume of cells where VOF is below a threshold. However, if bubble volume is defined as the sum of unity subtracted by VOF value, it may be overestimated due to residual VOF fragments suspended in the domain. These findings highlight that ICSs involving VOF diffusion can problematically yield qualitatively different bubble volume trends depending on the definition used. To investigate the cause of VOF diffusion in THINC/WLIC, Zalesak’s solid rotation was analyzed using a novel visualization method capable of capturing minute VOF values. The results suggest that VOF fragments are stripped from bubble bodies by shear forces near the interface. These findings indicate that THINC/WLIC might not be suitable for accurate void fraction prediction. The original THINC offers better volume conservation and is a viable alternative when PLIC is unavailable. However, reproducing more detailed characteristics such as bubble diameter distribution remains challenging.
Fukuda et al. (Tue,) studied this question.