Comparative evaluation of the interface capturing schemes in bundle bubbly flow

Fukuda, Takanari ; Uesawa, Shinichiro  ; Yamashita, Susumu   ; Suzuki, Takayuki*

Advancements in high-performance computing are enabling the application of computational fluid dynamics (CFD) to engineering-scale multi-phase flow problems. The volume of fluid (VOF) method, which tracks interface movement via scalar VOF value transport, is widely used in CFD. Among interface capturing schemes (ICSs), the piecewise linear interface calculation (PLIC) is the most geometrically accurate but computationally complex. In contrast, the tangent of hyperbola interface capturing/weighted line interface calculation (THINC/WLIC) offers a simpler algorithm but suffers from numerical diffusion, degrading interface quality. To address this tradeoff, we developed THINC/Advanced WLIC (THINC/AWLIC), which balances implementation cost and interface sharpness. Although these ICSs have undergone numerical benchmarking, their performance in complex engineering scenarios remains underexplored. To evaluate their applicability to boiling water reactor (BWR) core flows, a liquid-gas two-phase flow in a 33 bundle system experiment was simulated using PLIC, THINC/WLIC, and THINC/AWLIC. The results showed that PLIC and THINC/AWLIC maintained sharp interfaces and provided realistic results but required nearly three times the computational time of THINC/WLIC. While THINC/WLIC was computationally efficient, it exhibited qualitative discrepancies, including unphysical bubble coalescence and volume dissipation. This led to reduced void fractions near the pin-gap region due to fewer bubble coalescences, attributed to bubble size reduction from volume dissipation. A comparison between numerical simulations and experimental void fraction data will be presented to facilitate further discussion.