Evaluation of the THINC/AWLIC scheme for two-phase flow in pin bundle geometry

Fukuda, Takanari ; Uesawa, Shinichiro  ; Yamashita, Susumu   ; Yoshida, Hiroyuki  

The volume of fluid (VOF) method is a prominent multiphase flow simulation method. Among different interface capturing schemes (ICSs) in the VOF method, the algorithm of the piecewise linear interface calculation (PLIC) is geometrically rigrous but complex to implement. 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 practival engineering conditions has not been sufficiently investigated. To evaluate their applicability to boiling water reactor (BWR) core flows, a liquid-gas two-phase flow in a pin bundle geometry was simulated using PLIC, THINC/WLIC, and THINC/AWLIC, and compared with the void fraction data obtained by an experiment. The notable result is that the void fraction values for simply coded THINC/AWLIC are nearly identical with those of PLIC, which maximizes the geometrical fidelity with the expense of the algorithmic complexity. The results indicate the generally high applicability of THINC/AWLIC in predicting void fraction in pin bundle geometry and its advantages over conventional ICSs. However, regardless of ICSs, the simulation based on the VOF method still fails to reproduce experimental void fraction at low gas flow rates, where bubble coalescence is minimal in experiment.