Modelling of Gas-Liquid Two-Phase Flows in Vertical Pipes using PHOENICS

The PHOENICS code is employed to perform numerical simulations of gas-liquid two-phase bubbly flows in large vertical flow channels. Air-water and steam-water flows in large diameter pipes are simulated using the built-in two-fluid option of the code where liquid and gas are modeled as two interacting continua. The code is utilized in conjunction with advanced twophase flow models, accounting for the interfacial drag, lift, pressure and virtual mass forces and the bubble induced turbulence. Numerical results obtained for both air-water and steam-water bubbly flows are in reasonably good agreement with experimental data available for largediameter pipes from the open literature. The sensitivity study, showing the effects of various model parameters on flow characteristics, has been conducted. There is a significant effect of bubble diameter and lift force coefficient on the predicted lateral void fraction profiles. The void fraction peaking in the pipe wall region is discussed in more detail. The numerical results show that a further development of constitutive relations for interfacial transfer terms is needed to validate the two-fluid model under churn bubbly flow conditions.