Verification of the slip velocity obtained from the two-fluid model in PHOENICS

摘要

The report presents a research project with the main objective of testing the treatment of phase slip in PHOENICS on various two-phase test cases. For spherical air bubbles rising the stagnant water, the slip can be determined from the governing equations to be equal to 0.268 m/s. This is based on the assumption that the convection and diffusion terms are negligible compared to the pressure, gravity and interphase friction terms. Four two-dimensional test cases have been examined using the two-fluid model implemented in PHOENICS v.2.0. The cases examined were: (1) two-phase flow in a vertical straight duct, (2) two-phase flow in a vertical duct with a backward-facing step, (3) as case (1), but where an orifice has been installed at the inlet and (4) separation of gas and liquid in a square box. In all cases gravity was acting against the main flow direction. Two of the test cases verified a slip equal to 0.268 m/s. In the two other cases, a recirculation zone was formed, and the slip in the vertical direction was found to deviate from the preliminary calculated value of 0.268 m/s. For such flow problems, the convection and diffusion terms can not be neglected in the determination of the slip velocity. 10 refs., 38 figs., 4 tabs.