Experiments and numerical simulations of horizontal two-phase flow regimes using an interfacial area density model

Abstract

Stratified two-phase flow regimes can occur in the main cooling lines of Pressurized Water Reactors, Chemical plants and Oil pipelines. A relevant problem occurring is the development of wavy stratified flows, which can lead to slug generation. In the last decade, stratified flows have increasingly been modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. Recent improvements of the multiphase flow modelling in the ANSYS CFX code, now make it possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, a high spatial and temporal resolution of measurement data are required. For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model based on the implemented mixture model was introduced, which allows the detection of the morphological form of the two-phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result, this model can distinguish between bubbles, droplets and the free surface using the local value of the volume fraction of the liquid phase. The behaviour of slug generation and propagation was qualitatively reproduced by the simulation, while local deviations require a continuation of the work.