Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry

Gas-liquid two-phase flow modelling is of highest relevance in nuclear safety analyses. This concerns e.g. the modelling of steam-water two-phase flow and heat transfer in the reactor core, the steam generators, the containment and the spent fuel pool under accident conditions. Prediction of flow conditions by Computational Fluid Dynamics (CFD) tools is of particular interest for supporting safety assessments. However, achieving physically correct simulations is quite challenging due to the complexity of the flow, which includes turbulence, highly deformable gas-liquid interfaces and heat, mass and momentum transfer across the interfaces. Today, two-phase flow models contain a large number of empirical correlations and closure models, which are derived from experimental data. The role of thermal hydraulics experiments nowadays still lies in the creation of such data but moreover they are also needed for model validation.
This contribution describes an experimental study of a generic three-dimensional two phase flow, which should serve as a future benchmark experiment for CFD code validation. The experiments were conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) and are a continuation of earlier studies, which were performed using a moveable flow obstacle and the wire-mesh sensor technique. Although these investigations already provided very good data for a generic two-phase flow, the intrusiveness of both sensor and obstacle motion unit lead to some non-idealities with respect to the fully undisturbed flow. With a new imaging technique, ultrafast electron beam X-ray tomography, we are now able to perform investigations fully non-intrusively and to study the gas phase dynamics with high temporal and spatial resolution in two planes simultaneously. Furthermore, the previous studies did not provide measurement data of liquid velocities, which are required for CFD code validation. Thus, for this study ultrafast X-ray tomography and hot-film anemometry was used in combination to extend the available experimental database. This paper presents selected results of this experimental study.