Local-scale experimental investigation of a two-phase cross-flow in a tube bundle and flow-induced vibration: Intermittent/Churn flow

Two-phase cross-flows in tube bundle can induce vibrations. This occurs in many industrial situations, such as nuclear power plant U-tube Steam Generator (SG). With the purpose of gathering high quality data for the validation of multiphase CFD simulation tools, a new experimental apparatus was designed and put in operation. The facility is instrumented for the two-phase air–water flow and tube vibration characterization. This article deals with experimental results in the churn/intermittent two-phase flow conditions. The experimental study was achieved by means of three measurement techniques: high-speed camera, optical dual-tip probe and wire mesh sensor. The behavior of the two-phase flow upstream of the tube bundle, characterized by the continuous generation of large gas structures, is detailed: high-speed camera and wire mesh sensor data reveal the prevalence of dispersed bubbles near the wall and large gas structures in the core region. The rising frequency of the large gas structures could be determined. Profiles of void fraction and gas velocity were measured within the tube bundle.The flow regime map of the experiment is proposed and is correlated with the study of flow-induced tube vibration. It highlights the role played by gas structure size distribution, thus flow pattern in the structural response in intermittent flow regimes with a local-scale characterization of the flow. Finally, the present work is a major contribution to improve and validate local-scale numerical simulation.