题目：High Fidelity Measurement of Two-Phase Flow using Optical Methods
Dr. Yang Liu is an assistant professor of the Mechanical Engineering Department at Virginia Tech. Prior to his current position, he was a postdoctoral research associate in the Thermal-hydraulics and Reactor Safety Laboratory at Purdue University. His research interests include nuclear reactor thermal hydraulics, multiphase flow and heat transfer, fast X-ray densitometry, and high speed optical imaging, etc. He severs on the executive committee of the thermal-hydraulics division of the American Nuclear Society. He has authored/co-authored more than 70 research publications in international journals and conferences. Dr. Liu received his B.S. in 2000, M.S. in 2003 from Shanghai Jiao Tong University, and his Ph.D. in 2008 from Purdue University, all in nuclear engineering.
High-quality and high-resolution two-phase flow data is important for developing and validating advanced computer codes which have become essential tools for various engineering applications. This talk will introduce several measurement techniques which have been recently developed to obtain such data. The first technique is based on a high-speed imaging system and advanced image processing algorithms. A comprehensive image processing package has been developed to deal with issues such as separation of overlapping bubbles, 2-D outline reconstruction, bubble tracking, and identification of bubble interaction mechanisms. To accurately measure bubble shape and volume, a 3-D imaging system consisting of four high-speed cameras has been established in this study. Space carving method is used to reconstruct the 3-D bubble shape based on the recorded high-speed images from different view angles. Time-resolved 3-D bubble information could be obtained using this system for low void fraction bubbly flows. Another technique is based on PIV (Particle Image Velocimetry) and PLIF (Planar Laser Induced Fluorescence), which has been developed to measure the liquid-phase velocity and turbulence characteristics. In this system, fluorescent particles are used to seed the liquid flow and an optical phase separation method is adopted to remove the bubbles recorded on the PIV images. It is expected that various two-phase flow regimes can be measured more accurately with these newly developed measurement techniques.