In order to clarify the mechanism of the severe erosion mainly resulted by the singular vortex cavitation, we carefully try to observe the vortex cavitation associated with the erosion around a butterfly valve by means of a high-speed video-camera, whose maximum framing rate is 40, 500 per seconds. The velocity of cavitating flow are measured with the correlation method, one of the digital-image processing-technique. It is worth noticing that the vortex cavitation develops in the boundary region between the main flow region, i. e., the orifice-jet, and the recirculating region. The cavitating vortex core consists of several tiny vortex cavitation. And the rotating velocity of the highly erosive vortex cavitation can be also detected by the technique.
A buoyancy-driven exchange flow through an opening in a partition can be induced by density difference between the gases of each side. The exchange flow rate and flow behavior depend on the density difference and the geometric configuration of the opening. The geometry of the opening is characterized by its diameter, length and inclination angle. This paper describes an experimental study on the buoyancy-driven exchange flow between helium filled in a chamber and the outside air through a small opening by means of visualization. The opening with large length-to-diameter ratio appears at the top of the chamber. Buoyancy-driven exchange flows through the opening are visualized by making use of laser-light-sheet technique. The results of visualization show exchange flow behavior by turbulent diffusion and its transition to stratified flow caused by increasing of inclination angle of the opening. Key words : Buoyancy-driven Exchange Flow, Visualization, Laser-light-sheet Technique, Turbulent Diffusion, Stratified Flow