AN EXPERIMENTAL STUDY ON THE SHUT-OFF OF THE FLOW IN A SIPHON PIPE BY AIR ADMISSION

摘要

In micro hydro turbine systems, there are cases to adopt a siphon pipe for the penstock to reduce the cost for civil works in the construction. As imagined, the siphon has the feature that the flow in the pipe is easy to stop at the load rejection of a hydro turbine not by using a valve but by using air admission. However, few works have been made to treat siphon phenomena and to develop the air admission method for the load rejection. Thus, the present experimental study is aimed to make clear the effect of admitted air on the flow in a siphon-pipe. To clarify the transient phenomena from the beginning of air admission to the shut-off of the flow, water and air flow rates, wall pressure near the air port in a siphon-pipe (50 mm in dia.) were measured. Flow visualization was also made to see the flow behavior, which was taken by a CCD camera. From this study, we can find the correlation between the required time for shut-off and air-water velocity ratio.