Abstract
Noise generated by the annular film-flow plunging into a water surface in a vertical drain-pipe was investigated experimentally to obtain a basic idea to suppress noises related to a bubble entrainment. The correlation among the noise level, entrainment of bubbles and state of film-flow when it plunged into a water surface was observed. It was found that when the turbulent film-flow plunged into the water surface, the sound pressure level of the noise increased abruptly, and the number and size of bubbles also increased. The major frequency of the noise was explained by bubble-cloud oscillation rather than an oscillation of a single bubble. The bubbles regarded as a noise source were in the recirculating region near the water surface. The recirculating region found to become larger when the plunging velocity of the film-flow increased.
