Abstract
Deeply under the ground, especially in redevelopment area in mega cities like Tokyo, drainage pipe system with huge-diameter has been laid in recent years. The water flow containing air-mass or bubbles in a drainage pipe shows the different hydraulic characteristics than usual open channel flow, and the compressed air in horizontal pipes occasionally blows manhole covers off when heavy and concentrated rainfall occurs and massive water rushes into the drainage pipe system. In order to simulate such complicated hydraulic phenomena of the flow in drainage pipe, we proposed an unsteady numerical model which can express the effects of compressed air-mass over the free surface of the flow or compressed bubbles in closed channels to the water flow. The air-flow discharge outgoing through vertical pipes and air pressure was calculated. Comparing the simulated results with the hydraulic experiments conducted by the authors, we could confirm the validity of the present numerical model.
