A One-Dimensional Numerical Model to Predict Pressure and Velocity Oscillations of a Compressed Air Pocket in a Vertical Shaft Filled with Water

A sewer geyser is an explosive overflow of a mixture of gas and water through a vertical pipe of a sewer system. According to reported field observations, the explosive overflows occurred in a form of ejecting water columns that persisted for several seconds. In previous studies, the presence of entrapped air pockets in sewer systems were argued to be the direct cause of the sewer geyser occurrence. The mechanisms of air-water interaction in a vertical pipe during a sewer geyser lease were investigated. A one-dimensional numerical model was developed to simulate the flow. The vertical shaft was closed at the bottom and open to the ambient pressure at the top. Initially, the lower section of the vertical shaft was filled with compressed air and the water column sat above the air pocket. Once the simulation was triggered, the interaction between the pressurized air and the water column exhibited an oscillatory motion which decayed over time. The results were compared with three dimensional numerical simulations conducted using a commercial computational fluid dynamics software.