Energy exchange analysis of a closed conduit transient mixed flow following an air pocket entrapment using a simplified shock-fitting approach

The effects of different variables of closed conduit transient partially pressurized flows on the maximum air pressure are investigated from an energy exchange perspective. It was found that when the air length increases, the maximum pressure decreases because a larger portion of the driving energy will be stored as kinetic energy in the pressurized flow and is dissipated by the friction force. In contrast, when the water depth of the free-surface flow increases, the kinetic energy and dissipating energy of the pressurized flow decrease. Thus, the energy absorbed by the air pocket increases, and the maximum pressure increases. However, after a water depth ratio of 0.8, the maximum pressure decreases even though the kinetic energy and dissipating energy decrease. The reason is that the moving interface receives enough energy, and pressurization of the free-surface flow zone occurs. Note that this pressurization was experimentally observed by Hamam and McCorquodale (1982).