Non-Dimensional Metrics for Detection of Air Entrapment in Stormwater Pipes

Stormwater network models, such as EPA-SWMM, are designed to simulate pressurized and non-pressurized flow conditions in pipes under the assumption of smooth air venting, i.e., no airwater interaction. However, such interactions are known to cause destructive geysers erupting from manholes. Intense storm events, which lead to inflows at discrete entry points into the stormwater network, can locally pressurize air escape paths with water, ultimately resulting in air entrapment. Current stormwater models simulate the filling of these entrapped pockets while assuming the absence of air under such conditions. Consequently, designers require prior knowledge of these scenarios to detect situations that the model would fail to highlight. We propose a nondimensional metric dependent on the local geometric and inflow parameters of a uniform circular pipe to quantify the potential for air entrapment. This metric can assist designers in optimizing network designs to keep pipes within permissible limits and/or evaluating existing networks for potential air entrapment locations. These locations can then be further extracted and studied using advanced computational tools.

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