Modeling the Motion and Spread of Air Pockets within Stormwater Sewers

Abstract

There are important adverse e ects linked to the presence of entrapped air pockets in stormwater systems. These e ects include loss of conveyance, surging caused by air compression, loss of storage, and geysering. The capability to monitor the formation and motion of entrapped air pockets is highly desirable when modeling extreme rain events in stormwater systems. Experimental investigations conducted at Auburn University have led to a better understanding of important ow features related to the motion of entrapped air in closed conduit ows. Results from these studies, which are summarized in this work, have supported the development of an innovative approach to perform simulations of the air pocket motion based on Benjamin's (1968) work on air cavity motion. The proposed model accounts for surface tension in a similar manner to Wilkinson (1982) but incorporates background ows and circular cross-sections. Air motion is described with a non-Boussinesq integral gravity current model approach, assuming a steady state ow for the water. Measured and predicted values for the air pocket leading edge coordinate and celerity are compared. Results indicate that the proposed model is fairly accurate and may constitute an e cient model to describe entrapped air pocket kinematics in closed conduit ows.