Simulation of Air Pockets Motion Using GC Integral Model Framworks

T.M. Hatcher, C.D. Chosie and J.G. Vasconcelos


There are important adverse effects linked to the presence of entrapped air pockets in stormwater systems. These effects include loss of conveyance, surging caused by air compression, loss of storage and geysering. The ability of monitoring the formation and motion of entrapped air pockets is thus highly desirable when modeling extreme rain events in stormwater systems. Experimental investigation conducted at Auburn University has addressed the kinematics of air pocket motion in a scale model apparatus that allowed systematic variation of ambient flow velocity, pipeline slopes and initial entrapped air pocket volume. Experimental results indicate that for a first approximation the motion of the leading edge of air pockets is controlled by the initial air pocket volume and the ambient flow velocity. Also, an innovative approach to perform simulations of the air pocket has been proposed based on gravity current flows. This approach uses an expression that relates the thickness of the front and its celerity presented in Wright and Vasconcelos (2008). The integral approach also assumes that the air pocket thickness is uniform over its length. A comparison between measured experimental velocities and modeling predictions indicate that the latter is fairly accurate, and may constitute an in innovative way to approach the description of entrapped air pocket kinematics in closed conduit flows.

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