Pressure Transients due to Compression of Trapped Air in Rapidly Filling Combined Sewer Overflow Storage Tunnels

摘要

Numerical simulations of rapidly filling combined sewer overflow storage tunnels indicate that hydraulic bores may develop, resulting in the entrapment of discrete pockets of air. The air compression can result in significant transient pressures due to the high bore speeds in large systems. Laboratory experiments measuring transient air pressures were conducted in which the propagation of a pipe filling bore was allowed to compress air pockets of various sizes. Both maximum and minimum air pressures were obtained. The magnitude of the peak pressures is a function of the air pocket volume as well as the strength of the bore. In an attempt to scale the laboratory results to prototype applications, a dimensional analysis was developed based on heuristic arguments related to the propagating bore characteristics. The dimensionless presentation of experimental results indicates that this approach can explain much of the variation in the peak pressures and that a single dimensionless relation describes the maximum (or minimum) transient pressure as a function of air volume.