Storm sewer pressurization transient – an experimental investigation

ABSTRACT

Pipe pressurization is examined experimentally by 144 laboratory experiments in a circular tilting pipe between two tanks, in which the transient was triggered by sudden closing of the downstream tank outlet. The experiments cover ranges of values of slope, velocity and filling ratio of the open-channel flow not explored in previous studies. Situations involving considerable air quantity and consequent intense pressure oscillations were also reproduced. Two different pressurization patterns, defined as “smooth” and “abrupt”, were observed, but only the abrupt pattern produced intense pressure oscillations. The comparison among all the abrupt pressurization surges showed how the oscillations changed in starting time, intensity and duration as the pipe slope, the flow rate and the free-surface flow filling ratio varied. The experimental results also stressed the major role of entrapped air in determining the oscillation characteristics, showing that oscillations were actually produced by the pulsating of large air pockets during their migration along the pipe and their release through the upstream manhole.

Keywords:

• Air–water flow
• pressurization
• storm sewer system
• transition
• unsteady flow
• urban drainage

Acknowledgements

The writers wish to thank Dr Dora Ferreri and Dr Emanuele Di Lucia who, with dedication and systematic work, carried out the experiments and made the measurements, and finally placed the latter at our disposal, as well as Dr Salvatore Falzone, who effectively collaborated in numerical simulations which helped the writers in better interpreting the experimental diagrams.