Identifying head accumulation due to transient wave superposition in pipelines

Abstract

Fluctuations in pressures are part of the normal behavior of water distribution systems. The common perception is that transient events dissipate quickly in a network without significant consequences; however, under certain circumstances, the superposition of waves from a transient event can magnify the pressure response, effectively accumulating head in a pipeline. This paper studies this accumulation phenomenon in a single pipeline from a theoretical point of view, with supporting numerical simulation and laboratory validation. Transient wave propagation analysis shows that after the generation of a transient event, multiple wave reflections induce an increase in the head. A cycle of accumulation is defined and the potential maximum number of cycles is studied for a pipeline connected to a long, large impedance pipe section. The analysis is then extended to a system connected to a shorter large impedance pipe section where the maximum head accumulation is not reached. Expressions to calculate the potential maximum head accumulation in pipeline systems are proposed and numerically validated. A general classification for the head accumulation is presented to specify how severe a head accumulation event may be. Experimental validation of the phenomenon has been conducted, showing that under a proposed configuration, the head in the pipeline increases significantly after the first small head rise due to a valve closure. A comparison between the maximum measured head in the laboratory and the theoretical expected maximum head has been undertaken. More realistic configurations that could result in the same phenomenon are briefly discussed.