Surge Effects in Pressure Systems for Different Pipe Materials

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Abstract

In pressurised transient flows the cavitation or water column separation, will induce the presence of free gas/vapour which will affect the elastic wave speed, as well as the propagation of transient pressure waves. Hence, several transient tests have been tested to calibrate simplified numerical models developed by using the Method of Characteristics with local gas cavities along the pipe and with variable wave speed. The developed analysis aims at the parameterisation of special dynamic effects. Extreme pressures, even with small duration, can reach excessive values with undesired safe and operational conditions: the maximum pressure values can cause ruptures in pipes and fittings, while low values can induce the collapse of the pipe-wall, air admission and release or the formation of vapour cavities. The analysis of surge effects due to cavitation occurrence in two pipelines with different pipe materials (i.e., metal and plastic), as well as the modelling of an air-valve behaviour for different pipe profiles, type of manoeuvres and quantity of retained air, are performed. Mathematical models are increasingly more used in design, as well as in the daily management and control of hydraulic systems, in particular for the prediction of unstable dynamic conditions.

This work is supported by FCT through the projects POCTI/ECM/58375/2004 and PTDC/ECM/65731/2006, as well as CEHIDRO, the Hydro-systems’ research centre from the Department of Civil Engineering, at Instituto Superior Técnico (Lisbon, Portugal).