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Dynamic effects of transient flows with cavitation in pipe systems

: Borga, A.; Ramos, H.; Covas, D.; Dudlik, A.; Neuhaus, T.

Murray, S.J. ; BHR Group, Cranfield/Bedford:
The practical application of surge analysis for design and operation. Vol.2 : Papers presented at 9th International Conference on Pressure Surges, Chester, UK, 24 - 26 March 2004
Cranfield: BHR Group, 2004 (Transferring technology)
ISBN: 1-85598-051-7
ISBN: 1-85598-053-3
International Conference on Pressure Surges <9, 2004, Chester>
Fraunhofer UMSICHT Oberhausen ()
Kavitation; Druckstoß; pressure surge

In pressurised transient flows with cavitation or water column separation, the presence of free or dissolved air affects the elastic wave speed, as well as the propagation of transient pressure waves. Several transient tests have been carried out to calibrate simplified numerical models developed using the Method of Characteristics with localised air cavities and variable wave speed to describe the presence of air. The developed analysis aims at the parameterisation of special dynamic effects induced during a fast transient. This analysis enables the distinction of different types of system responses and to better understand associated phenomena. Collected transient data were compared with numerical results taking into account pressure variations in time. These analyses include the characterisation of the most relevant issues, such as maximum and minimum observed pressures, oscillation time period, damping effect and the influence of a leak. Numerical results have shown that the localised cavity model (or vapour-liquid model) simulates reasonably well the shape of observed transient pressures. As this type of model is easier to implement and to use in practice, its accuracy was improved by incorporating additional dissipative-dispersive terms in the basic fluid equations, in order to describe these special dynamic effects.