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Examination of numerical methods and physical modelling of condensation induced water hammer including gas release

: Neuhaus, T.; Dudlik, A.; Fahlenkamp, H.

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

Pressure surges generated from condensation induced water hammers may lead to dynamic stresses which are induced in the walls of pipelines and their support structures. This can cause serious safety risks for human and environment. Besides it can finally lead to operational problems of the pipe plant system. It is desirable to minimise the safety risks already during the design phase of a pipework. This can be achieved using calculation software, that predicts possible pressure surges as exact as possible.
This contribution presents simulation results from two numerical schemes, the method of characteristics (MOC) in combination with a discrete vapour cavity (DVC) model and from a finite volume method (FVM), that solves 4, 5 and 6 partial differential equations. Problems that are typical for the two numerical methods are shown, that is for the FVM the choice of a reasonable spatial discretisation and time step.
Theoretical test cases have been chosen to show deficiencies of the numerical methods. Furthermore experimental results from the investigation of cavitation induced water hammers at the test facility at Fraunhofer UMSICHT have been taken for validation. These data have been obtained within the EURATOM project WAHALoads.
It is shown that the effect of gas release during the experiments is not negligible. Hence models with and without air using different approaches for the mass transfer of air between the gas and the liquid phase have been examined and validated.