Water hammer simulation in two-phase flow regimes using open source code openfoam

Water hammer phenomena in pipe systems are simulated with the open source code OpenFOAM-v7. Effects like dynamic pressure changes caused by fast closing valves, wave propagation, reflection and interference as well as cavitation and fluid structure interaction are focussed in detailed CFD analysis. In this paper two experiments conducted at the,Cold Water Hammer Test Facility" (CWHTF) at Helmholtz-Zentrum Dresden-Rossendorf, Germany are simulated. The experiments show large steam bubbles collapse causing a pressure wave to travel within the pipe system. In order to capture cavitation effects the model basis of the Volume of Fluid based, fully compressible, multi fluid solver compressibleMultiphaseInterFoam is modified. The implementation of the mass transfer terms as well as the modification of the Kunz cavitation model is described and first simulation results are presented. Furthermore, an analytical approach is implemented to model effects of fluid structure interaction with the surrounding pipe. This approach computes the liquid sonic speed in relation with structural parameters of the deformable pipe in combination with a modified equation of state. The simulation results show that the bubble collapsing speed is computed in good accordance to the experiment regarding the timing of the initial pressure peak fits the experimental data. However, the amplitude of the pressure peak is overestimated by 22% neglecting any fluid structure interaction effects. Using the analytical approach to calculate the pipe deformation effects the overestimation of the pressure peak reduces to 8%.