Discrete vapour cavity model with efficient and accurate convolution type unsteady friction term

This paper presents experimental data and numerical simulations of transient vaporous cavitation events generated by a downstream fast valve closure in a pipeline. The experimental apparatus comprises a 37.2 m long constant-sloping pipe of 22.1 mm internal diameter connecting two pressurized tanks. The simulation results show that improper selection of the weighting function in the convolution-based unsteady friction term in the discrete vapour cavity model (DVCM) may significantly attenuate some measured high-frequency pressure pulses and speed-up the timing of the main pressure pulses. Introduction Transient vaporous cavitation (including column separation) occurs in piping systems when the liquid pressure falls to the vapour pressure. Cavitation may occur as a localized vapour cavity (large void fraction) or as distributed vaporous cavitation (small void fraction). A number of vaporous cavitation models have been developed including discrete cavity and interface models (Ref 1). The discrete vapour cavity model (DVCM) with steady pipe flow friction term is widely used in standard water hammer software packages (Ref 2). The DVCM may generate unrealistic pressure pulses (spikes) due to the collapse of multi-cavities, but the model gives reasonably accurate results when the number of reaches is restricted. It is recommended that the maximum volume of the discrete cavity at a section is less than 10 % of the reach volume (Ref 3).