Numerical simulation of column separation in pipelines by discrete vapor cavity model with gas release

Water hammer with column separation is a highly dangerous phenomenon in long-distance water transmission pipelines, potentially leading to structural damage or even loss of life. During the transient process, when pressure drops below the saturation pressure of dissolved gases, dissolved gases are released. However, the classical discrete vapor cavity model (DVCM) does not fully account for this effect, causing deviations in predicting the pressure peak and phase. This study innovatively incorporates a variable-mass gas release model into the DVCM, establishing the discrete vapor cavity model with gas release (DVCM-GR). Sensitivity analyses on grid resolution, weighting factors, and semi-empirical gas release rate coefficients were conducted, with results compared to both classic DVCM and experimental data. The results indicate that the prediction of pressure wave peak by the DVCM-GR model is mainly influenced by grid resolution, while the phase of the pressure wave is affected by the combined effect of all three factors. Specifically, an increase in grid resolution and semi-empirical gas release rate coefficient enhances the released gas mass, decreasing wave speed and causing phase delay, whereas a larger weighting factor produces the opposite effect. Compared with the DVCM, the DVCM-GR mitigates phase deviation and improves both peak and waveform predictions, especially when coupled with the Vardy and Brown friction model. This study highlights the significance of gas release effects in the simulation of water hammer with column separation, providing a new model option and theoretical foundation for more accurate transient analysis in pressurized pipelines.