Abstract
The traditional calculation method for a transient process has high accuracy when the pipeline only contains liquid, but when the pipeline contains both gas and liquid the accuracy is greatly reduced. The coupling characteristics of gas–liquid interface movement in hydraulic transient processes are not clear due to the lack of high-precision mathematical model and experimental verification. This paper proposes a novel mathematical model of a gas–liquid pipeline system in a hydropower station based on Preissman’s implicit difference scheme and the method of characteristics. The solving mechanism of the transient process of gas–liquid movement was developed on the gas–liquid interface tracking method. Subsequently, the models proposed in this paper were applied in two typical scenarios of a gas–liquid transient process in a hydropower system, and their accuracy were verified in a field experiment. The comparison results showed that the novel model could accurately capture the movement of the gas–liquid interface, and the average relative error of the characteristic parameter was about 7.2%. Under the load rejection condition, the change speed of characteristic parameters was positively correlated with the pipeline slope. Under the pump failure after low-head startup condition, the maximum pumping discharge was negatively correlated with startup water level and the maximum reversal discharge and speed were positively correlated with the pump failure water level. Compared with the conventional method, the proposed model has advantages in solving the complex transient process coupling gas–liquid. It has potential value in applications such as the safe operation of hydropower stations, the transient process of water diversion projects and in urban pipe network operation.
Highlights
With the low-carbon transition of the global energy, the operation mode of hydropower has changed, and its flexible regulation ability has attracted more and more attention
To study the stability of the unit under pump failure after a low-head startup condition and the influence mechanism of the gas–liquid coupling interface on the hydraulic transient process, based on the mathematical model, solution method and calculation program proposed in this paper, four different pump failures after low-head startup conditions were selected for analysis
Thereafter, the solving mechanism of the transient process of gas–liquid movement was developed on the gas–liquid interface tracking method
Summary
With the low-carbon transition of the global energy, the operation mode of hydropower has changed, and its flexible regulation ability has attracted more and more attention. The current transient process simulation method of a pumped storage power station can simulate relatively accurate results when the pipeline only contains liquid. Zhao et al [5,6] simulated the transient process of a pumped storage power station by the equivalent circuit method and reconciled the contradiction between simulation efficiency and accuracy through the novel pump-turbine model and space-time discretization. Chaudhry and Hussaini [7] solved the water hammer equation by MacCormak and Gabutti’s explicit FD methods, and they found that these second-order schemes required fewer computing nodes and less time for the same calculation accuracy compared with the MOC method. (3) Compared with other gas–liquid two-phase flow problems, the gas–liquid two-phase transient process in a pumped storage power station is a water filling or draining process in the pipeline.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
