Influence mechanism of Valve opening on flow field stability of bypass valve of conventional island Steam Turbine

The bypass valve of the steam turbine is one of the most critical valves in a conventional island. Its flow field stability is directly related to the nuclear power plant's long-term safe and stable operation. In this paper, the high-pressure labyrinth bypass valve, which is widely used in the conventional island of a nuclear power plant, is taken as the object of study. Based on the compressibility of the working mass, the accuracy of the numerical model is verified by first comparing it with the experimental value, and then the correlation between the valve opening and the stability of the flow field in the valve is studied. The results show that with the increase of valve opening, the resistance characteristics of the valve show a “three-segment” distribution, and the friction coefficient reaches the maximum value at 30% opening; the labyrinth component plays a majorly throttling role when the valve opening degree is less than 60%, the stability of the pressure field and velocity field in this opening range gradually increases with the increase of valve opening, and the changes are comparatively sensitive; however, when the valve opening degree is more than 60%, the local flow in the valve core is transformed into the supersonic flow, and the irreversible loss at the cage network structure is comparatively large. With the increase of the valve opening, the stability of the pressure field is lower. And the velocity field is slightly enhanced, but the sensitivity to the change of the valve opening is comparatively low. The results play a guiding role in regulating the bypass valve set of the steam turbine and bear great significance to the safe operation of the unit and tapping the exploitation of energy-saving potential.