Analysis on flow separation characteristics of last stage blade in steam turbine under small volume flow condition

The inlet steam flow of steam turbine is obviously reduced and even in the state of small volume flow when the thermal power unit is involved in peak load operation, which greatly influences the safety of steam turbine. The last stage flow field of steam turbine under small volume flow condition is calculated by the CFX to study the formation, development, influencing range, and the variation rule of the flow separation vortex cores. The results show that the flow separation vortices appear near last stage blade at 30% of the rated volume flow. With the decrease of volume flow, the flow separation vortices gradually spread to the root of blade. When the volume flow decreases to 8% of the rated volume flow, the flow separation vortices almost occupy the whole blade. The position of the flow separation vortex cores shifts from 72.7% of the relative blade height to 49.1%. The results of this paper lay a foundation for the safety analysis of the last stage blade in the steam turbine under the small volume flow condition.