Numerical Study on Flow and Temperature Rise Characteristics in Low Pressure Cylinder of Steam Turbine under Low Flow Condition

Aiming at the problem that the steam turbine low pressure cylinder is in the low flow condition due to the zero output transformation, a calculation model of single-side six-cascade single-channel flow field of a steam turbine low pressure cylinder is established as the research object. Under varying working conditions, especially under low flow condition, the flow structure and aerodynamic performance inside the low pressure cylinder are numerically studied. Under the low flow condition, the windage heating characteristics of the last rotor blade are analyzed. The results show that: under low flow condition, steam flow separation and reflux phenomenon appear in the last cascade. Steam flow separation first appears at the root of the last rotor blade, and gradually develops to the upstream cascade and tip of blade with the continuous decrease of inlet flow. Local vortex current appears in the last cascade channel accompanied by the negative angle of attack phenomenon at the inlet of the rotor blade, which seriously hinders the steam flow. When the inlet flow rate is reduced to 10.0% of the rated condition, a local high temperature zone appears at the exit steam edge in the tip area of the last stationary blade, which is manifested as the windage heating effect of the last stage rotor blade. The windage heating effect will continue to intensify with the decrease of the inlet steam flow, including the expansion of the local high temperature zone and the increase of the maximum temperature. The effect of windage heating on the maximum surface temperature of the last stage stationary blade is significantly greater than that of the rotor blade. In the minimum inlet flow condition, the maximum surface temperature of the last stage stationary blade and the rotor blade is increased by 70.22% and 40.29% compared with the rated condition.