Numerical Study on Flow and Blast Heating Characteristics of Low-Pressure Cylinder of Steam Turbine Under Deep Peak Regulating Operation

In deep peak regulating operation, the low-pressure cylinder of steam turbine is in the low flow condition. At the same time, the internal flow and temperature rise of the last stage are very complicated, which brings challenges for deep peak regulating operation and zero output transformation of low-pressure cylinder. The low-pressure cylinder of a steam turbine in a power plant is taken as the research object, and the calculation model of the seven-stage cascades single-channel flow field of the low-pressure cylinder is established. The working performance, flow structure and blast heating characteristics of the low-pressure cylinder under different working conditions are numerically studied. The results show that when the flow rate of the low-pressure cylinder decreases to 2.91% of the rated operating condition, the low-pressure cylinder cannot output power. When the flow rate is very small, the low-pressure cylinder enters the blast heating station, and flow structures such as end wall separation zone, stator blade separation zone, casing torus vortex, and last stage bucket vortex appear in the last stage. Moreover, significant blast heating phenomenon appears at the tip of the last stage in the stator rotor clearance. When the flow rate is reduced to 1.05% of the rated operating condition, the average surface temperature of the last stage stator blade and rotor blade increase by 312.75K and 331.88K. Under the low flow condition, the working performance of the low-pressure cylinder is significantly reduced, and the temperature in the last stage deteriorates the working environment of the blade, which should be taken into consideration when the unit is in deep peak regulating operation.