Numerical Investigations on the Steam Cooling Performance of the First Two Middle Pressure Turbine Stages for Ultra-Supercritical Steam Turbines

摘要

This paper researches the steam cooling performance applied in ultra-supercritical steam turbines. The inlet main steam temperature of the middle pressure cylinder is the same or higher than that of the inlet main steam of the high pressure cylinder due to the reheated technology used in the ultra-supercritical steam turbines. The steam cooling design is used to decrease the thermal fatigue and high temperature creep of the rotor in high temperature operation environments for the ultra-supercritical steam turbines. The conjugation flow and heat transfer method was applied to investigate the cooling characteristics of the first two stages solid parts including the rotor blade, wheel disc and rotor blade root of the middle pressure cylinder. In addition, the influences of the cooling steam on aerodynamic performance parameters distribution of the first two stages were also analyzed by comparison of the through flow calculations without steam cooling. The results show that the steam cooling design can effectively cool the rotor system of the first stage, and the temperature of the solid part near the cooling hole decreases by up to 30K. The temperature of the steam flowing through the diaphragm seal of the second stage increases and is higher than that of the local main flow. Therefore, the temperature of the rotor system of the second stage is relative high. Furthermore, the cooling steam enters into the through flow passage and mixes with the main flow. This flow behavior leads to changes of the flow pattern and aerodynamic parameters distribution near the blade hub regions.