A High Performance Optimized Reaction Blade for High Pressure Steam Turbines

Abstract

A higher efficiency gain is necessary for steam turbine plants to reduce their fuel consumption rate and lessen their environmental disruption factor. Power plant manufacturers have continued to make an effort to raise steam turbine internal efficiency by developing new technologies. High pressure (HP) steam turbines should have increased efficiency owing to relatively shorter blade height compared with other turbine sections (intermediate and low pressure turbines). In order to increase efficiency, it is important to improve the steam path determined by design parameters such as degree of reaction, number of stages and rotor diameter and to develop a high performance blade applied to it. The advanced computational fluid dynamics (CFD) technique is a useful design tool, and has come to be applied generally to evaluate energy loss. A new rotating blade has been developed for small and mid-class steam turbines with a shorter blade height. The robust design method, based on the statistical theory for design of experiments, is used for the blade root profile design. It is combined with the inverse method and 2-D turbulent blade-to-blade flow analysis to evaluate the aerodynamic performance. The blade configuration is expressed by four control factors, which are turning angle, leading edge radius, pitch-chord ratio and maximum blade loading location. Linear cascade experiments are also carried out due to verify the blade performance under the optimized conditions obtained by the robust design. Consequently, the blade section has a blunt-nose, flat incidence characteristics and low energy loss, compared with the conventional one and the optimized conditions given by the robust design are aerodynamically reasonable. Finally, air turbine model tests and 3-D Reynolds-averaged Navier-Stokes analyses are performed to investigate the detailed flow pattern and stage performance of the new optimized reaction blade. An experimental investigation is still important to evaluate the performance in the real turbine stage structure, while the numerical analysis method is used based on the implicit TVD scheme with the modified k-ε turbulence model. It is found that the new optimized reaction blade has greatly improved stage efficiency of about 1.5% at the design point including the effect of leakage flow (3% improvement in stage efficiency excluding leakage flow) and realized an increase of pitch-chord ratio by about 35%. Consequently, the new optimized reaction blade is considered effective to raise the internal efficiency of the high-pressure steam turbine with improved steam path.