Applying state-of-the-art R&D to an old workhorse, the steam turbine

At the ASME Turbo Expo this year, Doosan Škoda Power Company presented topics, which reflect increasing demands for modern flexible turbines.

• Development of Highly Efficient and Robust Ultra-Long Last Stage Blade for High Backpressure
• Separation of Water Film from Last Stage Guide Blades of 1000 MW Steam Turbine
• Experimental and Numerical Evaluation of Losses From Turbine Hub Clearance Flow

The first topic is about an extensive and comprehensive development of a robust last stage blade for high back pressures. The demand for high back pressures makes the design of such a blade very challenging because some technical requirements and design features needed are mutually opposing. However, development of this blade can provide a competitive advantage in dry areas where only air-cooled condensers can be used and high backpressures are part of the operating conditions.

The main focus of the paper was on experimental testing of transonic and supersonic flow filed in the vicinity of the blades and on the investigation of self-induced vibrations, which are also known as flutter. Doosan Škoda Power Company has focused on flutter prediction thanks to many years of internal and external research development work, collaboration on the European FlexTurbine project, as well as the cooperation with NUM Solution.

The paper, "Separation of Water Film from Last Stage Guide Blades of 1000 MW Steam Turbine", presents experimental and partially numerical research of water and steam flow through the grooves in hollow stator blades of the steam turbine last stages. Measurements were taken on a steam turbine with nominal output 1,000 MW where it was possible to measure different turbine outputs. The results provide important information about the suction tract behavior and its ability to remove liquid water films from the stator blades surface. When using a properly dimensioned and correctly working suction system, erosion loading of LSB leading edges on the tip can be lowered by almost half. The presented work was financially supported by the Technology Agency of the Czech Republic; project TK01020029 Efficiency Increasing of Turbine Wet Steam Last Stages.

The third paper, "Experimental and Numerical Evaluation of Losses from Turbine Hub Clearance Flow", discussed the solving of another challenging blading problem. Development of 3D blading for HP and IP stages in reaction blading was presented. Its key idea is to include parasitic flows through the shaft and the shroud sealing and alternatively through the balance holes into the current consideration of the mainstream flow, i.e. through the nozzle and the bucket blades. This project is mostly focused on mutual interactions of these parasitic flows with the mainstream flow, resulting in a new loss model preparation for the more precise design of the flow path.