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Paper is considering the purpose and the process of development of last stage blade for intermediate pressure module of 13K215 steam turbine. In the last 20-30 years most of the steam turbine manufacturers were focused on improving such a turbine mainly by upgrading low pressure module. In a result of such a modernization technology were changed from impulse to reaction. The best results of upgrading were given by developing low pressure last stage blade. With some uncertainty and based on state of art knowledge, it can be stand that improving of this part of steam turbine is close to the end. These above indicators show an element on which future research should be focused on - in the next step it should be intermediate pressure module. In the primary design the height of intermediate pressure last stage blade was 500 mm but because of change of technology this value was decreased to 400 mm. When to focus on reaction technology, the height of the last stage blade is related to output power and efficiency. Considered here is the checking the possibility of implementing blades, in a reaction technology, higher than 400 mm and potentially highest. Article shows a whole chosen methodology of topic described above. It leads through the reasons of research, limitations of 13K215 steam turbine, creation of three-dimensional models, fluid flow calculations, mechanical integrity calculations and proposed solutions of design. [ABSTRACT FROM AUTHOR]

Recent trends in the electric energy market such as biomass, waste incineration or combined cycle power plants require innovative solutions in steam turbine design. Variable operating conditions cause significant changes in flow field surrounding the steam turbine last stage blades. Therefore, the enlargement of operating range for last stage blades presents new challenges in design of turbine cascades. Several turbine cascades were designed and analyzed by commercial and in-house software of CTU Prague. Selected profiles were experimentally validated in the high-speed wind tunnel for 2D cascade measurements of the Institute of Thermomechanics of the Czech Academy of Sciences which is equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard. Comparisons are presented of numerical results with optical and pneumatic measurements for a wide range of inlet and outlet Mach numbers for optimized hub and tip profile cascades. [ABSTRACT FROM AUTHOR]

The condensation of wet steam has important effects on the behavior of the flow field. To evaluate the aerodynamic performance of exhaust passage influenced by wet steam phase change condensation, a numerical investigation was conducted. Taking a 600 MW steam turbine as an example with consideration of the wet steam from the last stage blade and the steam exhaust of the BFPT (boiler feed water pump turbine), the governing equations of wet steam two-phase flow were adopted by the Eulerian-Eulerian approach. Results show that the wetness in the stator domain increases gradually while the wetness in the rotor domain varies little on the pressure surface and is in small increment on the suction surface. The velocity uniformity can be improved at condenser throat outlet as the mass flow or wetness increases. Moreover, the trend to improve the aerodynamic performance of exhaust passage benefits from the improvement of wetness at the last stage blade inlet. Conversely, with the increment of wetness at the BFPT inlet, the static pressure recovery coefficient reduces by 5.8% and the total pressure loss coefficient increases by 2.4%, resulting in a reduction of aerodynamic performance of exhaust passage. [ABSTRACT FROM AUTHOR]

The inlet steam flow of steam turbine is obviously reduced and even in the state of small volume flow when the thermal power unit is involved in peak load operation, which greatly influences the safety of steam turbine. The last stage flow field of steam turbine under small volume flow condition is calculated by the CFX to study the formation, development, influencing range, and the variation rule of the flow separation vortex cores. The results show that the flow separation vortices appear near last stage blade at 30% of the rated volume flow. With the decrease of volume flow, the flow separation vortices gradually spread to the root of blade. When the volume flow decreases to 8% of the rated volume flow, the flow separation vortices almost occupy the whole blade. The position of the flow separation vortex cores shifts from 72.7% of the relative blade height to 49.1%. The results of this paper lay a foundation for the safety analysis of the last stage blade in the steam turbine under the small volume flow condition. [ABSTRACT FROM AUTHOR]

Recent trends in the electric energy market such as biomass, waste incineration or combined cycle power plants require innovative solutions in steam turbine design. Variable operating conditions cause significant changes in flow field surrounding the steam turbine last stage blades. Therefore, the enlargement of operating range for last stage blades presents new challenges in design of turbine cascades. Several turbine cascades were designed and analyzed by commercial and in-house software of CTU Prague. Selected profiles were experimentally validated in the high-speed wind tunnel for 2D cascade measurements of the Institute of Thermomechanics of the Czech Academy of Sciences which is equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard. Comparisons are presented of numerical results with optical and pneumatic measurements for a wide range of inlet and outlet Mach numbers for optimized hub and tip profile cascades.

The 3 000 rpm 1 220 mm blade for a steam turbine was developed with application of new design features. The last stage moving blade is designed with an integral cover, a mid-span tie-boss connection and a fir-tree dovetail. With this configuration the blades are continuously coupled by the blade untwist due to the centrifugal force when the blades rotate at high speed, so that vibration control and increased structural damping are provided. Blade was tuned in order to eigen-frequencies were safely far from possible excitation. Because of connection members, the number of the resonant vibration modes can be reduced by virtue of the vibration characteristics of the circumferentially continuous blades. The last stage airfoil was optimalized from view of minimalization of its centrifugal force. In order to develop the 3 000 rpm 1 220 mm blade, the advanced analysis methods to predict dynamics behavior of the bladed structure were applied. Coupled rotor-blade analysis was also aim of the attention. To validate calculated results the verification measurement such as rotational vibration tests was carried out in the high-speed test rig. Relation of the friction damping of the bladed structure on amount of excitation level was also monitored and evaluated.

Abstract: A crack of the last stage blade in a low-pressure steam turbine is studied. From non-destructive inspection, the crack was found at the trailing edge fillet of the last stage blade. On further examination using the replication of the crack and scanning electron microscopy, the crack was induced by stress corrosion cracking. The blade integrity is evaluated for several crack-removal conditions to repair the cracked blade. Finite element analysis is utilized to determine the stresses and dynamic characteristic of the blade for these conditions. The assessment of high cycle fatigue is performed by modified Goodman diagram. From the results, it is found that the crack-removal blade satisfies the design criteria for the fatigue life and has the sufficient margin from resonant condition of vibration. Repair for the cracked blade would be recommended on the basis of the careful analysis. For the repaired blade, periodic inspection is needed and replacement of the blade will be necessary when an indication is found. [Copyright &y& Elsevier]