Hiroharu Ohyama

Blade Row Interaction in a High-Pressure Steam Turbine

This paper presents a study of the three-dimensional flow field within the blade rows of a high-pressure axial flow steam turbine stage. Compound lean angles have been employed to achieve relatively low blade loading for hub and tip sections and so reduce the secondary losses. The flow field is investigated in a Low-Speed Research Turbine using pneumatic and hot-wire probes downstream of the blade row. Steady and unsteady numerical simulations were performed using structured 3D Navier-Stokes solver to further understand the flow field. Agreement between the simulations and the measurements has been found. The unsteady measurements indicate that there is a significant effect of the stator flow interaction in the downstream rotor blade. The transport of the stator viscous flow through the rotor blade row is described. Unsteady numerical simulations were found to be successful in predicting accurately the flow near the secondary flow interaction regions compared to steady simulations. A method to calculate the unsteady loss generated inside the blade row was developed from the unsteady numerical simulations. The contribution of various regions in the blade to the unsteady loss generation was evaluated. This method can assist the designer in identifying and optimizing the features of the flow that are responsible for the majority of the unsteady loss production. An analytical model was developed to quantify this effect for the vortex transport inside the downstream blade.Copyright

Effect of Material Damping of Steam Turbine Vane on Flutter Suppression

The vane used in a low pressure end of steam turbine is usually fixed to shroud and casing by welding both ends. In such a vane structure, the damping in loading operation is comprised of the material damping and the aerodynamic damping, because the structural damping is very small. In this paper, first, the vane is modeled by the uniform beam fixed at both ends, and the effect of the material damping on the vane flutter is studied. In the stability analysis, the simple one-degree-of-freedom model is applied, where the linear aerodynamic model is used. In other words, it is assumed that the aerodynamic force due to the working fluid is proportional to the vane velocity and the negative damping coefficient does not change with amplitude. The allowable aerodynamic damping for the vane flutter is calculated and compared for the solid vane and the hollow vane. In addition, the vibration analysis of the actual steam turbine vane is carried out by 3D FEA (Finite Element Analysis), and the material damping of the solid and hollow vane is calculated by use of the results by FEA. The stability of the solid vane and the hollow vane on the flutter is also evaluated by use of the results calculated by FEA. From these results, the material damping characteristics of the steam turbine vane are clarified, as well as the effect of the material damping of the steam turbine vane on the flutter suppression.Copyright

Investigations on the Flow Pattern and Aerodynamic Performance of Last Stage and Exhaust Hood for Large Power Steam Turbines

The aerodynamic performance and internal flow behavior of the last stage and exhaust hood for large power steam turbine was numerically investigated using commercial CFD software ANSYS-CFX. The computational domain includes all stator and rotor blades of last stage and exhaust hood including bracing tubes and strengthening plates. The Reynolds-Averaged Navier-Stokes (RANS) solution was utilized to analyze aerodynamic performance of last stage and static pressure recovery coefficient of exhaust hood. For comparison, the internal flow pattern of the individual exhaust hood was also analyzed without consideration of the last stage effects. The static pressure and Mach number distribution at the meridional plane of the last stage was illustrated. The velocity vector distribution at different cross sections in the exhaust hood with and without consideration of the last stage influence was compared. In addition, the static pressure and pressure loss contours distribution in the exhaust hood were also studied. The obtained results show that the outflow of the last stage can significantly influence the aerodynamic performance and flow pattern of the exhaust hood. To obtain a reliable prediction of the aerodynamic performance of the exhaust hood, it is necessary to consider the interaction between the last stage and exhaust hood.© 2012 ASME

Development and Verification of 3000 rpm 48 Inch Integral Shroud Blade for Steam Turbine

The 3000 rpm 48 inch blade for steam turbine was developed as one of the new standard series of LP end blades. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. Therefore, the number of the resonant vibration modes can be reduced by virtue of the vibration characteristics of the circumferentially continuous blades, and the resonant stress can be decreased due to the additional friction damping generated at shrouds and stubs. In order to develop the 3000 rpm 48 inch blade, the latest analysis methods to predict the vibration characteristics of the ISB structure were applied, after confirming their validity to the blade design. Moreover, the verification tests such as rotational vibration tests and model turbine tests were carried out in the shop to confirm the reliability of the developed blade. As the final verification test, the field test of the actual steam turbine was carried out in the site during the trial operation, and the vibration stress of the 3000 rpm 48 inch blade was measured by use of telemetry system. In the field test, the vibratory stress of the blade was measured under various operating conditions for more than one month. This paper first presents the up-to-date design technology applied to the design of the 3000 rpm 48 inch blade. In the second place, the results of the various verification tests carried out in the shop are presented as well as their procedure. Lastly, the results of the final verification tests of 3000 rpm 48 inch blade carried out in the site are presented.Copyright

Vibration Response Characteristics of Bladed Disk With Continuous Ring Type Structure Losing Shroud and Stab

This paper presents a simple analysis method for predicting vibration response characteristics of a bladed disk with continuous ring type structure losing a shroud or a shroud and a stab between two blades. This loss introduces a mistuning of the system and the whole bladed disk model must be used to conduct the study. However, the vibration modes change regularly from a sine and a cosine mode, if the bladed disk consists of many blades. By utilizing this phenomenon, the simple formulation of vibration response of a bladed disk can be derived. Second, the parametric study on the vibration response characteristics of a bladed disk losing a shroud or a shroud and a stab is carried out extensively, utilizing the analysis method proposed here. From the calculated results, the vibration response characteristics of a bladed disk are clarified for both of resonant vibration and random vibration. Lastly, the results calculated by the simple analysis method proposed are compared with the results obtained from FEA (Finite Element Analysis) in order to verify the validity of the analysis method.Copyright

Development and Operating Experience of a Two-Casing 600MW Ultra-Super-Critical Steam Turbine

600MW class steam turbines are typically manufactured in three casing configurations with two low-pressure casings. Mitsubishi Heavy Industries (MHI) has developed and manufactured a 600MW two-casing Ultra Super Critical turbine for the Hirono No.5, Tokyo Electric Power Co. in Japan, which comprises one combined high- and intermediate-pressure casing and one double-flow low-pressure casing. This unit started the commercial operation in July 2004. Two-casing design simplifies construction and maintenance requirements and saves capital cost of the plant. This compact design was realized mainly due to the development of 3000 rpm 48 inch steel low-pressure end blades, the longest steel blade in the industries for 3000 rpm machines. In addition, a highly efficient and compact design in achieving 600°C steam condition was realized by employing a combined high- and intermediate-pressure frame. This paper addresses the design features of the 600MW two-casing USC turbine, operating condition of the Hirono No.5 and the results of the verification tests performed.Copyright

Vibrational Response Analysis of Mistuned Bladed Disk System of Grouped Blades

For the purpose of the efficient analysis of a mistuned bladed disk system, a new analysis method which applies the substructure synthesis method and the modal analysis method is proposed. Using the proposed method, the vibrational characteristics of the grouped blades structure are studied. From the results, it is found that the grouped blades structure is very sensitive to the mistuning. It is also found that the mixed grouped blades structure (a bladed disk system consisting of some different types of grouped blades relating to the number of blades contained) has an undesirable effect on the forced response. Moreover, by comparing the vibrational characteristics of the integral shroud blades (ISB) structure with those of the grouped blades structure, it is clarified that the reliability of the ISB structure is superior to other structures also from the viewpoint of the mistuning.Copyright