Yoshio Shikano

Non-Equilibrium Homogeneously Condensing Flow Analyses as Design Tools for Steam Turbines

In order to get the details of flow fields in steam turbines, three-dimensional turbulent flow calculations are useful. However in a design procedure, three-dimensional flow calculations are only possible in the last design stage, because they need in-depth boundary conditions of both geometries and flows. At such a late time in the procedure, it is difficult to go back and change main design parameters, such as flow area and stage load. Both three-dimensional flow patterns and non-equilibrium condensation caused by rapid expansions of steam have important roles with respect to steam turbine performance particularly in low-pressure sections. The steam turbine internal efficiency can be improved by taking account of these effects in the early design stage, especially in flow pattern design. This paper describes a multi-stage through-flow calculation technique including both three-dimensional flow efffects and phase changes from vapour to small droplets. To compute the high-speed two phase steam flow, a flux-splitting procedure including non-equilibrium homogeneously condensation is introduced. Three-dimensional blade forces are calculated by using angles of both blade camber and radial lean. The blade camber lines can be decided without in-depth blade geometries. Therefore this computational technique is applicable in the flow pattern design. The calculation results agree well with fully three-dimensional flow calculation and the calculation can predict supersaturating states and Wilson lines which are defined as the maximum supercooling.© 2002 ASME

A High Performance Optimized Reaction Blade for High Pressure Steam Turbines

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-e 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.Copyright

A Numerical Analysis of Three-Dimensional Compressible Turbulent Flows in Cascades and Ducts

Since most of the aerodynamic losses in turbomachinery are directly related to the various viscous flow phenomena, a reliable computer program for three-dimensional compressible viscous flows in cascades and ducts is an effective design tool for improving the performance of modern turbines and compressors. The recent remarkable advances in computer capabilities and solution algorithms enable the calculation of fully three-dimensional viscous flows and several such computer programs have been developed in recent years. Moore et al. (1979) and Hah (1983) proposed the computer programs for three-dimensional viscous compressible flows in ducts and cascades. Although both of them are available for compressible flow calculations, they are hardly applicable to transonic flow analysis.

Prediction of Unsteady Force for Axial Turbine Buckets (Effects of Nozzle-Bucket Axial Gap Length and Blade Count Ratio)

The purpose of this study is to investigate the unsteady force acting on steam turbine buckets which is induced by a potential field and a wake. The authors have already proposed a new method that can separate the unsteady force into a potential field interaction and a wake interaction from the unsteady viscous flow computation. It is understood from the previous work that simple expressions may be written for the relationships between the nozzle-bucket axial gap length and the unsteady force, which means the amplitude and the phase of the unsteady force with the nozzle passing frequency component.This paper adopts the blade count ratio as the factor to study the unsteady force of the bucket sections with different bucket heights in the same stage. Four points are seen from the results; points (a)–(c) do not depend on the blade count ratio. (a) The amplitudes of the unsteady force of each interaction can be approximated by an exponential or a power function of axial gap length. (b) The amplitudes of each interaction tend to become large when bucket turning angle is large. (c) The phase of the unsteady force of each interaction with the nozzle passing frequency component has a linear relationship with axial gap length. (d) The amplitudes of each interaction become the maximum value when the blade count ratio is 1.5.Copyright

Numerical analysis of two-dimensional compressible turbulent flows in a turbine stage

A numerical analysis based on the compressible Reynolds-averaged Navier-Stokes equation has been developed for the analysis of two-dimensional compressible turbulent flows in a turbine stage (nozzle and bucket). In the present flow analysis, governing equations are solved by the use of a time dependent explicit method and a two-equation model of turbulence is employed to estimate turbulence effects. To calculate nozzle and bucket flow fields simultaneously, a steady interaction between these flows is assumed. For spatial discretization of the governing equations, a control volume method combined with a body-fitted curvilinear coordinate system is developed to calculate the flows in arbitrarily shaped cascades. In order to assure the effectiveness of the present method, computations are carried out for a two-dimensional section at a blade midspan in a turbine stage. The method gives satisfactory results about boundary layers on blade surfaces, nozzle wake profiles and pitchwise averaged turbine design parameters at each blade exit.