Hiroharu Ooyama

Numerical and Experimental Investigations of Unsteady 3-D Wet-Steam Flows Through Two-Stage Stator-Rotor Cascade Channels

Unsteady 3-D flows through two-stage stator-rotor cascade channels in a low-pressure steam turbine model developed by Mitsubishi Heavy Industry (MHI) are numerically and experimentally investigated assuming dry and wet-steam conditions. The fundamental equations for condensate flows derived by the authors are applied to the present flow computations. The high-order high-resolution finite-difference method based on the fourth-order compact MUSCL TVD (Compact MUSCL) scheme and the Roe’s approximate Riemann solver are used for the space discretization of convection terms. The pipelined LU-SGS scheme optimized for the parallel-implicit time-integration is also employed. MHI measured the total pressures, static pressures and yaw angles of flow velocity vectors at the outlet of first-stage rotor, second-stage stator, and second-stage rotor. The calculated results are compared with the experimental results. In addition, unsteady condensate mass fractions are numerically visualized and the influence of wakes and secondary vortices to the condensation is discussed.Copyright

Unsteady Wake and Vortex Interactions in 3-D Steam Turbine Low Pressure Final Three Stages

A practical unsteady 3-D wet-steam flow through stator-rotor blade rows in a low-pressure steam turbine final three stages is numerically investigated. In ASME Turbo Expo 2013, we presented numerical results of unsteady 3-D wet-steam flows through three-stage stator-rotor low-aspect blade rows in a low-pressure steam turbine model designed by Mitsubishi Heavy Industry (MHI) assuming nonequilibrium condensation. The last study is extended to the final three stages with large aspect blade rows. The discussion in this paper is mainly focused on the effect of unsteady wake and vortex interactions on nonequilibrium condensation computed by our in-house code “Numerical Turbine System (NTS)”. In addition, the NTS and the future perspective are also briefly introduced.Copyright

Development of New High-Performance Labyrinth Seal Using Aerodynamic Approach

As key technologies to improve the performance of steam turbines, various types of high performance seal, such as active clearance control (ACC) seals and leaf seals, have been developed by Mitsubishi Heavy Industries, LTD (MHI). Moreover, a new seal concept has also been developed, which remarkably reduces the leakage flow through the blade tip/base clearance by using an aerodynamic approach.The main concept of this technology is to control and utilize the vortex structure in the cavities of the labyrinth seal by optimizing the cavity geometry. In the optimized geometry, locally-controlled flow on the upstream side of the fin tip causes a strong contraction of the leakage flow and reduces the discharge coefficient significantly. This concept allows for a remarkably reduced leakage flow, whilst keeping clearance at the same level as that of conventional set-up, and thus the risk of contact between rotating and stationary parts low. Therefore, this technology realizes reliable and durable seals with high performance. In addition, it is possible to keep manufacturing cost at the same level as conventional seals, since the structure of this seal is basically the same as the conventional one.In the development of this technology, a parametric study using Computational Fluid Dynamics (CFD) was carried out to optimize the cavity geometry. The verification test was carried out for the optimized geometry under the real steam conditions. From the results, we confirmed that the optimized geometry reduced the discharge coefficient by up to 30%, compared to conventional seals.Copyright

Simulation of Unsteady 3-D Wet-Steam Flows Through Three-Stage Stator-Rotor Blade Rows With Equilibrium and Nonequilibrium Condensations

Unsteady 3-D wet-steam flows through three-stage stator-rotor blade rows in a low-pressure steam turbine model developed by Mitsubishi Heavy Industry (MHI) are numerically investigated. In this study, a new and simple meshing strategy is introduced to improve the prediction of end-wall flows near the shroud and the hub. Dry and wet-steam conditions are taken into account and the calculated results changing the grid system are compared with the experiments. As a practical usage, coarse-grid computations using a PC cluster are also conducted and the results are compared with those using a fine grid and a supercomputer. In addition, a super-cooled condition is assumed and the computation is further conducted. Finally, the effect of homogeneous nucleation and the nonquilibrium condensation on the present flow is evaluated.Copyright

Eulerian-Lagrangian Numerical Simulation of Wet Steam Flow Through Multi-Stage Steam Turbine

In this paper, we present an inclusive tracking algorithm for water droplets in a wet steam flow through a multi-stage steam turbine. This algorism is based on the Eulerian-Lagrangian coupled solver. The solver continuously computes water droplet growth, kinematic non-equilibrium between vapor and droplets, capture and kinetics of droplets on turbine blades, departure of large droplets from the trailing edge of blades, acceleration and atomization of large droplets, and recollisions between blades and droplets.Our Eulerian-Lagrangian coupled solver is used to predict wetness in unsteady three-dimensional (3D) wet steam flows through three-stage stator rotor cascade channels in a low pressure (LP) steam turbine model which is developed by Mitsubishi Heavy Industries (MHI). Droplet groups tracked by the discrete droplet model (DDM) are placed in the computational domain according to the predicted wetness. Interference from the gas phase on the droplets is considered, to track their kinetic and behavior, until they reach the outlet of the computational domain.The aim of this research is to investigate those multi-physics phenomena that trigger all forms of loss in steam turbines. In addition, this method will also be applied to multi-physics problems such as erosion in future work. This paper is presented as a first step in the research. Overviews of model of current coupling solver and several test calculations are presented.Copyright

Vibration Response Analysis of Mistuned Bladed Disk Consisting of Directionally Solidified Blade

Recently, DS (Directionally Solidified) and SC (Single Crystal) alloys have been widely applied for gas turbine blades instead of CC (Conventionally Casting) alloys. In this study, the mistuning analysis of the bladed disk consisting of DS blades is carried out, considering the deviations of the elastic constant and the crystal angle of the DS blade. The FMM is used to analyze the mistuned bladed disk. The maximum amplitude of the mistuned bladed disk of the DS blade is estimated by the Monte Carlo simulation combining with the response surface method, and the calculated results are compared with those of the CC blade.

Analysis and Verification Test of Damping Characteristics of Steam Turbine Hollow Vane With Friction Damper

A vane used in a low pressure end of a steam turbine is usually fixed to a shroud and a 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 the blade and vane of high-capacity steam turbine units, the aerodynamic damping may become negative under the high loading operation, and some papers reported the self-excited vibration of the blade and vane caused by the negative aerodynamic damping. Recently, in order to increase the reliability of the steam turbine vane, a hollow vane with a friction damper has been proposed. In such a steam turbine vane, the curved damper piece made of the thin plate is inserted into the hollow vane, and the structural damping is added by use of the friction between the damper piece and the vane. In this paper, for the purpose of clarifying the damping characteristics of the hollow vane with the friction damper, first, the excitation test of the model vane is carried out. In the excitation test of the model vane, the damping characteristics of the model vane consisting of two flat plates and the thin curved damper piece are measured, changing the excitation force. Second, the analysis method for predicting the damping characteristics of the hollow vane with the friction damper, which utilizes the conventional modal analysis method and the harmonic balance method, is proposed. The validity of the analysis method is verified by comparing the measured damping with the calculated ones. After verifying the analysis method, the actual steam turbine hollow vane with the friction damper is also analyzed, and the effect of the damper stiffness on the damping characteristics is examined. Finally, the actual hollow vane with the friction damper for the high-capacity steam turbine unit is designed and manufactured, and the excitation test of the actual hollow vane is carried out. From these results, the damping characteristics of the hollow vane with the friction damper are clarified.Copyright

Development and Verification of Ultra-Long-Blade for Next Generation Steam Turbine

Mitsubishi Heavy Industries, Ltd. (MHI) has developed “LP-End Blades Series” by employing the ISB (I ntegral S hroud B lade) structure and has lead high efficiency and reliability of the steam turbine. The latest technology has been integrated into Ultra-Long-Blades design for the next generation’s steam turbine. This paper describes the design summary of 3600rpm-50inch/3000rpm-60inches and 1800/1500rpm-74/62inches Blades and results of the verification tests.Copyright

Unsteady Wet-Steam Flows Through Low Pressure Turbine Final Three Stages Considering Blade Number

Unsteady three-dimensional wet-steam flows through stator–rotor blade rows in the final three stages of a low-pressure steam turbine, taking the blade number into consideration, are numerically investigated. In ASME Turbo Expo 2014, we presented the numerical results of the unsteady flow assuming the same blade number. Here, this previous study is extended to flow simulations using the real blade number. The flows under three flow conditions, with and without condensation and considering the same and real blade numbers are simulated, and the numerical results are compared with each other and with the experimental results. Finally, the effect of the blade number on unsteady wet-steam flows in real low-pressure steam turbines is discussed.Copyright

Numerical Investigation of Two-Phase Wet Steam Flow With Spontaneous Condensation Based on Euler S2 Calculation Method

The Euler equation suitable for the S2 stream surface calculation is derived in the arbitrary orthogonal coordinate system firstly. The numerical method for the two-phase wet steam flow with the spontaneous condensation is then developed on basis of the Euler S2 calculation code, the Eulerian/Eulerian multiphase model and the classic nucleation theory.To adapt the complex geometry of the turbine blades, the Euler equations for the S2 stream surface calculation method are derived in the body-fitted coordinate system. The mathematical model for the third order TVD scheme with the non-conservative variables is also developed for the gas phase governing equation. The 2nd order NND and the VanLeer scheme are applied to the variable reconstruction and the numerical flux calculation respectively in the liquid equations solving process. The pressure and the droplet radii distribution fit well with the experimental data for both the high pressure nozzle and the low pressure nozzle. The S2 calculation method is also employed to predict the performance of a 3-stage low pressure steam turbine with spontaneous steam condensation, and the reasonable results are obtained.The numerical method developed in the present work is able to predict the real wet steam flow with the spontaneous condensation and its impact on the flow field and the aerodynamic parameters distribution reasonably, supplying a fast and accurate technic and method to the steam turbine design.Copyright