Rotor Dynamic Analysis on Partial Admission Control Stage in a Large Power Steam Turbine

2010 ◽  
Author(s):  
Lin Gao ◽  
Yiping Dai
Keyword(s):  
Steam Turbine ◽  
Phase Angle ◽  
Low Frequency ◽  
Deep Understanding ◽  
Labyrinth Seal ◽  
Steam Turbines ◽  
Large Power ◽  
Stiffness Coefficients ◽  
Control Stage ◽  
Partial Admission

Partial admission is used widely for steam turbines to match their output power to the load demand. The occurrences or thresholds of most self-induced low-frequency vibrations are under partial admission conditions. But the destabilizing forces which cause rotor instability are seldom investigated under partial admission conditions especially for large power steam turbines. Full 3D CFD model is built for the control stage of a 600 MW steam turbine applying commercial codes. N-S equations are solved to investigate the flow fields in the control stage including all the blade passages and the labyrinth seal over the shroud. Interesting flow distributions are observed for the seal spaces at partial admission conditions. A correction formula is presented for partial admission labyrinth seal based on the classical one and a method is discussed for the estimation of partial-admission phase-angle-dependent stiffness coefficients. The destabilizing forces acting on the rotor system are calculated for different eccentricity angles and are compared with those under the concentric condition. The stiffness coefficients are solved under typical partial admission conditions. They are found to change dramatically with the phase angle. The results may be helpful for a deep understanding of the low-frequency variation problems of large power steam turbines under partial admission conditions.

Rotordynamic Stability Under Partial Admission Conditions in a Large Power Steam Turbine

2009 ◽  
Author(s):  
Lin Gao ◽  
Yiping Dai ◽  
Zhiqiang Wang ◽  
Yatao Xu ◽  
Qingzhong Ma
Keyword(s):  
Steam Turbine ◽  
Fluid Model ◽  
Rotor System ◽  
System Stability ◽  
Steam Turbines ◽  
Large Power ◽  
Control Stage ◽  
Partial Admission ◽  
The Stability ◽  
Load Conditions

At present, the majority of power steam turbines operate under part-load conditions during most of their working time in accordance with the fluctuation of power supply. The load governing method may cause partial admission in control stage and even some pressure stages, which impacts much on the stability of the rotor system. In this paper, CFD and FEM method were used to analyze the effect of partial admission on rotor system stability. A new approach is proposed to simplify the 3D fluid model for a partial admission control stage. Rotordynamic analysis was carried out to test the stability of the HP rotor of a 600 MW steam turbine under different load conditions. 13 different governing modes on the rotor stability were conducted and data were analyzed. It is found that rotor stability varies significantly with different governing modes and mass flow rates, which is consistent with the operation. Asymmetric fluid forces resulted from partial admission cause a fluctuation of the dynamic characteristics of the HP bearings, which consequently affect the stability of the rotor system. One of the nozzle governing modes in which the diagonal valves open firstly is demonstrated as the optimal mode with the maximum system stability. The optimization has been applied to 16 power generation units in China and result in improved rotor stabilities.

Unsteady Load of Partial Admission Control Stage Rotor of a Large Power Steam Turbine

2004 ◽  
Author(s):  
Piotr Lampart ◽  
Mariusz Szymaniak ◽  
Romuald Rza˛dkowski
Keyword(s):  
Steam Turbine ◽  
Rotor Blades ◽  
Pressure Pulsations ◽  
Unsteady Forces ◽  
Large Power ◽  
Control Stage ◽  
Partial Admission ◽  
Geometrical Imperfections ◽  
Sst Turbulence Model ◽  
2D Model

Partial admission flow in the control stage of a 200MW steam turbine is investigated with the help of a RANS solver with k-ω SST turbulence model in the code Fluent. A 2D model of flow at the mid-span section of the full annulus is assumed. The results exhibit interesting details of the process of expansion in the control stage. Unsteady forces acting on the single rotor blades of the control stage are calculated, and are subject to Fourier analysis. Single blade forces are summed up to obtain the unsteady load at the rotor (forces acting at the rotor disc are neglected due to the assumed 2D model). The calculations take into account pressure pulsations at the entry to the nozzle boxes and rotor blade mistuning / geometrical imperfections.

Modeling Partial Admission in Control Stages of Small Steam Turbines With CFD

2018 ◽  
Author(s):  
Juri Bellucci ◽  
Filippo Rubechini ◽  
Andrea Arnone
Keyword(s):  
Steam Turbine ◽  
Three Dimensional ◽  
Admission Rate ◽  
Point Of View ◽  
Test Case ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Performance Curves ◽  
Partial Admission ◽  
The Impact

This work aims at investigating the impact of partial admission on a steam turbine stage, focusing on the aerodynamic performance and the mechanical behavior. The partialized stage of a small steam turbine was chosen as test case. A block of nozzles was glued in a single “thick nozzle” in order to mimic the effect of a partial admission arc. Numerical analyses in full and in partial admission cases were carried out by means of three-dimensional, viscous, unsteady simulations. Several cases were tested by varying the admission rate, that is the length of the partial arc, and the number of active sectors of the wheel. The goal was to study the effect of partial admission conditions on the stage operation, and, in particular on the shape of stage performance curves as well as on the forces acting on bucket row. First of all, a comparison between the flow field of the full and the partial admission case is presented, in order to point out the main aspects related to the presence of a partial arc. Then, from an aerodynamic point of view, a detailed discussion of the modifications of unsteady rows interaction (potential, shock/wake), and how these ones propagate downstream, is provided. The attention is focused on the phenomena experienced in the filling/emptying region, which represent an important source of aerodynamic losses. The results try to deepen the understanding in the loss mechanisms involved in this type of stage. Finally, some mechanical aspects are addressed, and the effects on bucket loading and on aeromechanical forcing are investigated.

Suppression of Subsynchronous Vibrations in a 11 MW Steam Turbine Using Integral Squeeze Film Damper Technology at the Exhaust Side Bearing

2016 ◽  
Author(s):  
Riccardo Ferraro ◽  
Michael Catanzaro ◽  
Jongsoo Kim ◽  
Michela Massini ◽  
Davide Betti ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Labyrinth Seal ◽  
Squeeze Film ◽  
Stable Operation ◽  
Steam Turbines ◽  
Squeeze Film Damper ◽  
Full Load ◽  
Steam Admission ◽  
Before And After ◽  
Full Speed

The presence of high subsynchronous vibrations and other rotordynamic instabilities in steam turbines can prevent operation at full speed and/or full load. The destabilizing forces generating subsynchronous vibrations can be derived from bearings, seals, impellers or other aerodynamic sources. The present paper describes the case of an 11 MW steam turbine, driving a syngas centrifugal compressor train, affected by subsynchronous vibrations at full load. After the occurrence of anomalous vibrations at high load and a machine trip due to the high vibrations, the analysis of data collected at the site confirmed instability of the first lateral mode. Further calculations identified that the labyrinth seal at the balance drum was the main source of destabilizing effects, due to the high pre-swirl and the relatively tight seal clearance. The particular layout of the turbine, a passing-through machine with a combined journal/double thrust bearing on the steam admission side, together with the need for a fast and reliable corrective action limited the possible solutions. Based on the analyses performed, adjusting the clearance and preload of the journal bearings could not have ensured stable operation at each operating condition. The use of swirl brakes to reduce the steam pre-swirl at the recovery seal entrance would have required a lengthy overhaul of the unit and significant labor to access and modify the parts. The final choice was a drop-in replacement of only the rear bearing (on the steam exhaust side) with a bearing featuring integral squeeze film damper (ISFD) technology. In addition to being a time efficient solution, the ISFD technology ensured an effective tuning of stiffness and damping, as proven by the field results. The analyses carried out to understand the source of the subsynchronous vibrations and to identify possible corrective actions, as well as the comparison of rotordynamic data before and after the application of the bearing with ISFD technology, are discussed.

Stability of High Pressure Turbine Under Partial Admission Condition

2005 ◽  
Author(s):  
Hiroshi Kanki ◽  
Akinori Tanitsuji
Keyword(s):  
High Pressure ◽  
Theoretical Analysis ◽  
Steam Turbine ◽  
High Capacity ◽  
Low Frequency ◽  
Initial Position ◽  
Experimental Results ◽  
Qualitative Description ◽  
Scale Model ◽  
Partial Admission

Subsynchronous vibration of high-pressure steam turbine is one of the difficult problems to improve the reliability of power plant. Extensive work has been done to prevent the low frequency vibration of high-capacity steam turbine and most of the problems were practically solved[1][2]. In the future, we must build up theoretical approach to design a new turbine operating under the steam condition of high-temperature and high-pressure. To design such an advanced steam turbine, it is necessary to solve the effect of partial admission on control stage of the steam turbine. This paper describes the experimental results from the scale model of the steam turbine and theoretical analysis of Alford force considered partial admission condition to solve the problem. (1) Subsynchronous vibration was reproduced in the scale model test. (2) Partial admission gave larger destabilizing force compared with full admission condition for same total flow rate. (3) Initial position of shaft center to the phase of admission arc on the partial admission had some effect on the stability of the rotor system. (4) Theoretical analysis of destabilizing force considered partial admission condition gave qualitative description of the experimental results from the scale model.

Effect of Partial Admission and Swirl Brakes on Destabilization Force of Labyrinth Gas Seal

2020 ◽  
Author(s):  
Makoto Iwasaki ◽  
Rimpei Kawashita ◽  
Naoto Omura ◽  
Kazuyuki Matsumoto ◽  
Kenichi Murata ◽  
...  
Keyword(s):  
Steady State ◽  
Steam Turbine ◽  
Large Scale ◽  
Labyrinth Seal ◽  
Cfd Analysis ◽  
Analysis Method ◽  
Labyrinth Seals ◽  
Fluid Force ◽  
Swirl Velocity ◽  
Partial Admission

Abstract Destabilization forces in labyrinth seals can cause subsynchronous vibration and many researchers have investigated the destabilization force under full admission (FA). It is known that partial admission (PA) can increase rotor instability, but there is little knowledge about seal fluid force under PA. In this study the experiment was conducted in order to confirm the effect of PA and swirl brakes (SB) on swirl velocity and destabilization force. For the experiment, a 500mm diameter rotor was used so that size of the labyrinth seal can be close to the large-scale steam turbine. According to the experimental results, it was found that (1) average swirl velocity and destabilization force under PA became larger than FA, (2) relationship between average swirl velocity and destabilization force under PA was almost same with that of FA, (3) seal fluid force under PA had anisotropy by the instant rotor position, (4) SB reduced 70% of swirl velocity and destabilization force under both FA and PA. Also it was found that CFD analysis could predict the effect of PA and SB on swirl velocity and seal fluid force. For predicting the effect of SB under FA, new steady state CFD analysis method applying frozen rotor interface at SB region was proposed.

Direct Constrained Computational Fluid Dynamics Based Optimization of Three-Dimensional Blading for the Exit Stage of a Large Power Steam Turbine

2002 ◽  
Vol 125 (1) ◽  
pp. 385-390 ◽  
Author(s):  
P. Lampart ◽  
S. Yershov
Keyword(s):  
Steam Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Steam Turbines ◽  
Original Design ◽  
Large Power ◽  
Wide Range

The paper describes results of direct constrained optimization using Nelder-Mead’s method of deformed polyhedron and a Reynolds-averaged Navier-Stokes (RANS) solver to optimize the shape of three-dimensional blading for the exit stage of a large power steam turbine. The computations of the flowfield in the stator and rotor are compressible, viscous, and three-dimensional. Turbulence effects are taken into account using the modified model of Baldwin-Lomax. The objective function is the stage efficiency, with the exit energy considered a loss, and with constraints imposed on the mass flow rate in the form of a penalty function if the mass flow rate falls beyond the required range. The blade sections (profiles) are assumed not to change during the optimization. Two optimization tasks are reported in this paper, first—optimizing the stator straight and compound circumferential lean, and also stator and rotor stagger angles to keep the flow rate unchanged, giving a total number of optimized parameters equal to 5; second—optimizing the stator straight and compound axial sweep, also with stator and rotor stagger angles, also giving five optimized parameters. The process of optimization is carried out for a nominal load; however, due to the fact that exit stages of steam turbines operate over a wide range of flow rates away from the nominal conditions, the original and final geometries are also checked for low and high loads. The process of optimization gives new designs with new three-dimensional stacking lines of stator blades, and with significantly increased efficiencies, compared to the original design, at least for a larger part of the assumed range of load.

Thermally Sprayed Abradable Coatings in Steam Turbines: Design Integration and Functionality Testing

2010 ◽  
Author(s):  
Dieter Sporer ◽  
Scott Wilson ◽  
Petr Fiala ◽  
Ruediger Schuelein
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Gas Turbines ◽  
Labyrinth Seal ◽  
Test Methods ◽  
Steam Turbines ◽  
Coating Materials ◽  
Design Integration ◽  
Abradable Coatings ◽  
Thermally Sprayed

The concept of thermally sprayed abradable sealing technology has successfully been used in aero engines and industrial gas turbines for several decades now. More recently efforts were undertaken to implement the concept of seal coatings in steam turbine designs. As these typically use labyrinth type sealing, the application and test methods for sprayed seals applied to improve efficiency and reduce emissions need to be tailored to this particular seal configuration. This paper reviews how steam turbines can benefit from abradable coating technology and how it can be implemented into existing labyrinth seal designs for various seal locations in a steam turbine. A detailed review of high temperature rig abradability testing capabilities for labyrinth seal layouts using abradable coatings will be provided. Coating materials and their performance in a high temperature steam environment at 650 °C ( 1200 °F ) will be discussed. The application of coatings to various steam turbine components including large casings will be reviewed.

Numerical Analysis of Partial Admission Flow in an Industrial Steam Turbine

2012 ◽  
Author(s):  
Tobias J. Kalkkuhl ◽  
David Engelmann ◽  
Ulrich Harbecke ◽  
Ronald Mailach
Keyword(s):  
Steam Turbine ◽  
Cfd Simulation ◽  
Computational Cost ◽  
Turbulence Models ◽  
Typical Feature ◽  
Control Stage ◽  
Gap Flow ◽  
Partial Admission ◽  
Flow Effects ◽  
Simulation Parameters

A partially admitted control stage is a typical feature of an industrial steam turbine. Its purpose is to provide efficient part-load operation and to reduce losses caused by an adverse blade height to tip gap ratio by closing segmental arcs of the inlet annulus. On the other hand partial admission naturally causes circumferential nonuniformity of the flow, because the flow enters the control stage rotor over only a portion of the annulus. This induces not only unsteady blade forces but also additional losses in comparison to a full-admission turbine. So the advantage of partial admission is reduced. In order to analyze partial admission flow effects a 3D CFD model of an industrial steam turbine needs to be developed. It consists of three parts: i) The nozzle groups covering only a portion of the annulus and the rotor of the impulse-type control stage, ii) a cross-over channel directing the flow to a reduced diameter, and iii) the downstream reaction-type turbine stages. The results show considerable flow nonuniformity downstream of the cross-over channel which affects performance of the adjacent full-admission stages. Different operating points of the turbine are investigated. Circumferential periodicity is utilized to minimize computational cost of the simulation. Customary guidelines to CFD-simulation are taken into account and simulation parameters are carefully checked for their influence on the results: turbulence models, meshing parameters and boundary conditions are varied. The influence of gap flow is checked. The results are finally compared to experimental data to check simulation quality.

scholarly journals Demonstration of a Dynamic Clearance Seal in a Rotating Test Facility

2017 ◽  
Author(s):  
Andrew Messenger ◽  
Richard Williams ◽  
Grant Ingram ◽  
Simon Hogg ◽  
Stacie Tibos ◽  
...  
Keyword(s):  
Steam Turbine ◽  
High Speed ◽  
Labyrinth Seal ◽  
Test Facility ◽  
Steam Turbines ◽  
Rotor Position ◽  
Seal Design ◽  
Start Up ◽  
Steam Turbine Plant ◽  
Transient Events

The successful demonstration of the “Aerostatic Seal” in a half scale rotating facility is described in this paper. The Aerostatic seal is a novel dynamic clearance seal specifically designed for steam turbine secondary gas path applications. The seal responds to radial rotor excursions, so a reduced clearance can be maintained compared to conventional labyrinth seal without damage to the seal. This enables increased turbine performance through reduced leakage and increased tolerance of turbine transient events typically found during start up. The seal is an extension of the existing retractable seal design already deployed in commercial steam turbines. The seal was tested in the Durham Rotating Seals Rig, which was developed specifically to test this device. The rig featured a rotor designed to run with large eccentricities to model high speed radial rotor excursions, and the seal was instrumented to measure the real time seal response to the rotor. The experimental campaign has conclusively demonstrated the ability of the seal to dynamically respond to the rotor position. The key result is that the seal is able to track the rotor position at high speed, and hence maintain a mean seal clearance that is lower than the rotor eccentricity. Overall this work marks a key milestone in the development of the Aerostatic Seal, and leads the way to testing in a steam environment and application in steam turbine plant.

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