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.

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.

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.

Numerical Investigations on Aerodynamic Performance of Nozzle Control Stage of a 600MW Steam Turbine Under Different Backing Pressure Conditions

2011 ◽  
Author(s):  
Gangyun Zhong ◽  
Jun Li ◽  
Zhigang Li ◽  
Xin Yan ◽  
Qilin Wu
Keyword(s):  
Steam Turbine ◽  
Control Valve ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Computational Domain ◽  
Aerodynamic Efficiency ◽  
Control Stage ◽  
Backing Pressure ◽  
Partial Admission

Partial admission aerodynamic performance of a nozzle control stage for a 600MW steam turbine was numerically investigated using the Reynolds-Averaged Navier-Stokes (RANS) solutions. Two inlet main steam pipe, four control valves, four nozzle groups including strengthening ribs and full stator blades, and full rotor blades were considered in the present computational domain. The partial admission with three control vales opening and the fourth control valve closed under five different backing pressures were calculated to analyze the aerodynamic efficiency and total pressure losses distributions. The maximum aerodynamic efficiency of the nozzle control stage was obtained at five different backing pressure operating conditions. The flow fields in the nozzle control stage at specified backing pressure with consideration of the partial admissions effects were also illustrated.

Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Narmin Baagherzadeh Hushmandi ◽  
Jens E. Fridh ◽  
Torsten H. Fransson
Keyword(s):  
Pressure Field ◽  
Dynamic Pressure ◽  
Turbine Blades ◽  
Leading Edge ◽  
Rotational Frequency ◽  
Rotor Blades ◽  
Computational Domain ◽  
Unsteady Forces ◽  
Partial Admission ◽  
Unsteady Force

A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage’s stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage’s stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.

Forced Response in Axial Turbines Under the Influence of Partial Admission

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Jens Fridh ◽  
Björn Laumert ◽  
Torsten Fransson
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Validation Data ◽  
Pressure Transducers ◽  
Control Stage ◽  
Engine Order ◽  
Partial Admission

High cycle fatigue (HCF) due to unforeseen excitation frequencies, underestimated force magnitudes, or a combination of both causes control-stage failures for steam turbine stakeholders. This paper provides an extended design criteria toolbox, as well as validation data, for control-stage design based on experimental data to reduce HCF incidents in partial-admission turbines. The upstream rotor in a two-stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees extend from 28.6% to 100%, as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of the first stator vanes with aerodynamically shaped filling blocks. Sweeps across a speed range of 50%–105% of design speed are performed at a constant turbine pressure ratio during simultaneous high-speed acquisition. A forced-response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low-engine-order forced responses because of the blockage, pumping, loading, and unloading processes. Combinations of the number of rotor blades and low-engine-order excitations are the principal sources of forced-response vibrations for the turbine studied here. Altering the stator and/or rotor pitches changes the excitation pattern. We observed that a relationship between the circumferential lengths of the admitted and nonadmitted arcs dictates the excitation forces and may serve as a design parameter.

Forced Response in Axial Turbines Under the Influence of Partial Admission

2012 ◽  
Author(s):  
Jens Fridh ◽  
Björn Laumert ◽  
Torsten Fransson
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Validation Data ◽  
Pressure Transducers ◽  
Control Stage ◽  
Engine Order ◽  
Partial Admission

High cycle fatigue (HCF) due to unforeseen excitation frequencies or due to under predicted force magnitudes, or a combination of both causes control stage failures for steam turbine stakeholders. The objectives of this paper is to provide an extended design criteria toolbox and validation data for control stage design based on experimental data, with the aim to decrease HCF incidents for partial admission turbines. The upstream rotor in a two stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees stretching from 28.6% to 100% as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of first stator vanes by aerodynamically shaped filling blocks. Sweeps across a speed range from 50 to 105% of design speed are performed at constant turbine pressure ratio during simultaneous high speed acquisition. A forced response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low engine order forced responses because of the blockage, pumping, loading and unloading processes. Combinations of the number of rotor blades and low engine order excitations are the principal sources of forced response vibrations for the turbine studied herein. Altering the stator and/or rotor pitches will change the excitation pattern. A relation between the circumferential lengths of the admitted and non-admitted arcs that dictates the excitation forces is observed that may serve as a design parameter.

Numerical Study of Unsteady Flow Phenomena in a Partial Admission Axial Steam Turbine

2008 ◽  
Author(s):  
Narmin B. Hushmandi ◽  
Jiasen Hu ◽  
Jens Fridh ◽  
Torsten H. Fransson
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Surface Pressure ◽  
Cross Sections ◽  
Static Pressure ◽  
Three Dimensional ◽  
Rotor Blades ◽  
Strong Mixing ◽  
Partial Admission ◽  
Flow Phenomena

This paper presents a numerical investigation of unsteady flow phenomena in a two-stage partial admission axial steam turbine. Results from unsteady three-dimensional computations are analyzed and compared with the available experimental data. Partial admission in the present study is introduced into the model by blocking only one segmental arc of the inlet guide vanes. Blocking only one segment (which corresponds to the experimental setup) makes the model unsymmetrical; therefore it is necessary to model the whole annulus of the turbine. The first stage rotor blades experience large static pressure change on their surface while passing the blocked channel. The effect of blockage on the rotor blades’ surface pressure can be seen few passages around the blocked channel. Strong changes of the blades’ surface pressure impose large unsteady forces on the blades of first stage rotor row. The circumferential static pressure plots at different cross sections along the domain indicate how the non-uniformity propagates in the domain. A peak pressure drop is seen at the cross section downstream of the first stage stator row. At further downstream cross sections, the static pressure becomes more evenly distributed. Entropy generation is higher behind the blockage due to the strong mixing and other loss mechanisms involved with partial admission. Analysis of the entropy plots at different cross sections indicates that the peak entropy moves in a tangential direction while traveling to the downstream stages. Comparisons of the unsteady three-dimensional numerical results and the experimental measurement data show good agreement in tendency. However some differences are seen in the absolute values especially behind the blockage.

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.

Unsteady Forces Acting on the Rotor Blades and Shaft in the Control Stage for Different Steam Admission Variants

2010 ◽  
Author(s):  
Romuald Rza˛dkowski ◽  
Marek Solin´ski
Keyword(s):  
Rotor Blade ◽  
Gas Flow ◽  
Low Frequency ◽  
Ideal Gas ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Unsteady Forces ◽  
Control Stage ◽  
Start Up ◽  
Steam Admission

This paper concerns the unsteady high- and low-frequency excitation forces acting on the rotor blades and shaft in the control stage of a 200 MW steam turbine. An ideal gas flow through mutually moving stator and rotor blades was described in the form of unsteady Euler conservation equations, which were integrated using the Godunov-Kolgan explicit monotonous finite-volume difference scheme and a hybrid H-H grid. The effect of rotor blade mistuning on the unsteady forces acting on both the blades and the shaft was examined. Four different control stage steam admission variants were analysed. The actual levels of the stationary components of particular forces were determined by changes in the operating conditions of individual nozzle segments. Different mistuning variants generated different distributions of unsteady rotor blade force harmonics. The presented results show that the first harmonic does not always dominate the spectrum. When considering forces acting on the rotor blades and shaft, there exists an optimal procedure of turbine start-up.

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