Modeling of a Steam Turbine Including Partial Arc Admission for Use in a Process Simulation Software Environment

2011 ◽  
Author(s):  
Eric Liese
Keyword(s):  
Steam Turbine ◽  
Process Simulation ◽  
Process Model ◽  
Constant Pressure ◽  
Pressure Ratio ◽  
Simulation Software ◽  
State Variables ◽  
Steam Turbines ◽  
Software Environment ◽  
Last Stage

A dynamic process model of a steam turbine, including partial arc admission operation, is presented. Models were made for the first stage and last stage, with the middle stages presently assumed to have a constant pressure ratio and efficiency. A condenser model is also presented. The paper discusses the function and importance of the steam turbines entrance design and the first stage. The results for steam turbines with a partial arc entrance are shown, and compare well with experimental data available in the literature, in particular, the “valve loop” behavior as the steam flow rate is reduced. This is important to model correctly since it significantly influences the downstream state variables of the steam, and thus the characteristic of the entire steam turbine, e.g., state conditions at extractions, overall turbine flow, and condenser behavior. The importance of the last stage (the stage just upstream of the condenser) in determining the overall flowrate and exhaust conditions to the condenser is described and shown via results.

Modeling of a Steam Turbine Including Partial Arc Admission for Use in a Process Simulation Software Environment

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Eric Liese
Keyword(s):  
Steam Turbine ◽  
Flow Rate ◽  
Process Model ◽  
Constant Pressure ◽  
Pressure Ratio ◽  
Simulation Software ◽  
State Variables ◽  
Steam Turbines ◽  
Software Environment ◽  
Last Stage

A dynamic process model of a steam turbine, including partial arc admission operation, is presented. Models were made for the first stage and last stage, with the middle stages assumed to have a constant pressure ratio and efficiency. A condenser model is also presented. The paper discusses the function and importance of the steam turbine's entrance design and the first stage. The results for steam turbines with a partial arc entrance are shown and compare well with experimental data available in the literature; in particular, the “valve loop” behavior as the steam flow rate is reduced. This is important to model correctly since it significantly influences the downstream state variables of the steam, and thus the characteristic of the entire steam turbine, e.g., state conditions at extractions, overall turbine flow, and condenser behavior. The importance of the last stage (the stage just upstream of the condenser) in determining the overall flow rate and exhaust conditions to the condenser is described and shown via results.

A Numerical Investigation of Rotating Instability in Steam Turbine Last Stage

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
L. Y. Zhang ◽  
L. He ◽  
H. Stüer
Keyword(s):  
Steam Turbine ◽  
Dynamic Instability ◽  
Computational Study ◽  
Fluid Dynamic ◽  
Pressure Ratio ◽  
Separated Flow ◽  
Test Model ◽  
Steam Turbines ◽  
Last Stage ◽  
Rotating Instability

The unsteady flow phenomenon (identified as rotating instability) in the last stage of a low-pressure model steam turbine operated at very low mass flow conditions is numerically studied. This kind of instability has been observed previously in compressors and can be linked to the high structural stress levels associated with flow-induced blade vibrations. The overall objective of the study is to enhance the understanding of the rotating instability in steam turbines at off design conditions. A numerical analysis using a validated unsteady nonlinear time-domain CFD solver is performed. The 3D solution captures the massively separated flow structure in the rotor-exhaust region and the pressure ratio characteristics around the rotor tip of the test model turbine stage in good comparison with the experiment. A computational study with a multi-passage whole annulus domain on two different 2D blade sections is subsequently carried out. The computational results clearly show that a rotating instability in a turbine blading configuration can be captured by the 2D model. The frequency and spatial modal characteristics are analyzed. The simulations seem to be able to predict a rotating fluid dynamic instability with the similar characteristic features to those of the experiment. In contrast to many previous observations, the results for the present configurations suggest that the onset and development of rotating instabilities can occur without 3D and tip-leakage flows, although a quantitative comparison with the experimental data can only be expected to be possible with fully 3D unsteady solutions.

A Numerical Investigation of Rotating Instability in Steam Turbine Last Stage

2011 ◽  
Author(s):  
L. Y. Zhang ◽  
L. He ◽  
H. Stu¨er
Keyword(s):  
Steam Turbine ◽  
Dynamic Instability ◽  
Computational Study ◽  
Fluid Dynamic ◽  
Pressure Ratio ◽  
High Stress ◽  
Test Model ◽  
Steam Turbines ◽  
Last Stage ◽  
Rotating Instability

In the present study, the unsteady flow phenomenon (identified as rotating instability) in the last stage of a low-pressure model steam turbine operated at very low mass flow conditions is studied through numerical investigations. This kind of instability has been observed previously in compressors and is believed to be the cause of high stress levels associated with the corresponding flow-induced blade vibrations. The overall purpose of the study is to enhance the understanding of the rotating instability in steam turbines at off design conditions. A numerical analysis using a validated unsteady nonlinear time-domain CFD solver is adopted. The 3D solution captures the massively separated flow structure in the rotor-exhaust region and the pressure ratio characteristics around the rotor tip of the test model turbine stage, which compare well with those observed in the experiment. A computational study with a multi-passage whole annulus domain on two different 2D blade sections is subsequently carried out. The computational results clearly show that a rotating instability in a turbine blading configuration can be captured by the 2D model. The frequency and spatial modal characteristics are analyzed. The simulations seem to be able to predict a rotating fluid dynamic instability with the similar characteristic features to those of the experiment. In contrast to the previous observations and conventional wisdom, the present work reveals that the formation and movement of the disturbance can occur without 3D and tip-leakage flows, even though a quantitative comparison with the experimental data can only be expected to be possible with full 3D unsteady solutions.

The Effect of Stage-Diffuser Interaction on the Aerodynamic Performance and Design of LP Steam Turbine Exhaust Systems

2018 ◽  
Author(s):  
Bowen Ding ◽  
Liping Xu ◽  
Jiandao Yang ◽  
Rui Yang ◽  
Yuejin Dai
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Rotor Blades ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Part Load ◽  
Last Stage ◽  
Load Conditions ◽  
Turbine Exhaust ◽  
Exhaust Systems

Modern large steam turbines for power generation are required to operate much more flexibly than ever before, due to the increasing use of intermittent renewable energy sources such as solar and wind. This has posed great challenges to the design of LP steam turbine exhaust systems, which are critical to recovering the leaving energy that is otherwise lost. In previous studies, the design had been focused on the exhaust diffuser with or without the collector. Although the interaction between the last stage and the exhaust hood has been identified for a long time, little attention has been paid to the last stage blading in the exhaust system’s design process, when the machine frequently operates at part-load conditions. This study focuses on the design of LP exhaust systems considering both the last stage and the exhaust diffuser, over a wide operating range. A 1/10th scale air test rig was built to validate the CFD tool for flow conditions representative of an actual machine at part-load conditions, characterised by highly swirling flows entering the diffuser. A numerical parametric study was performed to investigate the effect of both the diffuser geometry variation and restaggering the last stage rotor blades. Restaggering the rotor blades was found to be an effective way to control the level of leaving energy, as well as the flow conditions at the diffuser inlet, which influence the diffuser’s capability to recover the leaving energy. The benefits from diffuser resizing and rotor blade restaggering were shown to be relatively independent of each other, which suggests the two components can be designed separately. Last, the potentials of performance improvement by considering both the last stage rotor restaggering and the diffuser resizing were demonstrated by an exemplary design, which predicted an increase in the last stage power output of at least 1.5% for a typical 1000MW plant that mostly operates at part-load conditions.

Sequential vs Multidisciplinary Coupled Optimization and Efficient Surrogate Modelling of a Last Stage and the Successive Axial Radial Diffuser in a Low Pressure Steam Turbine

2014 ◽  
Author(s):  
Kevin Cremanns ◽  
Dirk Roos ◽  
Arne Graßmann
Keyword(s):  
Steam Turbine ◽  
Design Process ◽  
Energy Demand ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Low Pressure ◽  
Steam Turbines ◽  
Low Pressure Turbine ◽  
Pressure Steam ◽  
Last Stage

In order to meet the requirements of rising energy demand, one goal in the design process of modern steam turbines is to achieve high efficiencies. A major gain in efficiency is expected from the optimization of the last stage and the subsequent diffuser of a low pressure turbine (LP). The aim of such optimization is to minimize the losses due to separations or inefficient blade or diffuser design. In the usual design process, as is state of the art in the industry, the last stage of the LP and the diffuser is designed and optimized sequentially. The potential physical coupling effects are not considered. Therefore the aim of this paper is to perform both a sequential and coupled optimization of a low pressure steam turbine followed by an axial radial diffuser and subsequently to compare results. In addition to the flow simulation, mechanical and modal analysis is also carried out in order to satisfy the constraints regarding the natural frequencies and stresses. This permits the use of a meta-model, which allows very time efficient three dimensional (3D) calculations to account for all flow field effects.

Experimental Verification of the Improvements Achieved by a New LP-Blade Design in a Steam Turbine

1992 ◽  
Author(s):  
H. Stetter ◽  
G. Eyb ◽  
C. Zimmermann ◽  
H.-G. Hosenfeld
Keyword(s):  
Steam Turbine ◽  
Entire Range ◽  
Flow Characteristics ◽  
Radial Pressure ◽  
Blade Design ◽  
Steam Turbines ◽  
Guide Vanes ◽  
Last Stage ◽  
The University

In order to verify the improvements in the understanding of the flow in turbomachinery, extensive investigations were carried out at the LP-steam turbine at the University of Stuttgart. This paper initially focuses on the specific measuring technique in steam turbines with respect to problems of condensation. The stator wakes, noticeable in all measuring planes of the stage, require the determination of the flow vector over a large portion of the cross-section to obtain representative values. The application of a newly designed last stage for LP-steam turbines, which is characterized by curved guide-vanes, led to considerable improvements of the flow over the entire range of operation. The results gained by measurements on that stage are compared to former measurements on a stage version with straight guide-vanes. A significant change of flow characteristics over the blade span can be noticed. Particularly, the flow in the hub region was improved by balancing the radial pressure distribution.

The Influence of Non-Equilibrium Wet Steam Effects on the Aeroelastic Properties of a Turbine Blade Row

2016 ◽  
Author(s):  
Christopher Fuhrer ◽  
Marius Grübel ◽  
Damian M. Vogt ◽  
Paul Petrie-Repar
Keyword(s):  
Steam Turbine ◽  
Turbine Blade ◽  
Ideal Gas ◽  
Test Case ◽  
Steam Turbines ◽  
Wet Steam ◽  
Flow Conditions ◽  
Flutter Analysis ◽  
Last Stage ◽  
Non Equilibrium

Turbine blade flutter is a concern for the manufacturers of steam turbines. Typically, the length of last stage blades of large steam turbines is over one meter. These long blades are susceptible to flutter because of their low structural frequency and supersonic tip speeds with oblique shocks and their reflections. Although steam condensation has usually occurred by the last stage, ideal gas is mostly assumed when performing flutter analysis for steam turbines. The results of a flutter analysis of a 2D steam turbine test case which examine the influence of non-equilibrium wet steam are presented. The geometry and flow conditions of the test case are supposed to be similar to the flow near the tip in a steam turbine as this is where most of the unsteady aerodynamic work contributing to flutter is done. The unsteady flow simulations required for the flutter analysis are performed by ANSYS CFX. Three fluid models are examined: ideal gas, equilibrium wet steam (EQS) and non-equilibrium wet steam (NES), of which NES reflects the reality most. Previous studies have shown that a good agreement between ideal gas and EQS simulations can be achieved if the prescribed ratio of specific heats is equal to the equilibrium polytropic index of the wet steam flow through the turbine. In this paper the results of a flutter analysis are presented for the 2D test case at flow conditions with wet steam at the inlet. The investigated plunge mode normal to chord is similar to a bending mode around the turbine axis for a freestanding blade in 3D. The influence of the overall wetness fraction and the size of the water droplets at the inlet are examined. The results show an increase of aerodynamic damping for all investigated interblade phase angles with a reduction of droplet size. The influence of the wetness fraction is in comparison of less importance.

3-D Time Domain Unsteady Computation of Rotating Instability in Steam Turbine Last Stage

2012 ◽  
Author(s):  
L. Y. Zhang ◽  
L. He ◽  
H. Stüer
Keyword(s):  
Mass Flow ◽  
Large Scale ◽  
Flow Behavior ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Frequency Pattern ◽  
Last Stage ◽  
Rotating Instability

The rotating instability phenomenon in a last stage of steam turbines at low mass flow conditions has been previously identified experimentally. Recently, the rotating instability has also been numerically studied in a whole annulus domain on 2D blade sections. In the present work, 3D simulations of unsteady flows are carried out on two model steam turbines over a range of mass flow conditions. The pressure-ratio volume-flow characteristics in rotor row tip region under different flow conditions are well captured in the computations in comparison with the experiment. The effect of blade scaling is examined to identify the influence of changing blade counts for a circumferential domain reduction, showing relatively small effects on the overall performance characteristics. The present 3D unsteady solutions on a reduced multi-passage domain have been able to predict a rotating instability in the rotor blade tip region, in accord with the corresponding experiment. Further Fourier analysis is carried out to examine the frequency pattern and spatial modal features. The 3D flow behavior is highlighted by comparison between the 3D and 2D calculations. The present results seem to suggest that the rotating instability onset in the rotor tip region is largely independent of the large scale flow separation in the downstream diffusor.

Numerical Investigation of the Influence of Flow Deflection at the Upper Hood on Performance of Low Pressure Steam Turbine Exhaust Hoods

2019 ◽  
Author(s):  
Dickson Munyoki ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Mach Number ◽  
Steam Turbine ◽  
Swirling Flows ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Design Load ◽  
Last Stage ◽  
Flow Deflection ◽  
Turbine Exhaust ◽  
Loss Mechanisms

Abstract Most of the world’s power is produced by large steam turbines using fossil fuel, nuclear and geothermal energy. The LP exhaust hoods of these turbines are known to contribute significantly to the losses within the turbine, hence a minor improvement in their performance, which results in a lower backpressure and thus higher enthalpy drop for the steam turbine, will give a considerable benefit in terms of fuel efficiency. Understanding the flow field and the loss mechanisms within the exhaust hood of LP steam turbines is key to developing better optimized exhaust hood systems. A detailed analysis of loss generation within the exhaust hood was done by the authors [1]. It was found that most losses occur at the upper hood and are caused by the swirling flows, which mostly start at the diffuser outlet, especially for the top diffuser inlet sector flows that have a complex path to the condenser. The authors further numerically investigated the influence of hood height variation on performance of an LP turbine exhaust hood [2], which further contributed to the knowledge of the loss mechanisms. With the loss mechanisms in exhaust hoods reasonably well understood, flow deflection at the upper hood is investigated in the current paper. The deflection is aimed at minimizing the intensity of the vortices formed thus reducing the exhaust losses. The deflector configurations analyzed are modifications of the walls of the reference configuration’s outer casing. The numerical models of the reference configuration which are based on a scaled axial-radial diffuser test rig operated by ITSM have already been validated by the authors at design and overload operating conditions and three tip jet Mach numbers (0, 0.4 and 1.2)[1]. Deflector configurations investigated are found to re-direct the flow at the upper hood and minimize the intensity of the swirling flows hence leading to improvement in performance of LP steam turbine exhaust hoods. The best performing deflector configuration is found to give a considerable improvement in performance of 20% at design load and 40% at overload both at tip jet Mach number of 0.4 (corresponding to shrouded last stage blades). At design load and tip jet Mach number of 1.2 (corresponding to unshrouded last stage blades), the improvement is found to be moderate. About 7% performance increase is observed.

Investigation of Moisture Removal on Last Stage Stationary Blade in Actual Steam Turbine

2020 ◽  
Author(s):  
Hideaki Sato ◽  
Soichiro Tabata ◽  
Naoto Tochitani ◽  
Yasuhiro Sasao ◽  
Ryo Takata ◽  
...  
Keyword(s):  
Power Systems ◽  
Water Level ◽  
Steam Turbine ◽  
Pressure Ratio ◽  
Internal Flow ◽  
Moisture Removal ◽  
Operating Environment ◽  
Choked Flow ◽  
Measurement Result ◽  
Last Stage

Abstract This paper presents an investigation for wet steam flow through the slit on the last stage hollow stationary blades of a steam turbine. The aim of this investigation is to evaluate the moisture removal performance by measuring the quantity of drain and “Motive steam” from some kinds of slit configurations under the actual turbine operating environment. Motive steam is effective steam sucked from the slit and removed together with drain. The measurement was carried out on a 105 MW class steam turbine at “T-point”, a verification power plant owned by Mitsubishi Hitachi Power Systems, Ltd. [MHPS]. The measurement system was constructed right under the turbine. Even though both drain and steam were sucked from the slit on the stationary blade, drain was separated by the cyclone separator and measured by detecting the water level accumulated in the water level tank by the optical pulse sensor. For the measurement of the motive steam quantity, the choked flow rate measured by the critical nozzle was used to obtain the slit characteristic data of pressure ratio (ratio of blade surface static pressure to outer ring inner pressure). The critical nozzles were arranged in parallel, and the measurement was carried out by adopting a multi-valve switching system. And CFD slit analysis, in which the drain discharge path inside the last stage hollow stationary blade is modeled, was also carried out. The CFD slit analysis was compared with the measurement result to examine the internal flow. The corresponding CFD was calculated by ANSYS CFX. And the coarse water droplets analysis by the kinetic equation of the discrete droplet model was also carried out. From the measurement result and the evaluation, it was confirmed that the slit with groove configuration is more effective than the normal slit under the actual turbine operating environment.

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