Determination of the Flow Field in LP Steam Turbines

1986 ◽  
Author(s):  
J. Wachter ◽  
G. Eyb
Keyword(s):  
Flow Field ◽  
Measuring Equipment ◽  
Short Description ◽  
Test Stand ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Flow Measurements ◽  
Last Stage ◽  
The University

Up to now the determination of flow conditions across the entire circumference in LP steam turbines appears to be a difficult undertaking. The difficulties are mainly caused by the condensing medium steam and by the limited access to the stage from outside. The Last Stage Test Stand at the University of Stuttgart is a suitable facility for flow measurements in the LP part of steam turbines. Besides a short description of the test stand itself, the measuring equipment and the newly developed methods for data acquisition and evaluation are presented. Finally the flow field behind the last stage is shown and the results interpreted.

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 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.

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.

scholarly journals Turbulent Flow through Random Vegetation on a Rough Bed

Water ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 2564
Author(s):  
Francesco Coscarella ◽  
Nadia Penna ◽  
Aldo Pedro Ferrante ◽  
Paola Gualtieri ◽  
Roberto Gaudio
Keyword(s):  
Flow Field ◽  
Flow Conditions ◽  
Bed Sediments ◽  
Turbulence Characteristics ◽  
Rigid Vegetation ◽  
Laboratory Flume ◽  
Rough Bed ◽  
Flow Through ◽  
Bed Roughness

River vegetation radically modifies the flow field and turbulence characteristics. To analyze the vegetation effects on the flow, most scientific studies are based on laboratory tests or numerical simulations with vegetation stems on smooth beds. Nevertheless, in this manner, the effects of bed sediments are neglected. The aim of this paper is to experimentally investigate the effects of bed sediments in a vegetated channel and, in consideration of that, comparative experiments of velocity measures, performed with an Acoustic Doppler Velocimeter (ADV) profiler, were carried out in a laboratory flume with different uniform bed sediment sizes and the same pattern of randomly arranged emergent rigid vegetation. To better comprehend the time-averaged flow conditions, the time-averaged velocity was explored. Subsequently, the analysis was focused on the energetic characteristics of the flow field with the determination of the Turbulent Kinetic Energy (TKE) and its components, as well as of the energy spectra of the velocity components immediately downstream of a vegetation element. The results show that both the vegetation and bed roughness surface deeply affect the turbulence characteristics. Furthermore, it was revealed that the roughness influence becomes predominant as the grain size becomes larger.

A Combined Numerical Model and Optimization for Low Pressure Exhaust System in Steam Turbine

2007 ◽  
Author(s):  
Tao Fan ◽  
Yonghui Xie ◽  
Di Zhang ◽  
Bi Sun
Keyword(s):  
Numerical Model ◽  
Flow Field ◽  
Exhaust System ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Inhomogeneous Flow ◽  
Last Stage

Computational fluid dynamics is widely used in the aerodynamic performance analysis of the low pressure exhaust system (LPES) which consists of the exhaust hood and condenser neck. However, most of the former studies analyzed the exhaust system separately without considering the effect on flow field from the last stage. In order to get the detailed information of flow field in LPES of steam turbines and reduce energy loss, a numerical model includes condenser neck, exhaust hood and last stage was constructed. This model can describe the effect of unsymmetrical inlet flow on the aerodynamic performance of LPES, so the effect of the inhomogeneous flow from the last stage was taken into account. The Reynolds averaged N-S equations with RNG k-ε turbulence model were adopted to analyze the flow field in the exhaust system considering the interaction between the exhaust system and the last stage, the mixing plane approach was used. The combined model can provide more reasonable numerical results of LPES, it shows that the inhomogeneous flow from the last stage is one of the main reasons leading to flow separation in diffuser. The influence of inner low pressure heater and the diffuse function of the condenser neck structure are the main reasons for the nonuniform velocity distribution of the flow field at the LPES outlet. Furthermore, based on the numerical results, an optimal LPES which has better aerodynamic performance and more reasonable flow is obtained. The optimal structure has low steam resistance and low exhaust pressure, so it can increase the efficiency of turbine.

Unsteady Flow Field and Coarse Droplet Measurements in the Last Stage of a Low Pressure Steam Turbine With Supersonic Airfoils Near the Blade Tip

2016 ◽  
Author(s):  
Ilias Bosdas ◽  
Michel Mansour ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Shigeki Senoo
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Leading Edge ◽  
Suction Side ◽  
Fast Response ◽  
Operating Conditions ◽  
Electricity Production ◽  
Test Facility ◽  
Steam Turbines ◽  
Last Stage

The largest share of electricity production worldwide belongs to steam turbines. However, the increase of renewable energy production has led steam turbines to operate under part load conditions and increase in size. As a consequence long rotor blades will generate a relative supersonic flow field at the inlet of the last rotor. This paper presents a unique experiment work that focuses at the top 30% of stator exit in the last stage of an LP steam turbine test facility with coarse droplets and high wetness mass fraction under different operating conditions. The measurements were performed with two novel fast response probes. A fast response probe for three dimensional flow field wet steam measurements and an optical backscatter probe for coarse water droplet measurements ranging from 30 up to 110μm in diameter. This study has shown that the attached bow shock at the rotor leading edge is the main source of inter blade row interactions between the stator and rotor of the last stage. In addition, the measurements showed that coarse droplets are present in the entire stator pitch with larger droplets located at the vicinity of the stator’s suction side. Unsteady droplet measurements showed that the coarse water droplets are modulated with the downstream rotor blade-passing period. This set of time-resolved data will be used for in-house CFD code development and validation.

Unsteady Flow Field and Coarse Droplet Measurements in the Last Stage of a Low-Pressure Steam Turbine With Supersonic Airfoils Near the Blade Tip

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Ilias Bosdas ◽  
Michel Mansour ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Shigeki Senoo
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Leading Edge ◽  
Low Pressure ◽  
Fast Response ◽  
Operating Conditions ◽  
Electricity Production ◽  
Test Facility ◽  
Steam Turbines ◽  
Last Stage

The largest share of electricity production worldwide belongs to steam turbines. However, the increase of renewable energy production has led steam turbines to operate under part load conditions and increase in size. As a consequence, long rotor blades will generate a relative supersonic flow field at the inlet of the last rotor. This paper presents a unique experiment work that focuses at the top 30% of stator exit in the last stage of an low pressure (LP) steam turbine test facility with coarse droplets and high wetness mass fraction under different operating conditions. The measurements were performed with two novel fast response probes: a fast response probe for three-dimensional flow field wet steam measurements and an optical backscatter probe for coarse water droplet measurements ranging from 30 μm up to 110 μm in diameter. This study has shown that the attached bow shock at the rotor leading edge is the main source of interblade row interactions between the stator and rotor of the last stage. In addition, the measurements showed that coarse droplets are present in the entire stator pitch with larger droplets located at the vicinity of the stator's suction side. Unsteady droplet measurements showed that the coarse water droplets are modulated with the downstream rotor blade-passing period. This set of time-resolved data will be used for in-house computational fluid dynamics (CFD) code development and validation.

Significance of Damping and its Simulation in Fatigue Damage

2013 ◽  
Author(s):  
J. S. Rao
Keyword(s):  
Aircraft Engine ◽  
Analytical Determination ◽  
Steam Turbines ◽  
Life Estimation ◽  
Foreign Objects ◽  
Unknown Factor ◽  
Last Stage ◽  
Fatigue Failures ◽  
Very High

Aircraft engine fan blades and Steam turbine LP stage blades are the longest blades in a given turbomachine and are prone for fatigue failures. The alternating stresses induced are very high due to foreign objects ingestion in aircraft engines and off-design operations of steam turbines causing high stresses in the last stage blades. Damping is the main unknown factor in life estimation of such blades and this paper describes a procedure of analytical determination of damping due to hysteresis, macro and microslip damping mechanisms and determination of resonant stresses leading to accurate life estimation.

Experimental and Numerical Investigation of the Nonlinear Vibrational Behavior of Steam Turbine Last Stage Blades With Friction Bolt Damping Elements

2015 ◽  
Author(s):  
R. Drozdowski ◽  
L. Völker ◽  
M. Häfele ◽  
D. M. Vogt
Keyword(s):  
Nonlinear Effects ◽  
Low Pressure ◽  
Special Focus ◽  
Steam Turbines ◽  
Blade Vibration ◽  
Good Efficiency ◽  
Frictional Damping ◽  
Scale Test ◽  
Last Stage ◽  
The University

Low-pressure last stage blades of industrial steam turbines are subjected to high dynamic loading. Especially in variable speed applications resonant blade vibration cannot be avoided. Thus, the aim of the blade layout is to reach a robust design that can cover high vibrational amplitudes while still keeping good efficiency. An effective way to keep vibration amplitudes low is the introduction of friction damping elements to the blades. In this paper the structural behavior of a low-pressure last stage blade coupled by friction bolt damping elements is described by means of linear and nonlinear Finite Element Method. Special focus is put on the nonlinear effects of the contact between blade and damping element to investigate the frictional damping performance of the system. The obtained numerical results are validated by strain gauge and tip timing measurements in a full scale test turbine under real steam conditions at the Institute of Thermal Turbomachinery and Machinery Laboratory of the University of Stuttgart.

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