Three-Dimensional Blade Stacking Strategies and Understanding of Flow Physics in Low-Pressure Steam Turbines—Part II: Stacking Equivalence and Differentiators

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
Said Havakechian ◽  
John Denton
Keyword(s):  
Guide Vane ◽  
Three Dimensional ◽  
Low Pressure ◽  
Cfd Modeling ◽  
Steam Turbines ◽  
Flow Parameters ◽  
Pressure Steam ◽  
Computational Fluid Dynamics Cfd ◽  
Last Stage ◽  
Two Stages

Optimization of blade stacking in low-pressure (LP) steam turbine development constitutes one of the most delicate and time-consuming parts of the design process. This is the second part of two papers focusing on stacking strategies applied to the last stage guide vane and represents an attempt to discern the aerodynamic targets that can be achieved by each of the well-known and most often used basic stacking schemes. The effects of lean and twist have been investigated through an iterative process, involving comprehensive 3D computational fluid dynamics (CFD) modeling of the last two stages of a standard LP, where the basic lean and twist stacking schemes were applied on the last stage guide vanes while keeping the throat area (TA) unchanged. It has been found that it is possible to achieve the same target value and pattern of stage reaction by applying either tangential lean or an equivalent value of twist. Moreover, the significance of axial sweep on hub reaction has been found to become pronounced when the blade sweep is carried out at constant TA. The importance of hub-profiling has also been demonstrated and assessed. Detailed analysis of the flow fields has provided an overall picture, revealing the differences in the main flow parameters as produced by each of the alternative basic stacking schemes.

Three-Dimensional Blade-Stacking Strategies and Understanding of Flow Physics in Low-Pressure Steam Turbines—Part I: Three-Dimensional Stacking Mechanisms

2015 ◽  
Vol 138 (5) ◽  
Author(s):  
Said Havakechian ◽  
John Denton
Keyword(s):  
Guide Vane ◽  
Three Dimensional ◽  
Low Pressure ◽  
Stagnation Pressure ◽  
Steam Turbines ◽  
Wet Steam ◽  
Pressure Steam ◽  
Computational Fluid Dynamics Cfd ◽  
Last Stage ◽  
3D Stacking

Optimization of blade stacking in the last stage of low-pressure (LP) steam turbines constitutes one of the most delicate and time-consuming parts of the design process. This is the first of two papers focusing on the stacking strategies applied to the last stage guide vane (G0). Following a comprehensive review of the main features that characterize the LP last stage aerodynamics, the three-dimensional (3D) computational fluid dynamics (CFD) code used for the investigation and options related to the modeling of wet steam are described. Aerodynamic problems related to the LP last stage and the principles of 3D stacking are reviewed in detail. In this first paper, the results of a systematic study on an isolated LP stator row are used to elucidate the effects of stacking schemes, such as lean, twist, sweep, and hub profiling. These results show that stator twist not only has the most powerful influence on the reaction variation but it also produces undesirable spanwise variations in angular momentum at stator exit. These may be compensated by introducing a positive stagnation pressure gradient at entry to the last stage.

3D Blade Stacking Strategies and Understanding of Flow Physics in Low Pressure Steam Turbines: Part II — Stacking Equivalence and Differentiators

2015 ◽  
Author(s):  
Said Havakechian ◽  
John Denton
Keyword(s):  
Iterative Process ◽  
Guide Vane ◽  
Low Pressure ◽  
Main Flow ◽  
Steam Turbines ◽  
Cfd Modelling ◽  
Flow Parameters ◽  
Pressure Steam ◽  
Last Stage ◽  
Two Stages

Optimization of blade stacking in Low Pressure (LP) steam turbine development constitutes one of the most delicate and time consuming parts of the design process. This is the second part of two papers focusing on stacking strategies applied to the last stage guide vane and represents an attempt to discern the aerodynamic targets that can be achieved by each of the well-known and most often used basic stacking schemes. The effects of lean and twist have been investigated through an iterative process, involving comprehensive 3D CFD modelling of the last two stages of a standard LP, where the basic lean and twist stacking schemes were applied on the last stage guide vanes whilst keeping the throat area unchanged. It has been found that it is possible to achieve the same target value and pattern of stage reaction by applying either tangential lean or an equivalent value of twist. Moreover, the significance of axial sweep on hub reaction has been found to become pronounced when the blade sweep is carried out at constant throat area. The importance of hub-profiling has also been demonstrated and assessed. Detailed analysis of the flow fields has provided an overall picture, revealing the differences in the main flow parameters as produced by each of the alternative basic stacking schemes.

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.

3D Blade Stacking Strategies and Understanding of Flow Physics in Low Pressure Steam Turbines: Part I — 3D Stacking Mechanisms

2015 ◽  
Author(s):  
Said Havakechian ◽  
John Denton
Keyword(s):  
Angular Momentum ◽  
Guide Vane ◽  
Low Pressure ◽  
Stagnation Pressure ◽  
Steam Turbines ◽  
Wet Steam ◽  
Comprehensive Review ◽  
Pressure Steam ◽  
Last Stage ◽  
3D Stacking

Optimization of blade stacking in the last stage of Low Pressure (LP) steam turbines constitutes one of the most delicate and time consuming parts of the design process. This is the first of two papers focusing on the stacking strategies applied to the last stage guide vane (G0). Following a comprehensive review of the main features that characterize the LP last stage aerodynamics, the 3D CFD code used for the investigation and options related to modeling of wet steam are described. Aerodynamic problems related to the LP last stage and the principles of 3D stacking are reviewed in detail. In this first paper the results of a systematic study on an isolated LP stator row are used to elucidate the effects of stacking schemes such as lean, twist, sweep and hub profiling. These results show that stator twist has the most powerful influence on the reaction variation but it also produces undesirable spanwise variations in angular momentum at stator exit. These may be compensated by introducing a positive stagnation pressure gradient at entry to the last stage.

An Experimental Investigation of the Influence of Flash-Back Flow on Last Three Stages of Low Pressure Steam Turbines

2014 ◽  
Author(s):  
Naoki Shibukawa ◽  
Yoshifumi Iwasaki ◽  
Yoshiaki Takada ◽  
Itaru Murakami ◽  
Takashi Suzuki ◽  
...  
Keyword(s):  
Reverse Flow ◽  
Flow Region ◽  
Low Pressure ◽  
Detailed Examination ◽  
Steam Turbines ◽  
Back Flow ◽  
Large Size ◽  
Vibration Stress ◽  
Last Stage ◽  
Two Stages

A shutdown operation of a large size steam turbine could possibly cause flashing phenomena of the pooled drain water in low-pressure heaters. The boiled steam is sometimes in the same amount as the main flow in the case where shutdown is executed during low load conditions, and returns to the steam flow path through the extraction lines. A series of experimental work with a subscale model turbine facility has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressures under the flashing back conditions. It was observed that the blades of the two stages before the last stage (L-2) and a stage before the last stage (L-1) presented their peak vibration stresses immediately after the flash-back flow reached the turbine. In the meantime, the vibration stresses of the last stage (L-0) blades were reduced for a few tens of seconds. It can be thought that the flash-back flow pushed out the reverse flow region around the L-0 blades and allow the blades to be more stable. A detailed examination with measured data of the L-2 blade explained that, as long as the flash-back flow has small wetness, the blade is excited in its specific vibration modes in larger than 8th harmonic of rotational speed, but once the flash back flow carries water droplets, the fluid force in random frequencies remarkably increases and excites the blade in less than 7th harmonic range.

Some Aspects of CFD Modeling in the Analysis of a Low-Pressure Steam Turbine

2007 ◽  
Author(s):  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Stefano Cecchi ◽  
Federico Dacca`
Keyword(s):  
Steam Turbine ◽  
Computational Cost ◽  
Three Dimensional ◽  
Low Pressure ◽  
Design Tool ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Sources And Sinks ◽  
Leakage Flows ◽  
Pressure Steam

A three-dimensional, multistage, Navier-Stokes solver is applied to the numerical investigation of a four stage low-pressure steam turbine. The thermodynamic behavior of the wet steam is reproduced by adopting a real-gas model, based on the use of gas property tables. Geometrical features and flow-path details consistent with the actual turbine geometry, such as cavity purge flows, shroud leakage flows and partspan snubbers, are accounted for, and their impact on the turbine performance is discussed. These details are included in the analysis using simple models, which prevent a considerable growth of the computational cost and make the overall procedure attractive as a design tool for industrial purposes. Shroud leakage flows are modeled by means of suitable endwall boundary conditions, based on coupled sources and sinks, while body forces are applied to simulate the presence of the damping wires on the blades. In this work a detailed description of these models is provided, and the results of computations are compared with experimental measurements.

An Experimental Investigation of the Influence of Flash-Back Flow on Last Three Stages of Low Pressure Steam Turbines

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Naoki Shibukawa ◽  
Takao Fukushima ◽  
Yoshifumi Iwasaki ◽  
Yoshiaki Takada ◽  
Itaru Murakami ◽  
...  
Keyword(s):  
Reverse Flow ◽  
Flow Region ◽  
Low Pressure ◽  
Detailed Examination ◽  
Steam Turbines ◽  
Back Flow ◽  
Large Size ◽  
Vibration Stress ◽  
Last Stage ◽  
Two Stages

A shutdown operation of a large size steam turbine could possibly cause flashing phenomena of the pooled drain water in low-pressure heaters. The boiled steam is sometimes in the same amount as the main flow in the case where shutdown is executed during low load conditions, and returns to the steam flow path through the extraction lines. A series of experimental work with a subscale model turbine facility has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressures under the flashing back (FB) conditions. It was observed that the blades of the two stages before the last stage (L-2) and a stage before the last stage (L-1) presented their peak vibration stresses immediately after the flash-back flow reached the turbine. In the meantime, the vibration stresses of the last stage (L-0) blades were reduced for a few tens of seconds. It can be thought that the flash-back flow pushed out the reverse flow region around the L-0 blades and allow the blades to be more stable. A detailed examination with measured data of the L-2 blade explained that, as long as the flash-back flow has small wetness, the blade is excited in its specific vibration modes in larger than eighth harmonic of rotational speed, but once the flash-back flow carries water droplets, the fluid force in random frequencies remarkably increases and excites the blade in less than seventh harmonic range.

A Methodology for a Detailed Loss Prediction in Low Pressure Steam Turbines

2017 ◽  
Author(s):  
Marius Grübel ◽  
Robin M. Dovik ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Boundary Layer ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Low Pressure ◽  
Steam Turbines ◽  
Cfd Simulations ◽  
Depth Analysis ◽  
Pressure Steam ◽  
The Impact ◽  
Loss Mechanisms

An evaluation method for CFD simulations is presented, which allows an in-depth analysis of different loss mechanisms applying the approach of entropy creation proposed by Denton. The entropy creation within each single mesh element is determined based on the entropy flux through the cell faces and therefore the locations, where losses occur, can be identified clearly. By using unique features of the different loss mechanisms present in low pressure steam turbines, the losses are categorized into boundary layer, wake mixing and shock losses as well as thermodynamic wetness losses. The suitability of the evaluation method is demonstrated by means of steady state CFD simulations of the flow through a generic last stage of a low pressure steam turbine. The simulations have been performed on streamtubes extracted from three-dimensional simulations representing the flow at 10 % span. The impact of non-equilibrium steam effects on the overall loss composition of the stator passage is investigated by comparing the results to an equilibrium steam simulation. It is shown, that the boundary layer losses for the investigated case are of similar magnitude, but the shock and wake losses exhibit significant differences.

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

2015 ◽  
Author(s):  
Satoshi Miyake ◽  
Hironori Miyazawa ◽  
Satoru Yamamoto ◽  
Yasuhiro Sasao ◽  
Kazuhiro Momma ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Low Pressure ◽  
Numerical Results ◽  
Steam Turbines ◽  
Wet Steam ◽  
Flow Simulations ◽  
Low Pressure Turbine ◽  
Blade Number ◽  
Pressure Steam ◽  
Three Stages

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.

CFD Modeling of Low Pressure Steam Turbine Radial Diffuser Flow by Using a Novel Multiple Mixing Plane Based Coupling: Simulation and Validation

2015 ◽  
Author(s):  
Peter Stein ◽  
Christoph Pfoster ◽  
Michael Sell ◽  
Paul Galpin ◽  
Thorsten Hansen
Keyword(s):  
Steam Turbine ◽  
Heat Rate ◽  
Low Pressure ◽  
Cfd Modeling ◽  
Steam Turbines ◽  
Multiple Mixing ◽  
Diffuser Flow ◽  
Wide Range ◽  
Pressure Steam ◽  
The One

The diffuser and exhaust of low pressure steam turbines shows significant impact on the overall turbine performance. The amount of recovered enthalpy leads to a considerable increase of the turbine power output, and therefore a continuous focus of turbine manufacturers is put on this component. On the one hand, the abilities to aerodynamically design such components is improved, but on the other hand a huge effort is required to properly predict the resulting performance and to enable an accurate modeling of the overall steam turbine and therewith plant heat rate. A wide range of approaches is used to compute the diffuser and exhaust flow, with a wide range of quality. Today it is well known and understood, that there is a strong interaction of rear stage and diffuser flow, and the accuracy of the overall diffuser performance prediction strongly depends on a proper coupling of both domains. The most accurate, but also most expensive method is currently seen in a full annulus and transient coupling. However, for a standard industrial application of diffuser design in a standard development schedule, such a coupling is not feasible and more simplified methods have to be developed. The paper below presents a CFD modeling of low pressure steam turbine diffusers and exhausts based on a direct coupling of the rear stage and diffuser using a novel multiple mixing plane. It is shown that the approach enables a fast diffuser design process and is still able to accurately predict the flow field and hence the exhaust performance. The method is validated against several turbine designs measured in a scaled low pressure turbine model test rig using steam. The results show a very good agreement of the presented CFD modeling against the measurements.

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