Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows—Part I: Design Concept and Typical Performance of a Swirl Breaker

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Takanori Shibata ◽  
Hisataka Fukushima ◽  
Kiyoshi Segewa
Keyword(s):  
Incidence Angle ◽  
Tangential Velocity ◽  
Design Concept ◽  
Leakage Flow ◽  
Axial Distance ◽  
Angle Distribution ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Typical Performance ◽  
Stage Efficiency

In high and intermediate pressure (HIP) steam turbines with shrouded blades, it is well known that shroud leakage losses contribute significantly to overall losses. Shroud leakage flow with a large tangential velocity creates a significant aerodynamic loss due to mixing with the mainstream flow. In order to reduce this mixing loss, two distinct ideas for rotor shroud exit cavity geometries were investigated using computational fluid dynamics (CFD) analyses and experimental tests. One idea was an axial fin placed from the shroud downstream casing to reduce the axial cavity gap, and the other was a swirl breaker placed in the rotor shroud exit cavity to reduce the tangential velocity of the leakage flow. In addition to the conventional cavity geometry, three types of shroud exit cavity geometries were designed, manufactured, and tested using a 1.5-stage air model turbine with medium aspect ratio blading. Test results showed that the axial fin and the swirl breaker raised turbine stage efficiency by 0.2% and 0.7%, respectively. The proposed swirl breaker was judged to be an effective way to achieve highly efficient steam turbines because it not only reduces the mixing losses but also improves the incidence angle distribution onto the downstream blade row. This study is presented in two papers. The basic design concept and typical performance of the proposed swirl breaker are presented in this part I, and the effect of axial distance between a swirl breaker and rotor shroud on efficiency improvement is discussed in part II [8].

Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows: Part I — Design Concept and Typical Performance of a Swirl Breaker

2018 ◽  
Author(s):  
Takanori Shibata ◽  
Hisataka Fukushima ◽  
Kiyoshi Segawa
Keyword(s):  
Steam Turbine ◽  
Tangential Velocity ◽  
Design Concept ◽  
Leakage Flow ◽  
Angle Distribution ◽  
Efficiency Improvement ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Typical Performance ◽  
Stage Efficiency

In high and intermediate pressure (HIP) steam turbines with shrouded blades, it is well known that shroud leakage losses contribute significantly to overall losses. Shroud leakage flow with a large tangential velocity creates a significant aerodynamic loss due to mixing with the mainstream flow. In order to reduce this mixing loss, two distinct ideas for rotor shroud exit cavity geometries were investigated using computational fluid dynamics (CFD) analyses and experimental tests. One idea was an axial fin placed from the shroud downstream casing to reduce the axial cavity gap, and the other was a swirl breaker placed in the rotor shroud exit cavity to reduce the tangential velocity of the leakage flow. In addition to the conventional cavity geometry, three types of shroud exit cavity geometries were designed, manufactured and tested using a 1.5-stage air model turbine with medium aspect ratio blading. Test results showed that the axial fin and the swirl breaker raised turbine stage efficiency by 0.2% and 0.7%, respectively. The proposed swirl breaker was judged to be an effective way to achieve highly efficient steam turbines because it not only reduces the mixing losses but also improves the incidence angle distribution onto the downstream blade row. This study is presented in two papers. The basic design concept and typical performance of the proposed swirl breaker are presented in the first paper Part I, Design Concept and Typical Performance of a Swirl Breaker, and the efficiency improvement effect of the swirl breaker when applied to a real steam turbine is discussed in Part II – Effect of Axial Distance between a Swirl Breaker and Rotor Shroud on Efficiency Improvement.

Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows—Part II: Effect of Axial Distance Between a Swirl Breaker and a Rotor Shroud on Efficiency Improvement

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Chongfei Duan ◽  
Hisataka Fukushima ◽  
Kiyoshi Segewa ◽  
Takanori Shibata ◽  
Hidetoshi Fujii
Keyword(s):  
Structural Reliability ◽  
Tangential Velocity ◽  
Maximum Pressure ◽  
Leakage Flow ◽  
Axial Distance ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Entire Flow ◽  
The Difference ◽  
Stage Efficiency

The basic principle of a distinct idea to reduce an aerodynamic mixing loss induced by the difference in tangential velocity between mainstream flow and rotor shroud leakage flow is presented in “Part I: Design Concept and Typical Performance of a Swirl Breaker.” When the swirl breaker is installed in the circulating region of leakage flow at the rotor shroud exit cavity, the axial distance between the swirl breaker and the rotor shroud is a crucial factor to trap the leakage flow into the swirl breaker cavity. In Part II, five cases of geometry with different axial distances between the swirl breaker and the rotor shroud, which covered a range for the stage axial distance of actual high and intermediate pressure (HIP) steam turbines, were investigated using a single-rotor computational fluid dynamics (CFD) analysis and verification tests in a 1.5-stage air model turbine. By decreasing the axial distance between the swirl breaker and the rotor shroud, the tangential velocity and the mixing region in the tip side which is influenced by the rotor shroud leakage flow were decreased and the stage efficiency was increased. The case of the shortest axial distance between the swirl breaker and the rotor shroud increased turbine stage efficiency by 0.7% compared to the conventional cavity geometry. In addition, the measured maximum pressure fluctuation in the swirl breaker cavity was only 0.7% of the entire flow pressure. Consequently, both performance characteristics and structural reliability of swirl breaker were verified for application to real steam turbines.

Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows: Part II — Effect of Axial Distance Between a Swirl Breaker and Rotor Shroud on Efficiency Improvement

2018 ◽  
Author(s):  
Chongfei Duan ◽  
Hisataka Fukushima ◽  
Kiyoshi Segawa ◽  
Takanori Shibata ◽  
Hidetoshi Fujii
Keyword(s):  
Steam Turbine ◽  
Structural Reliability ◽  
Tangential Velocity ◽  
Leakage Flow ◽  
Axial Distance ◽  
Cfd Analysis ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Sst Model ◽  
Stage Efficiency

The basic principle of a distinct idea to reduce an aerodynamic mixing loss induced by the difference in tangential velocity between mainstream flow and rotor shroud leakage flow is presented in “Part I – Design Concept and Typical Performance of a Swirl Breaker” The design concept offers an effective geometry for improving steam turbine stage efficiency. When the swirl breaker is installed in the circulating region of leakage flow at the rotor shroud exit cavity, the axial distance between the swirl breaker and rotor shroud is a crucial factor to trap the leakage flow into the swirl breaker cavity. In this Part II of the study, five cases of swirl breaker geometry with different axial distances between the swirl breaker and rotor shroud, which covered a range for the stage axial distance of actual high and intermediate (HIP) pressure steam turbines, were investigated using computational fluid dynamics (CFD) analysis and tests. Compared to a conventional single-stage CFD analysis, by conducting an additional single-rotor analysis with the modified shear stress transport (SST) model coefficient, the prediction accuracy for typical improvements in stage efficiency was increased in comparison to the single-stage analysis with the default SST model. Based on CFD results, the verification tests were conducted in a 1.5-stage air model turbine. By decreasing the axial distance between the swirl breaker and rotor shroud, the tangential velocity and the mixing region in the tip side which is influenced by the rotor shroud leakage flow were decreased and the stage efficiency was increased. The case of the shortest axial distance between the swirl breaker and rotor shroud increased turbine stage efficiency by 0.7% compared to the conventional cavity geometry. In addition, the unsteady pressure was measured in the swirl breaker cavity to evaluate the structural reliability of the swirl breaker. These results showed the maximum pressure fluctuation was only 0.7% of the entire flow pressure. Consequently, both performance characteristics and structural reliability of swirl breaker were verified for application to real steam turbines.

Numerical Investigation of Unsteady Blade Row Interactions With Leakage Flow in Steam Turbines

2009 ◽  
Author(s):  
Keramat Fakhari ◽  
Thomas Hofbauer ◽  
Anton Weber
Keyword(s):  
Labyrinth Seal ◽  
Leakage Flow ◽  
Axial Distance ◽  
Mixing Process ◽  
Steam Turbines ◽  
Leakage Flows ◽  
Numerical Studies ◽  
Real Gas Effects ◽  
Two Stages ◽  
The Impact

This paper focuses on the interaction of labyrinth seal leakage flows within two stages of a HP and an IP steam turbine. Numerical studies have been carried out with the DLR in-house code TRACE [1] to show the impact of the labyrinth seal leakage flow on the total loss generation in both steady and time accurate simulations. CFD results are verified by the in-house 2D through-flow method of Siemens Energy. The investigations are divided into five steps: 1. Real gas effects, 2. Steady simulations of the core flow alone and its interaction with the cavity flow to provide insights about loss production contributed by the mixing process of the re-entering leakage flow into the main flow, 3. Understanding and modeling of unsteady phenomena within such interacting flows, 4. Effects of reduction of the axial distance between the two stages on the mixing process in time accurate simulations. 5. Comparison of blade loads calculated by Siemens’ CAE tools and predicted by TRACE.

Design and Analysis of a Novel Split Sliding Variable Nozzle for Turbocharger Turbine

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Liangjun Hu ◽  
Harold Sun ◽  
James Yi ◽  
Eric Curtis ◽  
Jizhong Zhang
Keyword(s):  
Internal Combustion Engines ◽  
Operating Conditions ◽  
Small Radius ◽  
Nozzle Flow ◽  
Leakage Flow ◽  
Efficiency Improvement ◽  
Turbine Stage ◽  
Flow Passage ◽  
Flow Capacity ◽  
Stage Efficiency

Variable geometry turbine (VGT) has been widely applied in internal combustion engines to improve engine transient response and torque at light load. One of the most popular VGTs is the variable nozzle turbine (VNT) in which the nozzle vanes can be rotated along the pivoting axis and thus the flow passage through the nozzle can be adjusted to match with different engine operating conditions. One disadvantage of the VNT is the turbine efficiency degradation due to the leakage flow in the nozzle endwall clearance, especially at small nozzle open condition. With the purpose to reduce the nozzle leakage flow and to improve turbine stage efficiency, a novel split sliding variable nozzle turbine (SSVNT) has been proposed. In the SSVNT design, the nozzle is divided into two parts: one part is fixed and the other part can move along the partition surface. When sliding the moving vane to large radius position, the nozzle flow passage opens up and the turbine has high flow capacity. When sliding the moving vane to small radius position, the nozzle flow passage closes down and the turbine has low flow capacity. As the fixed vane does not need endwall clearance, the leakage flow through the nozzle can be reduced. Based on calibrated numerical simulation, there is up to 12% turbine stage efficiency improvement with the SSVNT design at small nozzle open condition while maintaining the same performance at large nozzle open condition. The mechanism of efficiency improvement in the SSVNT design has been discussed.

Design and Analysis of a Novel Split Sliding Variable Nozzle for Turbocharger Turbine

2017 ◽  
Author(s):  
Leon Hu ◽  
Harold Sun ◽  
James Yi ◽  
Eric Curtis ◽  
Jizhong Zhang
Keyword(s):  
Suction Side ◽  
Nozzle Flow ◽  
Leakage Flow ◽  
Variable Geometry ◽  
Efficiency Improvement ◽  
Turbine Stage ◽  
Flow Passage ◽  
Flow Capacity ◽  
Variable Geometry Turbine ◽  
Stage Efficiency

Variable geometry turbine (VGT) has been widely applied in internal combustion engines to improve the engine transient response and torque at low speed. One of the most popular variable geometry turbine is the variable nozzle turbine (VNT), in which the nozzle vanes can be rotated along the pivoting axis and thus the flow passage through the nozzle can be adjusted to match with different engine operating conditions. One disadvantage of the VNT is the turbine efficiency degradation due to the leakage flow in the nozzle endwall clearance, which is needed to allow the nozzle vanes to rotate without sticking. Especially at small nozzle open condition, there is large loading on the nozzle and high pressure gradient between the nozzle pressure and suction side. Strong leakage flow exists inside the nozzle endwall clearance from pressure side to suction side, leading to large flow loss and turbine stage efficiency degradation. In the present paper, a novel split sliding variable nozzle turbine (SSVNT) has been proposed to reduce the nozzle leakage flow and to improve turbine stage efficiency. The idea is to divide the nozzle into two parts: one part is fixed and the other part can slide along the partition surface. The mechanism of nozzle flow passage variation in SSVNT is different from that of the traditional pivoting VNT. The sliding vane and the fixed vane together form an integrated vane. The flow of the turbine is determined by the passage of the integrated vanes. When moving the sliding vane to large radius position, the nozzle flow passage opens up and the turbine has high flow capacity. When moving the sliding vane towards small radius position, the nozzle flow passage closes down and the turbine has low flow capacity. As the fixed vane doesn’t need endwall clearance, there is no leakage flow inside the fixed vane and the total leakage flow through the integrated vane can be reduced. Based on calibrated numerical modeling, the analysis results showed that there is up to 12% turbine stage efficiency improvement with the SSVNT design at small nozzle open condition while maintaining the same flow capacity and efficiency at large nozzle open condition, compared to the conventional VNT. The mechanism of efficiency improvement in the SSVNT design has also been discussed.

The Effect of Tip Shroud Geometries on Last Turbine Stage Efficiency

2018 ◽  
Author(s):  
Andrey Granovskiy ◽  
Igor Afanasiev
Keyword(s):  
Flow Structure ◽  
Radial Distribution ◽  
Gas Turbines ◽  
Rotor Blades ◽  
Loss Reduction ◽  
Steam Turbines ◽  
Turbine Stage ◽  
Last Stage ◽  
Partial Shroud ◽  
Stage Efficiency

Last stages of steam turbines and heavy-duty power gas turbines contribute significantly to output power and efficiency of whole turbine. Moreover, radial distribution of parameters downstream of the last stage provides boundary conditions for diffuser design. Thus, the increase of the last stage efficiency and obtainment of favorable radial distribution downstream of the last rotor blade is very important. Due to the long blades of last stages, resonance might occur. To avoid dangerous frequencies a damping wire or damping bolts are used. Such damping elements result in additional losses, so to minimize these losses a damping shroud is used instead. In general, the full damping shroud has to provide both the aerodynamic loss reduction and the resonance frequency offset. However, in most cases due to mechanical integrity limits instead of the full shroud a partial shroud is used. In this case the loss reduction feature of the partial shroud is diminished as compared with the full shroud. Sometimes, the use of the partial shroud results in the decrease of the efficiency compared with a stage with unshrouded rotor blades at small tip clearances. In this paper, a numerical investigation of the flow structure around full and partial shrouds with various geometries as well as the effect of the various shroud geometries on the turbine stage efficiency is carried out. Eight geometries with different number of fins of various heights are studied. Moreover, stage efficiencies for both shrouded and unshrouded blade are compared. Based on this comparison, reasonable design recommendations aimed to reduce the losses within the radial gap over the shroud are developed. In particular, filling the space in the gap with the additional honeycombs is considered and the effect on the flow structure and the last stage efficiency investigated. Numerical results obtained in the paper correspond well to the published test data.

Aerodynamic Optimization of Winglet-Cavity Tip in an Axial High Pressure Turbine Stage

2020 ◽  
Vol 37 (4) ◽  
pp. 399-411
Author(s):  
Zhihua Zhou ◽  
Shaowen Chen ◽  
Songtao Wang
Keyword(s):  
High Pressure ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Aerodynamic Optimization ◽  
High Pressure Turbine ◽  
Tip Leakage ◽  
Stage Efficiency

AbstractA new geometry parametric method of winglet-cavity tip has been introduced in the optimization procedure based on three-dimensional steady CFD numerical calculation and analysis. Firstly, the reliability of numerical method and grid independency are studied. Then an aerodynamic optimization is performed in an unshrouded axial high pressure turbine with winglet-cavity tip. The optimum winglet-cavity tip has higher turbine stage efficiency and smaller tip leakage mass flow rate than the cavity tip and flat tip. Compared with the results of cavity tip, the effects of the optimum winglet-cavity tip indicate that the stage efficiency is improved effectively by 0.41% with less reduction of tip leakage mass flow rate. The variation of turbine stage efficiency with tip gap states that the optimum winglet-cavity tip obtains the smallest efficiency change rate ∆η/(∆τ/H). For the optimum winglet-cavity tip, the endwall flow and blade tip leakage flow pattern are used to analysis the physical mechanical of losses. In addition, the effects of pressure-side winglet and suction-side winglet are analyzed respectively by the deformation of the optimum winglet-cavity tip. The numerical results show that the pressure-side winglet reduces the tip leakage flow effectively, and the suction-side winglet shows a great improvement on the turbine stage efficiency.

A High Performance Optimized Reaction Blade for High Pressure Steam Turbines

2004 ◽  
Author(s):  
Kiyoshi Segawa ◽  
Yoshio Shikano ◽  
Tsuyoshi Takano
Keyword(s):  
High Pressure ◽  
Steam Turbine ◽  
Robust Design ◽  
High Performance ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Pressure Steam ◽  
Internal Efficiency ◽  
Optimized Conditions ◽  
Stage Efficiency

A higher efficiency gain is necessary for steam turbine plants to reduce their fuel consumption rate and lessen their environmental disruption factor. Power plant manufacturers have continued to make an effort to raise steam turbine internal efficiency by developing new technologies. High pressure (HP) steam turbines should have increased efficiency owing to relatively shorter blade height compared with other turbine sections (intermediate and low pressure turbines). In order to increase efficiency, it is important to improve the steam path determined by design parameters such as degree of reaction, number of stages and rotor diameter and to develop a high performance blade applied to it. The advanced computational fluid dynamics (CFD) technique is a useful design tool, and has come to be applied generally to evaluate energy loss. A new rotating blade has been developed for small and mid-class steam turbines with a shorter blade height. The robust design method, based on the statistical theory for design of experiments, is used for the blade root profile design. It is combined with the inverse method and 2-D turbulent blade-to-blade flow analysis to evaluate the aerodynamic performance. The blade configuration is expressed by four control factors, which are turning angle, leading edge radius, pitch-chord ratio and maximum blade loading location. Linear cascade experiments are also carried out due to verify the blade performance under the optimized conditions obtained by the robust design. Consequently, the blade section has a blunt-nose, flat incidence characteristics and low energy loss, compared with the conventional one and the optimized conditions given by the robust design are aerodynamically reasonable. Finally, air turbine model tests and 3-D Reynolds-averaged Navier-Stokes analyses are performed to investigate the detailed flow pattern and stage performance of the new optimized reaction blade. An experimental investigation is still important to evaluate the performance in the real turbine stage structure, while the numerical analysis method is used based on the implicit TVD scheme with the modified k-ε turbulence model. It is found that the new optimized reaction blade has greatly improved stage efficiency of about 1.5% at the design point including the effect of leakage flow (3% improvement in stage efficiency excluding leakage flow) and realized an increase of pitch-chord ratio by about 35%. Consequently, the new optimized reaction blade is considered effective to raise the internal efficiency of the high-pressure steam turbine with improved steam path.

Design and Numerical Analysis of a Forepart Rotation Vane for a Variable Nozzle Turbine

2019 ◽  
Vol 36 (3) ◽  
pp. 233-244 ◽  
Author(s):  
Dengfeng Yang ◽  
Dazhong Lao ◽  
Ce Yang ◽  
Leon Hu ◽  
Harold Sun
Keyword(s):  
Numerical Analysis ◽  
Shock Waves ◽  
Flow Field ◽  
Rotor Blades ◽  
Leakage Flow ◽  
Exhaust Gas ◽  
Turbine Stage ◽  
And Shock Waves ◽  
Stage Performance ◽  
Stage Efficiency

AbstractThe influence of nozzle clearance on the flow field for a variable nozzle turbine, and moreover on the turbine stage performance was numerically investigated. Meanwhile, unsteady calculations were also performed to capture the shock waves which were induced by excessive acceleration of the exhaust gas. Aiming at improving the turbine stage performance and mitigating the shock waves, a forepart rotation vane was proposed and investigated in this work. The results indicated that by using the forepart rotation vane, the stage efficiency is increased by 6 % and the shock waves were eliminated successfully at small nozzle openings. Additionally, the intensity of pressure fluctuation that acts on the rotor blades was reduced by mitigation of clearance leakage flow and shock waves, which is beneficial for the reliability of rotor blades.

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