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.

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 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].

Tip Leakage in Small Radial Turbines: Optimum Tip-Gap and Efficiency Loss Correlations

2010 ◽  
Author(s):  
Jasper Kammeyer ◽  
Christoph Natkaniec ◽  
Joerg R. Seume
Keyword(s):  
Internal Combustion Engines ◽  
Operating Conditions ◽  
Test Facility ◽  
Leakage Flow ◽  
Combustion Engines ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Flow Mechanisms ◽  
Radial Turbines

The tip-leakage flow mechanisms in turbocharger turbines used for downsized internal combustion engines and the associated losses are investigated over a range of operating conditions. Experiments are performed on a small, 35 mm diameter turbocharger turbine with varying tip-gap heights in a turbocharger test facility and numerical simulations are presented for extending the parameter range to sizes not covered experimentally. The sensitivity of turbine efficiency to tip-gap is evaluated and correlations for the estimation of tip-leakage related loss of efficiency are developed. An optimum applicable tip-gap size for radial turbines is suggested. The results show that the magnitude of the tip-leakage losses, e.g. in downsizing turbocharger turbines, provides a high potential for their 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.

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.

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.

Computational Studies on High Pressure Turbine Rim Seal Cavities

2017 ◽  
Author(s):  
Manjunath B. Chengappa ◽  
Karthik Srinivasan ◽  
Rohit Chouhan ◽  
Simon Bather ◽  
Eric Blidmark
Keyword(s):  
High Pressure ◽  
Flow Path ◽  
Operating Conditions ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Operating Environment ◽  
High Pressure Turbine ◽  
Hot Gas ◽  
Design Philosophy ◽  
Component Design

The efficiency of a turbine stage is impacted by a number of factors such as the component design philosophy, operating environment, leakage flow and its interaction with the main gas flow path. When looking at improving a turbine stage performance, there is a natural tendency amidst the designers to look into the factors listed above. Every engine manufacture has a unique style of component design philosophy and hence there are fewer opportunities to radically change the design. On the other hand, the operating environment or operating conditions are usually becoming more challenging. Hence, component designers typically look for opportunities to reduce the leakage or to reduce the losses due to interactive effect of the leakage with the gas path. The rim seal flow and its interaction with the gas path has been of interest for the past few decades and many studies have been carried out to understand the impact of cavity geometry, leakage flows and the ingestion of the hot gas into the rim seal cavities. The rim seal cavities functionally act as a buffer cavity to dilute and dampen the effect of the hot gas ingested into the secondary air flow path and to prevent the discs from being exposed to ingested hot gas. The successful function of the rim seal cavity depends on multiple factors like rotor-stator axial clearance, cavity volume, cavity shape, cavity approach to the gas path and its interface, in addition to the leakage flow into the main flow path. The present paper aims at providing a review of a typical rim seal cavity used in the High Pressure Turbine based on systematic CFD studies of the rim seal cavities. While the paper does not present validation data for the approach, the authors attempt to provide references to specific design aspects that are already available in the literature, which are usually less noticed.

Efficiency Improvements in an Industrial Steam Turbine Stage: Part 1

2016 ◽  
Author(s):  
Srikanth Deshpande ◽  
Marcus Thern ◽  
Magnus Genrup
Keyword(s):  
Steam Turbine ◽  
Total Pressure ◽  
Rotor Blades ◽  
Efficiency Improvement ◽  
Turbine Stage ◽  
Design Modification ◽  
Ansys Cfx ◽  
Baseline Case ◽  
Profile Losses ◽  
Stage Efficiency

The present work approaches the idea of increasing the efficiency of an industrial steam turbine stage. For this endeavor, an industrial steam turbine stage comprising of prismatic stator and rotor is considered. With the velocity triangles as input, airfoil design is carried out. Firstly, the rotor is redesigned to take care of any incidence issues in the baseline case. In rotor blades, the peak Mach number is reduced in blade to blade flow passage and hence, efficiency of stage is increased. Rotor is made front loaded. After finalizing the rotor, the stator is redesigned. Stator is made more aft-loaded when compared to the baseline case. By making the stator aft-loaded, the efficiency increased by reducing profile losses. This design modification also showed advantage in secondary losses. The total pressure loss in the stator was reduced by a delta of 0.15. When creating an airfoil for stator or rotor, MISES was used in order to evaluate profile losses. The design verification for the stage was numerically done using commercial CFD software ANSYS CFX. Steady state RANS simulations were carried out. The stator and the rotor still being prismatic, only by virtue of airfoil design, the total to total stage efficiency improvement of 0.33% was predicted.

The Effect of the Operating Conditions of the Last Turbine Stage on the Performance of an Axial Exhaust Diffuser

2011 ◽  
Author(s):  
Victor Opilat ◽  
Joerg R. Seume
Keyword(s):  
Gas Turbines ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Test Facility ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Inlet Flow ◽  
Tip Leakage

The exhaust diffusers studied in this paper are installed behind the last turbine stage of gas turbines, including those used in combined cycle power plants. For the design of efficient diffusers, the effects caused by the last turbine stage need to be taken into account. In the present paper, results are presented to estimate the performance of a diffuser operating under a variation of multiple modelling parameters: tip leakage flow, the swirl, and the rotating blade wakes. To provide a better understanding of the flow parameters, a test facility with a turbine stage simulator is used to model these flow effects and an optical endoscopic planar measurement technique based upon Particle Image Velocimetry (PIV) is applied. The pressure recovery is estimated for various turbine conditions using a variety of relevant parameters. Within a range of conditions, a PIV study is performed to try to understand the typical flow phenomena which influence the performance of axial diffusers. The rise of turbulent energy in the inlet flow positively affects the diffuser performance. A small positive swirl angle in the inlet flow (behind the rotating bladed wheel in experiments) has a stabilizing effect on the diffuser. The tip leakage flow from the last turbine stage can also positively affect the pressure recovery in the diffuser.

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