2015
Giovannini, Matteo; Marconcini, Michele; Rubechini, Filippo; Arnone, Andrea; Bertini, Francesco
Scaling 3D Low-Pressure Turbine Blades for Low-Speed Testing Conference
ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, vol. 2B: Turbomachinery, ASME ASME, Montreal, Canada, June 15–19, 2015, 2015, ISBN: 978-0-7918-5664-2, (ASME paper GT2015–42176).
@conference{964,
title = {Scaling 3D Low-Pressure Turbine Blades for Low-Speed Testing},
author = {Matteo Giovannini and Michele Marconcini and Filippo Rubechini and Andrea Arnone and Francesco Bertini},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2427901&resultClick=3},
doi = {10.1115/GT2015-42176},
isbn = {978-0-7918-5664-2},
year = {2015},
date = {2015-01-01},
booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition},
volume = {2B: Turbomachinery},
publisher = {ASME},
address = {Montreal, Canada, June 15–19, 2015},
organization = {ASME},
abstract = {The present activity was carried out in the framework of the Clean Sky European research project ITURB (Optimal High-Lift Turbine Blade Aero-Mechanical Design), aimed at designing and validating a turbine blade for a geared open rotor engine. A cold-flow, large-scale, low-speed (LS) rig was built in order to investigate and validate new design criteria, providing reliable and detailed results while containing costs. This paper presents the design of a LS stage, and describes a general procedure that allows to scale 3D blades for low-speed testing. The design of the stator row was aimed at matching the test-rig inlet conditions and at providing the proper inlet flow field to the blade row. The rotor row was redesigned in order to match the performance of the high-speed one, compensating for both the compressibility effects and different turbine flow paths. The proposed scaling procedure is based on the matching of the 3D blade loading distribution between the real engine environment and the LS facility one, which leads to a comparable behavior of the boundary layer and hence to comparable profile losses. To this end, the datum blade is parameterized, and a neural-networkbased methodology is exploited to guide an optimization process based on 3D RANS computations. The LS stage performance were investigated over a range of Reynolds numbers characteristic of modern low-pressure turbines by using a multi-equation, transition-sensitive, turbulence model.},
note = {ASME paper GT2015–42176},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The present activity was carried out in the framework of the Clean Sky European research project ITURB (Optimal High-Lift Turbine Blade Aero-Mechanical Design), aimed at designing and validating a turbine blade for a geared open rotor engine. A cold-flow, large-scale, low-speed (LS) rig was built in order to investigate and validate new design criteria, providing reliable and detailed results while containing costs. This paper presents the design of a LS stage, and describes a general procedure that allows to scale 3D blades for low-speed testing. The design of the stator row was aimed at matching the test-rig inlet conditions and at providing the proper inlet flow field to the blade row. The rotor row was redesigned in order to match the performance of the high-speed one, compensating for both the compressibility effects and different turbine flow paths. The proposed scaling procedure is based on the matching of the 3D blade loading distribution between the real engine environment and the LS facility one, which leads to a comparable behavior of the boundary layer and hence to comparable profile losses. To this end, the datum blade is parameterized, and a neural-networkbased methodology is exploited to guide an optimization process based on 3D RANS computations. The LS stage performance were investigated over a range of Reynolds numbers characteristic of modern low-pressure turbines by using a multi-equation, transition-sensitive, turbulence model.
Pinelli, Lorenzo; Poli, Francesco; Bellucci, Juri; Giovannini, Matteo; Arnone, Andrea
Evaluation of Fast Numerical Methods for Turbomachinery Blade Flutter Analysis Conference
14th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT), September 8–11, Stockholm, Sweden, 2015, (paper I14-S7-1).
@conference{975,
title = {Evaluation of Fast Numerical Methods for Turbomachinery Blade Flutter Analysis},
author = {Lorenzo Pinelli and Francesco Poli and Juri Bellucci and Matteo Giovannini and Andrea Arnone},
year = {2015},
date = {2015-01-01},
booktitle = {14th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT)},
address = {September 8–11, Stockholm, Sweden},
abstract = {Different numerical methods for blade flutter analysis were employed to evaluate the flutter stability of a typical low pressure turbine bladerow tested in the context of the European research project FUTURE.
This aeroelastic testcase was extensively studied during the project by a large number of partners, becoming a suitable benchmark to compare numerical techniques for flutter prediction.
In this study, two different uncoupled aeroelastic methods (time-linearized and non-linear) were used to assess the flutter stability. The results highlight a very good agreement between the two approaches even when the non-linear code was applied with some approximation strategies (non viscous endwalls and wall functions).
The two analyzed bladerow configurations (cantilever and interlock) show unstable and stable flutter behavior respectively, and the numerical flutter predictions are in agreement with the experimental evidences obtained during the project.
Finally the two methods were also evaluated in terms of computational time. This is due to the fact that flutter assessment methods are more and more used during the turbomachinery design, even during the bladerow optimization. },
note = {paper I14-S7-1},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Different numerical methods for blade flutter analysis were employed to evaluate the flutter stability of a typical low pressure turbine bladerow tested in the context of the European research project FUTURE.
This aeroelastic testcase was extensively studied during the project by a large number of partners, becoming a suitable benchmark to compare numerical techniques for flutter prediction.
In this study, two different uncoupled aeroelastic methods (time-linearized and non-linear) were used to assess the flutter stability. The results highlight a very good agreement between the two approaches even when the non-linear code was applied with some approximation strategies (non viscous endwalls and wall functions).
The two analyzed bladerow configurations (cantilever and interlock) show unstable and stable flutter behavior respectively, and the numerical flutter predictions are in agreement with the experimental evidences obtained during the project.
Finally the two methods were also evaluated in terms of computational time. This is due to the fact that flutter assessment methods are more and more used during the turbomachinery design, even during the bladerow optimization.
This aeroelastic testcase was extensively studied during the project by a large number of partners, becoming a suitable benchmark to compare numerical techniques for flutter prediction.
In this study, two different uncoupled aeroelastic methods (time-linearized and non-linear) were used to assess the flutter stability. The results highlight a very good agreement between the two approaches even when the non-linear code was applied with some approximation strategies (non viscous endwalls and wall functions).
The two analyzed bladerow configurations (cantilever and interlock) show unstable and stable flutter behavior respectively, and the numerical flutter predictions are in agreement with the experimental evidences obtained during the project.
Finally the two methods were also evaluated in terms of computational time. This is due to the fact that flutter assessment methods are more and more used during the turbomachinery design, even during the bladerow optimization.
Berrino, Marco; Bigoni, Fabio; Simoni, Daniele; Giovannini, Matteo; Marconcini, Michele; Pacciani, Roberto; Bertini, Francesco
Combined Experimental and Numerical Investigations on the Roughness Effects on the Aerodynamic Performances of LPT Blades Conference
12th International Symposium on Experimental and Computational Aerothermodynamics of Internal Flows, 13–16 July 2015, Lerici (SP), Italy, 2015, (paper n. 166).
@conference{973,
title = {Combined Experimental and Numerical Investigations on the Roughness Effects on the Aerodynamic Performances of LPT Blades},
author = {Marco Berrino and Fabio Bigoni and Daniele Simoni and Matteo Giovannini and Michele Marconcini and Roberto Pacciani and Francesco Bertini},
year = {2015},
date = {2015-01-01},
booktitle = {12th International Symposium on Experimental and Computational Aerothermodynamics of Internal Flows},
address = {13–16 July 2015, Lerici (SP), Italy},
abstract = {The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels (Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers (300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions. Computational fluid dynamics has been used to support and interpret experimental results, analyzing in detail the flow field on the blade surface and evaluating the non-dimensional local roughness parameters (which were not available from the experimental tests), further contributing to understand how and where roughness have some influence on the aerodynamic performance of the blade. The total pressure distributions in the wake region have been measured by means of a five-hole miniaturized pressure probe for the different flow conditions, allowing the evaluation of profile losses and of their dependence on the surface finish, as well as a direct comparison with the simulations. Results reported in the paper clearly highlight that only at the highest Reynolds number tested (Re=300000) surface roughness have some influence on the blade performance, both for steady and unsteady incoming flows. In this flow condition profile losses grow as the surface roughness increases, while no appreciable variations have been found at the lowest Reynolds number. The boundary layer evolution and the wake structure have shown that this trend is due to a thickening of the suction side boundary layer associated to an anticipation of transition process. On the other side, no effects have been observed on the pressure side boundary layer.},
note = {paper n. 166},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels (Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers (300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions. Computational fluid dynamics has been used to support and interpret experimental results, analyzing in detail the flow field on the blade surface and evaluating the non-dimensional local roughness parameters (which were not available from the experimental tests), further contributing to understand how and where roughness have some influence on the aerodynamic performance of the blade. The total pressure distributions in the wake region have been measured by means of a five-hole miniaturized pressure probe for the different flow conditions, allowing the evaluation of profile losses and of their dependence on the surface finish, as well as a direct comparison with the simulations. Results reported in the paper clearly highlight that only at the highest Reynolds number tested (Re=300000) surface roughness have some influence on the blade performance, both for steady and unsteady incoming flows. In this flow condition profile losses grow as the surface roughness increases, while no appreciable variations have been found at the lowest Reynolds number. The boundary layer evolution and the wake structure have shown that this trend is due to a thickening of the suction side boundary layer associated to an anticipation of transition process. On the other side, no effects have been observed on the pressure side boundary layer.
Giovannini, Matteo; Marconcini, Michele; Arnone, Andrea; Dominguez, Alain
A Hybrid Parallelization Strategy of a CFD Code for Turbomachinery Applications Conference
11th European Turbomachinery Conference, March 23-26, Madrid, Spain, 2015, ISSN: 2410-4833, (paper ETC2015-188).
@conference{962,
title = {A Hybrid Parallelization Strategy of a CFD Code for Turbomachinery Applications},
author = {Matteo Giovannini and Michele Marconcini and Andrea Arnone and Alain Dominguez},
url = {http://www.euroturbo.eu/paper/etc2015-188/},
issn = {2410-4833},
year = {2015},
date = {2015-01-01},
booktitle = {11th European Turbomachinery Conference},
address = {March 23-26, Madrid, Spain},
abstract = {This paper presents the serial optimization as well as the parallelization of the TRAF code, a 3D multi-row, multi-block CFD solver for the RANS/URANS equations. The serial optimization was carried out by means of a critical review of the most time-consuming routines in order to exploit vectorization capability of the modern CPUs preserving the code accuracy. The code parallelization was carried out for both distributed and shared memory systems, following the actual trend of computing clusters. Performance were assessed on several architectures ranging from simple multi-core PCs to a small slow-network cluster, and high performance computing (HPC) clusters (CINECA PLX cluster and Intel Grizzly Silver cluster). Code performance are presented and discussed for the pure MPI, pure OpenMP, and hybrid OpenMP-MPI parallelisms considering typical turbomachinery applications: a steady state multi-row compressor analysis and an unsteady computation of a low pressure turbine (LPT) module. Noteworthy, the present paper can provide code developers with relevant guidelines in the selection of the parallelization strategy without asking for a specific background in the parallelization and HPC fields.},
note = {paper ETC2015-188},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
This paper presents the serial optimization as well as the parallelization of the TRAF code, a 3D multi-row, multi-block CFD solver for the RANS/URANS equations. The serial optimization was carried out by means of a critical review of the most time-consuming routines in order to exploit vectorization capability of the modern CPUs preserving the code accuracy. The code parallelization was carried out for both distributed and shared memory systems, following the actual trend of computing clusters. Performance were assessed on several architectures ranging from simple multi-core PCs to a small slow-network cluster, and high performance computing (HPC) clusters (CINECA PLX cluster and Intel Grizzly Silver cluster). Code performance are presented and discussed for the pure MPI, pure OpenMP, and hybrid OpenMP-MPI parallelisms considering typical turbomachinery applications: a steady state multi-row compressor analysis and an unsteady computation of a low pressure turbine (LPT) module. Noteworthy, the present paper can provide code developers with relevant guidelines in the selection of the parallelization strategy without asking for a specific background in the parallelization and HPC fields.
2014
Giovannini, Matteo; Marconcini, Michele; Arnone, Andrea; Bertini, Francesco
Evaluation of Unsteady Computational Fluid Dynamics Models Applied to the Analysis of a Transonic High-Pressure Turbine Stage Journal Article
In: Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, vol. 228, pp. 813-824, 2014, ISSN: 0957-6509.
@article{932,
title = {Evaluation of Unsteady Computational Fluid Dynamics Models Applied to the Analysis of a Transonic High-Pressure Turbine Stage},
author = {Matteo Giovannini and Michele Marconcini and Andrea Arnone and Francesco Bertini},
url = {http://pia.sagepub.com/content/228/7/813},
doi = {dx.doi.org/10.1177/0957650914536170},
issn = {0957-6509},
year = {2014},
date = {2014-11-01},
journal = {Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy},
volume = {228},
pages = {813-824},
abstract = {This paper presents an efficient Phase-Lagged method developed for turbomachinery applications. The method is based on the Generalized-Shape-Correction model. Moving averages techniques as well as double-passage domain formulation were adopted in order to reduce memory requirements and improve the model robustness. The model was used to evaluate the aerodynamic performance of the high pressure transonic turbine stage CT3, experimentally studied at the von Karman Institute for Fluid Dynamics within the EU funded TATEF2 project. Results are discussed and compared with both the available experimental data and the results obtained by means of both steady and unsteady scaled Full-Annulus approaches. Computational requirements of the GSC model are evaluated and presented showing that nowadays unsteady results can be reached at an affordable computational cost.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper presents an efficient Phase-Lagged method developed for turbomachinery applications. The method is based on the Generalized-Shape-Correction model. Moving averages techniques as well as double-passage domain formulation were adopted in order to reduce memory requirements and improve the model robustness. The model was used to evaluate the aerodynamic performance of the high pressure transonic turbine stage CT3, experimentally studied at the von Karman Institute for Fluid Dynamics within the EU funded TATEF2 project. Results are discussed and compared with both the available experimental data and the results obtained by means of both steady and unsteady scaled Full-Annulus approaches. Computational requirements of the GSC model are evaluated and presented showing that nowadays unsteady results can be reached at an affordable computational cost.
2013
Bertini, Francesco; Credi, Martina; Marconcini, Michele; Giovannini, Matteo
A Path Toward the Aerodynamic Robust Design of Low Pressure Turbines Journal Article
In: ASME Journal of Turbomachinery, vol. 135, no. 2, pp. 021018, 2013, ISSN: 0889-504X.
@article{938,
title = {A Path Toward the Aerodynamic Robust Design of Low Pressure Turbines},
author = {Francesco Bertini and Martina Credi and Michele Marconcini and Matteo Giovannini},
url = {http://turbomachinery.asmedigitalcollection.asme.org/article.aspx?articleid=1676365},
doi = {10.1115/1.4007519},
issn = {0889-504X},
year = {2013},
date = {2013-11-01},
journal = {ASME Journal of Turbomachinery},
volume = {135},
number = {2},
pages = {021018},
abstract = {Airline companies are continuously demanding lower-fuel-consuming engines and this leads to investigating innovative configurations and to further improving single module performance. In this framework the low pressure turbine (LPT) is known to be a key component since it has a major effect on specific fuel consumption (SFC). Modern aerodynamic design of LPTs for civil aircraft engines has reached high levels of quality, but new engine data, after first engine tests, often cannot achieve the expected performance. Further work on the modules is usually required, with additional costs and time spent to reach the quality level needed to enter into service. The reported study is aimed at understanding some of the causes for this deficit and how to solve some of the highlighted problems. In a real engine, the LPT module works under conditions which differ from those described in the analyzed numerical model: the definition of the geometry cannot be so accurate, a priori unknown values for boundary conditions data are often assumed, complex physical phenomena are seldom taken into account, and operating cycle may differ from the design intent due to a nonoptimal coupling with other engine components. Moreover, variations are present among different engines of the same family, manufacturing defects increase the uncertainty and, finally, deterioration of the components occurs during service. Research projects and several studies carried out by the authors lead to the conclusion that being able to design a module whose performance is less sensitive to variations (robust LPT) brings advantages not only when the engine performs under strong off-design conditions but also, due to the abovementioned unknowns, near the design point as well. Concept and preliminary design phases are herein considered, highlighting the results arising from sensibility studies and their impact on the final designed robust configuration. Module performance is afterward estimated using a statistical approach.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Airline companies are continuously demanding lower-fuel-consuming engines and this leads to investigating innovative configurations and to further improving single module performance. In this framework the low pressure turbine (LPT) is known to be a key component since it has a major effect on specific fuel consumption (SFC). Modern aerodynamic design of LPTs for civil aircraft engines has reached high levels of quality, but new engine data, after first engine tests, often cannot achieve the expected performance. Further work on the modules is usually required, with additional costs and time spent to reach the quality level needed to enter into service. The reported study is aimed at understanding some of the causes for this deficit and how to solve some of the highlighted problems. In a real engine, the LPT module works under conditions which differ from those described in the analyzed numerical model: the definition of the geometry cannot be so accurate, a priori unknown values for boundary conditions data are often assumed, complex physical phenomena are seldom taken into account, and operating cycle may differ from the design intent due to a nonoptimal coupling with other engine components. Moreover, variations are present among different engines of the same family, manufacturing defects increase the uncertainty and, finally, deterioration of the components occurs during service. Research projects and several studies carried out by the authors lead to the conclusion that being able to design a module whose performance is less sensitive to variations (robust LPT) brings advantages not only when the engine performs under strong off-design conditions but also, due to the abovementioned unknowns, near the design point as well. Concept and preliminary design phases are herein considered, highlighting the results arising from sensibility studies and their impact on the final designed robust configuration. Module performance is afterward estimated using a statistical approach.
Rubechini, Filippo; Marconcini, Michele; Arnone, Andrea; Greco, Alberto Scotti Del; Biagi, Roberto
Special Challenges in the Computational Fluid Dynamics Modeling of Transonic Turbo-Expanders Journal Article
In: ASME Journal of Engineering for Gas Turbines and Power, vol. 135, no. 10, pp. 102701, 2013, ISSN: 0742-4795, (ASME paper GT2013-95554).
@article{934,
title = {Special Challenges in the Computational Fluid Dynamics Modeling of Transonic Turbo-Expanders},
author = {Filippo Rubechini and Michele Marconcini and Andrea Arnone and Alberto Scotti Del Greco and Roberto Biagi},
url = {http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=1734459},
doi = {10.1115/1.4025034},
issn = {0742-4795},
year = {2013},
date = {2013-08-01},
journal = {ASME Journal of Engineering for Gas Turbines and Power},
volume = {135},
number = {10},
pages = {102701},
publisher = {ASME},
abstract = {High pressure ratio turbo-expanders often put a strain on computational fluid dynamics (CFD) modeling. First of all, the working fluid is usually characterized by significant departures from the ideal behavior, thus requiring the adoption of a reliable real gas model. Moreover, supersonic flow conditions are typically reached at the nozzle vanes discharge, thus involving the formation of a shock pattern, which is in turn responsible for a strong unsteady interaction with the wheel blades. Under such circumstances, performance predictions based on classical perfect gas, steady-state calculations can be very poor. While reasonably accurate real gas models are nowadays available in most flow solvers, unsteady real gas calculations still struggle to become an affordable tool for investigating turbo-expanders. However, it is emphasized in this work how essential the adoption of a time-accurate analysis can be for accurate performance estimations. The present paper is divided in two parts. In the first part, the computational framework is validated against on-site measured performance from an existing power plant equipped with a variable-geometry nozzled turbo-expander, for different nozzle positions, and in design and off-design conditions. The second part of the paper is devoted to the detailed discussion of the unsteady interaction between the nozzle shock waves and the wheel flow field. Furthermore, an attempt is made to identify the key factors responsible for the unsteady interaction and to outline an effective way to reduce it.},
note = {ASME paper GT2013-95554},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
High pressure ratio turbo-expanders often put a strain on computational fluid dynamics (CFD) modeling. First of all, the working fluid is usually characterized by significant departures from the ideal behavior, thus requiring the adoption of a reliable real gas model. Moreover, supersonic flow conditions are typically reached at the nozzle vanes discharge, thus involving the formation of a shock pattern, which is in turn responsible for a strong unsteady interaction with the wheel blades. Under such circumstances, performance predictions based on classical perfect gas, steady-state calculations can be very poor. While reasonably accurate real gas models are nowadays available in most flow solvers, unsteady real gas calculations still struggle to become an affordable tool for investigating turbo-expanders. However, it is emphasized in this work how essential the adoption of a time-accurate analysis can be for accurate performance estimations. The present paper is divided in two parts. In the first part, the computational framework is validated against on-site measured performance from an existing power plant equipped with a variable-geometry nozzled turbo-expander, for different nozzle positions, and in design and off-design conditions. The second part of the paper is devoted to the detailed discussion of the unsteady interaction between the nozzle shock waves and the wheel flow field. Furthermore, an attempt is made to identify the key factors responsible for the unsteady interaction and to outline an effective way to reduce it.
Rubechini, Filippo; Marconcini, Michele; Arnone, Andrea; Greco, Alberto Scotti Del; Biagi, Roberto
Special Challenges in the CFD Modeling of Transonic Turbo-Expanders Proceedings
ASME, San Antonio, Texas, USA, June 3–7, 2013, vol. 6C: Turbomachinery, 2013, ISBN: 978-0-7918-5524-9, (ASME paper GT2013-95554).
@proceedings{954,
title = {Special Challenges in the CFD Modeling of Transonic Turbo-Expanders},
author = {Filippo Rubechini and Michele Marconcini and Andrea Arnone and Alberto Scotti Del Greco and Roberto Biagi},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1776645&resultClick=1},
doi = {dx.doi.org/10.1115/GT2013-95554},
isbn = {978-0-7918-5524-9},
year = {2013},
date = {2013-06-01},
journal = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition},
volume = {6C: Turbomachinery},
pages = {V06CT40A016; 10 pages},
publisher = {ASME},
address = {San Antonio, Texas, USA, June 3–7, 2013},
abstract = {High pressure ratio turbo-expanders often put a strain on CFD modeling. First of all, the working fluid is usually characterized by significant departures from the ideal behavior, thus requiring the adoption of a reliable real gas model. Moreover, supersonic flow conditions are typically reached at the nozzle vanes discharge, thus involving the formation of a shock pattern, which is in turn responsible for a strong unsteady interaction with the wheel blades. Under such circumstances, performance predictions based on classical perfect gas, steady-state calculations can be very poor. While reasonably accurate real gas models are nowadays available in most flow solvers, unsteady real gas calculations still struggle to become an affordable tool for investigating turbo-expanders. However, it is emphasized in this work how essential the adoption of a time-accurate analysis can be for accurate performance estimations. The present paper is divided in two parts. In the first part, the computational framework is validated against on-site measured performance from an existing power plant equipped with a variable-geometry nozzled turbo-expander, for different nozzle positions, and in design and off-design conditions. The second part of the paper is devoted to the detailed discussion of the unsteady interaction between the nozzle shock waves and the wheel flow field. Furthermore, an attempt is made to identify the key factors responsible for the unsteady interaction and to outline an effective way to reduce it.},
note = {ASME paper GT2013-95554},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
High pressure ratio turbo-expanders often put a strain on CFD modeling. First of all, the working fluid is usually characterized by significant departures from the ideal behavior, thus requiring the adoption of a reliable real gas model. Moreover, supersonic flow conditions are typically reached at the nozzle vanes discharge, thus involving the formation of a shock pattern, which is in turn responsible for a strong unsteady interaction with the wheel blades. Under such circumstances, performance predictions based on classical perfect gas, steady-state calculations can be very poor. While reasonably accurate real gas models are nowadays available in most flow solvers, unsteady real gas calculations still struggle to become an affordable tool for investigating turbo-expanders. However, it is emphasized in this work how essential the adoption of a time-accurate analysis can be for accurate performance estimations. The present paper is divided in two parts. In the first part, the computational framework is validated against on-site measured performance from an existing power plant equipped with a variable-geometry nozzled turbo-expander, for different nozzle positions, and in design and off-design conditions. The second part of the paper is devoted to the detailed discussion of the unsteady interaction between the nozzle shock waves and the wheel flow field. Furthermore, an attempt is made to identify the key factors responsible for the unsteady interaction and to outline an effective way to reduce it.
Giovannini, Matteo; Marconcini, Michele; Arnone, Andrea; Bertini, Francesco
Evaluation of Unsteady CFD Models Applied to the Analysis of a Transonic HP Turbine Stage Proceedings
Lappeenranta, Finland, 2013, ISBN: 978-952-265-385-7.
@proceedings{945,
title = {Evaluation of Unsteady CFD Models Applied to the Analysis of a Transonic HP Turbine Stage},
author = {Matteo Giovannini and Michele Marconcini and Andrea Arnone and Francesco Bertini},
isbn = {978-952-265-385-7},
year = {2013},
date = {2013-04-01},
journal = {10th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics (ETC 2013)},
pages = {840-853},
address = {Lappeenranta, Finland},
abstract = {This paper presents an efficient textquotedblleftPhase-Laggedtextquotedblright method developed for turbomachinery applications. The method is based on the Generalized-Shape-Correction model. Moving averages techniques as well as double-passage domain formulation were adopted in order to reduce memory requirements and improve the model robustness. The model was used to evaluate the aerodynamic performance of the high pressure transonic turbine stage CT3, experimentally studied at the von Karman Institute for Fluid Dynamics within the EU funded TATEF2 project. Results are discussed and compared with both the available experimental data and the results obtained by means of both steady and unsteady scaled Full-Annulus approaches. Computational requirements of the GSC model are evaluated and presented showing that nowadays unsteady results can be reached at an affordable computational cost.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
This paper presents an efficient textquotedblleftPhase-Laggedtextquotedblright method developed for turbomachinery applications. The method is based on the Generalized-Shape-Correction model. Moving averages techniques as well as double-passage domain formulation were adopted in order to reduce memory requirements and improve the model robustness. The model was used to evaluate the aerodynamic performance of the high pressure transonic turbine stage CT3, experimentally studied at the von Karman Institute for Fluid Dynamics within the EU funded TATEF2 project. Results are discussed and compared with both the available experimental data and the results obtained by means of both steady and unsteady scaled Full-Annulus approaches. Computational requirements of the GSC model are evaluated and presented showing that nowadays unsteady results can be reached at an affordable computational cost.
Bertini, Francesco; Ampellio, E; Marconcini, Michele; Giovannini, Matteo
ASME, San Antonio, TX, USA, June 3–7, vol. 6B: Turbomachinery, 2013, ISBN: 978-0-7918-5523-2, (ASME paper GT2013-94849).
@proceedings{935,
title = {A Critical Numerical Review of Loss Correlation Models and Smith Diagram for Modern Low Pressure Turbine Stages},
author = {Francesco Bertini and E Ampellio and Michele Marconcini and Matteo Giovannini},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleID=1776565},
doi = {10.1115/GT2013-94849},
isbn = {978-0-7918-5523-2},
year = {2013},
date = {2013-01-01},
journal = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition},
volume = {6B: Turbomachinery},
pages = {V06BT37A018-; 14 pages},
publisher = {ASME},
address = {San Antonio, TX, USA, June 3–7},
abstract = {The Smith diagram, originally published in 1965, has been largely exploited as a preliminary design (PD) tool for axial turbines. Currently, it is applied to aeronautical Low Pressure Turbines (LPTs) in order to define basic characteristics during the feasibility study and to compare different configurations. The Smith diagram represents a correlation of stage performance (η) as function of flow coefficient (φ) and loading factor (ψ), but it does not take into account the effects of some important input parameters (single contributions of loss, Reynolds number, Aspect Ratio, Rotor Tip Clearance (RTC)) and does not report some key design outputs (deflections (δ), profile weights and stresses), which have also a direct relation with the configuration position on the Smith diagram. This study employs meanline analyses incorporating two traditional loss correlation models used in the turbine field (Craig and Cox, Kacker and Okapuu) to compare results with the original Smith diagram. The correlation approach allows one to obtain other important multidisciplinary information (primarily aero-mechanical) which was previously absent, which leads to some strategic design achievements. The investigation process is based on a reference two-stage turbine properly set to match specific operating points on the Smith diagram. Several three-dimensional blade geometries have been designed and then detailed 3D CFD analyses have been performed in order to acquire confidence with respect to the meanline results. This research adds additional important information for turbine module design to the Smith chart and allows for a numerical revision of the diagram itself, fine tuning it with data obtained from the analyses of modern blades optimized for high stage performance. Finally numerically-based loss predictors, broadly applicable to LPTs during optimization procedures before detailed CFD analyses, are presented and discussed.},
note = {ASME paper GT2013-94849},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
The Smith diagram, originally published in 1965, has been largely exploited as a preliminary design (PD) tool for axial turbines. Currently, it is applied to aeronautical Low Pressure Turbines (LPTs) in order to define basic characteristics during the feasibility study and to compare different configurations. The Smith diagram represents a correlation of stage performance (η) as function of flow coefficient (φ) and loading factor (ψ), but it does not take into account the effects of some important input parameters (single contributions of loss, Reynolds number, Aspect Ratio, Rotor Tip Clearance (RTC)) and does not report some key design outputs (deflections (δ), profile weights and stresses), which have also a direct relation with the configuration position on the Smith diagram. This study employs meanline analyses incorporating two traditional loss correlation models used in the turbine field (Craig and Cox, Kacker and Okapuu) to compare results with the original Smith diagram. The correlation approach allows one to obtain other important multidisciplinary information (primarily aero-mechanical) which was previously absent, which leads to some strategic design achievements. The investigation process is based on a reference two-stage turbine properly set to match specific operating points on the Smith diagram. Several three-dimensional blade geometries have been designed and then detailed 3D CFD analyses have been performed in order to acquire confidence with respect to the meanline results. This research adds additional important information for turbine module design to the Smith chart and allows for a numerical revision of the diagram itself, fine tuning it with data obtained from the analyses of modern blades optimized for high stage performance. Finally numerically-based loss predictors, broadly applicable to LPTs during optimization procedures before detailed CFD analyses, are presented and discussed.