2017
Paradiso, Berardo; Gatti, Giacomo; Bellucci, Juri; Mora, Alessandro; Dossena, Vincenzo; Arcangeli, Lorenzo; Maceli, Nicola
An Experimental and Numerical Investigation of the Performance Impact of a Heavily Off-Design Inlet Swirl Angle in a Steam Turbine Stage Conference
ASME Turbo Expo 2017: Turbine Technical Conference and Exposition, Charlotte, NC, USA, 2017, (ASME paper GT2017-64561).
@conference{997,
title = {An Experimental and Numerical Investigation of the Performance Impact of a Heavily Off-Design Inlet Swirl Angle in a Steam Turbine Stage},
author = {Berardo Paradiso and Giacomo Gatti and Juri Bellucci and Alessandro Mora and Vincenzo Dossena and Lorenzo Arcangeli and Nicola Maceli},
year = {2017},
date = {2017-01-01},
booktitle = {ASME Turbo Expo 2017: Turbine Technical Conference and Exposition},
address = {Charlotte, NC, USA},
abstract = {The aim of this work is to provide an insight into the performance reduction of a 1.5 axial steam turbine stage working under extreme incidence conditions at the inlet. In particular, the main object of the study is the propagation of the loss cores across the blade rows, so as to assess how such operating conditions affect the full machine. Experimental data have been used to validate an unsteady three-dimensional numerical simulation, which provided the tools to investigate the flowfield in detail. To do so, the 1.5 turbine stage installed in the Low Speed Test Rig at Politecnico di Milano has been tested with design and off-design inlet conditions by modifying the IGV orientation. The inter-stage flowfield was investigated by traversing pressure probes in three different axial planes, downstream of each blade row. The numerical simulation has been carried out at University of Florence. The experimental data from probes traversing was used as boundary conditions so as to match as closely as possible the actual operative parameters of the stage. Data from flange-to-flange measurements on the test rig were also used to compare the stage efficiency. After the successful validation of the numerical results, the loss cores propagation study itself was carried out. Using CFD results, the unsteady nature of the separation occurring on the first stator in off-design condition is investigated. Subsequently, a detailed analysis of the propagation of the loss cores is presented, including loss coefficients calculation and entropy trends along the machines axial coordinate. The main outcome is that at the machine exit the loss structures appear to be mainly mixed out and, therefore, subsequent stages would operate under conditions not far from the nominal ones.},
note = {ASME paper GT2017-64561},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The aim of this work is to provide an insight into the performance reduction of a 1.5 axial steam turbine stage working under extreme incidence conditions at the inlet. In particular, the main object of the study is the propagation of the loss cores across the blade rows, so as to assess how such operating conditions affect the full machine. Experimental data have been used to validate an unsteady three-dimensional numerical simulation, which provided the tools to investigate the flowfield in detail. To do so, the 1.5 turbine stage installed in the Low Speed Test Rig at Politecnico di Milano has been tested with design and off-design inlet conditions by modifying the IGV orientation. The inter-stage flowfield was investigated by traversing pressure probes in three different axial planes, downstream of each blade row. The numerical simulation has been carried out at University of Florence. The experimental data from probes traversing was used as boundary conditions so as to match as closely as possible the actual operative parameters of the stage. Data from flange-to-flange measurements on the test rig were also used to compare the stage efficiency. After the successful validation of the numerical results, the loss cores propagation study itself was carried out. Using CFD results, the unsteady nature of the separation occurring on the first stator in off-design condition is investigated. Subsequently, a detailed analysis of the propagation of the loss cores is presented, including loss coefficients calculation and entropy trends along the machines axial coordinate. The main outcome is that at the machine exit the loss structures appear to be mainly mixed out and, therefore, subsequent stages would operate under conditions not far from the nominal ones.
2016
Gatti, Giacomo; Gaetani, Paolo; Paradiso, Berardo; Dossena, Vincenzo; Arcangeli, Lorenzo; Maceli, Nicola; Bellucci, Juri
An Experimental Study of the Aerodynamic Forcing Function in a 1.5 Steam Turbine Stage Journal Article
In: Journal of Engineering for Gas Turbines and Power, vol. 139, pp. 052503, 2016, ISSN: 0742-4795.
@article{989,
title = {An Experimental Study of the Aerodynamic Forcing Function in a 1.5 Steam Turbine Stage},
author = {Giacomo Gatti and Paolo Gaetani and Berardo Paradiso and Vincenzo Dossena and Lorenzo Arcangeli and Nicola Maceli and Juri Bellucci},
url = {http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2569877},
doi = {dx.doi.org/10.1115/1.4034967},
issn = {0742-4795},
year = {2016},
date = {2016-12-01},
journal = {Journal of Engineering for Gas Turbines and Power},
volume = {139},
pages = {052503},
abstract = {The usual ways to measure the aerodynamic forcing function are complex and expensive. The aim of this work is to evaluate the forces acting on the blades using a relatively simpler experimental methodology based on a time-resolved pressure measurement at the rotor discharge. Upstream of the rotor, a steady three holes probe has been used. The post processing procedures are described in detail, including the application of a phase-locked average and of an extension algorithm with phase-lag. The algorithm for the computation of the force components is presented, along with the underlying assumptions. In order to interpret the results, a preliminary description of the flow field, both upstream and downstream of the rotor, is provided. This gives an insight of the most relevant features that affect the computation of the forces. Finally, the analysis of the results is presented. These are first described and then compared with overall section-average results (torque-sensor), and with the results from 3D unsteady simulations (integral of pressure over the blade surface) in order to assess the accuracy of the method. Both the experimental and the numerical results are also compared for two different operating conditions with increasing stage load.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The usual ways to measure the aerodynamic forcing function are complex and expensive. The aim of this work is to evaluate the forces acting on the blades using a relatively simpler experimental methodology based on a time-resolved pressure measurement at the rotor discharge. Upstream of the rotor, a steady three holes probe has been used. The post processing procedures are described in detail, including the application of a phase-locked average and of an extension algorithm with phase-lag. The algorithm for the computation of the force components is presented, along with the underlying assumptions. In order to interpret the results, a preliminary description of the flow field, both upstream and downstream of the rotor, is provided. This gives an insight of the most relevant features that affect the computation of the forces. Finally, the analysis of the results is presented. These are first described and then compared with overall section-average results (torque-sensor), and with the results from 3D unsteady simulations (integral of pressure over the blade surface) in order to assess the accuracy of the method. Both the experimental and the numerical results are also compared for two different operating conditions with increasing stage load.
Pacciani, Roberto; Rubechini, Filippo; Marconcini, Michele; Arnone, Andrea; Cecchi, Stefano; Daccà, Federico
A CFD-Based Throughflow Method With An Adaptive Formulation For The S2 Streamsurface Journal Article
In: Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, vol. 230, pp. 16-28, 2016, ISSN: 0957-6509.
@article{967,
title = {A CFD-Based Throughflow Method With An Adaptive Formulation For The S2 Streamsurface},
author = {Roberto Pacciani and Filippo Rubechini and Michele Marconcini and Andrea Arnone and Stefano Cecchi and Federico Daccà},
url = {http://pia.sagepub.com/content/230/1/16},
doi = {dx.doi.org/10.1177/0957650915607091},
issn = {0957-6509},
year = {2016},
date = {2016-09-01},
journal = {Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy},
volume = {230},
pages = {16-28},
abstract = {The paper describes the development and validation of a novel CFD-based throughflow model. It is based on the axisymmetric Euler equations with tangential blockage and body forces and inherits its numerical scheme from state-of-the-art CFD solver (TRAF code), including real-gas capabilities. A crucial aspect of the numerical procedure is represented by an adaptive approach for the meridional flow surface, which employs a new time-dependent equation to accommodate incidence and deviation effects, and which allows the explicit calculation of the blade body force. A realistic distribution of entropy along the streamlines is proposed in order to compute dissipative forces on the base of a distributed loss model. The throughflow code is applied to the investigation of a four stage low-pressure steam turbine at design conditions. The performance of the method are evaluated by comparing predicted operating characteristics and spanwise distributions of flow quantities with the results of CFD, steady, viscous calculations and experimental data.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The paper describes the development and validation of a novel CFD-based throughflow model. It is based on the axisymmetric Euler equations with tangential blockage and body forces and inherits its numerical scheme from state-of-the-art CFD solver (TRAF code), including real-gas capabilities. A crucial aspect of the numerical procedure is represented by an adaptive approach for the meridional flow surface, which employs a new time-dependent equation to accommodate incidence and deviation effects, and which allows the explicit calculation of the blade body force. A realistic distribution of entropy along the streamlines is proposed in order to compute dissipative forces on the base of a distributed loss model. The throughflow code is applied to the investigation of a four stage low-pressure steam turbine at design conditions. The performance of the method are evaluated by comparing predicted operating characteristics and spanwise distributions of flow quantities with the results of CFD, steady, viscous calculations and experimental data.
Giovannini, Matteo; Marconcini, Michele; Rubechini, Filippo; Arnone, Andrea; Bertini, Francesco
Scaling Three-Dimensional Low-Pressure Turbine Blades for Low-Speed Testing Journal Article
In: ASME Journal of Turbomachinery, vol. 138, pp. 111001-1-9, 2016, ISSN: 0889-504X.
@article{984,
title = {Scaling Three-Dimensional 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://turbomachinery.asmedigitalcollection.asme.org/article.aspx?articleID=2512185},
doi = {dx.doi.org/10.1115/1.4033259},
issn = {0889-504X},
year = {2016},
date = {2016-05-01},
journal = {ASME Journal of Turbomachinery},
volume = {138},
pages = {111001-1-9},
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-network based 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.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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-network based 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.
Giovannini, Matteo; Rubechini, Filippo; Marconcini, Michele; Arnone, Andrea; Bertini, Francesco
Analysis of a LPT Rotor Blade For a Geared Engine. Part I: Aero-Mechanical Design and Validation Conference
ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition, vol. 2B: Turbomachinery, Seoul, South Korea, June 13–17, 2016, 2016, ISBN: 978-0-7918-4970-5, (GT2016-57746).
@conference{980,
title = {Analysis of a LPT Rotor Blade For a Geared Engine. Part I: Aero-Mechanical Design and Validation},
author = {Matteo Giovannini and Filippo Rubechini and Michele Marconcini and Andrea Arnone and Francesco Bertini},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleID=2554742},
doi = {10.1115/GT2016-57746},
isbn = {978-0-7918-4970-5},
year = {2016},
date = {2016-01-01},
booktitle = {ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition},
volume = {2B: Turbomachinery},
pages = {V02BT38A053; 12 pages},
address = {Seoul, South Korea, June 13–17, 2016},
abstract = {The rotational speed of low pressure turbines (LPT) for geared turbofan applications is significantly increased looking for potential benefit in performance, weight and overall dimensions. As a drawback, the high speed LPT are characterized by critical mechanical constraints due to the large centrifugal stresses in conjunction with the use of lightweight materials. 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. This two-part paper presents the redesign and the analysis of an optimized rotor blade starting from a baseline configuration, representative of a state-of-the-art LPT rotor. In the redesign activity high standard of performance were required in conjunction with tight mechanical and geometrical constraints. The design strategy was based on an effective multi-objective optimization strategy. The aerodynamic performance were evaluated by means of 3D steady multi-row viscous computations using a two-equation k-w turbulence model. At the same time, the mechanical integrity checks were mainly based on the evaluation of the maximum rotor tensile stress due to centrifugal forces. A simplified and very fast tool was developed in order to compute the centrifugal stress. Finally a response-surface approach based on neural-networks (ANNs) was adopted for the design space exploration. The design was validated by means of a comprehensive experimental campaign carried out in a low-speed turbine single-stage facility. A comparison between the numerical and experimental results are presented in terms of the main rotor performance for a fixed Reynolds number while varying the rotor incidence angle. Unsteady numerical analysis of both the baseline and the optimized blade were carried out by using a multi-equation, transition-sensitive, turbulence model and considering the boundary conditions measured on the test rig.},
note = {GT2016-57746},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The rotational speed of low pressure turbines (LPT) for geared turbofan applications is significantly increased looking for potential benefit in performance, weight and overall dimensions. As a drawback, the high speed LPT are characterized by critical mechanical constraints due to the large centrifugal stresses in conjunction with the use of lightweight materials. 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. This two-part paper presents the redesign and the analysis of an optimized rotor blade starting from a baseline configuration, representative of a state-of-the-art LPT rotor. In the redesign activity high standard of performance were required in conjunction with tight mechanical and geometrical constraints. The design strategy was based on an effective multi-objective optimization strategy. The aerodynamic performance were evaluated by means of 3D steady multi-row viscous computations using a two-equation k-w turbulence model. At the same time, the mechanical integrity checks were mainly based on the evaluation of the maximum rotor tensile stress due to centrifugal forces. A simplified and very fast tool was developed in order to compute the centrifugal stress. Finally a response-surface approach based on neural-networks (ANNs) was adopted for the design space exploration. The design was validated by means of a comprehensive experimental campaign carried out in a low-speed turbine single-stage facility. A comparison between the numerical and experimental results are presented in terms of the main rotor performance for a fixed Reynolds number while varying the rotor incidence angle. Unsteady numerical analysis of both the baseline and the optimized blade were carried out by using a multi-equation, transition-sensitive, turbulence model and considering the boundary conditions measured on the test rig.
Marconcini, Michele; Bianchini, Alessandro; Checcucci, Matteo; Ferrara, Giovanni; Arnone, Andrea; Ferrari, Lorenzo; Biliotti, Davide; Rubino, Dante Tommaso
ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition, vol. 2D: Turbomachinery, Seoul, South Korea, June 13–17, 2016, 2016, ISBN: 978-0-7918-4972-9, (GT2016-57604).
@conference{979,
title = {A 3D Time-Accurate CFD Simulation of the Flow Field Inside a Vaneless Diffuser During Rotating Stall Conditions},
author = {Michele Marconcini and Alessandro Bianchini and Matteo Checcucci and Giovanni Ferrara and Andrea Arnone and Lorenzo Ferrari and Davide Biliotti and Dante Tommaso Rubino},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleID=2554875},
doi = {10.1115/GT2016-57604},
isbn = {978-0-7918-4972-9},
year = {2016},
date = {2016-01-01},
booktitle = {ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition},
volume = {2D: Turbomachinery},
pages = {V02DT42A029; 11 pages},
address = {Seoul, South Korea, June 13–17, 2016},
abstract = {An accurate characterization of rotating stall in terms of inception modality, flow structures, and stabilizing force is one of the key goals for high-pressure centrifugal compressors. The unbalanced pressure field that is generated within the diffuser can be in fact connected to a non-negligible aerodynamic force and then to the onset of detrimental sub-synchronous vibrations which can prevent the machine from operating beyond this limit. An inner comprehension on how the induced flow pattern in these conditions affects the performance of the impeller and its mechanical stability can therefore lead to the development of a more effective regulation system able to mitigate the effects of the phenomenon and extend the left-side margin of the operating curve. In the present study, a 3D-unsteady CFD approach was applied to the simulation of a radial stage model including the impeller, the vaneless diffuser and the return channel. Simulations were carried out with the TRAF code of the University of Florence. The tested rotor was an industrial impeller operating at high peripheral Mach number, for which unique experimental pressure measurements, including the spatial reconstruction of the pressure field at the diffuser inlet, were available. The comparison between experiments and simulations showed a good matching and corroborated the CFD capabilities in correctly describing also some of the complex unsteady phenomena taking place in proximity of the left margin of the operating curve.},
note = {GT2016-57604},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
An accurate characterization of rotating stall in terms of inception modality, flow structures, and stabilizing force is one of the key goals for high-pressure centrifugal compressors. The unbalanced pressure field that is generated within the diffuser can be in fact connected to a non-negligible aerodynamic force and then to the onset of detrimental sub-synchronous vibrations which can prevent the machine from operating beyond this limit. An inner comprehension on how the induced flow pattern in these conditions affects the performance of the impeller and its mechanical stability can therefore lead to the development of a more effective regulation system able to mitigate the effects of the phenomenon and extend the left-side margin of the operating curve. In the present study, a 3D-unsteady CFD approach was applied to the simulation of a radial stage model including the impeller, the vaneless diffuser and the return channel. Simulations were carried out with the TRAF code of the University of Florence. The tested rotor was an industrial impeller operating at high peripheral Mach number, for which unique experimental pressure measurements, including the spatial reconstruction of the pressure field at the diffuser inlet, were available. The comparison between experiments and simulations showed a good matching and corroborated the CFD capabilities in correctly describing also some of the complex unsteady phenomena taking place in proximity of the left margin of the operating curve.
Marconcini, Michele; Bianchini, Alessandro; Checcucci, Matteo; Biliotti, Davide; Giachi, Marco; Rubino, Dante Tommaso; Arnone, Andrea; Ferrari, Lorenzo; Ferrara, Giovanni
Estimation of the Aerodynamic Force Induced by Vaneless Diffuser Rotating Stall in Centrifugal Compressor Stages Journal Article
In: Energy Procedia, vol. 101, pp. 734-741, 2016, ISSN: 1876-6102, (ATI 2016 – 71st Conference of the Italian Thermal Machines Engineering Association).
@article{985,
title = {Estimation of the Aerodynamic Force Induced by Vaneless Diffuser Rotating Stall in Centrifugal Compressor Stages},
author = {Michele Marconcini and Alessandro Bianchini and Matteo Checcucci and Davide Biliotti and Marco Giachi and Dante Tommaso Rubino and Andrea Arnone and Lorenzo Ferrari and Giovanni Ferrara},
url = {http://www.sciencedirect.com/science/article/pii/S1876610216313029},
doi = {http://dx.doi.org/10.1016/j.egypro.2016.11.093},
issn = {1876-6102},
year = {2016},
date = {2016-01-01},
journal = {Energy Procedia},
volume = {101},
pages = {734-741},
address = {Turin, Italy, 14-16 September 2016},
abstract = {Rotating stall in centrifugal compressors not only adversely affects the performance before surge, but also can generate high subsynchronous vibrations, marking the minimum flow limit of a machine. Recent works presented an experimental approach to estimate the stall force induced by the unbalanced pressure field in a vaneless diffuser from dynamic pressure measurements. In this study, the results of a 3D-unsteady simulation of a radial stage model were used to estimate the stall force and to compare it with the approximation obtained with an experimental-like approach. Results showed that: a) the experimental approach, using dynamic pressure sensors and an ensemble average approach for transposing data between time and space domains, is thought to give sufficiently accurate results; b) the momentum contribution gives negligible contributions to the intensity of the stall force.},
note = {ATI 2016 - 71st Conference of the Italian Thermal Machines Engineering Association},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Rotating stall in centrifugal compressors not only adversely affects the performance before surge, but also can generate high subsynchronous vibrations, marking the minimum flow limit of a machine. Recent works presented an experimental approach to estimate the stall force induced by the unbalanced pressure field in a vaneless diffuser from dynamic pressure measurements. In this study, the results of a 3D-unsteady simulation of a radial stage model were used to estimate the stall force and to compare it with the approximation obtained with an experimental-like approach. Results showed that: a) the experimental approach, using dynamic pressure sensors and an ensemble average approach for transposing data between time and space domains, is thought to give sufficiently accurate results; b) the momentum contribution gives negligible contributions to the intensity of the stall force.
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 Journal Article
In: Journal of Thermal Science, vol. 25, pp. 32-42, 2016, ISSN: 1003-2169.
@article{978,
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},
url = {http://link.springer.com/article/10.1007/s11630-016-0831-5},
doi = {dx.doi.org/10.1007/s11630-016-0831-5},
issn = {1003-2169},
year = {2016},
date = {2016-01-01},
journal = {Journal of Thermal Science},
volume = {25},
pages = {32-42},
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.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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.
2015
Bellucci, Juri; Rubechini, Filippo; Marconcini, Michele; Arnone, Andrea; Arcangeli, L; Maceli, Nicola; Dossena, Vincenzo
The Influence of Roughness on a High-Pressure Steam Turbine Stage: an Experimental and Numerical Study Journal Article
In: ASME Journal of Engineering for Gas Turbines and Power, vol. 137, no. 012602, pp. 1-9, 2015, ISSN: 0742-4795.
@article{943,
title = {The Influence of Roughness on a High-Pressure Steam Turbine Stage: an Experimental and Numerical Study},
author = {Juri Bellucci and Filippo Rubechini and Michele Marconcini and Andrea Arnone and L Arcangeli and Nicola Maceli and Vincenzo Dossena},
url = {http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=1896624},
doi = {dx.doi.org/10.1115/1.4028205},
issn = {0742-4795},
year = {2015},
date = {2015-08-01},
journal = {ASME Journal of Engineering for Gas Turbines and Power},
volume = {137},
number = {012602},
pages = {1-9},
abstract = {This work deals with the influence of roughness on high-pressure steam turbine stages. It is divided in three parts. In the first one, an experimental campaign on a linear cascade is described, in which blade losses are measured for different values of surface roughness and in a range of Reynolds numbers of practical interest. The second part is devoted to the basic aspects of the numerical approach, and consists of a detailed discussion of the roughness models used for computations. The fidelity of such models is then tested against measurements, thus allowing their fine-tuning and proving their reliability. Finally, comprehensive CFD analysis is carried out on a high-pressure stage, in order to investigate the influence of roughness on the losses over the entire stage operating envelope. Unsteady effects that may affect the influence of the roughness, such as the upcoming wakes on the rotor blade, are taken into account, and the impact of transition-related aspects on the losses is discussed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This work deals with the influence of roughness on high-pressure steam turbine stages. It is divided in three parts. In the first one, an experimental campaign on a linear cascade is described, in which blade losses are measured for different values of surface roughness and in a range of Reynolds numbers of practical interest. The second part is devoted to the basic aspects of the numerical approach, and consists of a detailed discussion of the roughness models used for computations. The fidelity of such models is then tested against measurements, thus allowing their fine-tuning and proving their reliability. Finally, comprehensive CFD analysis is carried out on a high-pressure stage, in order to investigate the influence of roughness on the losses over the entire stage operating envelope. Unsteady effects that may affect the influence of the roughness, such as the upcoming wakes on the rotor blade, are taken into account, and the impact of transition-related aspects on the losses is discussed.
Bellucci, Juri; Rubechini, Filippo; Arnone, Andrea
Some Experiences About the Impact of Unsteadiness in Turbine Flows Conference
ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, Montreal, Canada, 2015, ISBN: 978-079185663-5, (ASME paper GT2015-43122).
@conference{966,
title = {Some Experiences About the Impact of Unsteadiness in Turbine Flows},
author = {Juri Bellucci and Filippo Rubechini and Andrea Arnone},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2427871},
doi = {dx.doi.org/10.1115/GT2015-43122},
isbn = {978-079185663-5},
year = {2015},
date = {2015-06-01},
booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition},
address = {Montreal, Canada},
abstract = {This paper discusses the role of the unsteady interaction in turbine design. It focuses on aerodynamic performance, and its main motivation consists in trying to identify some design areas in which some further margins of improvement could be found, provided the designer chooses the proper computational framework. The underlying idea is that the approximations associated with the steady-state picture of a turbine stage might prevent from unlocking the full potential of the stage itself, especially when the design requirements imply a challenging aerodynamics. To this end, three common design topics are presented in which the step from the classical steady-state approach to the time-accurate one unveils relevant issues, which in turn have a relapse on aerodynamic performance: stator/rotor interaction in transonic stages, the choice of the axial gap between stator and rotor, and the choice of the blade count ratio. In all reported cases, significant departures are found between steady and time-averaged results, and the basic fluid mechanisms responsible for them are examined. In particular, an attempt is made to emphasize limitations deriving from of the steady-state picture of the turbine flow field, in order to warn the designer about the possible traps of the steady-state assumption.},
note = {ASME paper GT2015-43122},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
This paper discusses the role of the unsteady interaction in turbine design. It focuses on aerodynamic performance, and its main motivation consists in trying to identify some design areas in which some further margins of improvement could be found, provided the designer chooses the proper computational framework. The underlying idea is that the approximations associated with the steady-state picture of a turbine stage might prevent from unlocking the full potential of the stage itself, especially when the design requirements imply a challenging aerodynamics. To this end, three common design topics are presented in which the step from the classical steady-state approach to the time-accurate one unveils relevant issues, which in turn have a relapse on aerodynamic performance: stator/rotor interaction in transonic stages, the choice of the axial gap between stator and rotor, and the choice of the blade count ratio. In all reported cases, significant departures are found between steady and time-averaged results, and the basic fluid mechanisms responsible for them are examined. In particular, an attempt is made to emphasize limitations deriving from of the steady-state picture of the turbine flow field, in order to warn the designer about the possible traps of the steady-state assumption.