Publications

@conference{1000,

title = {Secondary Flows in LPT Cascades: Numerical and Experimental Investigation of the Impact of the Inner Part of the Boundary Layer},

author = {Matteo Giovannini and Filippo Rubechini and Michele Marconcini and Daniele Simoni and Vianney Yepmo and Francesco Bertini},

url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2700647},

doi = {10.1115/GT2018-76737},

isbn = {978-079185100-5},

year  = {2018},

date = {2018-01-01},

booktitle = {ASME Turbo Expo 2018: Turbine Technical Conference and Exposition},

volume = {Volume 2B: Turbomachinery},

pages = {pp. V02BT41A027; 13 pages},

publisher = {ASME},

address = {Oslo, Norway},

organization = {ASME},

abstract = {Due to the low level of profile losses already reached in the design of modern low-pressure turbines for turbofan applications, a renewed interest is devoted to the other sources of loss, and namely to the secondary losses. At the same time, the importance of secondary losses has been reinforced by the current design trend towards high-lift profiles. A great attention, therefore, is dedicated to reliable and effective prediction methods as well as on the correct understanding of the mechanisms that drive the secondary flows. In this context, a systematic numerical and experimental campaign was carried out focusing on the impact of different inlet boundary layer (BL) profiles and considering a state-of-the-art low-pressure turbine cascade. Starting from a computational environment representative of a design standard, detailed RANS analyses were carried out in order to establish dependable guidelines for the computational setup. As a major result, such analyses also underlined the importance of the shape of the inlet BL very close to the endwall, hence suggesting tight requirements for the characterization of the experimental environment. The impact of the inlet BL profile on the secondary flow development was experimentally investigated by varying the profile shape very close to the endwall as well as on the external part with respect to a reference condition. The effects on the cascade performance were evaluated focusing on the intensity of the over- under-turning as well as on the associated losses (intensity and penetration) by measuring the span-wise distributions of flow angle and total pressure losses at the cascade exit plane. For all the inlet conditions, comparisons between CFD and experimental results are discussed. Besides providing guidelines for a proper numerical and experimental setup, the present paper underlines the importance of a detailed characterization of the inlet BL for an accurate assessment of the secondary flows. From a broader perspective, when aiming at reproducing (numerically or experimentally) a real engine environment, this suggests that an in-depth matching of the inlet profiles is crucial for reliable estimates of the secondary losses.},

note = {paper GT2018-76737},

keywords = {},

pubstate = {published},

tppubtype = {conference}

}

@conference{1016,

title = {Flutter-free design of aeroderivative gas turbine nozzles with simplified aero-mechanical models},

author = {Lorenzo Peruzzi and Juri Bellucci and Lorenzo Pinelli and Michele Marconcini and G Gatta and S Colatoni and S Abhimanyu and G Natale},

year  = {2018},

date = {2018-01-01},

booktitle = {15th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT)},

address = {September 23-27, Oxford, UK},

abstract = {This work presents a simplified procedure to design a flutter free 

airfoil geometry for aeroderivative gas turbine stator blade rows. The 

common workflow for a fully 3D flutter numerical assessment with an 

uncoupled method firstly involves a FE modal analysis to obtain the 

airfoil mode shapes which will be used for unsteady aeroelastic 

computations with moving airfoil. Nozzle geometries are usually very 

complex: airfoils in a packet configuration and different mechanical 

features needed to attach the packet itself to the turbine casing make 

the structural meshing a not trivial task. 

 The aim of this paper is to demonstrate how, in the early 

aero-mechanical design phases simplified models including only the 

airfoil geometry and the endwalls chunks can be efficiently used to 

design flutter-free components. First of all, detailed comparisons 

between modal results from full and simplified mechanical models have 

been performed. Then, flutter computations have been carried out using 

modal results both from the full mechanical model (the sector or packet 

model) and two different simplified models (single airfoil models). 

 Finally, flutter results in terms of logarithmic decrement curves will 

be presented, showing the capability of this approach to guarantee 

flutter free geometries even from the early design stages. This aspect 

is essential to avoid bladerow redesign due to flutter issues which may 

occur during the final design of the airfoil.},

note = {paper ISUAAAT15-037},

keywords = {},

pubstate = {published},

tppubtype = {conference}

}

@conference{999,

title = {A Pre-Design Model to Estimate the Effect of Variable Inlet Guide Vanes on the Performance Map of a Centrifugal Compressor for Automotive Applications},

author = {Michele Becciani and Alessandro Bianchini and Matteo Checcucci and Lorenzo Ferrari and Michele De Luca and Luca Marmorini and Andrea Arnone and Giovanni Ferrara},

url = {http://papers.sae.org/2017-24-0020/},

doi = {10.4271/2017-24-0020},

year  = {2017},

date = {2017-09-01},

booktitle = {13th International Conference on Engines & Vehicles},

address = {September 10-14, 2017, Capri, Italy},

abstract = {The onset of aerodynamic instabilities in proximity of the left margin of the operating curve represents one of the main limitations for centrifugal compressors in turbocharging applications. An anticipated stall/surge onset is indeed particularly detrimental at those high boost pressures that are typical of engine downsizing applications using a turbocharger. Several stabilization techniques have been investigated so far to increase the rangeability of the compressor without excessively reducing the efficiency. One of the most exploited solutions is represented by the use of upstream axial variable inlet guide vanes (VIGV) to impart a pre-whirl angle to the inlet flow. In the pre-design phase of a new stage or when selecting, for example, an existing unit from an industrial catalogue, it is however not easy to get a prompt estimation of the attended modifications induced by the VIGV on the performance map of the compressor.A simplified model to this end is presented in the study. Figuring out a typical industrial pre-design phase, the model assumes the availability of the original performance data of the compressor without pre-whirl and only very few geometrical parameters. Based on fluid dynamic considerations and some additional models and correlations, a procedure is defined to correct the attended stage pressure ratio and efficiency as a function of the pre-whirl angle imposed by the VIGV. The model has been successfully validated using an experimental literature case study and is thought to represent a new useful preliminary tool for turbocharger designers.},

note = {SAE Technical Paper 2017-24-0020},

keywords = {},

pubstate = {published},

tppubtype = {conference}

}

@conference{990,

title = {Facing the Challenges in CFD Modelling of Multistage Axial Compressors},

author = {Lorenzo Cozzi and Filippo Rubechini and Michele Marconcini and Andrea Arnone and Pio Astrua and Andrea Schneider and Andrea Silingardi},

url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleID=2649617},

doi = {10.1115/GT2017-63240},

isbn = {978-0-7918-5079-4},

year  = {2017},

date = {2017-01-01},

booktitle = {ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition},

volume = {2B: Turbomachinery},

pages = {pp. V02BT41A007; 11 pages},

publisher = {ASME},

address = {Charlotte, NC, USA},

organization = {ASME},

abstract = {Multistage axial compressors have always been a great challenge for designers since the flow within these kind of machines, subjected to severe diffusion, is usually characterized by complex and widely developed 3D structures, especially next to the endwalls. The development of reliable numerical tools capable of providing an accurate prediction of the overall machine performance is one of the main research focus areas in the multistage axial compressor field. This paper is intended to present the strategy used to run numerical simulations on compressors achieved by the collaboration between the University of Florence and Ansaldo Energia. All peculiar aspects of the numerical setup are introduced, such as rotor/stator tip clearance modelling, simplified shroud leakage model, gas and turbulence models. Special attention is payed to the mixing planes adopted for steady-state computations because this is a crucial aspect of modern heavy-duty transonic multi stage axial compressors. In fact, these machines are characterized by small inter-row axial gaps and transonic flow in front stages, which both may affect non-reflectiveness and fluxes conservation across mixing planes. Moreover, the high stage count may lead to conservation issues of the main flow properties form inlet to outlet boundaries. Finally, the likely occurrence of part span flow reversal in the endwall regions affects the robustness of non-reflecting mixing plane models. The numerical setup has been validated on an existing machine produced and experimentally tested by Ansaldo Energia. In order to evaluate the impact on performance prediction of the mixing planes introduced in the steady-state computation, unsteady simulations of the whole compressor have been performed at different operating conditions. These calculations have been carried out both at the compressor design point and close to the surge-line to evaluate the effect of rotor/stator interaction along the compressor working line.},

note = {ASME paper GT2017-63240},

keywords = {},

pubstate = {published},

tppubtype = {conference}

}

@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}

}