| 1. |
- Benini, Ernesto, et al.
(author)
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Centrifugal compressor of a 100 kW microturbine : Part 1 - Experimental and numerical investigations on overall performance
- 2003
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In: Proceedings of the ASME Turbo Expo 2003. - New York : American Society of Mechanical Engineers. - 079183686X ; , s. 691-698
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Conference paper (peer-reviewed)abstract
- This paper describes on/off design performance of a centrifugal compressor of a 100 kW turbogenerator gas turbine engine used for small scale power generation. The compressor stage is made up of a radial impeller and a two-stage diffuser (radial and deswirl). Pan 1 deals with the experimental and numerical tests on overall compressor and diffuser performance: An extensive test series with steady probe measurements at impeller exit and diffuser exit is performed at different operating points and rotational speeds. This makes it possible to characterize both overall compressor and diffuser. The numerical model is based on a mixing plane at impeller-diffuser interface and therefore neglects the effect of unsteadiness due to rotor-stator interaction. Then, in part 2 the true time-dependent interaction is investigated by means of a numerical model where a sliding mesh technique is adopted. The unsteady results are then processed and compared with the steady ones regarding the flow in the diffuser. Finally, in part 3 the geometry of the compressor diffuser is optimized using an evolutionary algorithm coupled with a CFD code in order to improve compressor performance.
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| 2. |
- Benini, Ernesto, et al.
(author)
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Experimental and numerical analyses to enhance the performance of a microturbine diffuser
- 2006
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In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 30:5, s. 427-440
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Journal article (peer-reviewed)abstract
- This paper describes design and off-design behavior of a centrifugal compressor of a 100 kW gas turbine used for small scale power generation and establishes the guidelines to improve diffuser performance. The first part of the paper deals with the experimental and numerical tests on the overall machine: An extensive series of tests at different operating points and rotational speeds is performed using steady probe measurements at impeller exit and diffuser exit; the numerical model features a mixing plane at impeller-diffuser interface and therefore neglects the effect of unsteadiness due to rotor-stator interaction. In the second part of the paper, the true time-dependent rotor-stator interaction is investigated by means of a numerical model where a sliding mesh technique is adopted instead. The unsteady results are then processed and compared with the computed steady flow in the diffuser. Finally, the geometry of the compressor diffuser is optimized using an evolutionary algorithm coupled with a CFD code.
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| 3. |
- Dal Cin, Enrico, et al.
(author)
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A novel extension of the SYNTHSEP methodology for the optimal synthesis and design of supercritical CO2 cycles in waste heat recovery applications
- 2023
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In: Energy Conversion and Management. - : Elsevier Ltd. - 0196-8904 .- 1879-2227. ; 276
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Journal article (peer-reviewed)abstract
- The reduction of anthropogenic emissions of greenhouse gases requires decreasing the overall consumption of primary energy. Thus, waste heat recovery at medium-to-high temperature is an opportunity for generating electricity while reducing the need for primary resources. Recently, supercritical carbon dioxide power cycles (S-CO2) are emerging as a promising solution. However, a method lacks to simultaneously optimize their layout and design parameters, without relying on superstructures defined a priori. To this end, this paper suggests a novel extension of the superstructure free SYNTHSEP methodology, a bottom-up approach for the optimal synthesis and design of thermodynamic cycles, to handle also super- and transcritical cycles. An Evolutionary Algorithm combining elementary cycles makes it possible to define optimal S-CO2 configurations without limiting the search space of the optimization problem. The objective consists in finding the S-CO2 topology and design parameters that maximize the mechanical power extractable from waste heat streams in the temperature range from 200 to 700 °C, typical of the industrial sector. Results demonstrate the capability of the method to find optimal cycle layouts for any given waste heat temperature, and to achieve, at the same conditions, cycle efficiencies up to 5 % higher in relative terms than the best ones in the literature.
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| 4. |
- Gobbato, Paolo, et al.
(author)
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Acoustic analysis of a diffusion flame gas turbine combustor by means of non-reactive calculations
- 2014
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In: Proceedings of the 27th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2014. - Åbo : Åbo Akademi University Press. - 9781634391344
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Conference paper (peer-reviewed)abstract
- Combustion instabilities are unsteady phenomena that can affect premixed and diffusion flame combustors. They are spontaneously excited by a feedback loop between an oscillatory heat release and one or more natural acoustic modes of the combustor. When large instabilities occur, the associated oscillations of pressure and heat release may lead to premature failures due to vibrations and thermal loads at combustor walls. The prediction of natural acoustic modes is often used to identify the modes coupled to the unsteady heat release and to design damping systems. Thanks to the increase in computing capabilities, several modelling tools have been developed to obtain detailed information regarding the spatial shape of the acoustic modes. This paper presents the acoustic analysis of a non-premixed gas turbine combustor. The analysis is based on non-reactive computational fluid dynamics simulations performed on a coarse grid model to calculate the frequency and shape of natural modes. The simulations require very limited computational effort because simple numerical models are adopted and no combustion and heat transfer models need to be activated. The influence of temperature and gas composition on acoustic mode frequencies is considered through a simple post-processing correction. Thus, frequencies measured under limit cycle conditions can be directly compared to calculated values to identify which natural mode is excited by the unsteady heat release. The numerical results are validated against full-scale experimental measurements.
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| 5. |
- Gobbato, Paolo, et al.
(author)
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Analysis of the natural acoustic modes of a gas turbine combustor using isothermal CFD simulations
- 2017
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In: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 126, s. 489-499
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Journal article (peer-reviewed)abstract
- Thermoacoustic instabilities usually result from the coupling between the oscillatory heat release and one or more natural acoustic modes of the combustion system. When the shifting of system frequencies caused by the unsteady heat release is limited, the calculation of natural modes allows to identify which of them are excited by the flame once changes in flow temperature and composition due to combustion are considered. In this paper, isothermal computational fluid dynamics simulations are performed to predict the natural modes of a heavy-duty gas turbine combustor in reactive conditions. Combustion and heat transfer are neglected in the numerical analysis to simplify the model and limit the computational effort. The natural frequencies resulting from isothermal simulations are then corrected using a rather basic post-processing approach to account for temperature and gas composition changes due to combustion process. Frequency and amplitude of the calculated modes are finally compared to experimental measurements to evaluate the ability of the acoustic analysis to capture frequency and spatial shape of the combustor natural modes excited by the flame
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| 6. |
- Gobbato, Paolo, et al.
(author)
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Calculation of the flow field and NOx emissions of a gas turbine combustor by a coarse computational fluid dynamics model
- 2012
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 45:1, s. 445-455
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Journal article (peer-reviewed)abstract
- Gas turbine performance is strongly dependent on the flow field inside the combustor. In the primary zone, the recirculation of hot products stabilises the flame and completes the fuel oxidation. In the dilution zone, the mixing process allows to obtain the suitable temperature profile at turbine inlet. This paper presents an experimental and computational analysis of both the isothermal and the reactive flow field inside a gas turbine combustor designed to be fed with natural gas and hydrogen. The study aims at evaluating the capability of a coarse grid CFD model, already validated in previous reactive calculations, in predicting the flow field and NOx emissions. An experimental campaign was performed on an isothermal flow test rig to investigate the combustion air splitting and the penetration of both primary and dilution air jets. These experimental data are used to validate the isothermal computations. The impact of combustion on the calculated flow field and on air splitting is investigated as well. Finally, NOx emission trend estimated by a post-processing technique is presented. The numerical NOx concentrations at the combustor discharge are compared with experimental measurements acquired during operation with different fuel burnt (natural gas or hydrogen) and different amount of steam injected.
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| 7. |
- Gobbato, Paolo, et al.
(author)
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Numerical simulation of a hydrogen fuelled gas turbine combustor
- 2011
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In: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 36:13, s. 7993-8002
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Journal article (peer-reviewed)abstract
- The interest for hydrogen-fuelled combustors is recently growing thanks to the development of gas turbines fed by high content hydrogen syngas. The diffusion flame combustion is a well-known and consolidated technology in the field of industrial gas turbine applications. However, few CFD analyses on commercial medium size heavy duty gas turbine fuelled with pure hydrogen are available in the literature. This paper presents a CFD simulation of the air-hydrogen reacting flow inside a diffusion flame combustor of a single shaft gas turbine. The 3D geometrical model extends from the compressor discharge to the gas turbine inlet (both liner and air plenum are included). A coarse grid and a very simplified reaction scheme are adopted to evaluate the capability of a rather basic model to predict the temperature field inside the combustor. The interest is focused on the liner wall temperatures and the turbine inlet temperature profile since they could affect the reliability of components designed for natural gas operation. Data of a full-scale experimental test are employed to validate the numerical results. The calculated thermal field is useful to explain the non-uniform distribution of the temperature measured at the turbine inlet
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| 8. |
- Lazzaretto, Andrea, et al.
(author)
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A critical review of the thermoeconomic diagnosis methodologies for the location of causes of malfunctions in energy Systems
- 2006
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In: Journal of energy resources technology. - : ASME International. - 0195-0738 .- 1528-8994. ; 128:4, s. 335-341
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Journal article (peer-reviewed)abstract
- Thermoeconomic diagnosis procedures in the literature rely on the assumption that specific consumptions of resources in the components are the key to interpret the effects of malfunctions and then to trace a path towards the sources of anomalies. The main obstacle to a successful application of these approaches is represented by the actual interactions existing among components which cause a propagation of the alteration of component specific consumptions and therefore mask those effects that would allow a direct identification of the origin of malfunction. This paper presents an extensive discussion of potentialities and limits of diagnosis procedures proposed in the literature in distinguishing the effects induced by component interactions from those that are intrinsically generated by the anomaly, which is considered here as the main task to locate effectively causes of malfunctions in energy systems
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| 9. |
- Lazzaretto, Andrea, et al.
(author)
-
A critical review of the thermoeconomic diagnosis methodologies for the location of causes of malfunctions in energy systems
- 2003
-
In: Proceedings of the ASME Advanced Energy Systems Division - 2003. - New York : American Society of Mechanical Engineers. - 0791837084 ; , s. 345-354
-
Conference paper (peer-reviewed)abstract
- Thermoeconomic diagnosis procedures in the literature rely on the assumption that specific consumption of resources in the components are the key to interpret the effects of malfunctions and then to trace a path towards the sources of anomalies. The main obstacle to a successful application of these approaches is represented by the actual interactions existing among components which cause a propagation of the alteration of component specific consumptions and therefore mask those effects that would allow a direct identification of the origin of malfunction. This paper presents an extensive discussion of potentialities and limits of diagnosis procedures proposed in the literature in distinguishing the effects induced by component interactions from those that are intrinsically generated by the anomaly, which is considered here as the main task to locate effectively causes of malfunctions in energy systems.
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| 10. |
- Lazzaretto, Andrea, et al.
(author)
-
A method to separate the problem of heat transfer interactions in the synthesis of thermal systems
- 2008
-
In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 33:2, s. 163-170
-
Journal article (peer-reviewed)abstract
- Most of the efforts to improve energy system configurations are directed towards the recovery of internal heat, which reduces the contribution of the external hot source and enhance system efficiency accordingly. This problem is strictly related to the synthesis of different components into system topology, i.e. with the definition of the optimal system configuration according to specified objectives. A new method for the optimization of the heat transfer interactions within energy systems is presented here, based on the idea of cutting thermal links between the "basic" components of the system. The boundary temperatures of hot and cold flows that are generated as a consequence of these cuts are evaluated in an optimization procedure that involves the design parameters of the system as well. The high potential of the proposed method consists in separating the problem of defining the system configuration into two separate sub-problems, the first regarding the definition of the "basic" topology of the system (related to all components different from the heat exchangers), the second the optimal heat transfer interactions within the system. This feature makes complex systems today only marginally "optimizable", amenable to complete optimization. The method is applied to a humid air turbine (HAT) cycle plant, which represents a good test to prove its reliability and generality, due to the internal recirculation of mass and energy flows
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