- Trieste, Friuli Venezia Giulia, Italy
In questo lavoro vengono vengono presentati i primi risultati ottenuti per il calcolo numerico di problemi di convezione naturale laminare in cavit\ue0, caratterizzati da valori del numero di Rayleigh fra 10^5 e 10^8, e valori del numero... more
In questo lavoro vengono vengono presentati i primi risultati ottenuti per il calcolo numerico di problemi di convezione naturale laminare in cavit\ue0, caratterizzati da valori del numero di Rayleigh fra 10^5 e 10^8, e valori del numero di Prandtl pari a 0.71 (aria) e 7.1 (acqua). Tali risultati, ottenuti anche su griglie 256^2, sono stati conseguiti in modo economico facendo ricorso a tre diversi algoritmi iterativi di tipo accoppiato, accelerati da una procedura multigriglia di tipo conservativo. Le prestazioni della metodologia di calcolo, verificate anche nel caso isotermo della cavit\ue0 guidata per diversi valori del numero di Reynolds, dimostrano che la modalit\ue0 di trattamento numerico dell'accoppiamento temperatura-velocit\ue0, \ue8 di importanza fondamentale per il conseguimento economico di soluzioni accurate in problemi di convezione naturale e mista, altrimenti molto costose e pi\uf9 difficili impiegando le tradizionali procedure segregate
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Proposition de modeles mathematiques, reposant l'un sur la methode par element fini et l'autre sur la methode par volume fini, pour analyser la convection naturelle en regime turbulent dans une cavite rectangulaire, qui peut etre... more
Proposition de modeles mathematiques, reposant l'un sur la methode par element fini et l'autre sur la methode par volume fini, pour analyser la convection naturelle en regime turbulent dans une cavite rectangulaire, qui peut etre appliquee aux collecteurs solaires, four, regulation thermique de composants electroniques, ventilation d'un bâtiment, etc...
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Research Interests: Engineering, Mechanical Engineering, Aerospace Engineering, Materials Science, Computational Fluid Dynamics, and 11 moreHeat Transfer, Metal Foams, Permeability, Laminar Flow, Microtomography, Thermal Conductivity, Aluminium, Metal Foam, Nuclear Energy and Chemical Engineering, Reynolds Number, and Effective thermal conductivity
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In contrast to traditional mesh-based methods for the numerical solution of boundary value problems, e.g., Finite Element (FEM) and Finite Volume (FVM), in the recent period many meshfree approaches have been proposed in order to avoid... more
In contrast to traditional mesh-based methods for the numerical solution of boundary value problems, e.g., Finite Element (FEM) and Finite Volume (FVM), in the recent period many meshfree approaches have been proposed in order to avoid those typical issues due to the mesh. For example, the quality of the mesh greatly affects the reliability of the final solution in the case of CFD problems and the human intervention of a professional is often still needed when dealing with complex-shaped domains. This in turn increases both cost and time required for the reliable simulation of problems of engineering relevance. Meshless methods, on the other side, usually rely on a simpler distribution of nodes and do not require the storage of connectivity information. Among others, one of the most promising meshless methods in terms of accuracy and flexibility is the one based on the Radial Basis Function – Finite Difference (RBF-FD) scheme. RBF-FD methods, however, are usually affected by severe ill conditioning issues when Neumann boundary conditions are employed. This fact is the main responsible for the appearance of large discretization errors near the boundary and for the lack of stability of traditional time integration schemes. In order to address this issue, some new algorithms for the robust treatment of boundary conditions have been developed and successfully employed to solve fluid flow problems with heat transfer. Furthermore, it is well acknowledged that the efficient resolution of boundary layers arising in this class of problems requires an adequate spatial discretization in the neighbourhood of the boundary, i.e., increased node/mesh density along the direction of large gradients only. This result is achieved by employing anisotropic node distributions, which is a novelty in the context of the RBF-FD method to the best of the authors’ knowledge. The method described above is successfully employed for the accurate solution of a representative 3D heat transfer problem with incompressible fluid flow.
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Research Interests: Mechanical Engineering, Aerospace Engineering, Materials Science, Mechanics, Turbulence, and 12 moreHeat Transfer, Direct Numerical Simulation, Drag Reduction, Drag, Turbulent Flow, Laminar Flow, Heat Flux, Heat transfer enhancement, Interdisciplinary Engineering, Prandtl Number, Boundary Condition, and Reynolds Number
In this paper, natural convection is studied in a 2D-cavity with two vertical isothermal walls, kept at different temperatures, and two adiabatic walls which are either straight (rectangular cavity) or elliptic (modified rectangular... more
In this paper, natural convection is studied in a 2D-cavity with two vertical isothermal walls, kept at different temperatures, and two adiabatic walls which are either straight (rectangular cavity) or elliptic (modified rectangular cavity). The local mass, momentum and energy balance equations are written in a dimensionless form and solved numerically, by means of two different software packages based on Galerkin finite element methods. With reference to a Prandtl number of 0.71, two rectangular cavities are studied: a square one and a cavity with height double than width. Then, for each value of the ratio between height and width, two cavities with elliptic boundaries are investigated. The numerical solution shows that the elliptic boundaries enhance the mean Nusselt number and the dimensionless mean kinetic energy of the fluid
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Nowadays, the need for developing more effective heat exchange technologies and innovative materials, capable of increasing performances while keeping power consumption, size and cost at reasonable levels, is well recognized. Under this... more
Nowadays, the need for developing more effective heat exchange technologies and innovative materials, capable of increasing performances while keeping power consumption, size and cost at reasonable levels, is well recognized. Under this perspective, metal foams have a great potential for enhancing the thermal efficiency of heat transfer devices, while allowing the use of smaller and lighter equipments. However, for practical applications, it is necessary to compromise between the augmented heat transfer rate and the increased pressure drop induced by the tortuous flow passages. For design purposes, the estimation of the flow permeability and the thermal conductivity of the foam is fundamental, but far from simple. From this perspective, besides classical transport models and correlations, computational fluid dynamics (CFD) at the pore scale, although challenging, are becoming a promising approach, especially if coupled with a realistic description of the foam structure. For precisely recovering the microstructure of the foams, a 3D X-ray computed microtomography (-CT) can be adopted. In this work, the results of -CT-based CFD simulations performed on different open-cell aluminum foams samples will be discussed. The results demonstrate that open-cell aluminum foams are effective means for enhancing heat transfer
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Cavitating flows which can occur in a variety of practical cases, can be modelled with a wide range of methods. One strategy consists of using the RANS (Reynolds Averaged Navier Stokes) equations and an additional transport equation for... more
Cavitating flows which can occur in a variety of practical cases, can be modelled with a wide range of methods. One strategy consists of using the RANS (Reynolds Averaged Navier Stokes) equations and an additional transport equation for the liquid volume fraction, where mass transfer rate due to cavitation is modelled by a mass transfer model. Several mass transfer models are available in literature, but at least, the most popular employ some empirical coefficients to guide the condensation and evaporation processes. Moreover it seems that, to achieve accurate results, the empirical values of the models have to be properly tuned with respect to the solver and to the different cavitating regimes. For these reasons in this work we present a preliminary optimization strategy to properly tune and validate different mass transfer models. The optimization strategy is applied to the three popular mass transfer models, and the preliminary results for the cavitating flow around the Naca66(mod) hydrofoil are presented. The overall results suggest that the optimization strategy is stable, accurate and could be applied to additional mass transfer models and other cavitating flow phenomena
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The paper presents a selection of CFD investigations on ship and propeller hydrodynamics performed in the frame of an extensive benchmarking presently undertaken within the undergoing Project OpenSHIP - Highly reliable CFD simulations for... more
The paper presents a selection of CFD investigations on ship and propeller hydrodynamics performed in the frame of an extensive benchmarking presently undertaken within the undergoing Project OpenSHIP - Highly reliable CFD simulations for the prediction of the hydrodynamic performance of the hull-propeller system with OpenSource software - co-financed by the ERDF - European Regional Development Fund - Friuli Venezia Giulia Region Operational Programme 2007 - 2013, in the Call for industrial research projects in the field of shipbuilding industry and pleasure yachts. The simulations are conducted with the software OpenFOAM®. The wavy viscous flow induced by a foil at constant speeds underneath the free surface with an angle of attack of 5 degrees is presented first. The numerical results from VOF-RANSE simulations are systematically compared with experimental data from the literature in terms of free surface profile, forces and velocity profiles. This test case on a relatively simple geometric shape has been selected for the highly conservative nature of the generated 2D wave pattern, allowing a detailed analysis of the coupling between the flow solver and the free surface treatment in the perspective of its application to the more complex ship-shapes. The double model test case on the KCS Kriso hull is then presented with comparisons between the numerical results obtained and the experimental data available from the Gotheborg workshop 2010 on the wake at the propeller disk. The investigation has been mainly focused on the grid generation by means of snappyHexMesh. Finally the numerical predictions of the flow around the model scale propellers E779A and PPTC are presented. The comparison between simulations and experimental data in steady state regime and the preliminary results from unsteady simulations are shown.
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Turbulence in high Rayleigh number two dimensional confined free convection is modeled by two k-e formulations. Results are presented for a square cavity with Prandtl number of 0.71 and Rayleigh number ranging from 10 E10 to 10 E12. Also,... more
Turbulence in high Rayleigh number two dimensional confined free convection is modeled by two k-e formulations. Results are presented for a square cavity with Prandtl number of 0.71 and Rayleigh number ranging from 10 E10 to 10 E12. Also, numerical results and experimental measurements are compared for a 10:1 height-to-width aspect ratio cavity filled with water, and Rayleigh number of 8x10 E10. From the comparisons performed it is apparent that k-e modeling in free convection, although yelding acceptable predictions for several qualtities, tends to overestimate the heat-transfer rate
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INT. J. HEAT AND TECHNOLOG
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A two-dimensional direct numerical simulation of the natural convection flow of air (Pr = 0.71) in a differentially heated cavity is performed for a Rayleigh number oof 2x10^9. The simulation is initiated from isothermal and quiescent... more
A two-dimensional direct numerical simulation of the natural convection flow of air (Pr = 0.71) in a differentially heated cavity is performed for a Rayleigh number oof 2x10^9. The simulation is initiated from isothermal and quiescent conditions, and is allowed to proceed to a statistical steady state. The numerical algorithm integrates the time-dependent Navier-Stokes equations, in primitive form, with an implicit, second order accurate finite volume scheme. Preliminary results, obtained by post-processing the data collected during the simulation, are reported, with emphasis on the transient evolution of the temperature field. Selected frames from a video, generated from the computed data, help to clarify the evolution to chaotic motion, via the sequence of initial instability, proceeding through transition, and eventually reaching statistically steady state
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In questo lavoro, viene presentata e discussa la simulazione numerica della ventilazione e della qualit\ue0 dell\u2019aria dell\u2019inquinamento industriali in ambiente confinato. Lo studio, realizzato con un pacchetto commerciale agli... more
In questo lavoro, viene presentata e discussa la simulazione numerica della ventilazione e della qualit\ue0 dell\u2019aria dell\u2019inquinamento industriali in ambiente confinato. Lo studio, realizzato con un pacchetto commerciale agli elementi finiti basato sulla fluidodinamica computazionale, \ue8 motivato dalla particolare attenzione posta alla salute e al rischio sul posto di lavoro e alle emissioni inquinanti prodotte nelle aree industriali di lavoro, e dalle aspettative verso le capacit\ue0 predittive di un codice di calcolo commerciale nell\u2019analisi e nell\u2019efficienza dei sistemi di ventilazione industriale. A seguito della validazione della procedura numerica, \ue8 stato realizzato un modello fisico e effettuare delle misure sperimentali. Il modello \ue8 in scala, rappresentante un edificio industriale con una sorgente di calore al centro e tutto attorno guidata da una circolazione di aria naturale, introdotta da effetti di galleggiamento. E\u2019 stato realizzato un modello numerico bidimensionale della circolazione naturale d\u2019aria all\u2019interno dell\u2019edificio i cui risultati numerici concordano con le misure sperimentali. Inoltre, sono riportati i risultati preliminari per una sistema tridimensionale relativi al getto termoconvettivo di un forno elettrico ad arco nella fase di scoperchiamento dello stesso
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Metal foams have a great potential for enhancing the thermal performances of heat transfer devices, while allowing the use of smaller and lighter equipments. From a practical standpoint, it is necessary to compromise between the improved... more
Metal foams have a great potential for enhancing the thermal performances of heat transfer devices, while allowing the use of smaller and lighter equipments. From a practical standpoint, it is necessary to compromise between the improved heat transfer rate and the higher pressure drop induced by the tortuous flow passages. In order to investigate the structure and properties of metal foams, and to provide adequate information for design purposes, the prediction of the permeability and thermal conductivity as a function of the structural characteristics would be desirable. From this perspective, computational fluid dynamics (CFD) computations at the pore scale are becoming a challenging approach in addition to classical transport models. To investigate the microstructure of metal foams, a three-dimensional approach by using X-ray computed microtomography (\u3bc-CT) can be adopted. \u3bc-CT is a nondestructive characterization technique representing a powerful investigation tool in many different applications. It consists in recording a number of projections of the sample at different angles, and reconstructing a 3D image with the help of a suitable algorithm. The reconstructed 3D dataset can be employed, after adequate geometric manipulation, to perform a CFD simulation on a realistic medium. In this work, a review of the recent experimental and numerical advances in the characterization of metal foams transport properties will be illustrated. Moreover, we will present the results of a high resolution 3D \u3bc-CT imaging of three Aluminum foam samples, with different pore per inch values, performed at the TomoLab station, located at the Elettra Synchrotron Radiation Facility in Trieste
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Free convection combined with radiation and wall conduction is analysed for a two-dimensional square cavity with differentially heated vertical walls. Radiation is solved by incorporating the weight-sum-of-gray-gases (WSGG) model into a... more
Free convection combined with radiation and wall conduction is analysed for a two-dimensional square cavity with differentially heated vertical walls. Radiation is solved by incorporating the weight-sum-of-gray-gases (WSGG) model into a modified form of the Spherical Harmonic (P_N) Differential Approximation Method-P1. The governing equations with Boussinesq approximation are written in primitive variables, and transposed from the physical to the mathematical space by the BFC (Boundary-Fitted Coordinate) technique. Predictions are obtained for Rayleigh numbers in the range of 10^3 to 10^6. Results are presented for pure free convection, free convection and wall conduction, and free convection and radiation. Comparison with data available in the literature indicate that the prediction tool has good accuracy and reliability
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Enrico Nobile Sezione di Fisica Tecnica Dip. di Ingegneria Navale del Mare e per l'Ambiente University of Trieste, Trieste, 34127 ITALY Tel: +39 040-558-3507, Fax: +39 040 572-033 Email: nobile@units.it, WWW:... more
Enrico Nobile Sezione di Fisica Tecnica Dip. di Ingegneria Navale del Mare e per l'Ambiente University of Trieste, Trieste, 34127 ITALY Tel: +39 040-558-3507, Fax: +39 040 572-033 Email: nobile@units.it, WWW: http://www-dinma.univ.trieste.it/nirftc/
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A highly parallelised computer algorithm is presented to solve large large algebraic equation systems by discretisation of Navier-Stokes equations, based on Fortran structured multiprogramming
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Conjugate heat transfer is considered for a two dimensional developing laminar flow over heat generating blocks protruding in a parallel plate channel. The blocks simulate IC components on a circuit board
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An automatic methodology for the design process of a small gas turbine recuperator is presented. The different software tools are selected in order to be managed by means of a design-optimization platform, according to the concept of... more
An automatic methodology for the design process of a small gas turbine recuperator is presented. The different software tools are selected in order to be managed by means of a design-optimization platform, according to the concept of Multi Disciplinary Optimization (MDO). The methodology has been developed integrating a geometrical parametric model of the heat transfer surfaces, built inside an industrial CAD, a three dimensional meshing tool, a CFD solver. Final objectives of the research will be an optimization process designed to maximize the heat exchange rate and to minimize fluid dynamics losses. The paper deals with the parameterization technique and the numerical model, two methods for dealing with thermal boundary conditions in periodic domains are presented. The classical uniform temperature boundary conditions for periodic flows has been implemented in a commercial code. A new method that avoids the imposition of unrealistic boundary conditions on the interface wall of a counter current heat exchanger is presented
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La convezione naturale in una cavit`a quadrata, a numero di Rayleigh 1.5 7109 e numero di Prandtl 0.71, `e stata analizzata tramite simulazione numerica diretta. Le pareti verticali sono mantenute a temperature diverse e costanti, mentre... more
La convezione naturale in una cavit`a quadrata, a numero di Rayleigh 1.5 7109 e numero di Prandtl 0.71, `e stata analizzata tramite simulazione numerica diretta. Le pareti verticali sono mantenute a temperature diverse e costanti, mentre le pareti orizzontali sono state considerate perfettamente adiabatiche, caso A, ovvero perfettamente conduttive, caso B. Sono state effettuate simulazioni bi- e tridimensionali, al fine di evidenziare gli effetti di tridimensionalit`a del flusso in esame. `E stato rilevato che , a causa della stratificazione instabile che si genera in prossimit`a delle pareti orizzontali perfettamente conduttive, caso B, l\u2019intensit`a della turbolenza `e molto superiore rispetto al caso A. Questa osservazione giustifica la sostanziale tridimensionalit`a della turbolenza nel caso B. La metodologia di calcolo utilizza un algoritmo ai volumi finiti del secondo ordine. A causa della presenza di strati limite di spessore molto ridotto, adiacenti alle pareti verticali, `e stato necessario stabilizzare i termini advettivi nelle equazioni di conservazione tramite la procedura QUIC
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This paper presents a selection of CFD investigations on ship and propeller hydrodynamics performed in the frame of an extensive benchmarking activity, presently undertaken in the frame of the OpenSHIP Project - Highly reliable CFD... more
This paper presents a selection of CFD investigations on ship and propeller hydrodynamics performed in the frame of an extensive benchmarking activity, presently undertaken in the frame of the OpenSHIP Project - Highly reliable CFD simulations for the prediction of the hydrodynamic performance of the hull-propeller system with OpenSource software - co-financed by the ERDF - European Regional Development Fund - Friuli Venezia Giulia Region Operational Programme 2007 - 2013. Spilling breaking and non-breaking waves induced by a foil at constant speeds underneath the free surface are presented first. The wake at the propeller disk of a double model hull \u2013 MOERI KCS - is then analyzed, and finally the numerical predictions of the propulsive characteristics of two different model scale propellers are presented. All the simulations are carried out using the OpenFOAM-2.1.0 CFD package, and the numerical results are compared with available experimental data
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An experimental and numerical study is presented, analyzing the performance of a new bioclimatic building, featuring an integrated solar chimney roof. Laboratory tests on a 1/2 scale model building, and Computational Fluid Dynamics (CFD)... more
An experimental and numerical study is presented, analyzing the performance of a new bioclimatic building, featuring an integrated solar chimney roof. Laboratory tests on a 1/2 scale model building, and Computational Fluid Dynamics (CFD) simulations were performed, aimed to provide the needed predictive tools for the thermal behaviour of the full scale prototype. Experimental measurements and numerical results are compared, and they are in good agreement. The study lends support to the practice of combining Small-Scale Modelling and CFD for the evaluation of energy efficiency and comfort in buildings
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Free convection combined with radiation and wall conduction is analysed for a two-dimensional square cavity with differentially heated vertical walls. Radiation is solved by incorporating the weight-sum-of-gray-gases (WSGG) model into a... more
Free convection combined with radiation and wall conduction is analysed for a two-dimensional square cavity with differentially heated vertical walls. Radiation is solved by incorporating the weight-sum-of-gray-gases (WSGG) model into a modified form of the Spherical Harmonic (P_N) Differential Approximation Method-P1. The governing equations with Boussinesq approximation are written in primitive variables, and transposed from the physical to the mathematical space by the BFC (Boundary-Fitted Coordinate) technique. Predictions are obtained for Rayleigh numbers in the range of 10^3 to 10^6. Results are presented for pure free convection, free convection and wall conduction, and free convection and radiation. Comparison with data available in the literature indicate that the prediction tool has good accuracy and reliability
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A novel two-equations turbulence model is presented for the analysis of turbulent natural convection in internal flows. The case of a two-dimensional differentially heated vertical cavity is presented
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Proposition de modeles mathematiques, reposant l'un sur la methode par element fini et l'autre sur la methode par volume fini, pour analyser la convection naturelle en regime turbulent dans une cavite rectangulaire, qui peut etre... more
Proposition de modeles mathematiques, reposant l'un sur la methode par element fini et l'autre sur la methode par volume fini, pour analyser la convection naturelle en regime turbulent dans une cavite rectangulaire, qui peut etre appliquee aux collecteurs solaires, four, regulation thermique de composants electroniques, ventilation d'un bâtiment, etc...
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An experimental and numerical study is presented, analyzing the performance of a new bioclimatic building, featuring an integrated solar chimney roof. Laboratory tests on a 1/2 scale model building, and Computational Fluid Dynamics (CFD)... more
An experimental and numerical study is presented, analyzing the performance of a new bioclimatic building, featuring an integrated solar chimney roof. Laboratory tests on a 1/2 scale model building, and Computational Fluid Dynamics (CFD) simulations were performed, aimed to provide the needed predictive tools for the thermal behaviour of the full scale prototype. Experimental measurements and numerical results are compared, and they are in good agreement. The study lends support to the practice of combining Small-Scale Modelling and CFD for the evaluation of energy efficiency and comfort in buildings
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The use of CAE (Computer Aided Engineering) software, commonly applied to the design and verification of a great variety of manufactured products, is totally reliant on accurate numerical simulations. Classic mesh-based methods, e.g.,... more
The use of CAE (Computer Aided Engineering) software, commonly applied to the design and verification of a great variety of manufactured products, is totally reliant on accurate numerical simulations. Classic mesh-based methods, e.g., Finite Element (FEM) and Finite Volume (FVM), are usually employed for such simulations, where the role of the mesh is crucial for both accuracy and time consumption issues. This is especially true for complex 3D domains which are typically encountered in most practical problems. Meshless, or meshfree, methods have been recently introduced in order to replace the usual mesh with much simpler node distributions, thus purifying the data structures of any additional geometric information. Radial Basis Function-Finite Difference (RBF-FD) meshless methods have been shown to be able to easily solve problems of engineering relevance over complex-shaped domains with great accuracy, with particular reference to fluid flow and heat transfer problems. In this pap...