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110. Assessment of Additive Manufactured Micro-Channel Characteristics: Impact of Hydraulic Diameter Evaluation

Author

Bacci, Tommaso, Picchi, Alessio, Castelli, Niccolo’, Facchini, Bruno, Morante, Francesco, and Innocenti, Luca

Abstract

Among internal cooling techniques for gas turbine components, skin cooling is recognized as one of the most promising, especially thanks to the spread of additive manufacturing (AM) techniques. In this regard, several studies have tried to characterize heat transfer and pressure loss performance of additive manufactured micro-channels, as well as the impact of AM characteristic parameters, mainly in the form of building angle, and resulting surface roughness and channel shape. The open literature offers several correlations in terms of friction and heat transfer coefficient using a representative hydraulic diameter. Despite that, little attention is given on the importance of such characteristic length definition which may lead to under/over estimation of the cooling rates when correlations are used in the design. In this work, coupons featuring circular micro-channels with diameters of 0.5 and 1 mm and different building angles have been tested, to retrieve pressure losses and an average heat transfer coefficient through a lumped approach. The coupons were additive manufactured using the laser powder bed fusion technique. Exploiting the experimental survey, the impact of the considered hydraulic diameter was investigated, by comparing different approaches based on a direct measurement. An additional and new approach, aimed at the identification of an “effective” diameter, based on fluid-dynamic considerations, was also considered. The data correlation and the comparison with available correlations from different authors showed the newly proposed approach to provide superior scaling capabilities and, in turn, allowing for the development of more accurate prediction methods.

Published
2025
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119. RANS MODELING OF FLOW IN ROTATING CAVITY SYSTEM

Author

Poncet, Sébastien, Da Soghe, Riccardo, Facchini, Bruno, Modélisation et Simulation Numérique (en mécanique des fluides) (M2P2), Centre National de la Recherche Scientifique (CNRS)-Université de Provence - Aix-Marseille 1-Université Paul Cézanne - Aix-Marseille 3-Université de la Méditerranée - Aix-Marseille 2, Energy Engineering Department S. Stecco, Università degli Studi di Firenze = University of Florence [Firenze] (UNIFI), Université de la Méditerranée - Aix-Marseille 2-Université Paul Cézanne - Aix-Marseille 3-Université de Provence - Aix-Marseille 1-Centre National de la Recherche Scientifique (CNRS), and Università degli Studi di Firenze = University of Florence (UniFI)

Subjects
Physics::Fluid Dynamics, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph]
Abstract

The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of gas turbine engine. The selection of a suitable turbulence model for the study of such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of the most used eddy viscosity RANS models available within the commercial CFD solvers Fluent and CFX together with an innovative Reynolds Stress Model closure. The predictions are compared to experimental data and previous numerical calculations available in the open literature for three test cases. Test case 1 corresponds to a rotating cavity with a radial outflow, considered experimentally by Owen and Pincombe. In that case, the main difficulty arises from the choice of the boundary conditions at the outlet. Several types of boundary conditions have been then considered. All models fail to predict the radial velocity distribution. Nevertheless, the RSM offers the best agreement against the experimental data in terms of the averaged tangential velocity in the core. Test case 2 corresponds to a Taylor-Couette system with an axial Poiseuille flow studied experimentally by Escudier and Gouldson. Even if the two-equation models provide reliable data for the mean velocity field, they strongly underestimate the turbulence intensities everywhere. The agreement between the RSM and the measurements is rather satisfactory for the mean and turbulent fields, though this second-order closure does not predict the asymmetry of the normal stresses. The main discrepancies appear indeed very close to the stator. Test case 3 is a rotor-stator system with throughflow, corresponding to the test rig of Poncet et al. All the models catch the main features of rotor-stator flows, such as the value of the entrainment coefficient or the location of the transition from the Stewartson to the Batchelor flow structures. The RSM improves especially the predictions of the shear stress.

Published
2010

128. Film Cooling Modeling for Gas Turbine Nozzles and Blades: Validation and Application.

Author

Andrei, Luca, Innocenti, Luca, Andreini, Antonio, Facchini, Bruno, and Winchler, Lorenzo

Subjects
GAS turbine blades, COOLING, NOZZLES
Abstract

The design of modern gas turbines cooling systems cannot be separated from the use of computational fluid dynamics (CFD) and the accurate estimation of the effect of film cooling. Nevertheless, a complete modeling of film cooling holes within the computational domain requires an effort both from the point of view of the mesh creation and from computational time. It is here proposed a new way to model the film cooling (FCM), capable of representing the effect of the coolant at hole exit. This is possible due to the introduction of local source terms near the hole exit in a delimited portion of the domain, avoiding the meshing process of perforations. The goal is to provide a reliable and accurate tool to simulate film-cooled turbine blades and nozzles without having to explicitly mesh the holes. The model was subjected to an intensive validation campaign, composed of two phases. During the first one, FCM results are compared to experimental data and numerical results (obtained with complete cooling holes meshing) on a series of test cases reproducing flat plate cooling configurations for different coolant conditions (in terms of blowing and density ratio). In the second phase, a film-cooled vane test case has been studied, in order to consider a real injection system and flow conditions: FCM predictions are compared to an in-house developed correlative approach and full conjugate heat transfer (CHT) results. Finally, a comparison between FCM predictions and experimental data was performed on an actual nozzle of a GE Oil & Gas heavy-duty gas turbine, in order to prove the feasibility of the procedure. The presented film cooling model (FCM) proved to be a feasible and reliable tool, able to evaluate adiabatic effectiveness, simplifying the design phase avoiding the meshing process of perforations. [ABSTRACT FROM AUTHOR]

Published
2017
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138. Heat Transfer Coefficient and Adiabatic Wall Temperature Measurements on High-Pressure Turbine Nozzle Guide Vanes With Representative Inlet Swirl and Temperature Distortions

Author

Bacci, Tommaso, Picchi, Alessio, Babazzi, Giulia, Facchini, Bruno, and Cubeda, Simone

Abstract

Combustor exit conditions in modern gas turbines are generally characterized by significant temperature distortions and swirl degree, which in turn is responsible for very high turbulence intensities. These distortions have become particularly important with the introduction of lean combustion, as a mean to control NOx pollutant emissions. For this reason, combustor–turbine interaction studies have recently gained a lot of importance. Past studies have focused on the description of the effects of turbulence, swirl degree, and temperature distortions on the behavior of the high-pressure stages of the turbine, both considering them as separated aspects and accounting for their combined impact. Aspects like pressure losses, hot streaks migration, and film-cooling behavior have been widely investigated. Even if some studies have focused on the characterization of the heat transfer coefficient (HTC) on the nozzle guide vane external surface, none of them have addressed this aspect from a purely experimental point of view. Indeed, when inlet conditions are characterized by both swirl and temperature distortions, they represent a severe challenge for the commonly adopted measurement techniques. The work presented in this paper was carried out on a non-reactive, annular, three-sector test rig made by a non-reactive combustor simulator and a nozzle guide vane cascade; it is able to create a representative combustor outflow, characterized by all the flow characteristics described before. A novel experimental approach, which was developed in a previous work, was exploited to experimentally retrieve the heat transfer coefficient and the adiabatic wall temperature distributions on a non-cooled nozzle guide vane. Temperature measurements on the cascade inlet and outlet planes were also used to provide boundary conditions and achieve a better understanding of the investigated phenomena. The results allowed to evidence the effect of the inlet swirl on the heat transfer coefficient distribution, as well as the evolution of the temperature distribution on the vane surface moving through the cascade, constituting the first attempt to evaluate these aspects from a purely experimental point of view.

Published
2023
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