Julien pellé - Academia.edu (original) (raw)

Papers by Julien pellé

Journal of Thermal Science and Engineering Applications

The present study focuses on oil cooling for electric motors. A 40 kW test machine in which oil w... more The present study focuses on oil cooling for electric motors. A 40 kW test machine in which oil was introduced at each side of the machine to directly cool the stator coil end-windings was previously implemented. The lumped system analysis is used to model the thermal behavior of this test electric machine. An inverse method is applied to interpret the data obtained by the experimental setup. The inverse method leads to interior convection coefficients that help describe the heat transfer mechanisms.

Ce travail porte sur l’étude expérimentale des transferts convectifs dans l’entrefer ouvert d’un ... more Ce travail porte sur l’étude expérimentale des transferts convectifs dans l’entrefer ouvert d’un système rotor stator. Le rotor est refroidi à l’aide de l’impact d’un jet d’air. Les nombres de Nusselt sont déterminés localement sur la surface du disque en rotation, par thermographie infrarouge. Cette communication porte sur l’étude de l’influence du diamètre du jet sur le refroidissement du rotor.

In this paper we present a new method to solve a constrained non-linear problem. The method is ba... more In this paper we present a new method to solve a constrained non-linear problem. The method is based on hybridizing the Particle Swarm Optimization and tabu-search meta-heuristics (PSO-TS). Tow tabu-lists are used within the PSO algorithm: the first one aims to diversify the best solutions obtained by particles when the second bans temporarily solutions non-respecting the constraints. The obtained meta-heuristic is validated on real thermal problem called T-junction problem. It consists on optimizing the thermal management of the system and minimizing its over heating by improving its design and the flow distribution. Our results are compared with Genetic algorithm. Constrained non-linear problem, Particle Swarm Optimization (PSO), Tabu-search (TS), hybrid method, flow and heat transfer optimization.

International Journal of Heat and Mass Transfer

Proceeding of THMT-12. Proceedings of the Seventh International Symposium On Turbulence, Heat and Mass Transfer Palermo, Italy, 24-27 September, 2012, 2012

Heat Transfer: Volume 3, 2005

Volume 1: Heat Transfer in Energy Systems; Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Transport Phenomena in Materials Processing and Manufacturing; Heat and, 2012

ABSTRACT Mass and heat transfer are experimentally investigated in a discoidal and unshrouded rot... more ABSTRACT Mass and heat transfer are experimentally investigated in a discoidal and unshrouded rotor-stator cavity where an air jet passes through the stator and impinges on the rotor center. Using a jet impingement is a way to bring fresh air inside the air gap and to increase shear stresses and so heat transfer over the rotor. This study focuses on comparisons between heat transfer coefficients and velocity fields obtained inside the air gap for the case of a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Two jet Reynolds numbers ranging from 16000 to 42000 and three rotational Reynolds numbers between 30000 and 516000 are considered. Mass transfers are investigated by Particle Image Velocimetry technique while the radial distribution of heat transfer coefficients over the rotor is obtained using a thick wall method and temperature measurements by infrared thermography.

Applied Thermal Engineering, 2015

Journal of Heat Transfer, 2014

Cooling of electrical machines is nowadays of high interest in order to improve their efficiency.... more Cooling of electrical machines is nowadays of high interest in order to improve their efficiency. In railway applications, electrical motors can be shrouded in order to avoid particles to be deposited inside. To ensure a satisfactory cooling, pipes are placed inside the rotor and are thus rotating. Improvements in convective heat transfer inside the rotating pipes were numerically investigated. Model was first validated against experimental data and after that several geometry modifications were tested. Influence of the angle of attack of the fluid at the inlet to the pipe was discussed and it was shown that heat transfer can be significantly increased near the pipe inlet. In addition to that changing a circular pipe with an elliptical pipe was investigated in two ways: fixing the same hydraulic diameter or the same equivalent diameter. It was shown that the cooling efficiency can be significantly increased. The best overall heat transfer enhancement of about 45% exhibited elliptic ...

Journal of Heat Transfer, 2011

The present work relates to an experimental study of the local convective heat transfer over the ... more The present work relates to an experimental study of the local convective heat transfer over the rotor surface in the air-gap of a discoidal rotor–stator system. This configuration is of interest namely, in electrical machines or tubomachinery. Following precedent studies obtained for a single rotating disk or a closed (but unshrouded) rotor–stator system, an air suction comes through the stator and enters the air-gap in this particular work. Determination of Nusselt numbers is based on the use of infrared thermography. The influence of the suction is discussed for an interdisk dimensionless spacing interval, G ranging from 0.01 to 0.16 and for a rotational Reynolds number, Re between 30,000 and 5,16,000. Results shows that the suction could locally provide better cooling than in the closed rotor–stator and in the single disk configurations, even if the main influence is a decrease in the convective heat transfer.

International Journal of Thermal Sciences, 2012

We present the thermal optimization study of a single inlet 90 T-junction. Head losses in associa... more We present the thermal optimization study of a single inlet 90 T-junction. Head losses in association with the lumped method are used to calculate the 2D temperature field from a specific geometrical configuration, heat sources, boundary conditions and available ventilation power. This simple case is used as a benchmark to show a possible optimization methodology and to test 4 optimization algorithms suitable to non-linear problems; they are the Active-Set, Interior Point, Genetic Algorithm and Particle Swarm Optimization. The optimization problem is defined by an Aggregated Objective Function (AOF) that depends on three geometrical parameters which are subjected to linear and non-linear constraints. In order to consider not only the global thermal behavior, but also local hotspots, the AOF combines mean solid temperature pondered by its volume and the maximal temperature. Five weights for these criteria were tested. The physical interpretation of different points helped to identify the optimal geometrical characteristics. All optimization algorithms demonstrated to be able to avoid local minima with this benchmark, if properly used.

International Journal of Thermal Sciences, 2013

Fluid flow and convective heat transfer in rotor-stator configurations, which are of great import... more Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steady-state (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infrared cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk, rotor-stator systems without and with impinging single jets, as well as multiple jets. Conclusions to the review outline perspectives of the further extension of the investigations of different kinds of the rotor-stator systems and their applications in engineering practice.

International Journal of Heat and Fluid Flow, 2013

New calculations using an innovative Reynolds Stress Model are compared to velocity measurements ... more New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k − ω SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor-stator system. The cavity is characterized by a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Jet Reynolds numbers ranging from 1.72 × 10 4 to 4.3 × 10 4 and rotational Reynolds numbers between 0.33×10 5 and 5.32×10 5 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotationdominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k − ω SST model overstimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.

IEEE Transactions on Industrial Electronics, 2000

The design of variable-speed electrical machines involves several fields of physics, such as elec... more The design of variable-speed electrical machines involves several fields of physics, such as electromagnetism, thermics, mechanics but also acoustics. This paper describes the analytical multi-physics models of a computer-aided design (CAD) software which is applied to inverter-fed traction induction machines. The electromagnetic model computes rotor and stator currents, the induction machine traction characteristics, and the radial air-gap flux density. The mechanical and acoustic model computes the motor audible magnetic noise level due to Maxwell forces. The thermal model based on 3D nodal network, computes the transient temperature of different parts of the motor. These fast models make it possible to couple the software with some optimization tools. Some simulation results are presented on a self-ventilated closed motor and compared to experiments.

IEEE Transactions on Industrial Electronics, 2000

Experimental Thermal and Fluid Science, 2007

This article presents an experimental study of the heat transfers in a discoidal rotor-stator sys... more This article presents an experimental study of the heat transfers in a discoidal rotor-stator system air-gap. Measurements are performed over the rotor, using an experimental technique based on infrared thermography, in order to determine the surface temperatures. Using a thermal balance, the local convective heat transfer coefficient is identified. The influences of the rotational Reynolds number Re and the dimensionless spacing between the two disks G are carried out and compared with literature data when available. Local convective heat transfer coefficients are obtained for Re ranging from 1.29 • 10 5 to 6.45 • 10 5 and for G between 0.01 and 0.16. Four heat transfer regimes are identified then correlated. Comparisons with our previous results concerning flow and heat transfers over a single rotating disk in still air are also carried out.

Experimental Heat Transfer, 2007

This article presents an experimental study of the local heat transfer on the rotor surface in a ... more This article presents an experimental study of the local heat transfer on the rotor surface in a discoidal rotor-stator system air-gap in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance was used to identify

Applied Thermal Engineering, 2009

Discoidal rotor-stator systems are nowadays sometimes used in electrical wind generator. The cool... more Discoidal rotor-stator systems are nowadays sometimes used in electrical wind generator. The cooling of such a system is a major problem due to the fact that high electrical losses are dissipated for relatively low rotational speed, responsible of the cooling. A new cooling solution is then investigated in this paper. So, this article presents an experimental study of the local heat transfers on the rotor surface in the air-gap of a discoidal rotor-stator system, in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance equation was used to identify the local convective heat transfer coefficient. The influence of the axial Reynolds number Re j and the rotational Reynolds number Re was measured and compared with the data available in the literature. Local convective heat transfer coefficients were obtained for an inter-disk dimensionless spacing interval G ranging from 0.01 to 0.16 for Re j between 0 and 41666 and for Re between 20000 and 516000. The rotating disk can thus be divided into zones: one dominated by the air jet near the center of the rotor and one affected by both the air jet and rotation. Even though these two zones are not located in the same place on the disk, the heat transfers with non-zero impinging jets appear to be continuously improved compared to those with no jets. Critical radii over the rotor surface are identified and correlations are given.

-Ce travail porte sur l'étude expérimentale des transferts de chaleur par convection dans l'entre... more -Ce travail porte sur l'étude expérimentale des transferts de chaleur par convection dans l'entrefer non confiné d'un système rotor stator de technologie discoïde. Les transferts de chaleur convectifs sont déterminés de manière locale en régime permanent sur la surface du rotor grâce à la thermographie infrarouge. Dans cette étude, une ouverture est placée au centre du stator. Une aspiration va alors se produire naturellement du fait de la rotation du rotor, qui dépend de 3 paramètres principaux : le diamètre de l'ouverture, l'espacement entre les deux disques et la vitesse de rotation du rotor. La comparaison des résultats obtenus avec ceux sans ouverture ou dans le cas d'un disque seul, permet de montrer une amélioration des transferts convectifs de manière très localisée. Nomenclature D Diamètre de l'ouverture, m e Espace entre rotor et stator, m F Facteur de forme r Rayon, m R Rayon extérieur du rotor, m T Température, K ε r ε Emissivité du rotor s Emissivité du stator λ Conductivité thermique, W.m-1 .K ν Viscosité cinématique, m-1 2 .s ω Vitesse de rotation, rad.s-1

-Le travail proposé porte sur l'étude expérimentale des transferts de chaleur par convection dans... more -Le travail proposé porte sur l'étude expérimentale des transferts de chaleur par convection dans l'entrefer non confiné d'un système rotor stator de technologie discoïde. Plus particulièrement, le rotor est ici refroidi à l'aide de l'impact d'un jet d'air en son centre. Les nombres de Nusselt sont déterminés de manière locale sur la surface entière du disque en rotation grâce à l'utilisation de la thermographie infrarouge. Une première campagne d'essais a permis de mettre en évidence des zones où les influences de la rotation et du jet sont prépondérantes pour le refroidissement du rotor. Cette communication sera essentiellement focalisée sur l'étude de l'influence du diamètre du jet sur le refroidissement du rotor et la détermination de corrélations reliant le nombre de Nusselt aux nombres de Reynolds relatifs à la rotation ou au jet. Nomenclature D Diamètre du jet, m e Espace entre rotor et stator, m F Facteur de forme r Rayon, m R Rayon extérieur, m T(r,x) Température, K V Vitesse, m.s-1 x Position axiale, m Symboles Grecs  r Emissivité du rotor  s Emissivité du stator  Conductivité thermique, W.m-1 .K-1  Viscosité cinématique, m 2 .s-1  Vitesse de rotation, rad.s-1 Indices et exposants jm Jet/Mixte r Radial zir Zircone Nombres sans dimension G Espacement adimensionné, = e / R Nu r Nombre de Nusselt local Re Nombre de Reynolds rotationnel, = R 2 /  air Re j Nombre de Reynolds relatif au jet, = V j D /  air

Journal of Thermal Science and Engineering Applications

The present study focuses on oil cooling for electric motors. A 40 kW test machine in which oil w... more The present study focuses on oil cooling for electric motors. A 40 kW test machine in which oil was introduced at each side of the machine to directly cool the stator coil end-windings was previously implemented. The lumped system analysis is used to model the thermal behavior of this test electric machine. An inverse method is applied to interpret the data obtained by the experimental setup. The inverse method leads to interior convection coefficients that help describe the heat transfer mechanisms.

Ce travail porte sur l’étude expérimentale des transferts convectifs dans l’entrefer ouvert d’un ... more Ce travail porte sur l’étude expérimentale des transferts convectifs dans l’entrefer ouvert d’un système rotor stator. Le rotor est refroidi à l’aide de l’impact d’un jet d’air. Les nombres de Nusselt sont déterminés localement sur la surface du disque en rotation, par thermographie infrarouge. Cette communication porte sur l’étude de l’influence du diamètre du jet sur le refroidissement du rotor.

In this paper we present a new method to solve a constrained non-linear problem. The method is ba... more In this paper we present a new method to solve a constrained non-linear problem. The method is based on hybridizing the Particle Swarm Optimization and tabu-search meta-heuristics (PSO-TS). Tow tabu-lists are used within the PSO algorithm: the first one aims to diversify the best solutions obtained by particles when the second bans temporarily solutions non-respecting the constraints. The obtained meta-heuristic is validated on real thermal problem called T-junction problem. It consists on optimizing the thermal management of the system and minimizing its over heating by improving its design and the flow distribution. Our results are compared with Genetic algorithm. Constrained non-linear problem, Particle Swarm Optimization (PSO), Tabu-search (TS), hybrid method, flow and heat transfer optimization.

International Journal of Heat and Mass Transfer

Proceeding of THMT-12. Proceedings of the Seventh International Symposium On Turbulence, Heat and Mass Transfer Palermo, Italy, 24-27 September, 2012, 2012

Heat Transfer: Volume 3, 2005

Volume 1: Heat Transfer in Energy Systems; Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Transport Phenomena in Materials Processing and Manufacturing; Heat and, 2012

ABSTRACT Mass and heat transfer are experimentally investigated in a discoidal and unshrouded rot... more ABSTRACT Mass and heat transfer are experimentally investigated in a discoidal and unshrouded rotor-stator cavity where an air jet passes through the stator and impinges on the rotor center. Using a jet impingement is a way to bring fresh air inside the air gap and to increase shear stresses and so heat transfer over the rotor. This study focuses on comparisons between heat transfer coefficients and velocity fields obtained inside the air gap for the case of a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Two jet Reynolds numbers ranging from 16000 to 42000 and three rotational Reynolds numbers between 30000 and 516000 are considered. Mass transfers are investigated by Particle Image Velocimetry technique while the radial distribution of heat transfer coefficients over the rotor is obtained using a thick wall method and temperature measurements by infrared thermography.

Applied Thermal Engineering, 2015

Journal of Heat Transfer, 2014

Cooling of electrical machines is nowadays of high interest in order to improve their efficiency.... more Cooling of electrical machines is nowadays of high interest in order to improve their efficiency. In railway applications, electrical motors can be shrouded in order to avoid particles to be deposited inside. To ensure a satisfactory cooling, pipes are placed inside the rotor and are thus rotating. Improvements in convective heat transfer inside the rotating pipes were numerically investigated. Model was first validated against experimental data and after that several geometry modifications were tested. Influence of the angle of attack of the fluid at the inlet to the pipe was discussed and it was shown that heat transfer can be significantly increased near the pipe inlet. In addition to that changing a circular pipe with an elliptical pipe was investigated in two ways: fixing the same hydraulic diameter or the same equivalent diameter. It was shown that the cooling efficiency can be significantly increased. The best overall heat transfer enhancement of about 45% exhibited elliptic ...

Journal of Heat Transfer, 2011

The present work relates to an experimental study of the local convective heat transfer over the ... more The present work relates to an experimental study of the local convective heat transfer over the rotor surface in the air-gap of a discoidal rotor–stator system. This configuration is of interest namely, in electrical machines or tubomachinery. Following precedent studies obtained for a single rotating disk or a closed (but unshrouded) rotor–stator system, an air suction comes through the stator and enters the air-gap in this particular work. Determination of Nusselt numbers is based on the use of infrared thermography. The influence of the suction is discussed for an interdisk dimensionless spacing interval, G ranging from 0.01 to 0.16 and for a rotational Reynolds number, Re between 30,000 and 5,16,000. Results shows that the suction could locally provide better cooling than in the closed rotor–stator and in the single disk configurations, even if the main influence is a decrease in the convective heat transfer.

International Journal of Thermal Sciences, 2012

We present the thermal optimization study of a single inlet 90 T-junction. Head losses in associa... more We present the thermal optimization study of a single inlet 90 T-junction. Head losses in association with the lumped method are used to calculate the 2D temperature field from a specific geometrical configuration, heat sources, boundary conditions and available ventilation power. This simple case is used as a benchmark to show a possible optimization methodology and to test 4 optimization algorithms suitable to non-linear problems; they are the Active-Set, Interior Point, Genetic Algorithm and Particle Swarm Optimization. The optimization problem is defined by an Aggregated Objective Function (AOF) that depends on three geometrical parameters which are subjected to linear and non-linear constraints. In order to consider not only the global thermal behavior, but also local hotspots, the AOF combines mean solid temperature pondered by its volume and the maximal temperature. Five weights for these criteria were tested. The physical interpretation of different points helped to identify the optimal geometrical characteristics. All optimization algorithms demonstrated to be able to avoid local minima with this benchmark, if properly used.

International Journal of Thermal Sciences, 2013

Fluid flow and convective heat transfer in rotor-stator configurations, which are of great import... more Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental/theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steady-state (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infrared cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk, rotor-stator systems without and with impinging single jets, as well as multiple jets. Conclusions to the review outline perspectives of the further extension of the investigations of different kinds of the rotor-stator systems and their applications in engineering practice.

International Journal of Heat and Fluid Flow, 2013

New calculations using an innovative Reynolds Stress Model are compared to velocity measurements ... more New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k − ω SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor-stator system. The cavity is characterized by a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Jet Reynolds numbers ranging from 1.72 × 10 4 to 4.3 × 10 4 and rotational Reynolds numbers between 0.33×10 5 and 5.32×10 5 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotationdominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k − ω SST model overstimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.

IEEE Transactions on Industrial Electronics, 2000

The design of variable-speed electrical machines involves several fields of physics, such as elec... more The design of variable-speed electrical machines involves several fields of physics, such as electromagnetism, thermics, mechanics but also acoustics. This paper describes the analytical multi-physics models of a computer-aided design (CAD) software which is applied to inverter-fed traction induction machines. The electromagnetic model computes rotor and stator currents, the induction machine traction characteristics, and the radial air-gap flux density. The mechanical and acoustic model computes the motor audible magnetic noise level due to Maxwell forces. The thermal model based on 3D nodal network, computes the transient temperature of different parts of the motor. These fast models make it possible to couple the software with some optimization tools. Some simulation results are presented on a self-ventilated closed motor and compared to experiments.

IEEE Transactions on Industrial Electronics, 2000

Experimental Thermal and Fluid Science, 2007

This article presents an experimental study of the heat transfers in a discoidal rotor-stator sys... more This article presents an experimental study of the heat transfers in a discoidal rotor-stator system air-gap. Measurements are performed over the rotor, using an experimental technique based on infrared thermography, in order to determine the surface temperatures. Using a thermal balance, the local convective heat transfer coefficient is identified. The influences of the rotational Reynolds number Re and the dimensionless spacing between the two disks G are carried out and compared with literature data when available. Local convective heat transfer coefficients are obtained for Re ranging from 1.29 • 10 5 to 6.45 • 10 5 and for G between 0.01 and 0.16. Four heat transfer regimes are identified then correlated. Comparisons with our previous results concerning flow and heat transfers over a single rotating disk in still air are also carried out.

Experimental Heat Transfer, 2007

This article presents an experimental study of the local heat transfer on the rotor surface in a ... more This article presents an experimental study of the local heat transfer on the rotor surface in a discoidal rotor-stator system air-gap in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance was used to identify

Applied Thermal Engineering, 2009

Discoidal rotor-stator systems are nowadays sometimes used in electrical wind generator. The cool... more Discoidal rotor-stator systems are nowadays sometimes used in electrical wind generator. The cooling of such a system is a major problem due to the fact that high electrical losses are dissipated for relatively low rotational speed, responsible of the cooling. A new cooling solution is then investigated in this paper. So, this article presents an experimental study of the local heat transfers on the rotor surface in the air-gap of a discoidal rotor-stator system, in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance equation was used to identify the local convective heat transfer coefficient. The influence of the axial Reynolds number Re j and the rotational Reynolds number Re was measured and compared with the data available in the literature. Local convective heat transfer coefficients were obtained for an inter-disk dimensionless spacing interval G ranging from 0.01 to 0.16 for Re j between 0 and 41666 and for Re between 20000 and 516000. The rotating disk can thus be divided into zones: one dominated by the air jet near the center of the rotor and one affected by both the air jet and rotation. Even though these two zones are not located in the same place on the disk, the heat transfers with non-zero impinging jets appear to be continuously improved compared to those with no jets. Critical radii over the rotor surface are identified and correlations are given.

-Ce travail porte sur l'étude expérimentale des transferts de chaleur par convection dans l'entre... more -Ce travail porte sur l'étude expérimentale des transferts de chaleur par convection dans l'entrefer non confiné d'un système rotor stator de technologie discoïde. Les transferts de chaleur convectifs sont déterminés de manière locale en régime permanent sur la surface du rotor grâce à la thermographie infrarouge. Dans cette étude, une ouverture est placée au centre du stator. Une aspiration va alors se produire naturellement du fait de la rotation du rotor, qui dépend de 3 paramètres principaux : le diamètre de l'ouverture, l'espacement entre les deux disques et la vitesse de rotation du rotor. La comparaison des résultats obtenus avec ceux sans ouverture ou dans le cas d'un disque seul, permet de montrer une amélioration des transferts convectifs de manière très localisée. Nomenclature D Diamètre de l'ouverture, m e Espace entre rotor et stator, m F Facteur de forme r Rayon, m R Rayon extérieur du rotor, m T Température, K ε r ε Emissivité du rotor s Emissivité du stator λ Conductivité thermique, W.m-1 .K ν Viscosité cinématique, m-1 2 .s ω Vitesse de rotation, rad.s-1

-Le travail proposé porte sur l'étude expérimentale des transferts de chaleur par convection dans... more -Le travail proposé porte sur l'étude expérimentale des transferts de chaleur par convection dans l'entrefer non confiné d'un système rotor stator de technologie discoïde. Plus particulièrement, le rotor est ici refroidi à l'aide de l'impact d'un jet d'air en son centre. Les nombres de Nusselt sont déterminés de manière locale sur la surface entière du disque en rotation grâce à l'utilisation de la thermographie infrarouge. Une première campagne d'essais a permis de mettre en évidence des zones où les influences de la rotation et du jet sont prépondérantes pour le refroidissement du rotor. Cette communication sera essentiellement focalisée sur l'étude de l'influence du diamètre du jet sur le refroidissement du rotor et la détermination de corrélations reliant le nombre de Nusselt aux nombres de Reynolds relatifs à la rotation ou au jet. Nomenclature D Diamètre du jet, m e Espace entre rotor et stator, m F Facteur de forme r Rayon, m R Rayon extérieur, m T(r,x) Température, K V Vitesse, m.s-1 x Position axiale, m Symboles Grecs  r Emissivité du rotor  s Emissivité du stator  Conductivité thermique, W.m-1 .K-1  Viscosité cinématique, m 2 .s-1  Vitesse de rotation, rad.s-1 Indices et exposants jm Jet/Mixte r Radial zir Zircone Nombres sans dimension G Espacement adimensionné, = e / R Nu r Nombre de Nusselt local Re Nombre de Reynolds rotationnel, = R 2 /  air Re j Nombre de Reynolds relatif au jet, = V j D /  air