Off-design considerations through the properties of some pressure-ratio line of radial inflow turbines

Radial turbines are commonly used in applications involving operation through severe off-design conditions. The emergence of variable-geometry systems leads to the distinction between two off-design concepts: operational and geometric off-designs. Both of these operating constraints should be integrated in the design procedure. Recent developments in prediction and optimization methods allowed such an integration, but involving complex algorithms is coupled with semiempiric loss models. This paper provides a basis to obtain simple information from an existing or predesigned machine, for both operational and geometric offdesign conditions. An alternative turbine map is defined using loading and flow coefficients. A one-dimensional analysis shows that the constant pressure-ratio lines are straight lines whose slope is remarkably correlated with the pressure-ratio value and geometrical characteristics. This theoretical approach is validated against the experimentation of two machines, the linearity is observed in both cases. The direct influence of the stator configuration on the pressure-ratio lines confirms the applicability of this work to variable-geometry stages. A dimensionless cross-section of the stator is thus defined. However, the unexpected displacement of the intercept of the pressure-ratio lines limits the application field of this method. Nevertheless, a simple performance prediction analysis is proposed for blocked mass flow operation

Performance Back-deduction from a Loading to Flow Coefficient Map: Application to Radial Turbine

Radial turbine stages are often used for applications requiring off-design operation, as turbocharging for instance. The off-design ability of such stages is commonly analyzed through the traditional turbine map, plotting the reduced mass-flow against the pressure-ratio, for reduced-speed lines. However, some alternatives are possible, such as the flow-coefficient (Ψ ) to loading-coefficient (φ) diagram where the pressure-ratio lines are actually straight lines, very convenient property to perform prediction. A robust method re-creating this map from a predicted Ψ−φ diagram is needed. Recent work has shown that this back-deduction quality, without the use of any loss models, depends on the knowledge of an intermediate pressure-ratio. A modelization of this parameter is then proposed. The comparison with both experimental and CFD results is presented, with quite good agreement for mass flow rate and rotational speed, and for the intermediate pressure ratio. The last part of the paper is dedicated to the application of the intermediate pressure-ratio knowledge to the improvement of the deduction of the pressure ratio lines in the Ψ−φ diagram. Beside this improvement, the back-deduction method of the classical map is structured, applied and evaluated

Potential of power recovery of a subsonic axial fan in windmilling operation

During the last decades, efforts to find efficient green energy solutions have been widely increased in response to environmental concerns. Among all renewable energies, this paper is focused on wind power generation. To this end, a windmilling axial fan in turbine operation is experimentally and numerically investigated. Under specific conditions, the studied fan is naturally freewheeling. Consequently, the main objective of this analysis is to determine whether or not this intrinsic windmilling behavior can be optimized for power generation. A preliminary study of the fan is dedicated to the knowledge of the fan characteristics in normal operating conditions. Then, two windmilling configurations (direct and reverse flow direction) are tested and compared on the basis of the output power. An analysis of the velocity triangle gives the opportunity to evaluate the energy recovery potential of both solutions. Of the two, the reversed configuration showed a higher level of output power than the direct one

Étude aérodynamique expérimentale des étages de turbines centripètes à géométrie variable

L'étude s'inscrit dans un contexte industriel, et concerne l'analyse de l'impact d'un système de distributeur à ouverture variable dans le fonctionnement d'étages de turbine centripète de petites dimensions, pour une application automobile : le turbocompresseur. L'examen de la problématique isole trois objectifs : identifier l'influence de la géométrie variable, qualifier l'adaptation de ce système aux autres éléments de l'étage, et intégrer ces connaissances aux procédures classiques de dimensionnement. La démarche, essentiellement expérimentale repose sur la définition et la conception d'un banc d'essai adapté aux conditions réelles de fonctionnement (600°C, 3bars). Une métrologie à deux niveaux y est associée: un niveau global concerne les paramètres caractéristiques d'entrée-sortie de l'étage. Un niveau plus local aux éléments, particulièrement en amont et en aval du distributeur ainsi qu'en sortie roue, s'intéresse à la structure de l'écoulement et au triangle des vitesses. Le découpage de l'investigation expérimentale se fait en trois phases. La première phase considère l'étude approfondie d'un étage à géométrie variable de définition industrielle comme référence. L'examen d'étages prototypes, dans la deuxième phase, permet d'isoler l'influence du rapport des sections minimales de passage du stator et du rotor. La troisième phase consiste en un plan factoriel complet articulé autour des paramètres géométriques dimensionnants du distributeur, et structuré suivant la méthode statistique de planification optimale

Aéro-thermodynamique des Turbomachines en Fonctionnement Hors-Adaptation

Thématiques de recherche : Les turbomachines assurent les échanges d’énergie/travail entre un système mécanique et un écoulement de fluide. La demande du secteur industriel en plage de fonctionnement se fait croissante. Or s’écarter des conditions de fonctionnement de conception implique une pénalité sur le rendement de l’échange, voire un danger pour la machine. L’origine en est essentiellement aérodynamique. Des situations non-conventionnelles de fonctionnement sont examinées dans ces travaux, pour différentes natures de turbomachines mono-étagées (ventilateurs en auto-rotation, turbines radiales à géométrie variable et en régime transitoire sévère, compresseurs centrifuges en limite de stabilité...). L’adoption du formalisme adéquat permet de rassembler ces situations extrêmes de fonctionnement, stationnaires ou non, jusqu’alors traitées comme des cas particuliers. Cet examen permet de formuler des recommandations de conception, de proposer des stratégies correctives, et de construire des modèles simples adaptés à l’analyse des systèmes complexes. Perspectives : Les questions de récupération d’énergie par les turbines doivent progresser. En stationnaire, on cherche à préciser la maîtrise du rendement pour des dispositifs mixtes (qui peuvent soit apporter, soit extraire de l’énergie), et/ou à géométrie variable. En phase transitoire, on suspecte un possible bénéfice de l’instationnarité, qui n’est pas exploité à l’heure actuelle. La deuxième perspective concerne la limite de fonctionnement imposée par la stabilité des systèmes de compression, qui reste un point focal de la communauté, en particulier l’itinéraire menant au décrochage tournant. Une troisième perspective s’insère dans la dynamique du département, tournée vers l’approche multi-physique et la modélisation de systèmes complexes. Enfin, à plus long terme, on recherche à asseoir une approche unifiée des turbomachines, alors que l’usage tend à cloisonner les architectures (turbines, compresseurs, axial, radial, rotor caréné ou libre…)

Étude aérodynamique expérimentale des étages de turbines centripètes à géométrie variable

L'étude s'inscrit dans un contexte industriel, et concerne l'analyse de l'impact d'un système de distributeur à ouverture variable dans le fonctionnement d'étages de turbine centripète de petites dimensions, pour une application automobile : le turbocompresseur. L'examen de la problématique isole trois objectifs : identifier l'influence de la géométrie variable, qualifier l'adaptation de ce système aux autres éléments de l'étage, et intégrer ces connaissances aux procédures classiques de dimensionnement. La démarche, essentiellement expérimentale repose sur la définition et la conception d'un banc d'essai adapté aux conditions réelles de fonctionnement (600°C, 3bars). Une métrologie à deux niveaux y est associée: un niveau global concerne les paramètres caractéristiques d'entrée-sortie de l'étage. Un niveau plus local aux éléments, particulièrement en amont et en aval du distributeur ainsi qu'en sortie roue, s'intéresse à la structure de l'écoulement et au triangle des vitesses. Le découpage de l'investigation expérimentale se fait en trois phases. La première phase considère l'étude approfondie d'un étage à géométrie variable de définition industrielle comme référence. L'examen d'étages prototypes, dans la deuxième phase, permet d'isoler l'influence du rapport des sections minimales de passage du stator et du rotor. La troisième phase consiste en un plan factoriel complet articulé autour des paramètres géométriques dimensionnants du distributeur, et structuré suivant la méthode statistique de planification optimale

Mise en relation analytique de la cinématique de l’écoulement et des performances d’un rotor caréné à Mach de vol intermédiaire

Reaching the European long-term air transport emission reduction goals impose shifting by 2050 toward hybridation/electrification of airplanes as well as global optimization of flight missions. This implies developping distributed propulsion systems through the multiplication of small shrouded rotors operating at high efficiency within a wide range. Present litterature lacks a low-order shrouded rotor model specifically designed to work on such wide operating range. In this paper, the working range of the existing models is benchmarked on the basis of similarity factors built on an innovative expression of the shrouded rotors problem. It is established here that the model of Jardin et al. [1] presents the wider working range thanks to the "homokinetic" surface definition but lacks robustness and needs an additional input that is related to the "homokinetic" surface. The extension of this model to the compressible domain increases its robustness and an empirical model of the "homokinetic" surface helps droping the additional input

Unified classification and characterization of axial turbomachines and propellers

Reaching the mid/long-term air transport emission reduction goals imposed by both European and American standards impose increasing the propulsive systems’ adaptability to various operating conditions, in order to maximize the aircraft overall efficiency all along the flight mission. This implies the enlargement of the design space of propulsive systems such that it can even be operated equally as a compressor or turbine, which leads to rethink the paradigm of designing turbomachines. The continuity in the definition and characterization of different types of turbomachines should be restored which is proposed through this contribution. Analytical relationships allowing to switch between compressor map, propeller map and map are developed. To minimize the inputs of the maps’ conversion relations, a methodology to extract mean flow features from any characterization map is presented, namely the rotor outlet relative flow angle and mean streamline radius. The application of the characterization maps’ conversion relations on a turbofan’s single-stage axial fan and on a propeller allowed their validation through the physical coherence of the results. The flow features extraction methodology also showed very satisfying results with comparison to experiments. Eventually, the ability of the formalism as a powerful performance analysis tool for all kind of turbomachines is stressed out, which makes it the best candidate for the unified treatment of turbomachines

Glass Polymorphism in TIP4P/2005 Water: A Description Based on the Potential Energy Landscape Formalism

The potential energy landscape (PEL) formalism is a statistical mechanical approach to describe supercooled liquids and glasses. Here we use the PEL formalism to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) using computer simulations of the TIP4P/2005 molecular model of water. We find that the properties of the PEL sampled by the system during the LDA-HDA transformation exhibit anomalous behavior. In particular, at conditions where the change in density during the LDA-HDA transformation is approximately discontinuous, reminiscent of a first-order phase transition, we find that (i) the inherent structure (IS) energy, $e_\text{IS}(V)$, is a concave function of the volume, and (ii) the IS pressure, $P_\text{IS}(V)$, exhibits a van der Waals-like loop. In addition, the curvature of the PEL at the IS is anomalous, a non-monotonic function of $V$. In agreement with previous studies, our work suggests that conditions (i) and (ii) are necessary (but not sufficient) signatures of the PEL for the LDA-HDA transformation to be reminiscent of a first-order phase transition. We also find that one can identify two different regions of the PEL, one associated to LDA and another to HDA. Our computer simulations are performed using a wide range of compression/decompression and cooling rates. In particular, our slowest cooling rate (0.01 K/ns) is within the experimental rates employed in hyperquenching experiments to produce LDA. Interestingly, the LDA-HDA transformation pressure that we obtain at $T=80$ K and at different rates extrapolates remarkably well to the corresponding experimental pressure.Comment: Manuscript and Supplementary Materia

Innovative fan design for both high compressor and windmilling performance

controlledwindmilling conditions is numerically investigated. Initially, the ram air is equipped with a classic fan, only conceived to work as a compressor. The purpose of the new fan is to be able to work in antagonist functioning modes with high efficiencies: a compressor mode during which energy is given to the flow and a turbine mode (windmilling conditions) where energy is extracted from it. A numerical study was conducted to check the results predicted by the design tool on the new geometry. Good efficiencies were observed in both compressor and turbine modes, confirming the relevance of the design method. Afterwards, a thorough local comparison was achieved between the two fans to better understand the flow topology of the new design