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Experimental analysis of the unsteady flow and instabilities in a high-speed multistage compressorCourtiade, Nicolas 22 November 2012 (has links) (PDF)
The present work is a result of collaboration between the LMFA (Laboratoire de Mécanique des Fluides et d'Acoustique, Ecole Centrale de Lyon - France), Snecma and the Cerfacs. It aims at studying the flow in the 3.5-stages high-speed axial compressor CREATE (Compresseur de Recherche pour l'Etude des effets Aérodynamique et TEchnologique - rotation speed: 11543 RPM, Rotor 1 tip speed: 313 m/s), designed and built by Snecma and investigated at LMFA on a 2-MW test rig. Steady measurements, as well as laser velocimetry, fast-response wall static and total pressure measurements have been used to experimentally investigate the flow. The analysis focuses on two main aspects: the study of the flow at stable operating points, with a special interest on the rotor-stator interactions, and the study of the instabilities arising in the machine at low mass flow rates.The description of the unsteady flow field at stable operating points is done through measurements of wall-static pressure, total pressure and velocity, but also total temperature, entropy and angle of the fluid. It is shown that the complexity and unsteadiness of the flow in a multistage compressor strongly increases in the rear part of the machine, because of the interactions between steady and rotating rows. Therefore, a modal analysis method developed at LMFA and based on the decomposition of Tyler and Sofrin is presented to analyze these interactions. It is first applied to the pressure measurements, in order to extract the contributions of each row. It shows that all the complex pressure interactions in CREATE can be reduced to three main types of interactions. The decomposition method is then applied to the entropy field extracted from URANS CFD calculations performed by the Cerfacs, in order to evaluate the impact of the interactions on the performance of the machine in term of production of losses.The last part of this work is devoted to the analysis of the instabilities arising in CREATE at low mass flows. It shows that rotating pressure waves appear at stable operating points, and increase in amplitude when going towards the surge line, until reaching a critical size provoking the onset a full span stall cell bringing the machine to surge within a few rotor revolutions. The study of these pressure waves, and the understanding of their true nature is achieved through the experimental results and the use of some analytical models. A precise description of the surge transient through wall-static pressure measurements above the rotors is also provided, as well as a description of a complete surge cycle. An anti-surge control system based on the detection of the amplitude of the pressure waves is finally proposed.
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Experimental analysis of the unsteady flow and instabilities in a high-speed multistage compressor / Analyse expérimentale des écoulements haute vitesse et instationnaires dans un compresseur multi-étages à forte charge aérodynamiqueCourtiade, Nicolas 22 November 2012 (has links)
Ce travail est le produit d’une collaboration entre le LMFA (Laboratoire de Mécanique des Fluides et d’Acoustique, École Centrale de Lyon – France), Snecma et le Cerfacs. Il vise à étudier l’écoulement se développant dans le compresseur haute-vitesse axial de 3.5 étages CREATE (Compresseur de Recherche pour l’Etude des effets Aérodynamique et TEchnologique – vitesse de rotation : 11543 tr/min, vitesse en tête de rotor 1 : 313 m/s), conçu et construit par Snecma et étudié au LMFA sur un banc d’essai de 2 MW. Pour étudier l’écoulement, des mesures stationnaires de pression et température, de la vélocimétrie laser et des mesures rapides de pression statique et totale ont été utilisées. L’analyse se concentre sur deux aspects principaux : l’étude de l’écoulement aux points de fonctionnement stables, avec un intérêt tout particulier pour les interactions rotor-stator, et l’étude des instabilités apparaissant dans la machine à faibles débits.La description de l’écoulement instationnaire aux points stables est faite par le biais de mesures de pression statique en parois, de pression totale et de vitesse, mais également de température totale, entropie et angle d’incidence du fluide. Il est montré que la complexité et l’instationnarité de l’écoulement dans un compresseur multiétagé augmente fortement à l’arrière de la machine à cause des interactions entre les roues fixes et mobiles. Ainsi, une méthode d’analyse modale basée sur la décomposition de Tyler et Sofrin a été développée pour analyser ces interactions. Elle est d’abord appliquée aux mesures de pression afin d’extraire les contributions de chaque roue. Il est ainsi montré que les interactions complexes de pression dans CREATE peuvent être réduites à trois principaux types d’interactions. La méthode de décomposition est enfin appliquée au champ d’entropie dans toute la machine extrait de calculs CFD URANS réalisés par le Cerfacs, afin d’évaluer l’impact des interactions sur les performances de CREATE en terme de génération de pertes.La dernière partie de ce travail est dédié à l’analyse des instabilités apparaissant dans CREATE à faible débit. Il est montré que des ondes de pression tournantes apparaissent aux points stables et augmentent en amplitude à mesure qu’on se rapproche de la ligne de pompage, jusqu’à atteindre une taille critique induisant l’apparition d’une cellule de décollement tournant sur toute la hauteur de veine. Cette cellule entraîne la machine en pompage en seulement quelques tours. L’étude de ces ondes de pression, et la compréhension de leur véritable nature sont réalisées grâce à l’application d’un modèle analytique aux mesures expérimentales. Une description précise du déclenchement et du cycle du pompage est également faite grâce aux mesures de pression statique au dessus des rotors. Un système de contrôle anti-pompage développé au laboratoire et basé sur la détection de l’amplitude des ondes de pression est finalement décrit. / The present work is a result of collaboration between the LMFA (Laboratoire de Mécanique des Fluides et d’Acoustique, Ecole Centrale de Lyon – France), Snecma and the Cerfacs. It aims at studying the flow in the 3.5-stages high-speed axial compressor CREATE (Compresseur de Recherche pour l’Etude des effets Aérodynamique et TEchnologique - rotation speed: 11543 RPM, Rotor 1 tip speed: 313 m/s), designed and built by Snecma and investigated at LMFA on a 2-MW test rig. Steady measurements, as well as laser velocimetry, fast-response wall static and total pressure measurements have been used to experimentally investigate the flow. The analysis focuses on two main aspects: the study of the flow at stable operating points, with a special interest on the rotor-stator interactions, and the study of the instabilities arising in the machine at low mass flow rates.The description of the unsteady flow field at stable operating points is done through measurements of wall-static pressure, total pressure and velocity, but also total temperature, entropy and angle of the fluid. It is shown that the complexity and unsteadiness of the flow in a multistage compressor strongly increases in the rear part of the machine, because of the interactions between steady and rotating rows. Therefore, a modal analysis method developed at LMFA and based on the decomposition of Tyler and Sofrin is presented to analyze these interactions. It is first applied to the pressure measurements, in order to extract the contributions of each row. It shows that all the complex pressure interactions in CREATE can be reduced to three main types of interactions. The decomposition method is then applied to the entropy field extracted from URANS CFD calculations performed by the Cerfacs, in order to evaluate the impact of the interactions on the performance of the machine in term of production of losses.The last part of this work is devoted to the analysis of the instabilities arising in CREATE at low mass flows. It shows that rotating pressure waves appear at stable operating points, and increase in amplitude when going towards the surge line, until reaching a critical size provoking the onset a full span stall cell bringing the machine to surge within a few rotor revolutions. The study of these pressure waves, and the understanding of their true nature is achieved through the experimental results and the use of some analytical models. A precise description of the surge transient through wall-static pressure measurements above the rotors is also provided, as well as a description of a complete surge cycle. An anti-surge control system based on the detection of the amplitude of the pressure waves is finally proposed.
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