In this investigation, casing mounted high frequency response pressure transducers are used to characterize the flow behavior near the aerodynamic stability limit of a low speed single stage axial flow compressor. Time variant pressure measurements are acquired at discrete operating points up to the stall inception point and during the transition to rotating stall, for a length of time no shorter than 900 rotor revolutions. The experimental data is analyzed using multiple techniques in the time and frequency domains. Experimental results have shown an increase in the breakdown of flow periodicity as the flow coefficient is reduced. Below a flow coefficient of 0.40 a two node rotating disturbance develops with a propagation velocity of approximately 23% rotor speed in the direction of rotation. During rotating stall, a single stall cell is present with a propagation velocity of approximately 35% rotor speed. The stall inception events present are indicative of a modal stall inception.

[pt] Os mapas de características do compressor axial representam o desempenho deste por toda sua faixa de operação. Estes mapas podem ser utilizados para determinar o ponto de operação na simulação off-design. O presente trabalho propõe uma metodologia de manipulação de mapas de características de compressores axiais, baseada nas metodologias já existentes. A rotina desenvolvida, denominada PCOMP, é capaz de obter uma nova linha de rotação, entre duas linhas adjacentes conhecidas. A distância entre duas linhas adjacentes conhecidas e a nova linha irá determinar a influência que cada uma terá nas características desta nova linha. Uma vez determinada a linha de rotação, os parâmetros são interpolados a fim de determinar a vazão mássica corrigida e eficiência isentrópica para a razão de pressão correspondente, dada na entrada da rotina. O método de ponderação para a determinação de novas linhas de rotação apresentou desvios menores que 3% para a vazão mássica corrigida e eficiência isentrópica. Comparando as saídas da rotina com dados de operação de uma usina real, foram encontrados desvios menores que 1% para a eficiência isentrópica. A rotina desenvolvida foi implementada no módulo de simulação do compressor da ferramenta de simulação de turbinas a gás denominada NGGT (Natural Gas & Gas Turbine), apresentando resultados satisfatórios. / [en] Axial compressor maps are able to represent the performance of all its operating range. These maps are used for determining the operating point in the off-design simulation. This thesis proposes a methodology for handling maps of axial compressors, based on existing methodologies. The model, called PCOMP, is able to obtain a new rotational speed line between two adjacent lines known. The distance between the known and the new line will determine the influence that each one will have in the characteristics of the new line. Once determined the speed line, one can find the operating point interpolating the known parameters to determine the corrected mass flow and isentropic efficiency for the corresponding pressure ratio given in the entry data of the routine. The weighting method using to determinate the new rotation speed line presented deviations smaller than 3% for the corrected mass flow and isentropic efficiency. By comparing the outputs of the developed code with the operating data of a real power plant, were found deviations smaller than 1% for the isentropic efficiency. The routine was successfully implemented in a gas turbine performance computer program, called NGGT (Natural Gas & Gas Turbine) model, which presented accurate and efficient simulations.

This paper presents the results of stator clocking investigations at a design point and an operating point near the stability limit in a low-speed research compressor (LSRC). The unsteady flow field of the LSRC at several clocking configurations was investigated using a three-dimensional unsteady, viscous solver. The unsteady pressure on the rotor blades at midspan (MS) was measured using time-resolving piezoresistive miniature pressure transducers. The effect of clocking on the unsteady pressure fluctuation at MS on the rotor blades is discussed for different operating points. Based on the unsteady profile pressures, the blade pressure forces were calculated. The peak-to-peak amplitudes of the unsteady blade pressure forces are presented and analysed for different clocking positions at both the design point and the operating point near the stability limit of the compressor.

No description available.

No description available.

The interaction between rotor blade tip leakage vortex and inflow disturbances, such as encountered in shrouded marine propulsors, was simulated in the Virginia Tech Linear Cascade Wind Tunnel equipped with a moving endwall system. Upstream of the blade row, idealized periodic inflow unsteadiness was generated using vortex generator pairs attached to the endwall at the same spacing as the blade spacing. At three tip gap settings, 1.7%c, 3.3%c and 5.7%c, the flow near the lower endwall of the center blade passage was investigated through three-component mean velocity and turbulence distributions measured by four-sensor hotwires. Besides time-averaged data, the measurements were processed for phase-locked analysis, with respect to pitchwise locations of the vortex generators relative to the blade passage. Moreover, surface pressure distributions at the blade tip were acquired at eight tip gaps from 0.87%c to 12.9%c. Measurements of pressure-velocity correlation were also performed with wall motion but without inflow disturbances. Achieved in this study is an understanding of the characteristics and structures of the tip leakage vortex at its initial formation. The mechanism of the tip leakage vortex formation seems to be independent of the tip gap setting. The tip leakage vortex consists of a vortical structure and a region of low streamwise-momentum fluid next to the endwall. The vortical structure is initially attached to the blade tip that creates it. This structure picks up circulation shed from that blade tip, as well as those from the endwall boundary layer, and becomes stronger with downstream distance. Partially induced by the mirror images in the endwall, the vortical structure starts to move across the passage resulting in a reduction in its rotational strength as the cross sectional area of the vortex increases but little circulation is added. The larger the tip gap, the longer the vortical structure stays attached to the blade tip, and the stronger the structure when it reaches downstream of the passage. Phased-averaged data show that the inflow disturbances cause small-scale responses and large-scale responses upstream and downstream of the vortex shedding location, respectively. This difference in scale is possibly dictated by a variation in the shedding location since the amount of circulation in the vortex is dependent on this location. The inflow disturbances possibly cause a variation in the shedding location by manipulating the separation of the tip leakage flow from the endwall and consequently the flow's roll-up process. Even though this manipulation only perturbs the leakage flow in a small scale, the shedding mechanism of the tip leakage vortex amplifies the outcome. / Ph. D.

<p>  </p> <p>The focus of this work was to characterize the overall performance effects due to altering the stagger angle of a variable inlet guide vane (VIGV) on a multistage axial compressor. Data were collected from the Purdue three-stage axial compressor (P3S). The stagger angle from the VIGV was varied thrice from the baseline configuration in increments of 5 degrees resulting in four configurations with angles of 4 deg, 9 deg, 14 deg, and 19, where the baseline configuration was 9 degrees. </p> <p>Compressor performance data were collected and analyzed for each stagger angle configuration along three corrected speeds (68%, 80%, 100%). Each speedline consisted of approximately six loading conditions for which the corrected mass flow rate was matched for each configuration to allow for a basis of comparison among the configurations. Stalling mass flow rates and stall inception were also investigated. Total pressure and total temperature rakes were installed throughout the compressor to investigate the performance at interstage locations for each loading condition. In addition to the rakes, static pressure taps were distributed along the compressor and unsteady pressure measurements were distributed circumferentially. Capacitance probes were installed over each of the three rotors to evaluate rotor tip clearance measurements during the tests. The effects of the stagger angle on the stability margin of the compressor were also characterized. Each speedline presented, thus, includes a representative stall point in addition to the six loading conditions where detailed flow field traverses were conducted. </p> <p>The results of this investigation showed that while the total pressure ratio (TPR) increased as the stagger angle decreased, the stability margin was reduced. The opposite trend was observed with a decrease in overall TPR across the compressor and an increase in stability margin for increased stagger angles. Based on findings from previous authors, this trend was anticipated. A similar metric for monitoring compressor performance is isentropic efficiency. This investigation utilized both temperature-based and torque-based isentropic efficiency. The greatest effect of the VIGV stagger angle on compressor isentropic efficiency occurred at the lowest loading conditions, and there was no discernible impact on isentropic efficiency at high loading conditions for this case. As VIGVs typically have the greatest impact on off-design conditions, this trend was expected. The varied stagger angle configurations had no discernible effect on the type of stall inception mechanism experienced by the compressor. The primary effect on stall that was consistent across the configurations was a noticeable increase in the duration and strength of modal oscillations present throughout the compressor with increased stagger angles, indicating an increase in stability. </p> <p>The data collected and presented herein provide a unique, robust dataset to improve understanding of the effects of changing stagger angles on variable inlet guide vanes on multistage axial compressors. These data correspondingly provide a unique training set and validation method for predictive technology. </p>

Wirkungsgradsteigerungen moderner Turbomaschinen machen dort auch zukünftig verstellbare Leitschaufeln unverzichtbar. Infolge komplexer Ringraumgeometrie entstehen bei der Schaufelverstellung betriebspunktabhängige Radialspalte, welche hinsichtlich Effizienzoptimierungen eine zunehmende Rolle spielen. Die vorliegende Arbeit charakterisiert die aerodynamischen Mechanismen und das Potential von spezifischen radialen Teilspalt- und Seitenwandkonturgeometrien solcher Verstellstatoren. Anders als bei durchgehenden radialen Spalten variiert der Einfluss der Teilspalte abhängig von deren axialer Position. Ein Teilspalt im hinteren Schaufelsehnenbereich erreicht reduzierte Totaldruckverluste gegenüber einer spaltfreien Referenz- beschaufelung. Dieser Vorteil vergrößert sich mit steigender Gitterbelastung und erhöht sich nochmals im Vergleich mit Konfigurationen eines vorderen Teilspaltes. Die Ergebnisse zei- gen, dass die Position entlang der Sehne der wesentliche Ein- flussfaktor auf die Radialspaltcharakteristik ist, die Spaltlänge als auch deren radiale Variation spielen nur eine untergeordnete, quantitative Rolle. Auch die untersuchten modellhaften Seitenwandkonturen wirken sich aufgrund sekundärer geome- trischer Einflüsse positiv auf Verlust und Gitterumlenkung in der Abströmung aus. Reduzierte Abmessungen der Teilspalte schwächen auch charakteristische Periodizitäten in Verbindung mit Spaltströmung bzw. resultierendem Spaltwirbel ab. Diese Erkenntnisse erlauben aerodynamische Optimierungen der Geometrie eines spezifischen Statordesigns. Ebenso ergibt sich ein Anwendungspotential im Randbereich starrer Leitschaufeln.

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.

Ce travail de thèse, mené dans le cadre d’une convention CIFRE entre Snecma, le CERFACS et le LMFA, s’inscrit dans un contexte d’amélioration des performances et d’extension de la plage de fonctionnement des compresseurs de type axial équipant les turboréacteurs. L’une des principales difficultés rencontrée dans cette démarche concerne la maîtrise des écoulements dans la zone de jeu en tête des aubes rotors et qui peuvent entraîner une perte de stabilité du système (pompage et décollement tournant).Une solution technologique prometteuse pour améliorer la stabilité est le traitement de carter qui consiste en un dispositif passif complexe de fentes implantées au carter au droit des rotors. En vue d’en améliorer sa conception, les travaux de thèse visent plus particulièrement à approfondir la compréhension des mécanismes d’action grâce à une approche numérique CFD avec le code elsA développé par l’ONERA et le CERFACS, en modélisation stationnaire et instationnaire. Ces travaux s’articulent autour de trois axes principaux. Le premier a eu pour objectif de développer un outil numérique d’aide à la compréhension des mécanismes d’action des traitements de carter et de diagnostic de leur efficacité. Le principe de l’outil, qui est une extension du modèle initialement proposé par Shabbir et Adamczyk, repose sur une évaluation des contributions des termes des équations de Navier-Stokes stationnaires et instationnaires sur un volume de contrôle pris dans l’écoulement. Dans le cas pratique, cela revient à quantifier les efforts appliqués sur le fluide. Le second axe traite de l’analyse des mécanismes d’action des traitements de carter axisymétriques dans deux compresseurs axiaux : l’un subsonique à carter cylindrique (CREATE) et l’autre transsonique à carter conique (NASA Rotor 37). Les enseignements de cette étude indiquent que ce type de géométrie est marqué par son effet d’aspiration de fluide dans la veine. Ce mécanisme est d’autant plus amplifié par un phénomène d’interaction complexe des fentes avec l’écoulement de jeu et la proximité de l’intrados de l’aube adjacente. Cette partie s’est également attardé à la réponse des rainures à un phénomène instationnaire de type sillage de roue amont. Les résultats ont montré que les fentes amortissent les fluctuations de gradient de pression adverse. Le troisième axe porte sur l’analyse des mécanismes des traitements de carter non-axisymétriques à travers l’étude numérique d’un cas test transsonique à carter cylindrique (CBUUA). Le mécanisme d’action améliorant la stabilité de la machine tient en la capacité des fentes à limiter la migration dans la direction circonférentielle du vortex de jeu. Les résultats montrent que ce type de géométrie est caractérisé par son effet de réinjection d’air qui vient ré-énergétiser l’écoulement proche carter. / This thesis work, conducted as part of a CIFRE agreement between Snecma, CERFACS and LMFA, deals with the context of improving performance and extending the operating range of axial compressors fitted turbojets. One of the main difficulties in this approach is the flow control in the rotor tip region, which can cause the loss of the system stability (surge and rotating stall). A promising technology known to bring substantial stability is the casing treatment. This passive control device consists of slots of complex geometry within the rotor casing. In order to improve its design, the thesis aimed specifically at improving the understanding of their mechanisms through a numerical approach using the CFD code elsA developed by ONERA and CERFACS, with steady and unsteady approaches. This work focused on three main axes. The first concerns the development of a numerical tool to support the understanding of casing treatment mechanisms and the diagnosis of their efficiency. The principle of the tool, which is an extension of the model originally proposed by Shabbir and Adamczyk, is based on an assessment of the contributions of the terms of the steady and unsteady Navier-Stokes equations on a control volume taken in the flow. In practice, this permits to quantify the forces applied to the fluid. The second axis deals with the analysis of the flow mechanisms induced by axisymetric casing treatments in two axial compressors : one subsonic with a cylindrical casing (CREATE) and the other transonic with a conical casing (NASA Rotor 37). The findings of this study indicate that this type of geometry is characterized by its bleeding effect. This mechanism is further amplified by a complex phenomenon of interaction between grooves, tip leakage vortex and the proximity to the pressure side of the adjacent blade. This part has also dwelt on the groove’s response to unsteady upstream stator wakes. The results showed that the slots are able to damp fluctuations of adverse pressure gradient. The third area concerns the analysis of the flow mechanisms induced by non-axisymmetric casing treatment through the numerical study of a transonic compressor with cylindrical casing (CBUUA). The mechanism leading to an enhancement of the stability results in slots ability to limit the migration in the circumferential direction of the tip leakage vortex. The results show that this type of geometry is characterized by its effect of re-injection of fluid that comes re-energize the near casing flow.