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Influence on tip leakage flow in a compressor cascade with plasma actuationWang, Haotian January 2019 (has links)
As one of the key components of aero engines, compressor is required to endure higher pressure, possess higher efficiency and wider operating range. Intensive studies have been made on tip leakage flow and researchers find that by reasonably organizing tip leakage flow, aero engines are more likely to achieve better performance and reliability. Conventional flow controlling methods like casing treatment and micro jet could substantially modify tip leakage flow, unfortunately with a price of additional loss, not to mention the difficulty in manufacturing such structure. Whereas plasma actuation flow control method uses plasma actuators, such equipment is easy to build, responses fast and has a wide excitation bandwidth. This method has become a new trend in internal flow active control field. In this research, a phenomenological model is adopted to simulate DBD plasma actuation in the flow field inside a compressor cascade. The aim is to find out how plasma actuation will influence tip leakage flow. Meanwhile possible means to improve plasma actuation performance are discussed. First of all, numerical simulation of flow inside a compressor cascade without plasma actuation is conducted to validate accuracy of the numerical methodology adopted and then determine one numerical approach that satisfies specific needs sufficiently. Meanwhile, influence of casing movement on tip leakage flow as well as possible mechanism of tip leakage vortex core generation is investigated in detail. The results indicate: 1. Generating position of tip leakage vortex moves towards leading edge with increasing moving speed of shroud. 2. As shroud moving speed increases, trajectory of tip leakage vortex moves away from suction side of blade and closely towards shroud. 3. Casing movement tends to transform tip leakage vortex from circular to oval shape due to circumferential shearing. 4. Casing movement has little influence on total pressure field concerning absolute pressure value. While total pressure loss does reduce slightly with increasing moving speed of shroud. 5.Vorticity transport from tip clearance into passage may be contributing significantly to generation of tip leakage vortex inner core. Secondly, a simplified model of DBD plasma actuation based on literature [1] is derived and applied through UDF function of commercial software Fluent into the flow field. Different actuation positions, voltages and frequencies are applied in simulation and compared. After that casing movement is included. Main conclusions are as follow: 6. Plasma actuation shows significant suppressing effect on tip leakage vortex on both size, trajectory and strength. 7. The suppressing effect on tip leakage vortex grows stronger as actuator moves towards leading edge. 8. Increasing actuation voltage results in stronger suppressing effect on tip leakage vortex. 9. Plasma actuation can effectively improve total pressure loss situation near shroud region with increasing actuation power. 10. Increasing actuation frequency results in stronger suppressing effect on tip leakage vortex as well. Additionally, frequency performs slightly better than voltage. 11. Casing movement tends to weaken suppressing effect of tip leakage vortex by plasma actuation. More actuation power is needed to achieve sufficient suppressing effect in real compressors. / Som en av de viktigaste komponenterna i flygmotorer krävs det att kompressorn utsätts för högre tryck, har högre effektivitet och större driftsintervall. Intensiva studier har gjorts om skovlarnas toppspel läckageflöde och man anser att det är mer sannolikt att flygmotorer uppnår bättre prestanda och tillförlitlighet genom att på ett rimligt sätt reglera läckageflödet i toppspelet. Konventionella metoder för reglering av flödet, som behandling av “casing” och mikrojet, skulle kunna ändra läckageflödet avsevärt, men medför tyvärr ytterligare förlust, för att inte tala om svårigheten att tillverka en sådan struktur. Samtidig flödeskontroll med hjälp av plasma aktuatorer som är relativt lätta att bygga, reagerar snabbt och har en bred excitationsbandvid. Denna metod har blivit en ny trend inom det interna flödesaktiva kontrollområdet. I denna forskning antas en modell för att simulera plasmaaktivering av DBD i flödesfältet i en kompressorskaskad. Man försöker ta reda på hur plasmaaktivering påverkar läckageflödet. Möjliga sätt att förbättra effekten av plasmaaktivering diskuteras. För det första genomförs numerisk simulering av flödet i en kompressorskaskad utan plasmaaktivering för att validera noggrannheten i den numeriska metoden. Därefter undersöks i detalj vilken inverkan den relativa rörelsen av ”casing” har på läckageflödet genom toppspelet och mekanismen för toppspelsvirvel analyseras. Resultaten visar: 1. Startposition för läckagevirveln rör sig mot skovelns framkant när man introducerar och ökar den relativa hastigheten för ”casing”. 2. I takt med att den relativa hastigheten ökar, kretsbanan för läckage virveln rör sig bort från skovelns sugsida och närmare mot ”casing”. 3. Den relativa rörelsen tenderar att omvandla virveln från cirkulär till oval form på grund av skjuvkrafter. 4. Den relativa rörelsen av ”casing” påverkar inte det totala tryckfältet när det gäller det absoluta tryckvärdet. Samtidigt som den totala tryckförlusten minskar något med ökad hastighet. 5. Virveltransport från toppspelet till huvudkanalen kan på ett betydande sätt bidra till att skapa virvelns inre kärna. I senare delen av arbetet utvecklas och tillämpas en förenklad modell för plasmaaktivering av DBD baserad på litteratur [1], genom att använda UDF‐funktionen i kommersiell CFD programvara Fluent. Olika aktuatorläge, spänningar och frekvenser prövas i simuleringen och jämförs. De viktigaste slutsatserna är följande: 6. Aktuering av plasma visar en betydande dämpningseffekt på läckagevirveln i toppspelet både va det gäller dess storlek, bana och styrka. 7. Den dämpande effekten på läckagevirveln blir starkare när aktuator monteras närmare skovelns framkant. 8. Ökad aktuatorspänning leder till en starkare dämpande effekt på läckagevirveln. 9. Ökad aktuatorfrekvens leder till starkare dämpningseffekt på läckagevortex också.mDessutom fungerar frekvensen något bättre än spänningen. 10. Den relativa rörelsen av ”casing” försvagar effekten av plasmaaktuering. För att uppnå tillräcklig dämpningseffekt i riktiga kompressorer krävs mer effekt till aktuatorn.
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Mise en place d'un modèle de fuite multi-états en secteur hydraulique partiellement instrumenté / Mastering losses on drinking water networkClaudio, Karim 19 December 2014 (has links)
L’évolution de l’équipement des réseaux d’eau potable a considérablement amélioré le pilotage de ces derniers. Le telérelevé des compteurs d’eau est sans doute la technologie qui a créé la plus grande avancée ces dernières années dans la gestion de l’eau, tant pour l’opérateur que pour l’usager. Cette technologie a permis de passer d’une information le plus souvent annuelle sur les consommations (suite à la relève manuelle des compteurs d’eau) à une information infra-journalière. Mais le télérelevé, aussi performant soit-il, a un inconvénient : son coût. L’instrumentation complète d’un réseau engendre des investissements que certains opérateurs ne peuvent se permettre. Ainsi la création d’un échantillon de compteurs à équiper permet d’estimer la consommation totale d’un réseau tout en minimisant les coûts d’investissement. Cet échantillon doit être construit de façon intelligente de sorte que l’imprécision liée à l’estimation ne nuise pas à l’évaluation des consommations. Une connaissance précise sur les consommations d’eau permet de quantifier les volumes perdus en réseau. Mais, même dans le cas d’une évaluation exacte des pertes, cela ne peut pas suffire à éliminer toutes les fuites sur le réseau. En effet, si le réseau de distribution d’eau potable est majoritairement enterré, donc invisible, il en va de même pour les fuites. Une fraction des fuites est invisible et même indétectable par les techniques actuelles de recherche de fuites, et donc irréparable. La construction d’un modèle de fuite multi-états permet de décomposer le débit de fuite suivant les différents stades d’apparition d’une fuite : invisible et indétectable, invisible mais détectable par la recherche de fuite et enfin visible en surface. Ce modèle, de type semi-markovien, prend en compte les contraintes opérationnelles, notamment le fait que nous disposons de données de panel. La décomposition du débit de fuite permet de fait une meilleure gestion du réseau en ciblant et adaptant les actions de lutte contre les fuites à mettre en place en fonction de l’état de dégradation du réseau. / The evolution of equipment on drinking water networks has considerably bettered the monitoring of these lasts. Automatic meter reading (AMR) is clearly the technology which has brought the major progress these last years in water management, as for the operator and the end-users. This technology has allowed passing from an annual information on water consumption (thanks to the manual meter reading) toan infra-daily information. But as efficient as AMR can be, it has one main inconvenient : its cost. A complete network instrumentation generates capital expenditures that some operators can’t allowed themselves. The constitution of a sample of meters to equip enables then to estimate the network total consumption while minimizing the investments. This sample has to be built smartly so the inaccuracy of the estimator shouldn’t be harmful to the consumption estimation. A precise knowledge on water consumption allowsquantifying the water lost volumes on the network. But even an exact assessment of losses is still not enough to eliminate all the leaks on the network. Indeed, if the water distribution network is buried, and so invisible, so do the leaks. A fraction of leaks are invisible and even undetectable by the current technologies of leakage control, and so these leaks are un-reparable. The construction of a multi-state model enables us to decompose the leakage flow according to the different stages of appearance of a leak : invisible and undetectable, invisible but detectable with leakage control and finally detectable. This semi-Markovian model takes into account operational constrains, in particular the fact that we dispose of panel data. The leakage flow decomposition allows a better network monitoring but targeting and adapting the action of leakage reduction to set up according to the degradation state of the network.
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Aero-thermal performance and enhanced internal cooling of unshrouded turbine blade tipsVirdi, Amandeep Singh January 2015 (has links)
The tips of unshrouded, high-pressure turbine blades are prone to significantly high heat loads. The gap between the tip and over-tip casing is the root cause of undesirable over-tip leakage flow that is directly responsible for high thermal material degradation and is a major source of aerodynamic loss within a turbine. Both must be minimised for the safe working and improved performance of future gas-turbines. A joint experimental and numerical study is presented to understand and characterise the heat transfer and aerodynamics of unshrouded blade tips. The investigation is undertaken with the use of a squealer or cavity tip design, known for offering the best overall compromise between the tip aerodynamics, heat transfer and mechanical stress. Since there is a lack of understanding of these tips at engine-realistic conditions, the present study comprises of a detailed analysis using a high-speed linear cascade and computational simulations. The aero-thermal performance is studied to provide a better insight into the behaviour of squealer tips, the effects of casing movement and tip cooling. The linear cascade environment has proved beneficial for its offering of spatially-resolved data maps and its ability to validate computational results. Due to the unknown tip gap height within an entire engine cycle, the effects of gap height are assessed. The squealer's aero-thermal performance has been shown to be linked with the gap height, and qualitative different trends in heat transfer are established between low-speed and high-speed tip flow regimes. To the author's knowledge, the present work is the first of its kind, providing comprehensive aero-thermal experimental research and a dataset for a squealer tip at engine-representative transonic conditions. It is also unique in terms of conducting direct and systematic validations of a major industrial computational fluid dynamics method for aero-thermal performance prediction of squealer tips at enginerepresentative transonic conditions. Finally, after recognising the highest heat loads are found on the squealer rims, a novel shaped squealer tip has been investigated to help improve the thermal performance of the squealer with a goal to improve its durability. It has been discovered that a seven percent reduction in tip temperature can be achieved through incorporating a shaped squealer and maximising the internal cooling performance.
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Evaluation of the ZDES method on an axial compressor : analysis of the effects of upstream wake and throttle on the tip-leakage flow. / Evaluation de la méthode ZDES sur un compresseur axial : analyse des effets de sillages venant de l’amont et du vannage sur le tourbillon de jeuRiera, William 27 November 2014 (has links)
L’écoulement de jeu dans les compresseurs axiaux est étudié à l’aide de la Zonal Detached Eddy Simulation (ZDES). L’objectif consiste à évaluer la capacité de méthodes hybrides URANS/LES à simuler l’écoulement de jeu d’un compresseur axial réaliste afin de mieux comprendre la physique de cet écoulement, notamment son comportement au vannage ainsi que l’effet de sillages venant du stator amont sur le rotor aval. Après avoir choisi la méthode hybride ZDES, un banc d’essai numérique est défini afin de simuler le premier rotor du compresseur de recherche CREATE. Ce banc a la particularité de pouvoir prendre en compte les effets instationnaires venant de la roue directrice d’entrée (RDE), notamment son sillage ainsi que les tourbillons générés en pied et en tête. Basé sur des critères de maillage ZDES, il est utilisé pour évaluer cette méthode comparativement aux méthodes classiques RANS et URANS. La ZDES est validée par étape jusqu’à une analyse spectrale de l’écoulement de jeu se basant sur des données expérimentales. Elle s’est révélée capable de capturer plus précisément l’intensité et la position des phénomènes instationnaires rencontrés en tête du rotor, notamment le tourbillon de jeu. Les densités spectrales de puissance analysées montrent que cela est dû en partie à une meilleure prise en compte du transfert d’énergie des grandes vers les petites structures de l’écoulement avant leur dissipation. De plus, l’écart entre les approches s’accentue lorsque le tourbillon de jeu traverse le choc en tête. Proche pompage, les effets d’interaction entre le choc, le tourbillon de jeu, la couche limite carter et le tourbillon venant de la tête de la RDE sont amplifiés. Le décollement de la couche limite carter s’accentue et une inversion locale de l’écoulement est observée. De plus, le tourbillon de jeu s’élargit et est dévié vers la pale adjacente, ce qui intensifie le phénomène de double écoulement de jeu. L’interaction du tourbillon venant de la tête de la RDE avec le choc et le tourbillon de jeu du rotor est ensuite étudiée au point de dessin. Un battement du tourbillon de jeu est rencontré lors de l’interaction de ce tourbillon avec le tourbillon de tête de la RDE, ce qui diminue le double écoulement de jeu. / The tip-leakage flow in axial compressors is studied with the Zonal Detached Eddy Simulation (ZDES). This study aims at evaluating the capability of hybrid URANS/LES methods to simulate the tip-leakage flow within a realistic axial compressor in order to better understand the involved physics, especially the behaviour of the flow near surge and the effects of stator wakes on the downstream rotor. Once the ZDES method is chosen, a numerical test bench is defined to simulate the first rotor of the research compressor CREATE. This bench takes into account the unsteady effects of the Inlet Guide Vane (IGV), such as its wake as well as vortices generated at the IGV hub and tip. It is based upon ZDES meshing criteria and is used to evaluate this method compared to classic RANS and URANS approaches. A method validation is carried out up to a spectral analysis compared to experimental data. The ZDES is capable to capture more accurately the intensity and position of the unsteady phenomena encountered in the tip region, especially the tip-leakage vortex. The power spectral densities highlight that this partly originates from a better capture of the energy transfer from large to small structures until their dissipation. The discrepancy between the methods is accentuated as the tip-leakage vortex crosses the shock. Near the surge line, the interactions between the shock, the tip-leakage vortex, the boundary layer developing on the shroud and the vortex generated by the IGV tip are amplified. The boundary layer on the shroud separates earlier and a local flow inversion occurs. Besides, the tip-leakage vortex widens and is deflected toward the adjacent blade. This strengthens the double leakage. At the design operating point, the interaction of the IGV tip vortex with the shock and the rotor tip vortex is studied. A vortex flutter is observed as the IGV tip vortex arrives on the rotor blade and stretches the rotor tip vortex. This phenomenon decreases the double leakage.
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Aero-thermal performance of transonic high-pressure turbine blade tipsO'Dowd, Devin Owen January 2010 (has links)
No description available.
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