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abstract: Efficient performance of gas turbines depends, among several parameters, on the mainstream gas entry temperature. At the same time, transport of this high temperature gas into the rotor-stator cavities of turbine stages affects the durability of rotor disks. This transport is usually countered by installing seals on the rotor and stator disk rims and by pressurizing the cavities by injecting air (purge gas) bled from the compressor discharge. The configuration of the rim seals influences the magnitude of main gas ingestion as well as the interaction of the purge gas with the main gas. The latter has aerodynamic and hub endwall heat transfer implications in the main gas path. In the present work, experiments were performed on model single-stage and 1.5-stage axial-flow turbines. The turbines featured vanes, blades, and rim seals on both the rotor and stator disks. Three different rim seal geometries, viz., axially overlapping radial clearance rim seals for the single-stage turbine cavity and the 1.5-stage turbine aft cavity, and a rim seal with angular clearance for the single-stage turbine cavity were studied. In the single-stage turbine, an inner seal radially inboard in the cavity was also provided; this effectively divided the disk cavity into a rim cavity and an inner cavity. For the aft rotor-stator cavity of the 1.5-stage turbine, a labyrinth seal was provided radially inboard, again creating a rim cavity and an inner cavity. Measurement results of time-average main gas ingestion into the cavities using tracer gas (CO2), and ensemble-averaged trajectories of the purge gas flowing out through the rim seal gap into the main gas path using particle image velocimetry are presented. For both turbines, significant ingestion occurred only in the rim cavity. The inner cavity was almost completely sealed by the inner seal, at all purge gas flow rates for the single-stage turbine and at the higher purge gas flow rates for 1.5-stage turbine. Purge gas egress trajectory was found to depend on main gas and purge gas flow rates, the rim seal configuration, and the azimuthal location of the trajectory mapping plane with respect to the vanes. / Dissertation/Thesis / M.S. Mechanical Engineering 2010

In the current climate crisis situation, the development and wide operating range of electric mobility is of great importance, with electric rail traction being the main form of electric transport over medium-long distances. In this sense, electric traction converters are undergoing a deep modification, moving towards more powerful, more compact converters with a wider operating range. This project addresses the problem of overheating of the internal air of a railway electric traction converter when it operates in extreme environments with high temperatures, around 50o C or 60o C. In these cases, the existing cooling system, which uses external air at ambient temperature as the coolant fluid, is not enough to ensure safe operation of the converter. This limits the operating range of electric trains with high power density converters, which cannot operate in hot climates. Furthermore, it poses a risk for other operating ranges in the near future, where the development of converters with higher current levels and thus higher power losses will again challenge conventional cooling systems. This project uses the MITRAC/TC1500TM traction converter developed by Alstom as a basis for proposing different additional cooling systems that complement the conventional one, with the use of different cooling technologies, including forced air convection, heat pipes, liquid-cooled cold plates and Peltier cells, also called thermoelectric coolers. The implementation of the different technologies is evaluated based on mathematical models developed in MATLAB® and computational fluid dynamics simulations in StarCCM+® . The results obtained allow to conclude that the use of heat pipes and Peltier cells is the most recommendable for the development of thermal management systems for electric traction converters, provided that they are implemented with a good external heat dissipation medium, preferably ambient temperature air flows already that already exist in the converter. Furthermore, it is shown that the same cooling technology can provide very different results depending on its implementation. / I den rådande klimatkrisen är det mycket viktigt att utveckla elektrisk mobilitet och att ha ett brett användningsområde, där elektrisk järnvägsdrift är den viktigaste formen av elektrisk transport över medellånga avstånd. Omvandlarna för elektrisk traktion genomgår därför en genomgripande förändring, mot kraftfullare och mer kompakta omvandlare med ett bredare driftsområde. Detta projekt behandlar problemet med överhettning av den inre luften i en elektrisk traktionsomvandlare för tåg när den används i extrema miljöer med höga temperaturer, runt 50o C eller 60oC. I dessa fall är det befintliga kylsystemet, som använder extern luft vid omgivningstemperatur som kylmedel, inte tillräckligt för att garantera en säker drift av omvandlaren. Detta begränsar användningsområdet för elektriska tåg med omvandlare med hög effektdensitet, som inte kan användas i varma klimat. Dessutom utgör det en risk för andra driftområden inom den närmaste framtiden, där utvecklingen av omvandlare med högre strömnivåer och därmed högre effektförluster återigen kommer att utmana konventionella kylsystem. I projektet används MITRAC/TC1500TM , en traktionsomvandlare som utvecklats av Alstom, som grund för att föreslå olika ytterligare kylsystem som kompletterar det konventionella, med användning av olika kyltekniker, inklusive luftkonvektion, värmerör, vätskekylda kylplattor och Peltierceller, även kallade termoelektriska kylare. Implementeringen av de olika teknikerna utvärderas baserat på matematiska modeller som utvecklats i MATLAB® och beräkningsflödesdynamiska simuleringar i StarCCM+®. De erhållna resultaten gör det möjligt att dra slutsatsen att användningen av värmerör och Peltier-celler är det mest rekommenderade för utvecklingen av termiska styrsystem för elektriska traktionsomvandlare, förutsatt att de implementeras med ett bra externt värmeavledningsmedium, helst luftflöden vid omgivningstemperatur som redan finns i omvandlaren. Dessutom visas att samma kylteknik kan ge mycket olika resultat beroende på hur den implementeras.