A thermal tip clearance control system provides a robust and flexible means of manipulating the closure between the casing and the rotating blade tips in a jet engine, reducing undesirable tip leakage flows. This may be achieved using an impingement cooling scheme on the external casing of the engine in conjunction with careful thermal management of internal over-tip seal segment cavity. For a reduction in thrust specific fuel consumption, the mass flow rate of air used for cooling must be minimised, be at as low a pressure as possible and delivered through a light weight structure surrounding the rotating components in the turbine. This thesis first characterises the effectiveness of a range of external impingement cooling arrangements in typical engine casing closure system. The effects of jet-to-jet pitch, number of jets, inline and staggered alignment of jets, arrays of jets on flange, on an engine representative casing geometry are assessed through comparison of the convective heat transfer coefficient distributions in a series of numerical studies. A baseline case is validated experimentally. The validation data allowed the suitability of different turbulence closure models to be assessed using a commercial RANS solver. Importantly for each configuration the thermal contraction of an idealised engine casing is predicted using thermo-mechanical finite element models, at a series of operating conditions representing engine idle to maximum take-off conditions. Cooling is provided by manifolds attached to the outside of the engine. The assembly tolerance of these components leads to variation in the standoff distance between the manifold and the casing. For cooling arrangements with promising performance, the study is extended to characterise the variation in closure with standoff distance. It is shown that where a sparse array of non-interacting jets is used the system can be made tolerant of large build misalignments. The casing geometry itself contributes to the thermal response of the system, and, in an additional study, the effect of casing thickness and circumferential thermal control flanges are investigated. Restriction of the passage of heat into the flanges was seen to be dramatically change their effectiveness and slight necking of the flanges at their root was shown to improve the performance disproportionally. High temperature secondary air flowing past the internal face of the engine casing tends to heat the casing, causing it to grow. Experimental and numerical characterisation of a heat transfer within a typical over-tip segment cavity heat transfer is presented in this thesis for the first time. A simplified modelling strategy is proposed for casing and a means to reduce the casing heat pickup by up to 25 % was identified. The overall validity of the modelling approach used is difficult to validate in the engine environment, however limited data from a test engine temperature survey became available during the course of the research. By modelling this engine tip clearance control system it was shown that good agreement to the temperature distribution in the engine casing could be achieved where full surface external heat transfer coefficient boundary conditions were available.

This thesis has been a collaboration between the Royal Institute of Technology (KTH) and Siemens Energy which invest in the research facility at KTH. The objective was to investigate the use of eddy current sensors in real-time monitoring of turbine blades. The main focus has been on finding a use for blade tip clearance and a correlation for the insufficient sampling that eddy current sensors suffer from. At the same time, it was desirable to also investigate the use of the same sampled data for blade tip vibration. The research on eddy current sensors is important for their relative low price compared to other instruments and how resistance it is to contamination found in turbines, enabling real-time monitoring.  The testing has been conducted at the Energy Technology department which utilizes a scaled version of a full-sized turbine to investigate performance measurements. It is scaled to have the same stage loading for both blisks investigated. Two different blisks have been used for this project, one with thicher but fewer blades and one with thinner but more blades. On each blisk different types of sampling have been done in order to capture suitable data for both tip timing and tip vibration. This resulted in sampling with static RPM and sweeps over certain regions as well as full sweeps from design RPM to standstill.  A computer model was developed to evaluate the sampled data. In the model, the sample points were interpolated to compensate for the insufficient sampling, enabling tip gap measurements. Measurements and calibration were done on the blisks for the possibility of using a compensation curve in order to be able to compensate for the signal error. The results show that eddy current sensors and setup used here have a good capability of capturing the tip clearance with precision in the range of hundreds of millimeter on the blisk with thicker blades and up to a certain rotational speed on the blisk with thinner blades. In regards to the tip vibration, eddy current system had problems capturing the time of arrival with sufficient precision correctly. / Den här uppsatsen har varit ett sammarbete mellan Kunglig Tekniska Högskolan (KTH) och Simens Energy vilka investerar i forskningen som bedrivs på KTH. Målet var att undersöka användningen av eddy current sensors för övervakning av turbinbliskar. Huvudfokus har varit att hitta användning av sensorerna för topspelsmätningar och ta fram en korregering av den otillräckliga insamlingen av data som eddy current sensorer lider av. Samtidigt var det önskvärt att samtidigt undersöka samma insamlade data för att utvärdera bladvibrationer. Forskning på eddy current sensorer är viktig för dess relativt låga pris jämfört med andra alternativ samt att de dess höga motståndskraft mot smuts som ofta finns i miljöer där turbiner används. Testerna har gjorts på instutitionen för Energiteknik vilka använder en nedskalad versioner av den verkliga storleken på turbinen för att utföra mätningar på. Två olika bliskar har använts för detta projekt, en med grövre men färre blad samt en med tunnare och fler blad. Stegbelastningen är dock samma för båda. På båda bladen har olika typer mätningar gjorts för att kunna fånga passade data för båda topspelsmätningar och bladvibrationer. Detta gav data med statiskt varvtal, långsamma svepningar över specialla regioner och svepningar över från designvarvtal ner till stillastående. En datormodell har utvecklats för utvärdera insamlade data. I modellen sker en interpolering som kompenserar för de låga antalet samplade punkter på bladet. Mätnigar och kalibreringar är gjorda på bliskarna för att skapa en kompenseringskurva åt signalfel i utdatan. Resultatet visar att eddy current systemet har goda möjligheter att visa rätt toppspel med god precition för blisken med tjocka blad och upp till ett visst varvtal på den med tunnare blad. När det kommer till bladvibrationer hade sensorerna och datormodellen svårt att fånga rätt ankomst tid för bladet med tillräckligt hög precision.