The objective of the work described in this thesis is twofold; to elucidate the nature of stall and surge in an axial flow aeroengine compressor, and to improve on current computational stall modelling techniques. Particular attention is paid to the initial stages of the stall/surge transient, and to the possibility of using active control techniques to prevent or delay the onset of stall/surge. A detailed analysis is presented of measurements of the stalling behaviour of a Rolls- Royce VIPER jet engine, showing a wide variety of stall inception and post-stall behaviour. Stall transients are traced from disturbances through to stable rotating stall or axisymmetic surge. The stall inception pattern at nearly all speeds is shown to conform to the short circumferential length scale pattern described by Day [1993a]. A multiple compressors in parallel stall model is developed using conventional stall modelling techniques, but extended to include the effects of the jet engine environment The model is shown to give a good representation of the overall stalling behaviour of the engine, although the details of the stall inception period are not accurately predicted. A system identification technique is applied to the results of the model in order to develop a method of active control of stall/surge. A new stall model is introduced and developed, based on a time-accurate three dimensional (but pitchwise averaged) solution of the viscous flow equations, with bladerow performance represented by body forces. The flow in the annulus boundary layers is calculated directly, and hence this new method is sufficiently complex to model the initial localised disturbances that lead to stall/surge. At the same time the computational power required is compatible with application to long multistage compressors.

ABSTRACT Developments in the field of microturbine technology and gas turbine driven aircraft has been progressing without much progress in light aircraft predominantly propelled by piston engines. Because of inhibitive maintenance and overhaul costs of such however, propulsion via a gas turbine engine has been proposed with the potential of eventually replacing current engine configurations. Subsequently, the objective was to conceptually design a replacement gas turbine engine in the 150 kW range. A selection of case studies was used to illustrate the changing technologies to illustrate the technological viability of micro-gas turbines for light aircraft. Advantages and disadvantages of both engine types were discussed and a concise description of gas turbine operations and its components was given. A brief overview of fundamentals as well as the transmission layout was also supplied. Three configurations were isolated, namely the single spool design, a twin spool design featuring a free power turbine and the effect of a fuel conserving recuperator. Calculations were performed using Microsoft Excel, which proved sufficient in effectively calculating complex formulae - even under the necessary iterative feed-back conditions the design process demanded. Eventually, variable-specific design criteria were derived regarding the three engine types. Because fuel consumption still proved inhibitive, the effect of recuperation was investigated which yielded a very competitive engine - should the possibility of recuperator technology exist on time. As a result, one particular recuperated, single spool gas turbine engine was successfully identified. Having met all the design criteria sufficiently, this preliminary prototype design was numerically described and put within context of principal, peripheral working components such as a compatible gearbox layout.

As usinas termelétricas a ciclo combinado empregadas na geração de energia elétrica são compostas basicamente por três elementos ou sistemas: a Turbina a Gás, a Caldeira de Recuperação e a Turbina a Vapor. A Turbina a Gás é responsável pela transformação da energia química do combustível em energia mecânica para acionar os geradores, e os gases de escapamento com alta temperatura são responsáveis pela geração de vapor para as turbinas de vapor nas caldeiras de recuperação. É por estes motivos que é importante manter disponível a Turbina a Gás. A disponibilidade de um sistema está relacionada com a confiabilidade dos seus componentes e com as políticas de manutenção associadas aos mesmos, que não só influenciam no tempo de retorno à operação após uma ação de manutenção programada ou não programada, como também na degradação da confiabilidade do sistema. Este trabalho apresenta um método de análise empregado para a estimativa da confiabilidade e disponibilidade de Turbinas a Gás empregadas em usinas termelétricas a ciclo combinado, baseado nos conceitos de Confiabilidade e Manutenção Centrada em Confiabilidade. O método baseia-se na avaliação dos tempos entre falhas das causas destas falhas, e dos tempos de reparo associados a cada uma das intervenções de operação associadas à ocorrência de falhas. Adicionalmente, apresenta-se uma aplicação deste método para Turbinas a Gás de grande porte, com potência nominal de 150MW instaladas em uma Usina Termelétrica com capacidade de geração superior a 500MW. Verifica-se a existência da diferencia na disponibilidade das duas turbinas instaladas na usina obtendo um valor de 99,35% e 96%, considerando um período de operação de 8760 horas. Finalmente, apresentam-se as principais conclusões do trabalho e uma discussão sobre a viabilidade de aplicação do método proposto. / The combined cycle thermoelectric power station presents three main equipments: the Gas Turbine, the Heat Recovery Steam Generator and the Steam Turbine. The Gas Turbine transforms the chemical energy generated by combustion in mechanical energy unit to rotate the generator\'s shaft and the exhaust gas in high temperature is used to heat water at the Heat Recovery Steam Generator to generate steam for the Steam Turbine. Taking in view the great importance of the gas turbine for power generation, its availability should be carefully evaluated to guarantee the power station full operational availability. The availability of a system is strongly associated with the parts reliability and their maintenance policy. That policy not only has influence on the parts repair time but also on the parts reliability, affecting the system degradation and availability. This study presents a method for reliability and availability evaluation of gas turbines installed in a combined cycle thermoelectric power station, based on system Reliability concepts and Reliability-Centered Maintenance. The methodology depended on time between failures, failure modes and time to repair associated to each failure that operation interruption. The method is applied on the analysis of a gas turbine with more than 150MW nominal output installed in a 500MW power plant. A difference between the gas turbines availability are identified. The calculator values are 99,35 % and 96 % for 8760 hours operation period. Finally, the main conclusions and a discussion about feasibility of application of the considered method are present at the end of the study.

This thesis experimentally investigates the phenomenon of ingress through gas turbine rim seals. The work focuses on developing experimental and numerical techniques for measuring the required sealing flow levels to purge the wheel-space against ingress and the effect of externally-induced ingress on the surface temperature as well as heat transfer to the rotor. Ingress is driven by a pressure difference between the mainstream annulus and wheel-space cavity resulting from the asymmetric external pressure profile in the annulus and/or the rotation of fluid in the rotor-stator wheel-space cavity. It can be prevented by pressurising the wheel-space through the supply of sealant flow. The University of Bath had measured and shown, for the first time, the thermal effects of ingress on the rotor in the wheel-space for a datum seal (axial-clearance seal) using thermo-chromic liquid crystal. However, as the previously used experimental technique with thermo-chromic liquid crystal was prone to large uncertainties, a non-intrusive temperature measurement technique using an infrared (IR) temperature sensor was developed. The new technique was successfully applied to the Bath one-stage gas turbine test facility and provided a full temperature history of the rotor surface in a transient heat transfer experiment. Moreover, a data analysis method appropriate for transient experiments using the IR temperature measurement technique was developed. The method was used to accurately calculate the heat transfer coefficient and the adiabatic surface temperature based on the full temperature history. A series of numerical experiments was carried out to develop the analysis method and the results from the numerical experiments were used to design new heat transfer experiments for both the 1 and 1.5-stage ingestion rigs of the University of Bath. Gas concentration measurements were made on the stator of the Bath one-stage gas turbine test rig to determine the variation of sealing effectiveness with sealant flow rate for four different seal geometries at design operational conditions. The IR temperature measurement technique was used to determine the effect of ingress on the heat transfer coefficient and the adiabatic wall temperature on the rotor of the ingestion test facility. Concurrent gas concentration measurements were made on the stator to compare the effects of ingress on the two discs (stator and rotor). Comparison between the adiabatic effectiveness on the rotor and the concentration effectiveness on the stator showed that the rotor was protected against the effects of ingress relative to the stator. The sealing air, which was drawn into the rotor boundary layer from the source region, thermally buffered the rotor against the ingested fluid in the core. Subsequently, a thermal buffer ratio hypothesis was developed and shown to be in good agreement with the experimental data. A previously published orifice model was modified so that the sealing effectiveness determined from the concentration measurements in a rig could be used to determine the effectiveness based on pressure measurements in an engine. There was good agreement between the effectiveness acquired from pressure measurement determined using the theoretical model and the sealing effectiveness determined from concentration measurements. It was also shown how parameters obtained from measurements of pressure and concentration in a rig could be used to calculate the sealing effectiveness in an engine.

A boost controlled continuously variable geometry turbocharger prototype has been designed, manufactured and tested. The prototype has been first rig tested and later fitted to a Perkins T6.354 diesel engine. The engine tests have included both steady state and transient runs. Torque back up has been improved considerably increasing from 34.3% to 55.8%, the former occurring at 1400rpm while the latter at 1200rpm. In the experimental programme, compressor surge has been the limiting parameter while in the theoretical investigations a wide mass flow compressor has been assumed and the limiting parameter was maximum cylinder pressure. In the theoretical investigations lower compression ratio and retarded injection timing have been considered to further improve the scope for higher torque back up and improved transient response. In addition the performance of the variable geometry turbocharged engine using a simple boost controlled turbine restriction schedule has been simulated. It is concluded that a simple boost controlled system will present sfc penalties in the part load regime and thus more sophisticated multi-variable schemes will have to be studied if sfc optimization is to be achieved. The experimental programme has been conducted using the 'zip fastener' design. This design has been found to be strongly non-linear with respect to turn down ratio in response to turbine restriction but will offer the required effects at the expense of a slight drop in turbine efficiency. However, in future investigations initial calibration studies have to be undertaken to ensure comparable swallowing capacities with the standard turbine which the variable geometry turbine replaces.

No description available.

<p> </p><p>Gas turbine discs are heavily loaded due to centrifugal and thermal loads and are therefore designed for a service lifetime specified in hours and cycles. New probabilistic design criteria have been worked out at Siemens Industrial Turbomachinery AB and this report is intended to evaluate if existing turbine discs meet the new design criteria. The evaluation is composed of two tasks, estimation of failure risk and investigation of which parameters that have large effect on the results.</p><p> </p><p>The outcome from the evaluations show that the failure risks are smaller than the maximum failure risks allowed in the design criteria. Further, creep strain rate, temperature and creep rupture strain are identified to have large effect on the results in the first case. In the second case blade load and other mechanical loads as well as yield stress show large effect on the results.</p><p> </p>

The hot gas temperature in gas turbine engines is far above the permissible metal temperatures. Advanced cooling technologies must be applied to cool the blades, so they can withstand the extreme conditions. Film cooling is widely used in modern high temperature and high pressure blades as an active cooling scheme. In this study, the film cooling effectiveness in different regions of gas turbine blades was investigated with various film hole/slot configurations and mainstream flow conditions. The study consisted of four parts: 1) effect of upstream wake on blade surface film cooling, 2) effect of upstream vortex on platform purge flow cooling, 3) influence of hole shape and angle on leading edge film cooling and 4) slot film cooling on trailing edge. Pressure sensitive paint (PSP) technique was used to get the conduction-free film cooling effectiveness distribution. For the blade surface film cooling, the effectiveness from axial shaped holes and compound angle shaped holes were examined. Results showed that the compound angle shaped holes offer better film effectiveness than the axial shaped holes. The upstream stationary wakes have detrimental effect on film effectiveness in certain wake rod phase positions. For platform purge flow cooling, the stator-rotor gap was simulated by a typical labyrinth-like seal. Delta wings were used to generate vortex and modeled the passage vortex generated by the upstream vanes. Results showed that the upstream vortex reduces the film cooling effectiveness on the platform. For the leading edge film cooling, two film cooling designs, each with four film cooling hole configurations, were investigated. Results showed that the shaped holes provide higher film cooling effectiveness than the cylindrical holes at higher average blowing ratios. In the same range of average blowing ratio, the radial angle holes produce better effectiveness than the compound angle holes. The seven-row design results in much higher effectiveness than the three-row design. For the trailing edge slot cooling, the effect of slot lip thickness on film effectiveness under the two mainstream conditions was investigated. Results showed thinner lips offer higher effectiveness. The film effectiveness on the slots reduces when the incoming mainstream boundary layer thickness decreases.

As a result of their unique heat recovery properties,Humidified Gas Turbine (HGT) cycles have the potential todeliver resource-effective energy to society. The EvaporativeGas Turbine (EvGT) Consortium in Sweden has been studying thesetypes of cycles for nearly a decade, but now stands at acrossroads, with commercial demonstration remaining. Thisthesis binds together several key elements for the developmentof humidified gas turbines: water recovery and air and waterquality in the cycle, cycle selection for near-term, mid-sizedpower generation, and identifying a feasible niche market fordemonstration and market penetration. Moreover, possiblesocio-technical hinders for humidified gas turbine developmentare examined. Through modelling saltcontaminant flows in the cycle andverifying the results in the pilot plant, it was found thathumidification tower operation need not endanger the hot gaspath. Moreover, sufficient condensate can be condensed to meetfeed water demands. Air filters were found to be essential tolower the base level of contaminant in the cycle. This protectsboth the air and water stream components. By capturing airparticles of a similar size to the air filters, the humidifieractually lowers air stream salt levels. Measures to minimisedroplet entrainment were successful (50 mg droplets/kg air) andmodels predict a 1% blow down from the water circuit issufficient. The condensate is very clean, with less than 1 mg/lalkali salts and easily deionised. Based on a core engine parameter analysis for three HGTcycle configurations and a subsequent economic study, asteam-cooled steam injected cycle complemented with part-flowhumidification is recommended for the mid-size power market.This cycle was found to be particularly efficient at highpressures and turbine inlet temperatures, conditions eased bysteam cooling and even intercooling. The recommended HGT cyclegives specific investment costs 30- 35% lower than the combinedcycles and cost of electricity levels were 10-18% lower.Full-flow intercooled EvGT cycles give high performances, butseem to be penalised by the recuperator costs, while stillbeing cheaper than the CC. District heating is suggested as asuitable niche market to commercially demonstrate the HGTcycle. Here, the advantages of HGT are especially pronounceddue their very high total efficiencies. Feasibility prices forelectricity were up to 35% lower than competing combinedcycles. HGT cycles were also found to effectively include wasteheat sources. <b>Keywords:</b>gas turbines, evaporative gas turbines,humidification, power generation, combined heat and powergeneration.

The average and fluctuating components in a model ring-type gas turbine combustor are characterized using a Large Eddy Simulation at a Reynolds number of 11,000, based on the bulk velocity and the mean channel height. A spatial filter is applied to the incompressible Navier-Stokes equations, and a high pass filtered Smagorinsky model is used to model the sub-grid scales. Two cases are studied: one with only the swirler inlet active, and one with a single row of dilution jets activated, operating at a momentum flux ratio J of 100. The goal of both of these studies is to validate the capabilities of the solver NEK5000 to resolve important flow features inherent to gas turbine combustors by comparing qualitatively to the work of Jakirlic. Both cases show strong evidence of the Precessing Vortex Core, an essential flow feature in gas turbine combustors. Each case captures other important flow characteristics, such as corner eddies, and in general predicts bulk flow movements well. However, the simulations performed quite poorly in terms of predicting turbulence shear stress quantities. Difficulties in properly emulating the turbulent velocity entering the combustor for the swirl, as well as mesh quality concerns, may have skewed the results. Overall, though small length scale quantities were not accurately captured, the large scale quantities were, and this stress test on the HPF LES model will be built upon in future work that looks at more complex combustors.