The analysis of turbulent flows provides a unique scientific challenge whose solution remains central to unraveling the fundamental nature of all fluid dynamics. Measuring and predicting turbulent flows becomes even more difficult when considering a two-phase flow, which is a commonly encountered engineering problem across many disciplines. One such example, the ingestion of foreign debris into a gas turbine engine, provided the impetus for this study. Despite more than 40 years of research, operation with a particle-laden inlet flow remains a significant problem for modern turbomachines. The purpose, therefore, is to develop experimental methods for investigating multi-phase flows relevant to the cooling of gas turbine components. Initially, several generic components representing turbine cooling designs were evaluated with a particle-laden flow using a special high temperature test facility. The results of this investigation revealed that blockage was highly sensitive to the carrier flowfield as defined by the cooling geometry. A second group of experiments were conducted in one commonly used cooling design using a Time Resolved Digital Particle Image Velocimetry (TRDPIV) system that directly investigated both the carrier flowfield and particle trajectories. Traditional PIV processing algorithms, however, were unable to resolve the particle motions of the two-phase flow with sufficient fidelity. To address this issue, a new Particle Tracking Velocimetry (PTV) algorithm was developed and validated for both single-phase and two-phase flows. The newly developed PTV algorithm was shown to outperform other published algorithms as well as possessing a unique ability to handle particle laden two-phase flows. Overall, this work demonstrates several experimental methods that are well suited for the investigation of wall-bounded turbulent two-phase flows, with a special emphasis on a turbine cooling method. The studies contained herein provide valuable information regarding the previously unknown fluid and particle dynamics within the turbine cooling system. / Ph. D.

The highly competitive gas turbine industry has been motivated by consumer demands for higher power-to-weight ratios, increased thermal efficiencies, and reliability while maintaining affordability. In its continual quest, the industry must continually try to raise the turbine inlet temperature, which according to the well-known Brayton cycle is key to higher engine efficiencies. The desire for increased turbine inlet temperatures creates an extremely harsh environment for the combustor liner in addition to the components downstream of the combustor. Shear layers between the dilution jets and the mainstream, as well as combustor liner film-cooling interactions create a complex mean flow field within the combustor, which is not easy to model. A completely uniform temperature and velocity profile at the combustor exit is desirable from the standpoint of reducing the secondary flows in the turbine. However, this seldom occurs due to a lack of thorough mixing within the combustor. Poor mixing results in non-uniformities, such as hot streaks, and allow non-combusted fuel to exit the combustor. This investigation developed a database documenting the thermal and flow characteristics within a combustor simulator representative of the flowfield within a gas turbine aero-engine. Three- and two-component laser Doppler velocimeter measurements were completed to quantify the flow and turbulence fields, while a thermocouple rake was used to quantify the thermal fields. The measured results show very high turbulence levels due to the dilution flow injection. Directly downstream of the dilution jets, an increased thickness in the film-cooling was noted with a fairly non-homogeneous temperature field across the combustor width. A highly turbulent shear layer was found at the leading edge of the dilution jets. Measurements also showed that a relatively extensive recirculation region existed downstream of the dilution jets. Despite the lack of film-cooling injection at the trailing edge of the dilution hole, there existed coolant flow indicative of a horse-shoe vortex wrapping around the jet. As a result of the dilution jet interaction with the mainstream flow, kidney-shaped thermal fields and counter-rotating vortices developed. These vortices serve to enhance combustor mixing. / Master of Science

No description available.

Hybrid solid oxide fuel cell / gas turbine (SOFC/GT) systems offer high efficiency power generation, but face numerous integration and operability challenges. This dissertation addresses the application of hardware-in-the-loop simulation (HILS) to explore the performance of a solid oxide fuel cell stack and gas turbine when combined into a hybrid system. Specifically, this project entailed developing and demonstrating a methodology for coupling a numerical SOFC subsystem model with a gas turbine that has been modified with supplemental process flow and control paths to mimic a hybrid system. This HILS approach was implemented with the U.S. Department of Energy Hybrid Performance Project (HyPer) located at the National Energy Technology Laboratory. By utilizing HILS the facility provides a cost effective and capable platform for characterizing the response of hybrid systems to dynamic variations in operating conditions. HILS of a hybrid system was accomplished by first interfacing a numerical model with operating gas turbine hardware. The real-time SOFC stack model responds to operating turbine flow conditions in order to predict the level of thermal effluent from the SOFC stack. This simulated level of heating then dynamically sets the turbine's "firing" rate to reflect the stack output heat rate. Second, a high-speed computer system with data acquisition capabilities was integrated with the existing controls and sensors of the turbine facility. In the future, this will allow for the utilization of high-fidelity fuel cell models that infer cell performance parameters while still computing the simulation in real-time. Once the integration of the numeric and the hardware simulation components was completed, HILS experiments were conducted to evaluate hybrid system performance. The testing identified non-intuitive transient responses arising from the large thermal capacitance of the stack that are inherent to hybrid systems. Furthermore, the tests demonstrated the capabilities of HILS as a research tool for investigating the dynamic behavior of SOFC/GT hybrid power generation systems.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The main components of a micro gas turbine engine are a centrifugal or mixed-flow compressor, a combustion chamber and a single stage axial-flow or radial-flow turbine. The goal of this thesis is to formulate a design methodology for small axial-flow turbines. This goal is pursued by developing five design-related capabilities and applying them to develop a turbine for an existing micro gas turbine engine. Firstly, a reverse engineering procedure for producing digital three-dimensional models of existing turbines is developed. Secondly, a procedure for generating candidate turbine designs from performance requirement information is presented. The third capability is to use independent analysis procedures to analyse the performance of a turbine design. The fourth capability is to perform structural analysis to investigate the behavior of a turbine design under static and dynamic loading. Lastly, a manufacturing process for prototypes of a feasible turbine design is developed. The reverse engineering procedure employs point cloud data from a coordinate measuring machine and a CT-scanner to generate a three-dimensional model of the turbine in an existing micro gas turbine engine. The design generation capability is used to design three new turbines to match the performance of the turbine in the existing micro gas turbine engine. Independent empirical and numerical turbine performance analysis procedures are developed. They are applied to the four turbine designs and, for the new turbine designs, the predicted efficiency values differ by less than 5% between the two procedures. A finite element analysis is used to show that the stresses in the roots of the turbine rotor blades are sufficiently low and that the dominant excitation frequencies do not approach any of the blade natural frequencies. Finally prototypes of the three new turbine designs are manufactured through an investment casting process. Patterns made of an organic wax-like material and a polystyrene material are used, with the former yielding superior results. / AFRIKAANSE OPSOMMING: Mikro-gasturbiene-enjins bestaan uit 'n sentrifugaal- of ‘n gemende-vloeikompressor, 'n verbrandingsruim en 'n enkel-stadium-aksiaalvloei- of ‘n radiaalvloei-turbine. Die doel van hierdie tesis is om 'n ontwerpsmetodologie vir klein aksiaalvloei-turbines saam te stel. Hierdie doel word deur die ontwikkeling en toepassing van vyf ontwerpsverwante vermoëns nagestreef. Eerstens word 'n tru-waartse-ingenieursproses ontwikkel om drie-dimensionele rekenaarmodelle van die bestaande turbines te skep. Tweedens word 'n metode om kandidaatturbineontwerpe vanaf werkverrigtingsvereistes te verkry, voorgestel. Die derde ontwerpsvermoë is om die werksverrigting van 'n turbineontwerp met onafhanklike analises te evalueer. Die vierde ontwerpsvermoë is om die struktuur van 'n turbinelem te analiseer sodat die effek van statiese en dinamiese belastings ondersoek kan word. Laastens word 'n vervaardigingsproses vir prototipes van geskikte turbineontwerpe ontwikkel. Die tru-waartse-ingenieursproses maak gebruik van 'n koördinaat-meet-masjien en 'n CT-skandeerder om puntewolkdata vanaf die turbine in 'n bestaande mikro-gasturbiene-enjin te verkry. Die data word dan gebruik om 'n drie-dimensionele model van die turbine te skep. Die ontwerpskeppingsvermoë word dan gebruik om drie kandidaatturbineontwerpe vir die bestaande mikro-gasturbiene-enjin te skep. Onafhanklike empiriese en numeriese prosedures om die werkverrigting van 'n turbineontwerp te analiseer word ontwikkel. Beide prosedures word op die vier turbineontwerpe toegepas. Daar word gevind dat die voorspelde benuttingsgraadwaardes van die nuwe ontwerpe met minder as 5% verskil vir die twee prosedures. 'n Eindige-element-analise word dan gebruik om te wys dat die spannings in die wortels van die turbinelemme laag genoeg is, asook dat die dominante opwekkingsfrekwensies nie die lem se natuurlike frekwensies nader nie. Laastens word prototipes van die drie nuwe turbineontwerpe deur 'n beleggingsgietproses vervaardig. In die vervaardigingproses word die effektiwiteit van twee materiale vir die gietpatrone getoets, naamlik 'n organiese wasagtige materiaal en 'n polistireen-materiaal. Daar word bevind dat die gebruik van die wasagtige gietpatrone tot beter resultate lei.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis details the methodology for developing a centrifugal compressor for application in a Micro Gas Turbine (MGT). This research forms part of a larger project, namely project Ballast, initiated by the South African Air Force (SAAF) in conjunction with Armscor. The methodology encompasses the development of a mean-line code that makes use of 1-dimensional theory in order to create an initial centrifugal compressor geometry which includes a rotor as well as radial vaned diffuser. This is followed by a Computational Fluid Dynamics (CFD) simulation process during which the compressor is optimised in order to maximise its performance. Before manufacturing a Finite Element Analysis (FEA) is done in order to ensure that the rotor does not fail during testing. The testing of the compressor is done to compare the numerical results with the experimental results and in so doing confirms the design process. A previous student had designed a rotor by making use of a mean-line code as well as a CFD optimisation process. The rotor had a measured total-static pressure ratio of roughly 2.8 at 121 kRPM and a total-total isentropic efficiency of 79.1 % at said rotational speed. The inclusion of a vaned diffuser resulted in a higher total-static pressure ratio and accordingly the compressor designed in this report has a CFD determined total-static pressure ratio of 3.0. The efficiency would however drop and as such a total-total isentropic efficiency of 76.5 % was determined theoretically. The theoretical results correlated well with the experimental results and as such it was concluded that the design methodology developed was sound. / AFRIKAANSE OPSOMMING: Hierdie tesis bespreek die metodologie vir die ontwikkeling van ‘n sentrifugale kompressor vir toepassing in ‘n Mikro-Gasturbine (MGT). Die tesis vorm deel van ‘n groter projek, genaamd die Ballast projek, wat deur die Suid-Afrikaanse Lugmag (SALM) daargestel is in samewerking met Krygkor. Die metodologie behels die ontwikkeling van ‘n middel-lyn kode wat gebruik maak van 1-dimensionele teorie om die aanvanklike geometrie van die kompressor te skep. Die geometrie bevat beide die rotor asook die gelemde radiale diffusor. Hierdie proses word gevolg deur ‘n Berekeningsvloeidinamika (BVD) simulasie waartydens die kompressor geoptimeer word om sodoende die verrigting ten volle te verbeter. Voordat vervaardiging plaasvind word ‘n Eindige Element Analise (EEA) toegepas om te verseker dat die rotor nie sal faal tydens toetse nie. Die toetse word gedoen sodat die eksperimentele resultate met die numeriese resultate vergelyk kan word. Sodoende word die proses waardeur die kompressor ontwikkel word bevestig. ‘n Vorige student het ‘n rotor ontwerp deur gebruik te maak van ‘n middel-lyn kode asook ‘n BVD optimerings proses. Die rotor het ‘n gemete totaal-statiese drukverhouding van ongeveer 2.8 teen 121 kRPM gelewer en ‘n totaal-totale isentropiese benutingsgraad van 79.1 % teen dieselfde omwentelingspoed. Met die insluiting van ‘n gelemde radiale diffuser word ‘n hoër totaal-statiese druk verhouding verwag en as sulks lewer die nuut-ontwerpte kompressor soos in die tesis bespreek ‘n teoretiese totaal-statiese drukverhouding van 3.0. Die benutingsgraad sal egter daal en daarvolgens het die nuwe kompressor ‘n totaal-totale isentropiese benutingsgraad van 76.5 % gelewer. Die eksperimentele resultate het goed ooreengestem met die teoretiese resultate en as sulks was dit besluit dat die ontwerps-metodologie goed is.

A full Strouhal number thermo-acoustic model is purposed for the feedback control of self excited noise driven combustors. The inclusion of time delays in the volumetric heat release perturbation models create unique behavioral characteristics which are not properly reproduced within current low Strouhal number thermo acoustic models. New analysis tools using probability density functions are introduced which enable exact expressions for the statistics of a time delayed system. Additionally, preexisting tools from applied mathematics and control theory for spectral analysis of time delay systems are introduced to the combustion community. These new analysis tools can be used to extend sensitivity function analysis used in control theory to explain limits to control effectiveness in self-excited combustors. The control effectiveness of self-excited combustors with actuator constraints are found to be most sensitive to the location of non-minimum phase zeros. Modeling the non-minimum phase zeros correctly require accurate volumetric heat release perturbation models. Designs that removes non-minimum phase zeros are more likely to have poles in the right hand complex plane. As a result, unstable combustors are inherently more responsive to feedback control.

Most mature oil reservoirs or fields tend to perform below expectations, owing to high level of associated gas production. This creates a sub-optimal performance of the oil production surface facilities; increasing oil production specific operating cost. In many scenarios oil companies flare/vent this gas. In addition to oil production constraints, associated gas flaring and venting consists an environmental disasters and economic waste. Significant steps are now being devised to utilise associated gas using different exploitation techniques. Most of the technologies requires large associated gas throughput. However, small-scale associated gas resources and non-associated natural gas reserves (commonly referred to as stranded gas or marginal field) remains largely unexploited. Thus, the objective of this thesis is to evaluate techno- economic of gas turbine engines for onsite electric power generation called gas- to-wire (GTW) using the small-scaled associated gas resources. The range of stranded flared associated gas and non-associated gas reserves considered is around 10 billion to 1 trillion standard cubic feet undergoing production decline. The gas turbine engines considered for power plant in this study are based on simple cycle or combustion turbines. Simple cycle choice of power-plant is conceived to meet certain flexibility in power plant capacity factor and availability during production decline. In addition, it represents the basic power plant module cable of being developed into other power plant types in future to meet different local energy requirements. This study developed a novel gas-to-wire techno-economic and risk analysis framework, with capability for probabilistic uncertainty analysis using Monte Carlo simulation (MCS) method. It comprises an iterative calculation of the probabilistic recoverable reserves with decline module and power plant thermodynamic performance module enabled by Turbomatch (an in-house code) and Gas Turb® software coupled with economic risk modules with @Risk® commercial software. This algorithm is a useful tool for simulating the interaction between disrupted gas production profiles induced by production decline and its effect on power plant techno-economic performance over associated gas utilization economic life. Furthermore, a divestment and make- up fuel protocol is proposed for management of gas turbine engine units to mitigate economical underperformance of power plant regime experienced due to production decline. The results show that utilization of associated gas for onsite power generation is a promising technology for converting waste to energy. Though, associated gas composition can be significant to gas turbine performance but a typical Nigerian associated gas considered is as good as a regular natural gas. The majority of capital investment risk is associated with production decline both natural and manmade. Finally, the rate of capital investment returns decreases with smaller reserves.

Resumo: Estudos têm sido realizados em relação à utilização de biodiesel em motores alternativos de ciclo Diesel, porém pouco material é encontrado quando se utiliza este combustível em turbinas a gás. Este trabalho analisou os parâmetros de desempenho e emissões de poluentes para várias misturas de biodiesel/querosene de aviação em um turboeixo Rover 1/S60. Os testes mostraram que não houve alterações significativas na operação do turboeixo. O estudo mostrou, também, que houve decréscimo de eficiência térmica e aumento de consumo de combustível com a utilização de misturas mais ricas em biodiesel. As emissões de poluentes também decresceram com o aumento de teor de biodiesel na mistura. / Abstract: Several tests have been performed comparing diesel and several kinds of esthers (biodiesel), most in reciprocating engines but also in micro-gas-turbines. This work studies a stationary turboshaft Rover 1/S60 performance and pollution emissions in the utilization of several blends of aviation kerosene and biodiesel. The tests also show that no significative changes occurred in turboshaft operation. This study also shows an increase of fuel consumption and a decrease in thermal efficiency and a decrease of pollutant species emission as the higher biodiesel proportion at blends are used at turboshaft operation. / Orientador: João Andrade de Carvalho Junior / Coorientador: Pedro Teixeira Lacava / Banca: Petronio Masanobu Tanisho / Banca: Luiz Daré Neto / Mestre

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The use of micro gas turbines (MGTs) for the propulsion of unmanned aerial vehicles (UAVs) has become an industry standard. MGTs offer better performance vs. weight than similar sized, internal combustion engines. The front component of an MGT serves the purpose of compressing air, which is subsequently mixed with a fuel and ignited to both power the turbine which drives the compressor, and to produce thrust. Centrifugal compressors are typically used because of the high pressure ratios they deliver per stage. The purpose of this project was to design a centrifugal compressor impeller, and to devise a methodology and the tools with which to perform the aforementioned. A compressor impeller adhering to specific performance and dimensional requirements was designed. The new compressor was designed using a mean-line performance calculation code. The use of the code was vindicated through comparison with the results from a benchmark study. This comparison included mean-line, Computational Fluid Dynamic (CFD), and experimental results: the new design mean-line results were compared to the results of CFD simulations performed on the same design. The new design was optimised using an Artificial Neural Network (ANN) and Genetic Algorithm. Prior to and during optimisation, the ANN was trained using a database of sample CFD calculations. A Finite Element Analysis (FEA) was done on the optimised impeller geometry to ensure that failure would not occur during operation. According to CFD results, the final design delivered good performance at the design speed with regards to pressure ratio, efficiency, and stall margin. The mechanical stresses experienced during operation were also within limits. Experimental results showed good agreement with CFD results of the optimised impeller. Keywords: micro gas turbine, centrifugal compressor, impeller, CFD, experimental, optimisation, FEA. / AFRIKAANSE OPSOMMING: Die gebruik van mikrogasturbines vir die aandrywing van onbemande vliegtuie het ‟n standaard geword in die industrie. Mikrogasturbines bied beter werkverrigting teen gewig as binnebrandenjins van soortgelyke grote. Hierdie eienskap verseker dat mikrogasturbines as aandryfmotors vir onbemande vliegtuie uiters voordelig is. Die voorste komponent van ‟n mikrogasturbine dien om lug saam te pers, wat dan met brandstof gemeng en daarna aan die brand gesteek word om krag aan die kompressor en stukrag te voorsien. Sentrifugaalkompressors word tipies gebruik as gevolg van die hoë drukverhoudings wat hierdie komponente per stadium kan lewer. Die doel van hierdie projek was om ‟n sentrifugaalkompressor te ontwerp, en ‟n metode en die hulpmiddels te ontwikkel om laasgenoemde uit te voer. ‟n Kompressor rotor wat voldoen het aan sekere werkverrigtings en dimensionele vereistes is ontwerp. Die nuwe kompressor rotor is met behulp van 1-dimensionele werkverrigting-berekeningskode ontwerp. Die berekeningsakkuraatheid van die kode en díé van ‟n kommersiële Berekenings Vloeidinamika pakket is bevestig deur die berekende resultate te vergelyk met die van eksperimente. Die nuwe rotor is gevolglik deur middel van ‟n Kunsmatige Neurale Netwerk en Genetiese Algoritme geoptimeer. Die Kunsmatige Neurale Netwerk is voor en gedurende optimering deur Berekenings Vloeidinamika simulasies opgelei. Die meganiese sterkte van die geoptimeerde rotor is nagegaan met behulp van ‟n Eindige Element Analise. Dit is gedoen om te verseker dat die rotor nie sal faal by die bedryfspunt nie. Berekenings Vloeidinamika resultate het getoon dat die finale rotor ontwerp ‟n goeie werkverrigting lewer by die ontwerpspoed, met betrekking tot drukverhouding, bennutingsgraad, en stakingsmarge. Eksperimentele resultate het goeie ooreenstemming met die Berekenings Vloeidinamika resultate van die geoptimeerde rotor getoon. Sleutelwoorde: mikrogasturbine, sentrifigaalkompressor, rotor, Berekenings Vloeidinamika, eksperimenteel, optimering, Eindige Element Analise.