<p> Rising costs and volatility in aviation fuel and increased regulations resulting from climate change  concerns have driven gas turbine engine manufacturers to focus on reducing fuel consumption.  Implementing centrifugal compressors as the last stage in an axial engine architecture allows for  reduced core diameters and higher fuel efficiencies. However, a centrifugal compressor's  performance relies heavily on its stationary diffusion system. Furthermore, the highly unsteady  and turbulent flow field exhibited in the diffusion system often causes CFD models to fall short of  reality. Therefore, rapid validation is required to match the speed at which engineers can simulate  different diffuser designs utilizing CFD. One avenue for this is through the use of additive  manufacturing in centrifugal compressor experimental research. This study focused on implementing a new generation of the Centrifugal Stage for Aerodynamic  Research (CSTAR) at the Purdue Compressor Research Lab that utilizes an entirely additively  manufactured diffusion system. In addition, the new configuration was used to showcase the  benefits of additive manufacturing (AM) in evaluating diffusion components. Two diffusion  systems were manufactured and assessed. The Build 2 diffusion system introduced significant  modifications to the diffusion system compared to the Build 1 design. The modifications included changes to the diffuser vane geometry, endwall divergence, and increased deswirl pinch and vane  geometries. The Build 2 diffusion system showed performance reductions in total and static  pressure rise, flow range, and efficiencies. These results were primarily attributed to the changes  made to the Build 2 diffuser. The end wall divergence resulted in end wall separation that caused  increased losses. The changes to the diffuser vane resulted in increased throat blockage and lower  pressure rise and mass flow rate. In addition to the experimental portion of this study, a computational study was conducted to study  the design changes made to the Build 2 diffusion system. A speedline at 100% corrected rotational  speed was solved, and the results were compared to experimental data. The simulated data matched  the overall stage and diffusion system performance relatively well, but the internal flow fields of  the diffusion components, namely the diffuser, were not well predicted. This was attributed to  16 using the SST turbulence model over BSL EARSM. The BSL EARSM model more accurately  predicted the diffuser flow field to the SST model.  </p>

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Compressed air makes up an important part of South African precious metal mining processes. Rising operational costs in the struggling mining sector increased the interest of the power utility, Eskom, and mine management in achievable electrical energy savings. Demand side management initiatives, funded by Eskom, realised a significant improvement in electrical energy efficiency of compressed air networks. Supply side interventions further aided optimisation by lowering operational costs. Previous research identified the need for integrating compressed air supply and demand side initiatives. Automated compressor control systems were needed in industry to realise missed opportunities due to human error on manual control systems. Automatic systems were found to be implemented in the industry, but missed savings opportunities were still encountered. This was due to the static nature of these control systems, requiring human intervention from skilled artisans. A comprehensive system is required that can adjust dynamically to the ever-changing demand and other system changes. Commercially available simulation software packages have been used by various mine groups to determine an optimal control philosophy. Satisfactory results were obtained, but the simulations were still based on static control inputs. No simulation system was found that could solve and optimise a system based on real-time instrumentation feedback. By combining simulation capabilities with dynamic control in real time, advanced optimisation could be achieved. Development was done on the theoretical design of the system, where mathematical calculations and the accuracy of the system were evaluated. This study proved that the new controller was viable and, as a result, the development of a fully dynamic control Automation of compressor networks through a dynamic control system iii system incorporating the verified mathematical models followed. All of this was done following a theoretical approach. Intricate control requirements on the supply side were evaluated to determine the impact of new intelligent compressor control strategies. It was found that improved compressor control realised an additional 6.2% electrical energy saving on top of existing savings initiatives. Practical limitations and human perception issues were also addressed. Financial cost-benefit analyses were used to evaluate the viability of using automated compressor control. Ample maintenance data obtained from two leading mining companies was used to evaluate the impact of increased stopping and starting of compressors. Financial cost savings from electrical energy efficiency control strategies were found to considerably outweigh the minimal increase in compressor maintenance. Savings potential on deep-level mines proved to be in the order of 5% of the baseline consumption. When these results are extrapolated to the remaining 22 South African deep-level gold and platinum mines already subjected to demand side management initiatives, potential savings of 12.67 MW can be realised. Based on the Eskom 2014/2015 Megaflex tariff structure, the financial cost saving from 12.67 MW is R61 million. / PhD (Electrical Engineering), North-West University, Potchefstroom Campus, 2015

Compressed air makes up an important part of South African precious metal mining processes. Rising operational costs in the struggling mining sector increased the interest of the power utility, Eskom, and mine management in achievable electrical energy savings. Demand side management initiatives, funded by Eskom, realised a significant improvement in electrical energy efficiency of compressed air networks. Supply side interventions further aided optimisation by lowering operational costs. Previous research identified the need for integrating compressed air supply and demand side initiatives. Automated compressor control systems were needed in industry to realise missed opportunities due to human error on manual control systems. Automatic systems were found to be implemented in the industry, but missed savings opportunities were still encountered. This was due to the static nature of these control systems, requiring human intervention from skilled artisans. A comprehensive system is required that can adjust dynamically to the ever-changing demand and other system changes. Commercially available simulation software packages have been used by various mine groups to determine an optimal control philosophy. Satisfactory results were obtained, but the simulations were still based on static control inputs. No simulation system was found that could solve and optimise a system based on real-time instrumentation feedback. By combining simulation capabilities with dynamic control in real time, advanced optimisation could be achieved. Development was done on the theoretical design of the system, where mathematical calculations and the accuracy of the system were evaluated. This study proved that the new controller was viable and, as a result, the development of a fully dynamic control Automation of compressor networks through a dynamic control system iii system incorporating the verified mathematical models followed. All of this was done following a theoretical approach. Intricate control requirements on the supply side were evaluated to determine the impact of new intelligent compressor control strategies. It was found that improved compressor control realised an additional 6.2% electrical energy saving on top of existing savings initiatives. Practical limitations and human perception issues were also addressed. Financial cost-benefit analyses were used to evaluate the viability of using automated compressor control. Ample maintenance data obtained from two leading mining companies was used to evaluate the impact of increased stopping and starting of compressors. Financial cost savings from electrical energy efficiency control strategies were found to considerably outweigh the minimal increase in compressor maintenance. Savings potential on deep-level mines proved to be in the order of 5% of the baseline consumption. When these results are extrapolated to the remaining 22 South African deep-level gold and platinum mines already subjected to demand side management initiatives, potential savings of 12.67 MW can be realised. Based on the Eskom 2014/2015 Megaflex tariff structure, the financial cost saving from 12.67 MW is R61 million. / PhD (Electrical Engineering), North-West University, Potchefstroom Campus, 2015

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.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Micro gas turbines used in the aerospace industry require high performance with a compact frontal area. These micro gas turbines are often considered unattractive and at times impractical due to their poor fuel consumption and low cycle efficiency. This led to a joint effort to investigate and analyze the components of a particular micro gas turbine to determine potential geometry and performance improvements. The focus of this investigation is the radial vaned diffuser which forms part of a centrifugal compressor. The size of the diffuser is highly constrained by the compact gas turbine diameter. The micro gas turbine under consideration is the BMT 120 KS. The radial vaned diffuser is analyzed by means of 1-D and 3-D (CFD) analyses using CompAero and FINETM/Turbo respectively. The aim is to design a diffuser that maximizes the total-to-static pressure recovery and mass flow rate through the compressor with minimal flow losses. An experimental test facility was constructed and the numerical computations were validated against the experimental data. Three new diffusers were designed, each with a different vane geometry. The static-to-static pressure ratio over the radial diffuser was improved from 1.39 to 1.44 at a rotational speed of 120 krpm. The static pressure recovery coefficient was improved from 0.48 to 0.73 with a reduction in absolute Mach number from 0.47 to 0.22 at the radial diffuser discharge. / AFRIKAANSE OPSOMMING: Mikro-gasturbines wat in die lugvaart industrie gebruik word, vereis ‘n hoë werkverrigting met ‘n kompakte frontale area. Hierdie gasturbines word menigmaal onaantreklik geag weens swak brandstofverbruik en n lae siklus effektiewiteit. Dit het gelei tot ‘n gesamentlike projek om elke komponent van ‘n spesifieke mikro-gasturbine te analiseer en te verbeter. Die fokus van dié ondersoek is die radiale lem diffusor wat deel vorm van ‘n sentrifugaalkompressor. Die deursnee van die diffusor word deur die kompakte gasturbine diameter beperk. Die mikro gasturbine wat ondersoek word is die BMT 120 KS. Die radiale lem diffusor word geanaliseer deur middel van 1-D en 3-D (BVD) berekeninge met behulp van CompAero en FINETM/Turbo onderskeidelik. Die doelwit is om ‘n diffusor te ontwerp met ‘n verhoogde massavloei en drukverhouding oor die kompressor. ‘n Eksperimentele toetsfasiliteit is ingerig om toetse uit te voer en word gebruik om numeriese berekeninge te bevestig. Die staties-tot-stasiese drukstyging oor die radiale diffusor is verbeter van 1.39 tot 1.44 by ‘n omwentelingspoed van 120 kopm. Die statiese drukherwinningskoeffisiënt is verbeter van 0.48 tot 0.73 met ‘n vermindering in die absolute Machgetal vanaf 0.47 tot 0.22 by die radiale diffusor uitlaat.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The use of gas turbines in central receiver solar power plant cycles has become an increasingly popular research topic. This has led to the need to investigate and analyse the effect of the solar receiver on the gas turbine cycle. The aim of this thesis is to construct an experimental gas turbine setup to accommodate further research on utilizing solar energy to power gas turbines. The gas turbine under consideration is the Rover Gas Turbines 1S/60. The focus of this investigation is the centrifugal compressor of the gas turbine. An increase in static pressure is required for the gas turbine to cope with anticipated pressure drops in the central receiver that will be part of the gas turbine cycle. The standard compressor design is analysed by means of 3-D (CFD) analysis using CFX® and experimental data. The new centrifugal compressor is designed by means of 1-D and 3-D (CFD) analysis using CompAero and CFX®. The aim is to design a compressor that maximizes the total-to-static pressure ratio. The size of the compressor is highly constrained by the geometry parameters of the gas turbine. Since the turbine rotor will remain unchanged, the power input, mass flow rate and rotational speed must stay the same. The experimental setup was build and the numerical results of the standard compressor were validated against the experimental results. A new centrifugal compressor was designed. The total-to-static pressure ratio was increased from 2.50 to 3.30 at an operating speed of 46 krpm. The efficiency of the compressor was improved from 63.8% to 85.6%. The input power of the new compressor design deviated 1.6% from the set benchmark, and 1.3% from the numerical data of the standard compressor. / AFRIKAANSE OPSOMMING: Die gebruik van gasturbines in sonkragstasiesiklusse met ’n sentrale ontvanger het gegroei tot ’n gewilde navorsingsonderwerp. Dit het gelei tot die behoefte om die effek van die sonontvanger op die gasturbinesiklus te ondersoek en te analiseer. Die doel van hierdie tesis is om ’n eksperimentele gasturbine opstelling te bou vir verdere navorsing oor die benutting van sonenergie om ’n gasturbine aan te dryf. Die gasturbine in oorweging is die Rover Gas Turbines 1S/60. Die fokus van hierdie ondersoek is die sentrifugale kompressor van die gasturbine. ’n Toename in statiese druk word benodig vir die gasturbine om die verwagte drukverlies in die sentrale ontvanger, wat deel uit maak van die gasturbinesiklus, te hanteer. Die standaard kompressor ontwerp is geanaliseer deur middel van 3-D Berekenings Vloeimeganika (BVM) analises met behulp van CFX® en eksperimentele data. Die nuwe sentrifugale kompressor is ontwerp deur middel van 1-D en 3-D BVM analises met behulp van CompAero en CFX®. Die doel is om ’n kompressor te ontwerp wat die totale-tot-statiese drukverhouding maksimeer. Die grootte van die kompressor is beperk deur die geometrie van die gasturbine omhulsel. Aangesien die turbinerotor onveranderd sal bly, moet die insetdrywing, massa-vloeitempo en rotasiespoed dieselfde bly. Die eksperimentele opstelling is gebou en die numeriese resultate van die standaard kompressor is teenoor die eksperimentele resultate gevalideer. ’n Nuwe sentrifugale kompressor is ontwerp. Die totale-tot-statiese drukverhouding is verhoog van 2.50 tot 3.30 teen ’n rotasiespoed van 46 000 omwentelings per minuut. Die doeltreffendheid van die kompressor is verbeter van 63.8% tot 85.6%. Die insetdrywing van die nuwe kompressor ontwerp het met 1.6% afgewyk van die vasgestelde maatstaf, en met 1.3% van die numeriese data van die standaard kompressor.

Le compresseur d'air alimentant en oxygène la pile est un élément important dans les systèmes pile à combustible. Le compresseur peut consommer jusqu'à 20% de l'électricité produite dans les cas les plus défavorables. Le choix et le dimensionnement du compresseur, ainsi que son système de contrôle associé, sont directement liés à la performance du système global. La taille et le poids du système de compression d'air doivent être réduits pour le rendre plus adapté aux applications automobiles. En outre, le contrôle du système de compression d'air est également une problématique importante car il affecte l'efficacité et la sécurité de fonctionnement de la pile à combustible. Pour éviter une sous-alimentation en oxygène de la pile, le débit massique d’air fourni doit être géré de façon appropriée en fonction de la demande de la charge électrique. Pendant ce temps, la pression ne doit pas montrer de trop grandes variations ou ondulations qui peuvent endommager la membrane de la pile.Un contrôle à découplage proposé récemment dans la littérature, nommé contrôle à découplage de perturbation (DDC), est utilisé pour le système de compression centrifuge. Le DDC traite les interactions internes comme une perturbation, puis les éliminent dans le contrôle. Les performances du DDC sont comparées à un dispositif de commande en mode glissant décentralisé. Grâce à la comparaison de ces deux contrôleurs, les résultats montrent que le DDC proposé est performant tant pour des cas stables que dynamiques. Le compresseur centrifuge est donc utilisable pour les systèmes pile à combustible automobiles. Sur un banc d'essai hardware-in-the-loop (HIL), le contrôleur proposé est validé avec un modèle de pile à combustible de 10 kW avec des demandes de charge variables. En outre, une méthode d'évitement d’instabilité, à savoir un limiteur de référence, est proposé pour empêcher le dépassement de la ligne de pompage du compresseur. Les résultats expérimentaux montrent que, dans tous les cas, la zone d’utilisation du compresseur est bien cantonnée à droite de la ligne de pompage. / Air compressor supplying the oxygen to the stack is an important component in the fuel cell systems. The compressor can consumes up to 20 % of the generated power in the most severe cases. The selecting of the compressor and corresponding control are directly related to the performance of the fuel cell. The size and weight of the air compressor has to be reduced to make them more feasible for automotive applications. Moreover, the control of the air compression system is also an important issue, which affects the efficiency and the safety of the fuel cell. To avoid oxygen starvation of the stack, the mass flow of the supplied air has to be controlled appropriately according to the load demand. Meanwhile, the pressure should not have large deviations or ripples which may damage the stack membrane.A recently proposed disturbance decoupling control (DDC) is used for the centrifugal compression system. DDC treats the internal interactions as a disturbance and then eliminates them in the control. The performance of the DDC is compared with a decentralized sliding mode controller. Through the comparison of those two controllers, the results show that the proposed DDC performs better in both the steady state and dynamic conditions, making the centrifugal compressor is capable of applying to the fuel cell in automotive applications. On a hardware-in-the-loop (HIL) testbench, the proposed controller is validated with a 10 kW fuel cell model under varied load demands. Moreover, a surge avoidance method, namely reference limiter, is proposed to prevent the compressor from surging. The experimental results show that the operation is restricted to the right of the surge line.

Air compressor supplying the oxygen to the stack is an important component in the fuel cell systems. The compressor can consumes up to 20 % of the generated power in the most severe cases. The selecting of the compressor and corresponding control are directly related to the performance of the fuel cell. The size and weight of the air compressor has to be reduced to make them more feasible for automotive applications. Moreover, the control of the air compression system is also an important issue, which affects the efficiency and the safety of the fuel cell. To avoid oxygen starvation of the stack, the mass flow of the supplied air has to be controlled appropriately according to the load demand. Meanwhile, the pressure should not have large deviations or ripples which may damage the stack membrane.A recently proposed disturbance decoupling control (DDC) is used for the centrifugal compression system. DDC treats the internal interactions as a disturbance and then eliminates them in the control. The performance of the DDC is compared with a decentralized sliding mode controller. Through the comparison of those two controllers, the results show that the proposed DDC performs better in both the steady state and dynamic conditions, making the centrifugal compressor is capable of applying to the fuel cell in automotive applications. On a hardware-in-the-loop (HIL) testbench, the proposed controller is validated with a 10 kW fuel cell model under varied load demands. Moreover, a surge avoidance method, namely reference limiter, is proposed to prevent the compressor from surging. The experimental results show that the operation is restricted to the right of the surge line.

<p>Rising fuel costs and growing environmental concerns have forced gas turbine engine manufacturers to place high value on reducing fuel burn. This trend has pushed compressor technology into new design spaces that are not represented by historical experience. Specifically, centrifugal compressor diffusers are trending toward higher pressure recovery and smaller diameters. The internal fluid dynamics in these new flow regimes are not well understood and additional study is necessary. This work outlines detailed experimental and numerical observations of the flow field through a vaned diffuser for aeroengine applications.</p> <p>The experimental data consist of extensive Laser Doppler velocimetry measurements of the unsteady velocity field from the impeller trailing edge through the majority of the diffuser passage. These data were obtained non-intrusively and yielded all three components of the velocity vector field at approximately 2,000 geometric points. The correlation between fluctuations in the three velocity components were also observed at several key locations to determine the components of the local Reynolds stress tensor.</p> <p>These data indicated a jet/wake profile at the impeller exit represented by a consistent velocity deficit region from hub to shroud adjacent to the suction surface of the passage. This region was more prevalent adjacent to the splitter blade. The unsteady fluctuations due to the propagation of the jet and wake through the diffuser passage persist to 40% downstream of the throat. A complex secondary flow field was also observed with large axial velocities and a passage-spanning vortex developing through the diffuser passage. The velocity data and total-pressure data indicated a region of flow separation developing along the pressure surface of the vane near the hub due to the unsteady propagation of the jet and wake flow through the diffuser. Although this region was stable in time, its development arose due to unsteady aspects of the flow. Finally, the strong interconnection between the jet and wake flow, unsteady fluctuations, secondary velocities, incidence, and flow separation was demonstrated. </p> <p>Computationally, a “best-practice” methodology for the modelling of a centrifugal compressor was developed by a systematic analysis of various turbulence models and many modelling features. The SST and BSL-EARSM turbulence models with the inclusion of fillets, surface roughness, and non-adiabatic walls was determined to yield the best representation of the detailed flow development through the diffuser in steady (mixing-plane) simulations. The accurate modelling of fillets was determined to significantly impact the prediction of flow separation with the SST turbulence closure model. Additionally, the frozen rotor approach was shown to not accurately approximate the influence of unsteady effects on the flow development.</p> <p>Unsteady simulations were also compared to the detailed experimental data through the diffuser. The BSL-EARSM turbulence model best matched the experimentally observed flow field due to the SST model’s prediction of flow separation in the shroud-pressure side corner of the passage. In general, lower levels of axial velocity were predicted numerically that resulted in less spanwise mixing between the endwall and freestream flows. Additionally, the turbulent kinetic energy levels in the computational results showed little streamwise variation through the vaneless and semi-vaneless space. The large variation observed experimentally indicated that the production and dissipation of turbulent kinetic energy through this region was not accurately predicted in the two turbulence models implemented for the unsteady simulations.</p>