Master of Science / Department of Mechanical and Nuclear Engineering / Kirby S. Chapman / Continued regulatory pressure necessitates the use of precisely designed turbochargers to create the design trapped equivalence ratio within large-bore stationary engines used in the natural gas transmission industry. The upgraded turbochargers scavenge the exhaust gases from the cylinder, and create the air manifold pressure and back pressure on the engine necessary to achieve a specific trapped mass. This combination serves to achieve the emissions reduction required by regulatory agencies. Many engine owner/operators request that an upgraded turbocharger be tested and verified prior to re-installation on engine. Verification of the mechanical integrity and airflow performance prior to engine installation is necessary to prevent field hardware iterations. Confirming the as-built turbocharger design specification prior to transporting to the field can decrease downtime and installation costs. There are however, technical challenges to overcome for comparing test-cell data to field conditions. This thesis discusses the required corrections and testing methodology to verify turbocharger onsite performance from data collected in a precisely designed testing apparatus. As the litmus test of the testing system, test performance data is corrected to site conditions per the design air specification. Prior to field installation, the turbocharger is fitted with instrumentation to collect field operating data to authenticate the turbocharger testing system and correction methods. The correction method utilized herein is the ASME Performance Test Code 10 (PTC10) for Compressors and Exhausters version 1997.

L’étude effectuée au cours de cette thèse a permis la caractérisation expérimentale des instabilités aérodynamiques se développant dans un compresseur centrifuge et une première évaluation de l’efficacité d’une stratégie de contrôle par aspiration de couche limite. Le compresseur, développé par Safran Helicopter Engines et dénommé Turbocel, est composé d’une roue directrice d’entrée, d’un rouet centrifuge splitté, d’un diffuseur radial aubé et splitté et d’un redresseur axial. Des travaux numériques antérieurs réalisés au Laboratoire de Mécanique des Fluides et d’Acoustique ont montré, aux bas régimes de rotation, un comportement singulier caractérisé par une structure d’écoulement dite « alternée » impliquant deux canaux adjacents du diffuseur radial. L’étude stationnaire réalisée sur l’ensemble des régimes de rotation du compresseur a conduit à une ségrégation des vitesses de rotation suite à l’établissement d’une variable– le taux d’asymétrie - caractérisant l’asymétrie de l’aérodynamique du diffuseur. Ce taux, quasi nul à très basse vitesse de rotation, croît jusqu’à atteindre un maximum à vitesse de rotation intermédiaire, puis s’effondre pour ré-augmenter légèrement. Une analyse fine des données instationnaires acquises à bas régimes a permis la description de deux modes de fonctionnement du compresseur associés à des structures de décollements différentes dans le diffuseur. Le premier mode est caractérisé par l’oscillation à une fréquence de l’ordre de 42 Hz d’un décollement localisé sur la face en dépression des aubes principales du diffuseur. Le second mode, à 12Hz, associé au pompage modéré du compresseur, correspond à la mise en place d’un schéma alterné et à son oscillation sur deux canaux adjacents du diffuseur.Les origines probables de ces différents modes de fonctionnement sont discutées à partir de considérations • aérodynamiques -- la mise en place d’une recirculation en tête de rouet est suspectée d’influer sur le taux d’asymétrie en modifiant l’incidence en entrée de diffuseur,• géométriques -- le nombre et le calage des aubes du diffuseur radial ainsi que la distance inter-roue indiquent une prédisposition du diffuseur à fonctionner en régime alterné sous certaines conditions d’incidence,• aéro-acoustiques -- un accrochage des fréquences aérodynamiques avec les fréquences des ondes acoustiques du banc d’essai semble se produire. Enfin, les résultats sur le contrôle d’écoulement par aspiration de couche limite à régime partiel sont présentés. Une amélioration du rendement est observée à certains points de fonctionnement, mais aucune extension de la plage de fonctionnement du compresseur n’est mesurée. Sans l’atténuer, l’aspiration permet de contrôler sur quels canaux s’établit le régime alterné. / This thesis presents an experimental characterization of the evolution of aerodynamic instabilities in a centrifugal compressor, and a first evaluation of the effectiveness of boundary layer suction as a control strategy. The compressor used in this study is Turbocel, a centrifugal compressor developed by Safran Helicopter Engines, featuring inlet guide vanes, a backswept splittered unshrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes.Previous numerical work, conducted at the Laboratoire de Mécanique des Fluides et d’Acoustique de Lyon, revealed a unusual behaviour of the compressor at low rotational speeds characterized by a distinctive alternate flow structure in the radial diffuser that develops across two adjacent blade channels. The steady analysis, which was conducted over the full operating range of rotational speeds, led to the distinction of different operating zones, following the establishment of a new indicator variable - the asymmetry rate - characterizing the asymmetry of the diffuser aerodynamics. This rate, which is close to zero at very low rotation speed, increases until it reaches a maximum value at intermediate rotational speed, before collapsing and slightly increasing again near the nominal rotational speed.Analysis of the unsteady data acquired at low speeds allowed for the characterization of two compressor operating modes, associated with different flow phenomena in the stalled diffuser. The first mode is characterized by the oscillation of a separation at 42 Hz, on the suction side of the main blades in the diffuser. The second mode, at 12Hz, associated with mild surge of the compressor, corresponds to the emergence of an alternate pattern of unsteady flow separation that occurs across two adjacent channels of the diffuser.The probable causes for these different operating modes are discussed in the context of different considerations:• aerodynamic -- the formation of a recirculation near the tip of the impeller is suspected to affect the asymmetry rate by changing the incidence angle at the diffuser inlet.• geometric -- the number and the stagger angle of the radial diffuser blades as well as the distance between the impeller and the diffuser may result in a predisposition of the diffuser to operate in an alternating mode, under certain conditions of incidence.• aero-acoustic -- as there is evidence of a lock-in of the aerodynamic frequencies with the acoustic modes of the test rig.Finally, boundary layer suction is explored as a means of flow control at partial rotational speed. Improvements in performance were observed for some operating points, however no extension of the compressor operating range was measured. Although boundary layer suction did not allow for the intensity of the oscillating separation pattern in the diffuser to be reduced, it was found to be an effective means of controlling the location of the alternate flow structure in the diffuser.

O desenvolvimento de tecnologia na área de turbomáquinas é essencial ao desenvolvimento da indústria nacional e o Laboratório de Engenharia Ambiental e Térmica da Escola Politécnica da Universidade de São Paulo tem compreendido ações para este propósito. Este trabalho tem por objetivo desenvolver um compressor para uma turbina a gás de pequeno porte de 500 kW, primeiro passo para o projeto e construção da turbina como um todo. A partir da análise do ciclo termodinâmico e da análise de adimensionais, o tipo de compressor a ser utilizado foi determinado. Optou-se pelo projeto de um compressor centrífugo. Iniciou-se o projeto através de análise e correlações unidimensionais com previsão de desempenho, definindo algumas geometrias iniciais a serem avaliadas nas fases seguintes. Realizou-se a análise bidimensional do impelidor com a ferramenta computacional Vista TF que utiliza o método de curvatura de linhas de corrente. Por fim, a geometria tridimensional foi definida com uso de simulações de dinâmica de fluidos computacional. De acordo com as simulações, o compressor projetado tem desempenho condizente com os requisitos impostos. / Technology development in turbomachinery is essential to the national industry development and the Laboratory of Environmental and Thermal Engineering of the Polytechnic School of the University of São Paulo is engaged on this purpose. This work intends to design a compressor for a small 500 kW gas turbine, the first step in the whole turbine design and construction. The compressor type was determined from thermodynamical cycle and adimensional analysis. The centrifugal type compressor was chosen. The design was initialized using one-dimensional analysis and correlations with performance prediction models, defining initial geometries to be evaluated in the upcoming design phases. The impeller was analyzed with a two dimensional computational tool named Vista TF, which uses the streamline curvature method. The tridimensional geometry was defined using computational fluid dynamics. According to the simulations, the design compressor performs satisfying the imposed requirements.

South Africa experienced a severe shortfall in electricity supply during 2008. Eskom, the national electricity supplier, implemented several strategies to alleviate the situation. The Power Conservation Programme set the mining sector a mandatory target to reduce its annual power consumption by 10%. The quickest way to achieve these savings is by optimising the largest power consumers on the mines. Compressed air is one of these, constituting approximately 40% of total electricity consumption on platinum mines. Several methods to reduce power consumption on compressed air systems were investigated. The investigation revealed that centrifugal air compressors on the mines are typically manually operated at a fixed delivery output. Attempts to reduce electricity consumption by reducing air demand will therefore not necessarily lead to savings. A control system that will enable the compressor to automatically match the supply with system demand is required. An optimised control strategy was then developed and implemented on three compressed air systems. Measurements demonstrated savings between 13% and 49%. With the Eskom tariffs proposed for 2010, this implies a total saving of R 46 million per year for these three case studies. This will achieve, and may even exceed, the mandatory reduction in electricity consumption of the mines. These results demonstrate that one of the quickest ways to reduce energy consumption on South African mines is by implementing optimised compressor controls. / Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2010

South Africa experienced a severe shortfall in electricity supply during 2008. Eskom, the national electricity supplier, implemented several strategies to alleviate the situation. The Power Conservation Programme set the mining sector a mandatory target to reduce its annual power consumption by 10%. The quickest way to achieve these savings is by optimising the largest power consumers on the mines. Compressed air is one of these, constituting approximately 40% of total electricity consumption on platinum mines. Several methods to reduce power consumption on compressed air systems were investigated. The investigation revealed that centrifugal air compressors on the mines are typically manually operated at a fixed delivery output. Attempts to reduce electricity consumption by reducing air demand will therefore not necessarily lead to savings. A control system that will enable the compressor to automatically match the supply with system demand is required. An optimised control strategy was then developed and implemented on three compressed air systems. Measurements demonstrated savings between 13% and 49%. With the Eskom tariffs proposed for 2010, this implies a total saving of R 46 million per year for these three case studies. This will achieve, and may even exceed, the mandatory reduction in electricity consumption of the mines. These results demonstrate that one of the quickest ways to reduce energy consumption on South African mines is by implementing optimised compressor controls. / Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2010

O desenvolvimento de tecnologia na área de turbomáquinas é essencial ao desenvolvimento da indústria nacional e o Laboratório de Engenharia Ambiental e Térmica da Escola Politécnica da Universidade de São Paulo tem compreendido ações para este propósito. Este trabalho tem por objetivo desenvolver um compressor para uma turbina a gás de pequeno porte de 500 kW, primeiro passo para o projeto e construção da turbina como um todo. A partir da análise do ciclo termodinâmico e da análise de adimensionais, o tipo de compressor a ser utilizado foi determinado. Optou-se pelo projeto de um compressor centrífugo. Iniciou-se o projeto através de análise e correlações unidimensionais com previsão de desempenho, definindo algumas geometrias iniciais a serem avaliadas nas fases seguintes. Realizou-se a análise bidimensional do impelidor com a ferramenta computacional Vista TF que utiliza o método de curvatura de linhas de corrente. Por fim, a geometria tridimensional foi definida com uso de simulações de dinâmica de fluidos computacional. De acordo com as simulações, o compressor projetado tem desempenho condizente com os requisitos impostos. / Technology development in turbomachinery is essential to the national industry development and the Laboratory of Environmental and Thermal Engineering of the Polytechnic School of the University of São Paulo is engaged on this purpose. This work intends to design a compressor for a small 500 kW gas turbine, the first step in the whole turbine design and construction. The compressor type was determined from thermodynamical cycle and adimensional analysis. The centrifugal type compressor was chosen. The design was initialized using one-dimensional analysis and correlations with performance prediction models, defining initial geometries to be evaluated in the upcoming design phases. The impeller was analyzed with a two dimensional computational tool named Vista TF, which uses the streamline curvature method. The tridimensional geometry was defined using computational fluid dynamics. According to the simulations, the design compressor performs satisfying the imposed requirements.

Master of Science / Department of Mechanical and Nuclear Engineering / Kirby S. Chapman / This thesis outlines the development of a centrifugal compressor model for the Turbocharger Component Matching System (TuCMS) software package that can be used to inexpensively analyze turbocharger performance. The TuCMS can also be used to match turbocharger components to integrate and optimize turbocharger-engine performance. The software system is being developed with the intent to reduce the time taken to experimentally match a turbocharger with an engine, a task that is key to engine emission reductions. The TuCMS uses one-dimensional thermo-fluid equations to analyze the compressor side of a turbocharger. For each compressor component, the program calculates the velocities, pressures, temperatures, pressure losses, work consumption, and efficiencies for a specified set of turbocharger geometry, atmospheric conditions, rotational speed, and fluid mass flow rate. The compressor includes established loss models found in the open literature. The TuCMS utilizes a component-based architecture to simplify model enhancements. The TuCMS can be used as a cost effective engineering tool for preliminary turbocharger testing during engine upgrades and modifications. In this thesis, the TuCMS compressor model was used as an analysis tool to further understand the Variable Geometry Turbocharger (VGT) experimental results. The VGT is a unique turbocharger that can change the diffuser vane angle over a wide range of positions. The change in diffuser vane angle results in optimal turbocharger performance at various operating conditions, and potentially increases the operating range. The purpose for the use of the TuCMS compressor model analysis is to identify the change in performance as the diffuser vane angles are adjusted. The TuCMS can ideally be used as a control program for the VGT to adjust the diffuser vane angles as the compressor load changes and insure the compressor is operating at the highest efficiency.

<p>The primary objective of this research was to shed light on the changes in performance observed in a high-speed, centrifugal compressor that occur during the transition from subsonic to transonic operating conditions, using experimental data collected on a research compressor developed by Honeywell Aerospace, as well as results from a numerical model of the compressor.</p> <p> An understanding of the flow behavior in transonic centrifugal compressors is critical as the drive for higher stage pressure ratios while maintaining a compact size results in higher rotational speeds and increased aspect ratios in the inducer of the impeller. Both of these design trends result in higher relative Mach numbers near the impeller leading edge, resulting in the formation of shocks and an increasingly complex flow field. Since it is necessary to maintain high efficiency and adequate surge margin at these conditions—to ensure the compressor is stable across the full operating range—it is important to understand the effects of the transition from subsonic to supersonic flow on performance and stability. Due to the limited availability of research in the open literature regarding transonic centrifugal impellers, especially experimental studies, these behaviors are still not fully understood.</p> <p>Experimental data collected during steady state operation as well as during speed transients, showed a sudden decrease in the variance of the unsteady pressure field throughout the compressor, but most dramatically in the inducer shroud. Analysis of the performance also showed a significant increase in impeller efficiency of approximately 2 points as speed was increased from 80% to 90% of the design speed. Temperature measurements upstream of the impeller leading edge indicated a dramatic reduction in the degree of flow recirculation in the same speed range, indicating the increase in performance is related to a decrease in the blockage near the impeller leading edge. A low pressure region was also observed in the inducer passage, which disappeared upon transition to the transonic operating regime, this coupled with decreased inducer static pressure rise and relative diffusion at lower speeds, strongly indicates that increased loss in the inducer at lower speeds is responsible for the observed performance deficiency during subsonic operation.</p> <p>Analysis of the numerical results revealed that the low pressure region in the inducer may be attributable to the interaction between the inlet shroud boundary layer and the low momentum tip leakage flow in the impeller passage, which at lower speeds, results in the tip leakage flow forming a large recirculation region in the inducer passage. It was also determined that the step change in instability coincides with the inducer shock extending to the shroud and reducing the strength of the interaction between the low momentum regions in the inlet and impeller passage, thereby allowing the tip leakage flow to form into a vortex and preventing the development of the recirculation region in the inducer. </p> <p>This research provides a possible explanation for the observed instability in the compressor, which may allow for further testing of techniques to mitigate the instability caused by the blockage in the inducer, such as casing treatment, bleed, or flow injection into the inducer shroud.</p>

The implementation of a ported shroud casing treatment is often used to extend the operating range of a centrifugal compressor. This work utilizes the STAR-CCM+ CFD package to analyze steady-state, single-passage simulations of a centrifugal compressor with and without a ported shroud to better understand how a ported shroud affects compressor flow physics. Verification and validation of simulations were conducted by comparison of results with a time-accurate full-annulus simulation and experimental data. Four different ported shroud revisions were considered and modeled along the full range of their stable operation, with emphasis placed on the flow limits of choke and stall. A ported shroud is found to improve the choked mass flow limit by increasing the aerodynamic area of the compressor. Near-stall operation is improved through flow recirculation through the ported shroud. This flow, which is induced with a large component of tangential velocity from having passed the impeller blades' leading edge once, reduces the impeller incidence. The influence of a strut is found to restrict both limits of operation by reducing the aerodynamic area and obstruction of tangential velocity. The revisions considered demonstrate that facilitation of flow entering the ported shroud under either near-stall or choked conditions causes a noteworthy improvement in performance. Such alterations, in this application, demonstrate a 3.3% improvement in choked mass flow rate under choked conditions and an 1.3 degree reduction in impeller incidence under near-stall conditions, as compared to the initial ported shroud design. Understanding the effect that a ported shroud casing treatment has on compressor flow physics, especially near its limits of operation, suggests methods for improving centrifugal compressor design to increase its stable operating range.

Performance of vacuum cleaners are affected by factors such static pressure, airflow rate and efficiency. In this thesis work, attempt has been made to design a fan to meet the requirements of suction static pressure and air flow rate and in the process understand the fan design parameters that affect these performance parameters. Parametric study has been conducted for the same, by choosing six fan design parameters. Additionally, ways to increase the fan efficiency has been investigated during the parametric study. Computational Fluid Dynamics is used to visualize the flow inside the fan casing and further to simulate fan performance at an operational point. Steady state RANS and moving reference frames was used to model the turbulence in the fluid flow and rotation of the fan, respectively. Performance curve showing the relation between static suction pressure and mass flow rate is plotted for the base model is in proximity to the required performance. Parametric study was conducted on the six fan design parameters: Fan diameter, number of impeller blades, blade outlet angle, radius of the curve connecting inlet to outlet section of the fan, diffuser exit length and splitter blade length. The range for each parameter analysis was restricted so that static pressure values are around the required performance. Greater performance variation was found with design parameters: fan diameter, blade outlet angle, radius of the curve connecting inlet to outlet section of the fan and diffuser exit length. This variation at low mass flow rate can be majorly attributed to the randomness in the flow captured by entropy contours. At high mass flow rate, blockage in the flow visualized by pressure contours reasoned for the performance variation. Greater performance variation was not when design parameters such as number of blades and splitter blade length were varied. Larger variation of these parameters is required to see better variation.