Approved for public release, distribution unlimited / A performance comparison between smooth-cast and rough-cast blades was conducted in a lowspeed multistage compressor. The purpose was to show that rough-cast blades can be used for initial performance tests of low-speed compressors. A baseline performance was established with smooth-cast epoxy blades and then compared to rough-cast aluminum blades. The pressure-rise coefficient versus flow coefficient and velocity triangles were used as the measure for comparison between the different blade types. The velocity triangles were constructed and compared across the span (hub-to-tip) of the secondstage. This was done by using two probes that could traverse radially along the blade and sense the flow velocity and angle relative to the compressor axis. Measurements were taken at six different locations from the hub-to-tip of the blade. The performance tests were conducted at four different throttle settings: near stall, open throttle, nominal operating point (NOP), and near the NOP. Results showed that although there were some differences between the smooth-cast and rough-cast blades, the overall performance was very similar. As a result, rough-cast blades could be used for initial performance tests or as the initial stages of a compressor in order to set up the flow for the evaluation of a new stage of smooth blades. The use of rough-cast blades in early stages would save the time and money needed to produce large numbers of high precision smooth-cast blades.

Approved for public release; distribution is unlimited / This thesis presents a simple, meanline analysis of the impact of blade roughness on the mass flow, work coefficient, and efficiency of a three-stage axial compressor as a function of the location of fouling. First, an extensive review is presented on the state-of-the-art of measuring compressor degradation and on the impact of roughness on loss and deviation in a compressor cascade. The performance of a baseline, three-stage compressor, which has hydrodynamically smooth blades, is predicted. Using this baseline geometry, the influence of roughness in the front, middle and rear stages is calculated using empirical data for the enhanced losses and increased deviation, with a stage stacking technique. Influence coefficients that relate percentage changes in one parameter to percentage changes in other parameters are calculated. This analysis predicts that the most sensitive parameter for predicting fouling in the front stages is the percentage change in mass flow and the most sensitive parameter for predicting fouling in the rear stages is the efficiency. / Lieutenant, United States Coast Guard

This thesis aims to contribute to the understanding of transitional flows in the blade boundary layers of axial compressors. Two experiments are described, the first examining in detail the transitional boundary layer on a simulated controlled-diffusion blade and the second surveying the mid-height flowfield in an embedded stage of a low-speed axial compressor. The velocity distribution on the simulated blade is identical to the Velocity distribution on the suction surface of the blades in the axial compressor. At 2 Reynolds numbers and 3 levels of freestream turbulence, a single hot wire was used to conduct a boundary layer survey on a simulated controlled-diffusion blade. Integral parameters of the boundary layers are explored to dene the length and nature of transition. At low Reynolds number there is a separated or near separated region at the leading edge which does not lead to turbulence. Transition covers a length of approximately 20% of the blade chord, starting between 20% and 30% chord. The position of transition is strongly influenced by the level of freestream turbulence. Most of the transition process occurs within the decelerating flow region which exists from 20% of the chord. At high Reynolds number, a leading edge separation bubble leads to transition within 2% of the blade chord. Abu-Ghannam & Shaws correlation for the start and length of transition was found to predict the start of transition well for attached flows, but could not be relied upon for separated flows. It is apparent that the correlation was not designed for the very strong Velocity gradients in the leading edge region, and probably not for separated flow. _ Three flow conditions in the axial compressor were used: design speed, peak efficiency, low Reynolds number at peak efficiency (the machine was slowed to one-quarter speed) and design speed near the stall. Using hot wires at mid-height, axial and circumferential velocity and turbulence information was obtained. Wakes and structure within wakes are visible in the turbulence and Reynolds stress distributions. The wakes of more than one upstream blade row are visible; the region where two wakes intersect gives some information about interaction between a stator blade Wake and a rotor blade boundary layer. Some information is available about the length scale 'distribution inside and outside wakes. Secondary flow in the axial-circumferential plane shows motion within wakes and a vortex in the near-stall flowfield, shed preferentially at one point in the blade-passing cycle.

Sistemas de refrigeração são sistemas reparáveis. Isto significa que os componentes destes sistemas podem sofrer manutenção várias vezes durante a vida útil do sistema como um todo. Em sistemas de refrigeração o mais conhecido é o que opera com ciclo por compressão de vapor. Neste ciclo, o compressor é o equipamento mais complexo e de maior custo. Dessa forma, deve-se tomar especial cuidado, pois além de problemas como desgaste e falta de lubrificantes, ele está sujeito a sofrer danos decorrentes do funcionamento incorreto ou falho de todos os outros componentes. Dentro dos compressores existentes, o compressor alternativo pode ser comercialmente considerado o cavalo de batalha da refrigeração industrial, dominando a faixa de capacidades inferiores a 300 kW (85 TRs). O compressor alternativo também pode ser utilizado, com vantagens, quando o controle de capacidade se faz necessário, através do procedimento de desativação dos cilindros. Este compressor possui a possibilidade de manutenção no campo de, praticamente, qualquer item construtivo. O termo confiabilidade vem do inglês \"reliability\" que é a probabilidade de um item poder desempenhar sua função requerida, por um intervalo de tempo estabelecido, sob condições definidas de uso. Testes de confiabilidade possibilitam, através de estimativa, com base em estudos de confiabilidade, caracterizar os comportamentos de confiabilidade, da probabilidade de falha e da taxa de falha em relação ao tempo de um componente ou sistema. Uma das ferramentas para permitir avaliar ações que aumentem a confiabilidade é a Análise de Modos e Efeitos de Falha ou FMEA (\"Failure Mode and Effect Analysis\"). Basicamente, esta ferramenta parte da definição das funções dos sistemas e subsistemas analisados, verificando em seguida as falhas que afetam cada função e todos os modos de falha que levam a cada falha. Para cada modo de falha, analisam-se os efeitos e define-se a necessidade de ações para reduzir a possibilidade de ocorrência deste evento, eliminá-lo ou, simplesmente controlar os efeitos indesejáveis. O objetivo deste trabalho é o estudo das principais falhas, modos de falha de compressores semi-herméticos alternativos de sistemas de refrigeração, suas ocorrências e o comportamento destes equipamentos no seu período de garantia, sob a ótica da confiabilidade. / Refrigeration systems are reparable systems. This means that one can perform maintenance actions on them several times during the system life cycle. The most common refrigeration system is the vapor compression cycle. In this cycle, the compressor is the most complex and expensive component. So, the user should take special care because , beside problems like wear and lubricant lack, the compressor can also suffer damages caused by the incorrect work or fault from the others system components. Among the compressor types, the reciprocating compressor can be considered as the most used in the industrial refrigeration, from lowers capacities to up to 300 kW. Also the reciprocating compressor has some advantages, where its cylinders can be disabled for capacity control purposes. One can perform field maintenance of almost every part for this compressor. The word reliability means the probability of some equipment can not perform its requested function for an established time period, under defined operation conditions.. One of the tools to allow actions to improve the reliability is the failure mode and effect analysis (FMEA). This tool is based on the analyzed function and sub function systems definitions seeking faults that affect each function and all fault modes that lead to every fault. For each fault mode, the effects are analyzed and the need of actions to decrease the occurrence of this event is defined, excluding or control this undesirable events. This work objective is to study the most important faults, fault modes of reciprocating semi-hermetic compressors, its occurrences and its behavior during the guarantee period under reliability point of view.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Axial compressors are used in a wide variety of aerodynamic applications and are one of the most important components in aero-engines. The operability of compressors is however limited at low-mass flow rates by fluid dynamic instabilities such as stall and surge. These instabilities can lead to engine failure and loss of engine power which can compromise the aircraft safety and reliability. Therefore, a better understanding of how stall occurs and the causes behind its inception is extremely important. In the vicinity of the stall line, the flow field is inherently unsteady due to the interactions between adjacent rows of blades, formation of separation cells, and the viscous effects including shock-boundary layer interaction. Accurate modeling of these phenomena requires a proper set of stable and accurate boundary conditions at the rotorstator interface that conserve mass, momentum and energy, while eliminating false reflections. As a part of this effort, an existing 3D Navier-Stokes analysis for modeling single stage compressors has been modified to model multi-stage axial compressors and turbines. Several rotor-stator interface boundary conditions have been implemented. These have been evaluated for the first stage (a stator and a rotor) of the two stage fuel turbine on the space shuttle main engine (SSME). Their effectiveness in conserving global properties such as mass, momentum, and energy across the interface, while yielding good performance predictions has been evaluated. While all the methods gave satisfactory results, a characteristic based approach and an unsteady sliding mesh approach are found to work best. Accurate modeling of the formation of stall cells requires the use of advanced turbulence models. As a part of this effort, a new advanced turbulence model called Hybrid RANS/KES (HRKES) has been developed and implemented. This model solves Menter's k--SST model near walls and switches to a Kinetic Eddy Simulation (KES) model away from walls. The KES model solves directly for local turbulent kinetic energy and local turbulent length scales, alleviating the grid spacing dependency of the length scales found in other Detached Eddy Simulation (DES) and Hybrid RANS/LES (HRLES) models. Within the HRKES model, combinations of two different blending functions have been evaluated for blending the near wall model to the KES model. The use of realizability constraints to bound the KES model parameters has also been studied for several internal and external flows. The current methodology is used in the prediction of the performance map for the NASA Stage 35 compressor configuration as a representative of a modern compressor stage. The present approach is found to satisfactory predict the onset of stall. It is found that the rotor blade tip leakage vortex and its interaction with the shock wave is mainly the reason behind the stall inception in this compressor stage.

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1930. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed November 30, 2009) Includes bibliographical references (p. 26).

Thesis (M.S.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 71-72). Also available via Humboldt Digital Scholar.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Garth V. Hobson. Includes bibliographical references (p. 63). Also available online.

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