No description available.

No description available.

A multichannel FM telemetry system was employed to measure the dynamic response of compressor rotor blade surface pressure profiles to changes in upstream conditions. Data taken while the experimental compressor was operating with a distortion screen upstream of the rotor was utilized to develop a transfer function to describe the dynamic response of the rotor blade row. The transfer function was developed by considering the dynamic total pressure loss distribution around the rotor to be a response function driven by a quasi-steady total pressure loss distribution as a forcing function. Fourier transforms of both the dynamic and the quasi-steady distributions were calculated. The quotient obtained by dividing the Fourier transform of the response function by the Fourier transform of the forcing function was the desired transfer function. This experimentally-determined transfer function was then used in a new semi-actuator disc model to predict the dynamic response of the experimental compressor. The basis of the model is a mathematical representation of the flow fields upstream and downstream of a compressor rotor. The compressor rotor is represented in the model by a semi-actuator disc. The results of the investigation show that the physical mechanisms which control the onset and propagation velocity of a rotating stall in a single-stage compressor can be modeled with the use of a transfer function in a semi-actuator disc model of the compressor. The transfer function represents the dynamic characteristics of the compressor rotor row as an amplitude ratio and a phase shift of the Fourier frequency components of the total pressure loss distribution. This transfer function representation of the dynamic characteristics of the blade row provides important advantages over previous techniques. / Ph. D.

The main objective of this research effort was the construction of a finger valve dynamics model using simplified theory based on steady flow conditions. The analytical valve positions were then compared to experimental measurements from an Ingersoll Rand model 242 two-stage air compressor. Proximity probes were used to measure the valve position at two points on the exhaust valve at two different exhaust valve stop heights and at two points on the intake valve at one intake valve stop height in the lower exhaust valve stop height configuration only. A data acquisition system was configured to signal average and digitize the analog data from the sensors using a digital oscilloscope. The data was then sent to and stored in data acquisition computer for future comparisons to analytical results. The comparisons of the analytical and experimental exhaust valve positions at both points and both valve stop heights were of good quality when the effects of oil stiction were taken into account. Also, the comparisons of the intake valve positions were of good quality after adjustments were made in the theoretical force on the valve calculation. The adjustments entailed accounting for flow-induced forces on the intake valve after piston reversal. Overall the simplified model predicted the valve positions with sufficient quality to warrant the model's use as a design tool. / Master of Science

No description available.

Approved for public release, distribution unlimited / This thesis presents a Computation Fluid Dynamics (CFD) analysis of the aerodynamic performance of circular and elliptical leading edges of compressor blades, with a range of leading-edge droop angles. Specifically, simulations were conducted, with a free stream Mach number of 0.65 to quantify the change in pressure distributions and boundary layer momentum thickness in the leading edge region for a range of incidences on a flat plate with various leading-edge ellipticity ratios, ranging from unity (circular) to 5.5. In addition, the impact of drooping the leading edge was analyzed over a range of incidence angles from zero to 13 degrees. Pressure distributions indicate that elliptical leading edges can eliminate separation bubbles at zero incidence. The results indicated that the minimum loss occurred at an ellipticity ratio of about 3 and elliptical leading edges with a droop slightly greater than the average incidence can significantly decreased aerodynamic losses over a wider range of incidences.

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.