Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Abstracted in Dissertation abstracts, v. 25 (1965) no. 10, p. 5829. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 169-174).

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1911. / The entire thesis text is included in file. Typescript. Illustrated by authors. Title from title screen of thesis/dissertation PDF file (viewed February 27, 2009)

M.Ing. (Electrical And Electronic Engineering) / The theme of this thesis is the time compression of energy in electrical systems with the aim of improving the efficiency and average power throughput capability of existing pulse compression systems. Recent success in the design of pulse lasers indicated successful operation at repetition rates of up to 2kHz, demanding more powerful pulse power supplies. These pulse lasers require unusually high peak power, not obtainable with conventional switching techniques. Typical pulse voltages of up to 40kV with peak currents of lOkA and rise times of 150ns are required. Traditionally thyratrons have been used for this application, but the limited lifetime of these devices is a major shortcoming, especially when operating at 2kHz. New switching techniques were needed. Excellent results have been obtained using saturable inductors as magnetic switches in pulse compressors, but notwithout limitations. The generation of heat due to core losses tends to limit the power throughput capability of these compressors, especially in the final stages. The minimisation of these losses is therefore of utmost importance. In order to improve the current systems, a study of the basic principles of compression was conducted. Loss-mechanisms, especially in the magnetic components, were modelled with the object of minimising losses. The limitations imposed on the system by flux conservation in magnetic and dielectric materials, led to the development of the new concept of bipolar compression. A full-scale bipolar compressor and pulse power supply was constructed and experimental results on this system are presented, showing an improvement in the efficiency. A new method for designing pulse compressors, incorporating core losses,evolved from this development

Compressor blades often have a small 'spike' in the surface pressure distribution at the leading edge. This may result from blade erosion, manufacture defects or compromises made in the original design process. In this thesis it is shown that these spikes will increase the loss generated by a blade only when they become large enough to initiate boundary layer transition at the leading edge through a separation bubble; this process increases profile loss by about 30%. A criterion is presented, based on the spike diffusion, which can be used to determine whether leading edge transition will occur or not; this criterion is simple and quick to determine and has to potential to be used on a production line to reject those leading edges that would otherwise be detrimental. The spikes are also shown to have a significant effect on the flow close to the endwalls. If they cause leading edge transition in this region then they will cause a growth in the size of the three-dimensional separations that exist in the corner between the blades' suction surfaces and the endwalls. On the low speed stator tested this process increased hub loss by around 100%. Thus to prevent spikes becoming large a new method for producing a 'spikeless' leading edge has been developed; this leading edge can be attached easily to the thickness distribution of any blade and was found to be sharp, that is with very high curvature at the leading edge point. This spikeless leading edge was also found to be the best when the effects of real manufacture deviations, measured off of a production line, were considered. Asymmetry was found to be detrimental and bluntness was only beneficial when unrealistically large deviations were considered. The best leading edge geometry is therefore sharp and symmetric.

No description available.

M.Tech. (Mechanical and Industrial Engineering) / Please refer to full text to view abstract

Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

An experimental investigation of reversed flow performance characteristics in a compressor cascade was conducted. The purpose was to gain a fundamental understanding of reversed flow in a compressor blade cascade, and to determine the effects of stagger angle and angle of attack on the reversed flow behavior in the cascade. Tests were conducted at two blade configurations, one to simulate reversed flow in a compressor rotor and one to simulate reversed flow in a compressor inlet guide vane. Three stagger angles were tested for each configuration with an absolute angle of attack range from 70 to 130 degrees. The investigation included total and static pressure measurements upstream and downstream of the cascade as well as blade surface measurements. Aerodynamic performance parameters were presented for a reversed flow cascade. Comparison of corrected total pressure loss curves suggested that blade rows of a compressor subjected to reversed flow may be treated as nearly equal loss producers. A comparison was made between total pressure loss coefficients from this investigation and experimental compressor performance. The total pressure loss coefficients compared favorably in magnitude and curve shape. / Master of Science

Oil ring seals are one major source of instability in high pressure centrifugal compressors. This thesis presents a method for analysis of an improved seal concept that has been used in very high pressure designs (900 PSI). The improved design uses a combination of ring seals and tilting pad bearing elements. The stable tilting pad is used to center the heavily grooved seal element. The eight stiffness and damping coefficients which represent the hydrodynamic forces between the journal and the seal assembly are computed by an automated computer code for evaluation of both the standard ring seal and the tilting pad elements. Both synchronous and nonsynchronous steady state characteristics have been included in the analysis. The nonsynchronous whirl of the rotor and its effects on the stiffness and damping coefficients of a 5 tilting pad seal have been given in the form of design curves. The effect of pad inertia which has been neglected in many bearing analysis codes has been incorporated in this seal analysis, and allowed the determination of the exact cross coupling stiffness and damping coefficients. / Master of Science

The current study investigates a range of issues relating to the use of a vane-recessed tubular-passage casing treatment as a passive stall control technique in a multistage axial-flow compressor. The focus of the research was to determine whether such a treatment could delay the initiation of stall at lower mass flow rates as well as providing the most beneficial improvement in flow characteristics without sacrificing compressor efficiencies. Specific objectives of this study were to examine possible improvements or deterioration in the flow characteristics including stall margin, peak pressure rise coefficients and maximum efficiency in a multistage axial flow compressor. A casing treatment in addition to several spacer rings was developed from two initial designs and tested on the first stage of a low speed three-stage axial-flow compressor with a (0.7) hub to tip diameter ratio. The treatment configuration consisted of three parts: an outer casing ring, with a tubular shaped passage on the inside diameter, a set of 120 evenly spaced curved vanes, and a shroud or inner ring. The casing treatment was positioned following the inlet guide vanes upstream and partly covering the tip of the rotor blades. The main parts of the casing treatment including the recessed vanes in addition to some of the spacer rings were manufactured from high quality acrylic. Eight additional spacer rings of various shapes and geometry were added. The first ring held and partly covered the IGVs, in front of the casing treatment. The rotor tip exposure ratio was thought to have a significant impact on the effectiveness of the casing treatment. Therefore the other seven rings were used to provide the desired uncovered region of the rotor tip axial chord of about 10% in order to provide a range of exposures of (23.2%, 33.3%, 43.4%, 53.5%, 63.6%, 73.7%, and 83.8%). The results showed significant improvements in stall margin in all treated casing configurations along with insignificant efficiency sacrifices in some compressor builds. About (28.56%) of stall margin improvement in terms of corrected mass flow rate was achieved using a casing treatment with a (33.3%) rotor tip exposure. The compressor build with (0.535) rotor exposure ratios was the best configuration in terms of efficiency gain and loss characteristics. This build was able to provide the highest values of the maximum efficiencies in comparison with the performance achieved from the solid casing. An improvement of (1.81%) in the maximum efficiency in terms of the overall total-total pressure ratio, in association with a (22.54%) stall margin improvement in terms of the corrected mass flow rates were achieved by the application of this treatment configuration. The improvement in the peak pressure rise coefficients in terms of the overall total-total pressure ratio, obtained from this build was (2.33%). The compressor configuration using a casing treatment with a (0.636) rotor exposure ratio was the best build in terms of the pressure rise coefficients. This configuration was able to provide highest value of the peak pressure rise in comparison with the characteristics achieved from the datum build. An improvement of (2.65%) in the peak pressure rise coefficient in terms of the overall total-total pressure ratio, in association with a (22.49%) improvement in stall margin in terms of the corrected mass flow rates was achieved from this casing treatment build. The improvement in maximum efficiency in terms of the overall total-total pressure ratio, obtained from this build was (1.03%). The results suggest that the vane-recessed tubular-passage casing treatment designed as part of this investigation achieved the objectives, which were established for the research. In the majority of instances it not only produced gains in flow range, pressure rise coefficients and efficiencies, but also enabled the rotating stall, which developed at much lower mass flow rates in the compressor, to become progressive rather than abrupt.