This dissertation discusses research on the leakage and rotordynamic characteristics of pocket damper seals (PDS) and see-through labyrinth seals, presents and evaluates models for labyrinth seal and PDS leakage and PDS force coefficients, and compares these seals to other annular gas seals. Low-pressure experimental results are used alongside previously-published high-pressure labyrinth and PDS data to evaluate the models. Effects of major seal design parameters; blade thickness, blade spacing, blade profile, and cavity depth; on seal leakage, as well as the effect of operating a seal in an off-center position, are examined through a series of non-rotating tests. Two reconfigurable seal designs were used, which enabled testing labyrinth seals and PDS with two to six blades. Leakage and pressure measurements were made with air as the working fluid on twenty-two seal configurations. Increasing seal blade thickness reduced leakage by the largest amount. Blade profile results were more equivocal, indicating that both profile and thickness affected leakage, but that the influence of one factor partially negated the influence of the other. Seal leakage increased with increased eccentricity at lower supply pressures, but that this effect was attenuated for higher pressure drops. While cavity depth effects were minor, reducing depths reduced leakage up to a point beyond which leakage increased, indicating that an optimum cavity depth existed. Changing blade spacing produced results almost as significant as those for blade thickness, showing that reducing spacing can detrimentally affect leakage to the point of negating the benefit of inserting additional blades. Tests to determine the effect of PDS partition walls showed that they reduce axial leakage. The pressure drop was found to be highest across the first blade of a seal for low pressure drops, but the pressure drop distribution became parabolic for high pressure drops with the largest drop across the last blade. Thirteen leakage equations made up of a base equations, a flow factor, and a kinetic energy carryover factor were examined. The importance of the carryover coefficient was made evident and a modified carryover coefficient is suggested. Existing fullypartitioned PDS models were expanded to accommodate seals of various geometries.

No description available.

The temperature of the flow entering a high-pressure turbine stage is inherently non-uniform, as it is produced by several discrete, azimuthally-distributed combustors. In general, however, industrial simulations assume inlet temperature uniformity to simplify the preparation process and reduce computation time. The effects of a non-uniform inlet field on the performance of a commercial, transonic, single-stage, high-pressure, axial turbine with a curved inlet duct have been investigated numerically by performing URANS (Unsteady Reynolds-Averaged Navier-Stokes equations) simulations with the SST (Shear Stress Transport) turbulence model. By adjusting the alignment of the experimentally-based inlet temperature field with respect to the stator vanes, two clocking configurations were generated: a vane-impinging (VI) case , in which each hot streak impinged on a vane; and a mid-pitch (MP) case, in which each hot streak passed between two vanes. In the VI configuration, the hot streaks produced higher time-averaged heat load on the vanes and lower heat load on the blades. As the hot streaks in the VI case passed over the stator vanes, they also spread spanwise due to the actions of the casing passage vortices and the radial pressure gradient; this resulted in a stream entering the rotor with relatively low temperature variations. The hot streaks in the MP case were convected undisturbed past the relatively cool vane section. Relatively high time-averaged enthalpy values were found to occur on the pressure side of the blades in the MP configuration. The non-uniformity of the time-averaged enthalpy on the blade surfaces was lower in the VI configuration. The flow exiting the rotor section was much less non-uniform in the VI case, but differences in calculated efficiency were not significant. / Pratt & Whitney Canada, NSERC

The provision of helical grooves on the surface of a plain journal bearing can improve the stability of a rotor-bearing system. However, the improvement depends on the arrangement of the grooves along the axial length of the bearing. In order to verify this improved stability three types of helical groove bearing and a reference plain journal bearing were investigated. The helical groove journal bearings were: a symmetrical, an asymmetrical and a partial grooved bearing. The bearing test rig was used to measure the oil flow rate, load carrying capacity, power losses, bearing surface temperatures, and stability characteristics. A theoretical model was developed to calculate the load carrying capacity, stiffness and damping coefficients, and stability characteristics of the various types of bearing. The experimental and theoretical results show that at the expense of a reduced load capacity the helical groove bearings are more stable particularly at low eccentricity ratios. However, the experimental observations showed that the partial helical groove bearing is not a practical bearing because the bearing becomes misaligned above certain load. For a given eccentricity ratio and speed the symmetrical bearing ran hotter and with greater power losses in comparison to the other three bearings. At the same eccentricity ratio and speed, the asymmetrical bearing ran at about the same temperature as the plain journal bearing.

An experimental and computational study, motivated by the need to improve current understanding of blade flutter in turbomachinery and provide 3D test data for the validation of advanced computational methods for the prediction of this aeroelastic phenomenon, is presented. A new, low speed flutter test facility has been developed to facilitate a detailed investigation into the unsteady aerodynamic response of a turbine blade oscillating in a three dimensional bending mode. The facility employs an unusual configuration in which a single turbine blade is mounted in a profiled duct and harmonically driven. At some cost in terms of modelling a realistic turbomachinery configuration, this offers an important benefit of clearly defined boundary conditions, which has proved troublesome in previous work performed in oscillating cascade experiments. Detailed measurement of the unsteady blade surface pressure response is enabled through the use of externally mounted pressure transducers, and an examination of the techniques adopted and experimental error indicate a good level of accuracy and repeatability to be attained in the measurement of unsteady pressure. A detailed set of steady flow and unsteady pressure measurements, obtained from five spanwise sections of tappings between 10% and 90% span, are presented for a range of reduced frequency. The steady flow measurements demonstrate a predominant two-dimensional steady flow, whilst the blade surface unsteady pressure measurements reveal a consistent three dimensional behaviour of the unsteady aerodynamics. This is most especially evident in the measured amplitude of blade surface unsteady pressure which is largely insensitive to the local bending amplitude. An experimental assessment of linearity also indicates a linear behaviour of the unsteady aerodynamic response of the oscillating turbine blade. These measurements provide the first three dimensional test data of their kind, which may be exploited towards the validation of advanced flutter prediction methods. A three dimensional time-marching Euler method for the prediction of unsteady flows around oscillating turbomachinery blades is described along with the modifications required for simulation of the experimental test configuration. Computationalsolutions obtained from this method, which are the first to be supported by 3D test data, are observed to exhibit a consistently high level of agreement with the experimental test data. This clearly demonstrates the ability of the computational method to predict the relevant unsteady aerodynamic phenomenon and indicates the unsteady aerodynamic response to be largely governed by inviscid flow mechanisms. Additional solutions, obtained from a quasi-3D version of the computational method, highlight the strong three dimensional behaviour of the unsteady aerodynamics and demonstrate the apparent inadequacies of the conventional quasi-3D strip methodology. A further experimental investigation was performed in order to make a preliminary assessment of the previously unknown influence of tip leakage flow on the unsteady aerodynamic response of oscillating turbomachinery blades. This was achievedthrough the acquisition of a comprehensive set of steady flow and unsteady pressure measurements at three different settings of tip clearance. The steady flow measurements indicate a characteristic behaviour of the tip leakage flow throughout the range of tip clearance examined, thereby demonstrating that despite the unusual configuration, the test facility provides a suitable vehicle for the investigation undertaken. The unsteady pressure data show the blade surface unsteady pressure response between 10% and 90% span to be largely unaffected by the variation in tip clearance. Although close examination of the unsteady pressure measurements reveal subtle trends in the first harmonic pressure response at 90% span, which are observed to coincide with localised regions where the tip leakage flow has a discernible impact on the steady flow blade loading characteristic. Finally, some recommendations for further work are proposed

No description available.

Industrial centrifugal air compressors can require a combination of a large range of mass flow, high efficiency, constant pressure ratio, and constant rotational speed, specifically when used for sewage effluent aeration treatment. In order to achieve this performance it is common to use variable inlet guide vanes (VIGV's). The performance characteristics of an existing VIGV design have been determined using both an experimental test facility and state of art numerical techniques. The results obtained from these techniques are far more comprehensive than earlier fullscale performance testing. Validation of the performance of the existing design using these techniques has led to the development of a new vane design and potential improvements to the inlet ducting geometry. The aerodynamic interaction between the VIGV system and the centrifugal compressor impeller has also been investigated using a 3-D computational model of the complete variable geometry compressor stage. The results of these investigations have been validated by data available from full scale experimental testing. Strong correlation was obtained between numerical and experimental techniques, and a predicted improvement in polytropic efficiency up to 3% at low flow rates using the re-designed variable inlet guide vanes has been achieved. The overall outcome of this research is a usable VIGV design technique for real industrial compressor environments, and confirmation that an acceptable design can be achieved that represents a rewarding improvement in performance.

Thesis (M.S. in Aeronautical Engineering) Naval Postgraduate School, June 1997. / Thesis advisor, Raymond P. Shreeve. AD-A333 428. Includes bibliographical references (p. 49-50). Also available online.

Acoustic experiments were conducted in an anechoic chamber with a 1/14th scale model of a supersonic aircraft engine inlet using Trailing Edge Blowing (TEB) to reduce the engine fan noise from a turbofan propulsion simulator (TPS). The TPS is 4.1 in. (10.4 cm) in diameter and is powered by compressed air. The supersonic inlet is connected to the TPS and is geometrically and acoustically scaled from a working design. The supersonic inlet is operated in a takeoff or landing operating condition where the inlet core flow is subsonic. TEB is the process of ejecting high pressure air to re-energize the wakes of upstream fan disturbances such as struts or inlet guide vanes (IGV). The elimination of the wakes will provide a uniform flow field at the engine fan face and reduce noise at the blade passing frequency. The TEB was implemented on six non-uniformly spaced support struts in the inlet. Acoustic tests were then performed at 40%, 60% and 88% of the fan design speed (PNC) to measure the reduction in the blade passing tone (BPT) due to TEB from the struts with and without the presence of IGV. The noise reductions without IGV at 40 PNC show the best results with the blade passing tone (BPT) being reduced by an average of 3.1 dB. The first harmonic of the BPT and the overall Sound Pressure Level (SPL) were also reduced by 1 dB. The addition of the IGV in the inlet reduced the effectiveness of the TEB. The addition of IGV changed the reduction in BPT at 40 PNC by 0.5 dB and the overall SPL was unchanged. At 60 PNC the addition of IGV reduced the reduction due to TEB in the BPT from an average of 2 dB to an average of 1 dB. The tests performed at 88 PNC showed negligible effects due to TEB. Aerodynamic experiments performed on the inlet that showed that the wakes of the IGV have a larger velocity defect than the struts, thus making the IGV a greater noise source. / Master of Science

The temperature of the flow entering a high-pressure turbine stage is inherently non-uniform, as it is produced by several discrete, azimuthally-distributed combustors. In general, however, industrial simulations assume inlet temperature uniformity to simplify the preparation process and reduce computation time. The effects of a non-uniform inlet field on the performance of a commercial, transonic, single-stage, high-pressure, axial turbine with a curved inlet duct have been investigated numerically by performing URANS (Unsteady Reynolds-Averaged Navier-Stokes equations) simulations with the SST (Shear Stress Transport) turbulence model. By adjusting the alignment of the experimentally-based inlet temperature field with respect to the stator vanes, two clocking configurations were generated: a vane-impinging (VI) case , in which each hot streak impinged on a vane; and a mid-pitch (MP) case, in which each hot streak passed between two vanes. In the VI configuration, the hot streaks produced higher time-averaged heat load on the vanes and lower heat load on the blades. As the hot streaks in the VI case passed over the stator vanes, they also spread spanwise due to the actions of the casing passage vortices and the radial pressure gradient; this resulted in a stream entering the rotor with relatively low temperature variations. The hot streaks in the MP case were convected undisturbed past the relatively cool vane section. Relatively high time-averaged enthalpy values were found to occur on the pressure side of the blades in the MP configuration. The non-uniformity of the time-averaged enthalpy on the blade surfaces was lower in the VI configuration. The flow exiting the rotor section was much less non-uniform in the VI case, but differences in calculated efficiency were not significant. / Pratt & Whitney Canada, NSERC