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IN THIS VOLUME


General

1975;():V01AT01A011. doi:10.1115/75-GT-12.
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This paper presents statistical information on the aircraft gas turbine engine rotor failures that occurred in U.S. commerical aviation during 1973. Based on FAA data, results are presented that establish (1) the incidence of rotor failure, (2) the type of fragments generated, (3) whether or not these fragments were contained, (4) the causes of failure, (5) where in the engine failure occurred, (6) what engines were affected and (7) what flight conditions prevailed at failure. The rate of uncontained rotor burst was considered to be significantly high.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A013. doi:10.1115/75-GT-14.
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Investigations concerning the flow patterns within centrifugal impeller channels have been made for many years. However, many of the problems remain unresolved about the secondary flow and the loss production mechanism within impeller channels. In the present study, measurements of the flow mechanism within impeller channels under the off-design conditions were performed by employing yaw probes to compare the results with those at the design point. The impellers with straight radial blades employed in the present study were of the same configuration except the shroud profiles which made diffusion ratios different from each other. From the present results, it became clear that the loss production mechanisms and the flow patterns within impeller channels were essentially unvaried both under design and off-design operations. The results thus obtained by the present study were furthermore compared with the others to examine the reliability of these results.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A014. doi:10.1115/75-GT-15.
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A numerical procedure is presented for the analysis of thermal and kinematic boundary layers behavior along the blades of a gas turbine stator. Dealing with both laminar and turbulent two-dimensional compressible flows, it solves by marching integration the B.L. equations, based on Spalding’s effective viscosity model, with quite general thermal boundary conditions. It accounts for main stream turbulent level influence and, using transition criteria based upon local profiles, is able to adapt itself to any flow modification like turbulent layer laminarization, laminar to turbulent transition, separation of laminar or turbulent type.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A015. doi:10.1115/75-GT-16.
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General consideration for matching combustion and steam turbines are discussed as a background for the typical Repowering study. Different arrangements of the combustion turbines and heat recovery boilers are presented, discussed, evaluated, and a comparison of the systems are made. To complete the investigation, a series of economic factors are considered for comparison between Repowering and an alternate form of generation. In conclusion, by incorporation of combustion turbines in Repowering of an old steam plant, the extended use of combustion turbines can be justified.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A016. doi:10.1115/75-GT-17.
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The attenuation of sound energy propagating through a turbine is analyzed using an actuator disk theory. The analysis is restricted to low frequency disturbances and subsonic relative flow. Mach number changes and flow turning across a stage element are taken into account. Results indicate that the attenuation of acoustic energy across a typical turbine stage is at least 10 dB.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A017. doi:10.1115/75-GT-18.
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In the late 1960’s the City of Clarksdale, Mississippi, decided to add 25,000-KW of additional generation, using a combined steam and gas turbine cycle. This paper describes the principal machinery characteristics and some of the important economic factors leading to this choice of equipment. The unit has now had over 14,000 hr of successful operation and has in general exceeded original expectations with regard to first cost and efficiency.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A018. doi:10.1115/75-GT-19.
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After discussion of the design and materials of construction of the RUSTON TA series gas turbines, information relating to applications and lifetimes is given. The main portion of the paper deals with a variety of interesting material problems and their solutions, that have arisen over the years. These have been reported under the headings of: Influence of atmosphere; influence of fuel; influence of temperature; influence of material; and influence of lubricating oil. Finally, reference is made to specific installations and their operating data in order to re-affirm the suitability of the industrial gas turbine as a power source in a very wide variety of demanding applications and environments.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A019. doi:10.1115/75-GT-20.
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The vorbix burner (acronym for Vortex Burning and Mixing) represents a new approach to a practical gas turbine combustor design. The concept exploits the Rayleigh instability of swirling flows to enhance the mixing and combustion rates. The combination of a two-stage fuel system with a piloted combustor leads to a unique high rate technique for fuel prevaporization within the combustor proper. This paper presents the fundamental concepts in the definition of the vorbix combustor and the results of exploratory tests conducted on can (tubular) and annular vorbix combustors. The results indicate that this type of combustor has unique performance characteristics that include excellent stability and high combustion efficiency over wide excursions in operating fuel air ratios in addition to substantially reduced emission levels during high power operation.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A020. doi:10.1115/75-GT-21.
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Observations of wave refraction in flowfields containing large transverse velocity gradients have suggested a means by which refraction effects could be used to aid suppression of the noise propagating forward through aircraft gas turbine inlets. The first part of this paper describes an experiment using a schlieren apparatus to observe waves passing through inlet-type flowfields. The second part describes a test program using model inlets to examine the feasibility of the refracting inlet concept.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A021. doi:10.1115/75-GT-22.
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A supersonic compressor stage has been designed for a high pressure ratio at a tip relative inlet Mach number of 2. The stage was operated in the original configuration, but serious inlet stall occurred at part-speed operation. An inlet blockage ring, a bleed system and a variable geometry inlet guide vane have been analyzed and applied to this configuration. The results obtained with the bleed system in the complete stage are presented. The rotor performance is discussed and compared with the stage performance.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A022. doi:10.1115/75-GT-23.
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A momentum-integral analysis of the three-dimensional flow on the turbine endwall is presented. The formulation is for a compressible turbulent boundary layer with a constant streamwise shape factor. The effect of compressibility enters through a coordinate transformation and an assumed energy equation. An aerodynamic loss model is derived using inner and outer expansions. The losses decompose into frictional losses on the annulus and a vortex loss. Results are predicted for four cascade tests. In addition, previously observed trends of loss versus inlet boundary layer thickness, blade height, and blade chord are predicted. To illustrate a possible application, a parametric study is presented showing the effect on losses and heat transfer of various inlet boundary layer thickness distributions, which simulates different secondary flow configurations.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A023. doi:10.1115/75-GT-24.
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Details are given of an integrated engine health monitoring (EHM) program for use by the staffs of Royal Naval ships primarily aimed eventually at engine removal “on condition” rather than on fixed overhaul life. The logic behind the choice of particular EHM methods is given followed by a description of the data collection and analysis procedures. Emphasis is placed on fault diagnosis, using formal charts to reduce the time and effort involved.

Topics: Engines , Gas turbines , Ships
Commentary by Dr. Valentin Fuster
1975;():V01AT01A024. doi:10.1115/75-GT-25.
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Subsonic cascade tests of a stator blade row are presented. A 48-deg cambered double circular arc blade section has been investigated at different inlet Mach numbers (M1 = 0.5, 0.64, 0.74), different inlet flow angles and various axial velocity density ratios. Optimum cascade performance has been obtained at negative incidence angles and near two-dimensional flow condition. The cascade results are compared with stator tests of the same blade section at corresponding flow conditions.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A025. doi:10.1115/75-GT-26.
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A prototype rotor has been designed to investigate the supersonic axial component at the inlet face of a compressor. A flexible inflatable nozzle is installed in the inlet duct in order to simulate a continuously variable inlet Mach number up to 1.5. A relative inlet Mach number of 2.4 was achieved at 90 percent of the design speed. The transition from the subsonic to the supersonic axial component is explored. A blade failure prevented completion of the research on the dynamic response of the compressor to throttle valve, speed and inlet nozzle variations.

Topics: Compressors
Commentary by Dr. Valentin Fuster
1975;():V01AT01A049. doi:10.1115/75-GT-50.
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The current energy crisis and substantial increases in the costs of liquid and gaseous fuels, combined with reduced pollutant emission requirements, make the higher efficiency recuperative gas turbine cycle economically attractive for industrial and vehicular application. For future low cost, high temperature, small gas turbines, with improved cycle efficiencies, it is postulated that the complete hot section of the engine (combustor, ducts, turbine nozzle and rotor) will be all ceramic and may include a ceramic heat exchanger. Few of the answers are available today in the areas of ceramic recuperator performance, cost and structural integrity and concentrated development efforts are required to demonstrate the viability of a fixed boundary ceramic gas turbine heat exchanger. This paper briefly outlines possible design and development trends in the areas of exchanger configuration, surface geometry and materials, and it includes specific sizes and economic aspects of ceramic recuperators for future advanced low SFC gas turbines.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A050. doi:10.1115/75-GT-51.
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The combined steam and gas turbine cycle provides the highest efficiency turbine system available today. In view of the rapidly escalating value of fuel the combined cycle therefore merits a review for pipeline applications. Such a review reveals the combined cycle has a number of advantages. First, the combined cycle efficiency is significantly higher than the efficiency of a standard regenerative cycle gas turbine. Second, and contrary to the characteristics of a standard gas turbine, the efficiency at a given load improves significantly as the ambient temperature increases, so that the combined cycle would be applicable in hot climates. Third, the adjustable speed capability of the combined cycle meets the usual pipeline service requirements. This paper briefly presents the results of a preliminary study of a combined cycle single drive system as it might be utilized in a gas pipeline station.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A051. doi:10.1115/75-GT-52.
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Isothermal Shape Rolling is a new hot metal shaping process developed by the Solar Division of International Harvester. The process is unique in that it uses refractory metal rolls with closed loop control of forming temperature. Heating is achieved by passage of electric current through the workpiece from the electrically conductive shaping rolls. The process eliminates much of the processing costs encountered in the more conventional rolling of airfoil sections in corrosion or heat resistant alloys. Cost reduction is made possible by single pass rolling to the finished airfoil, freedom from surface contamination of the rolled surface and the fine surface finish of the as-rolled section. The general characteristics of the process are described and examples of application to gas turbine components are presented.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A052. doi:10.1115/75-GT-53.
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To gain the economic advantages of size, the trend has been to use larger and larger compressor/driver units in many types of service. Coupled with this “economy of size” trend, the recent sharp increase in the cost of fuel has made driver efficiency a major consideration. This paper describes the application, and discusses the early experience, of a recent installation of a very large, efficient gas turbine driven compressor unit in a natural gas transmission pipeline station. The task of the compressor/driver unit and the station arrangement are described and details of the turbine and compressor are presented. Then a brief account of the operating history is given.

Topics: Gas turbines , Cycles
Commentary by Dr. Valentin Fuster
1975;():V01AT01A053. doi:10.1115/75-GT-54.
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Multistage compressor parameters are related to recent gas transmission applications having a diversity of requirements, ranging from large flows to high pressure.

Topics: Compressors
Commentary by Dr. Valentin Fuster
1975;():V01AT01A054. doi:10.1115/75-GT-55.
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Part programming by interactive graphics is a technique of communicating with a computer by means of simple words and diagrams on a cathode ray tube. A basic mini-computer system is described and an example of geometry input and tool path generation is given. The toolpath of a production lathe tape and examples of future 3 and 5 axis milling applications are shown. The current benefits of the system are also outlined.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A055. doi:10.1115/75-GT-56.
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Turbomachinery rotors may be engineered to be machined on 5-axis, numerically controlled machines using flank milling techniques. Engineering data can be converted to a graphic or computer data set which lends itself to unsophisticated numerically controlled programming for five-axis machines with short lead time production and a high degree of change flexibility.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A056. doi:10.1115/75-GT-57.
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The dynamic behavior of elastic circular disks mounted on a flexible rotor has been investigated by a three-dimensional finite element model (distributed masses). The results are discussed and compared with an equivalent system assuming rigid disks (concentrated mass) for the nonrotating case. Interactions between the disks and disk and shaft during resonances have been demonstrated. Natural modes of a disk component and of the entire structure, supported by flexible bearings, are shown by computer plots in orthographic projections.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A057. doi:10.1115/75-GT-58.
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A method to determine the transient response of damped single or multi-shaft rotor systems is presented. The rotor systems are idealized as rotating concentrated masses connected by massless beams, discrete springs, and dampers. The springs may have piecewise constant springs rates to simulate the stiffening effect of parts coming in contact after displacement through an initial offset. Arbitrary forcing functions are allowed. The method employs an incremental formulation in which damping gyroscopic and nonlinear terms are treated as external loads which are lagged in time. The equations of motion are uncoupled by performing a normal mode expansion of the response solution in terms of the non-rotating, undamped eigenvectors and their associated eigenvalues; modes and natural frequencies are obtained from a standard Prohl analysis. An analytical solution is used for each step of the incremental analysis. This technique has been used to study the response of a number of rotor systems to the sudden application of a rotating imbalance load. The systems studied include a dual shaft model of a rig, a single-shaft case from the written literature and a large multi-line (multi-shaft) system. The transient analysis was run out to steady-state and close agreement obtained with results from an independent steady-state forced response analysis. Orthogonality relations between the mode shapes were observed to be critical to the quality of the results. It was observed that transient analysis of multi-line systems can be accurately predicted only if the higher frequency modes which are participating in the response are included in the normal mode solution.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A058. doi:10.1115/75-GT-59.
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A modification is presented to the Emmons/Stenning analysis for predicting stall propagation, taking into account the unsteady flow through the end wall of a cascade row of compressor blades. It is shown that if radial flow from the blade channels is permitted, then the condition for flow instability is changed. The expression obtained for the flow coefficient at which stall occurs indicates an improvement in operating range, with virtually no effect on stall cell speed. Experimental evidence suggests that a mechanism such as that described may be the reason for the delay in stall onset produced by porous wall treatment of axial compressors.

Topics: Compressors
Commentary by Dr. Valentin Fuster
1975;():V01AT01A059. doi:10.1115/75-GT-60.
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The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot, and blade angle slot treatments were tested at low speeds. With the circumferential groove treatment the stalling flow was reduced 5.8 percent at negligible efficiency sacrifice. The axial-skewed slot treatment improved the stalling flow by 15.3 percent; 1.8 points in peak efficiency were sacrificed. The blade angle slot treatment improved the stalling flow by 15.0 percent; 1.4 points in peak efficiency were sacrificed. These values are consistent with previous experience at transonic speeds. The favorable stalling flow situations correlated well with observations of higher-than-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annulus wall pressure gradients, especially in the 50 to 75 percent chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations. Rotor blade wakes may be somewhat thinner in the presence of good treatments, particularly under operating conditions close to the baseline stall. Annulus wall boundary layer profiles are only slightly influenced by casing treatment.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A060. doi:10.1115/75-GT-61.
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There is evidence to show that the exhaust noise from gas turbines contains components which exceed the jet mixing noise at low jet velocities. This paper describes a theory developed to calculate the acoustic power produced by temperature fluctuations from the combustor entering the turbine. Using the turbine Mach numbers and flow directions at blade mid-height, and taking a typical value for the fluctuation in temperature, it has been possible to predict the acoustic power due to this mechanism for three different engines. In all three cases the agreement with measurements of acoustic power at low jet velocities is very good. Using a measured spectrum of the temperature fluctuation the prediction of the acoustic power spectrum agrees quite well with that measured.

Commentary by Dr. Valentin Fuster
1975;():V01AT01A061. doi:10.1115/75-GT-62.
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This paper presents the results of an experimental cascade investigation of the aerodynamic performance of a 1.524-cm (0.6-in.) blade height, low aspect ratio, highly loaded, cooled turbine. The experimental program was performed with a cold flow annual sector cascade with various geometric and aerodynamic perturbations. The perturbation included nozzle endwall contour, inlet turbulence and velocity distortion, stator and rotor solidity, rotor loading and nozzle cooling flow and point of injection. The turbine design evolved through a parametric analysis considering a turboshaft engine configuration required to have a 750-hr life at design power output and satisfy realistic mechanical constraints. The gas generator turbine configuration selected for investigation was a single-stage turbine with a turbine inlet temperature of 1316 C (2400 F) and an actual work output of 418.68 kJ/kg, (180 Btu/lb). The baseline turbine was sized for a stage work coefficient of 5.0 at the hub radius and an average flow coefficient of 0.675 for a best mechanical-aerothermodynamic compromise to meet realistic engine constraints.

Commentary by Dr. Valentin Fuster

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