bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Cost NOx Reduction Retrofit for Pump Scavenged Compressor Engines
Authors: Balles E. N. , Peoples R. C.
Published: February 2008

The Clean Air Act Amendments of 1990 and the resulting individual State Implementation Plans will require many natural gas pipeline operators to install NOx reduction equipment on existing compressor station engines. A program was undertaken to develop lower cost NOx control options for these engines as compared to traditional techniques. The initial work, described in this paper, focused on the development of a low-cost retrofit package for Cooper-Bessemer GMV and GMV-TF pump scavenged integral compressor engines. The retrofit concept relied on highly dilute combustion to achieve low engine-out NOx emission rates. A significant portion of the effort concentrated on low-cost methods for delivering the required air charge and ignition enhancements to achieve reliable and robust combustion. The prototype retrofit kit has been installed on a GMV-6 in gas compressor service. Performance results showed a 70 percent reduction in NOx emission rates without a corresponding increase in HC emission rates.
Effect of Steam-Injected Gas Turbines on the Unit Sizing of a Cogeneration Plant
Authors: Ito K. , Yokoyama R. , Matsumoto Y.
Published: February 2008

The effect of installing steam-injected gas turbines in a cogeneration plant is analyzed with respect to unit sizing and operational planning. An optimization method is used to determine the capacities of gas turbines and other auxiliary machinery in consideration of their operational strategies for variations of electricity and thermal energy demands. Through a numerical study on a plant for district heating and cooling, it is clarified how the installation of steam-injected gas turbines in place of simple-cycle ones can improve the economic and energy-saving properties. The influence of the capital cost of steam-injected gas turbines on the unit sizing and the above-mentioned properties is also clarified.
Measured Force/Current Relations in Solid Magnetic Thrust Bearings
Authors: Allaire P. E. , Fittro R. L. , Maslen E. H. , Wakefield W. C.
Published: February 2008

When magnetic bearings are employed in a pump, compressor, turbine, or other rotating machine, measurement of the current in the bearing coils provides knowledge of the forces imposed on the bearings. This can be a significant indicator of machine problems. Additionally, magnetic bearings can be utilized as a load cell for measuring impeller forces in test rigs. The forces supported by magnetic bearings are directly related to the currents, air gaps, and other parameters in the bearings. This paper discusses the current/force relation for magnetic thrust bearings. Force versus current measurements were made on a particular magnetic bearing in a test rig as the bearing coil currents were cycled at various time rates of change. The quasi-static force versus current relations were measured for a variety of air gaps and currents. The thrust bearing exhibits a hysteresis effect, which creates a significant difference between the measured force when the current is increasing as compared to that when the current is decreasing. For design current loops, 0.95 A to 2.55 A, at the time rate of change of 0.1 A/s, the difference between increasing and decreasing current curves due to hysteresis ranged from 4 to 8 percent. If the bearing is operated in small trajectories about a fixed (nonzero) operation point on the F/I (force/current) curve, the scatter in the measurement error could be expected to be on the order of 4 percent. A quasi-static nonlinear current/force equation was developed to model the data and curve-fit parameters established for the measured data. The effects of coercive force and iron reluctance, obtained from conventional magnetic materials tests, were included to improve the model, but theoretically calculated values from simple magnetic circuit theory do not produce accurate results. Magnetic fringing, leakage, and other effects must be included. A sinusoidal perturbation current was also imposed on the thrust bearing. Force/current magnitude and phase angle values versus frequency were obtained for the bearing. The magnitude was relatively constant up to 2 Hz but then decreased with frequency. The phase lag was determined to increase with frequency with value of 16 deg at 40 Hz. This effect is due to eddy currents, which are induced in the solid thrust-bearing components.
Damage Tolerance Based Life Prediction in Gas Turbine Engine Blades Under Vibratory High Cycle Fatigue
Authors: Walls D. P. , deLaneuville R. E. , Cunningham S. E.
Published: February 2008

A novel fracture mechanics approach has been used to predict crack propagation lives in gas turbine engine blades subjected to vibratory high cycle fatigue (HCF). The vibratory loading included both a resonant mode and a nonresonant mode, with one blade subjected to only the nonresonant mode and another blade to both modes. A life prediction algorithm was utilized to predict HCF propagation lives for each case. The life prediction system incorporates a boundary integral element (BIE) derived hybrid stress intensity solution, which accounts for the transition from a surface crack to corner crack to edge crack. It also includes a derivation of threshold crack length from threshold stress intensity factors to give crack size limits for no propagation. The stress intensity solution was calibrated for crack aspect ratios measured directly from the fracture surfaces. The model demonstrates the ability to correlate predicted missions to failure with values deduced from fractographic analysis. This analysis helps to validate the use of fracture mechanics approaches for assessing damage tolerance in gas turbine engine components subjected to combined steady and vibratory stresses.
Resonant Response of a Tapered Beam and Its Implications to Blade Vibration
Authors: Balaji G. N. , Griffin J. H.
Published: February 2008

The resonant response characteristics of a tapered beam are studied using Euler–Bernoulli beam theory. The sensitivity of the beam’s maximum stress to variations in its geometry is studied for three types of harmonic pressure loading. The implications to the response of airfoil chordwise bending modes are discussed.
Design and Analysis of a Sensorless Magnetic Damper
Authors: Chen H. M.
Published: February 2008

An analytical method for designing magnetic bearing controllers with no displacement sensors has been developed and laboratory tested. The method was applied to the design of a sensorless magnetic damper for replacing a rolling element bearing of a vertical rotor with a large unbalance. The synchronous vibration force transmitted to ground was predicted to be reduced by a factor of ten.
Vibration and Control of a Flexible Rotor in Magnetic Bearings Using Hybrid Method and H∞ Control Theory
Authors: Shiau T. N. , Sheu G. J. , Yang C. D.
Published: February 2008

The vibration and active control of a flexible rotor system with magnetic bearings are investigated using Hybrid Method (HM) and H∞ control theory with consideration of gyroscopic effect. The hybrid method, which combines the merits of the finite element method (FEM) and generalized polynomial expansion method (GPEM) is employed to model the flexible rotor system with small order of plant. The mixed sensitivity problem of H∞ control theory is applied to design the control of system vibration with spillover phenomena for the reduced order plant. The H2 control design is also employed for comparison with the H∞ design. The experimental simulation is used to illustrate the effects of control design. It is shown that the H∞ controller design can be very effective to suppress spillover phenomena. In addition, the H∞ control design has robustness to the variation of the model parameters. The application of the hybrid method (HM) together with H∞ control design is highly recommended for vibration control of flexible rotor systems with magnetic bearings.
An Evaluation of Indentation and Finishing Properties of Bearing Grade Silicon Nitrides
Authors: Dill J. F. , Gardos M. N. , Hardisty R. G.
Published: February 2008

This paper describes the results of studies of the machining performance and the indentation hardness and fracture toughness of different silicon nitride materials as part of an effort to better define the optimum machining conditions for bearing components. This work builds on prior efforts by two of the authors, Gardos and Hardisty (1993) who formulated a simple relationship between diamond grinding performance of silicon nitride bearing balls and a wear equation first detailed by Evans and Wilshaw (1976). The goal of this present work was to determine the general applicability of such a relationship, i.e., could simple indentation studies be used to define finishing conditions for different silicon nitride materials? The availability of such a simple test would reduce the time required for developing an acceptable process when a supplier changes his formulation, or when a new material becomes available. Quicker development of optimum finishing conditions would eventually result in a lower-cost product for users. The initial study by Gardos and Hardisty (1993) was based on limited data taken at a fixed set of conditions. This study expanded the range of conditions evaluated and the number of ceramic materials studied in an effort to define the universality of the relationship between grinding wear, hardness, and toughness. This study has shown that no simple relationship like that first envisioned by the authors exists. The results showed that the grinding wear of the individual silicon nitride materials increased at different rates as a function of load. Because of the differences found in the load dependence of grinding rates, no simple relationship between hardness, fracture toughness, and grinding rate could be found that fit the data over the range of conditions studied. This work is part of an ARPA funded effort to provide a tribological performance database on ceramic-bearing materials, including their grinding and finishing properties, and their interaction with standard bearing steels.
Trends in the Design and Analysis of Components Fabricated From CFCCs
Authors: Duffy S. F. , Palko J. L. , Sandifer J. B. , DeBellis C. L. , Edwards M. J. , Hindman D. L.
Published: February 2008

Continuous fiber ceramic composite materials (CFCCs) are being considered for an increasing number of commercial applications. They provide the potential for lighter, stronger, more corrosion-resistant components that can perform at higher temperature for long periods of time. Global competitiveness demands a shortening of the time for CFCC commercialization. Thus, considerable efforts has been expended to develop and improve the materials, and to a lesser extent, to develop component design methods and data bases of engineering properties. To shorten the time to commercialization, project efforts must be integrated, while balancing project resources between material development and engineering design. Currently a good balance does not exist for most materials development projects. To rectify this imbalance, improvements in engineering design and development technologies must be supported and accelerated, with a focus on component issues. This will require project managers to give increasing emphasis to component design needs in addition to their current focus on material development.
Predictions of Tensile Behavior and Strengths of a Si3N4 Ceramic at High Temperatures Based on a Viscoplastic Model
Authors: Liu K. C. , Brinkman C. R. , Ding J.-L. , Lin S.-B.
Published: February 2008

Tensile deformation and rupture behavior were simulated using a viscoplastic model developed recently. The model was formulated based on the state variable approach, which provides flexibility and versatility for characterizing the time-dependent behavior of ceramic materials under general thermomechanical loading conditions. Simulations portrayed by the model were compared with experimental tensile data obtained under two different tensile stressing rates. Results showed that the model was capable of simulating deformation behavior for all practical engineering purposes, but estimated high-temperature fracture strengths somewhat conservatively.
Measurements of Droplet Velocity and Size Downstream of the Moving Valves of a Four-Valve Engine With Manifold Injection, Operated Under Isothermal Steady Suction Conditions
Authors: Posylkin M. , Taylor A. M. K. P. , Whitelaw J. H. , Ishii K. , Miyano M.
Published: February 2008

The four-valve head of a VTEC engine was mounted on an open cylinder and the valves and fuel injection system operated as in the engine with a rotational speed of 1200 rpm. Local measurements of droplet characteristics were obtained with a phase-Doppler velocimeter and iso-octane injected over 5 ms intervals, corresponding to 36 crank angle degrees, with manifold depression of 20 mbar. The results show that most of the fuel droplets were located close to the liner and on the side of the cylinder adjacent to the exhaust valves. In the plane of the measurement, 10 mm below TDC, the liquid flux diminished as the initiation of injection was advanced before opening of the inlet valves. With injection with the inlet valves closed, there were two waves of droplets, one from each of the two valves and separated by 60 deg CA and both with the Sauter mean diameter of about 120 μm. With injection with the inlet valves open, most of the droplets emerged from the main inlet valve and with Sauter mean diameters of about 50 μm, smaller than those of the unconfined spray.
A Computational Study of Pressure Effects on Pollutant Generation in Gas Turbine Combustors
Authors: Amin E. M. , Andrews G. E. , Pourkashnian M. , Williams A. , Yetter R. A.
Published: February 2008

A numerical study of the effect of pressure on the formation of NOx and soot in an axisymmetric 30 deg counterrotating axial swirler lean low-NOx gas turbine combustor has been conducted. This has previously been studied experimentally and this CFD investigation was undertaken to explain the higher than expected NOx emissions. The combustion conditions selected for the present study were 300 K inlet air, 0.4 overall equivalence ratio, and pressures of 1 and 10 bar. The numerical model used here involved the solution of time-averaged governing equations using an elliptic flow-field solver. The turbulence was modeled using algebraic stress modeling (ASM). The thermochemical model was based on the laminar flame let formulation. The conserved scalar/assumed pdf approach was used to model the turbulence chemistry interaction. The study was for two pressure cases at 1 and 10 bar. The turbulence–chemistry interaction is closed by assumption of a clipped Gaussian function form for the fluctuations in the mixture fraction. The kinetic calculations were done separately from the flowfield solver using an opposed laminar diffusion flame code of SANDIA. The temperature and species profiles were made available to the computations through look-up tables. The pollutants studied in this work were soot and NO for which three more additional transport equations are required, namely: averaged soot mass fraction, averaged soot particle number density, and finally averaged NO mass fraction. Soot oxidation was modeled using molecular oxygen only and a strong influence of pressure was predicted. Pressure was shown to have a major effect on soot formation.
Fracture Toughness of Structural Ceramics Under Biaxial Stress State by Anticlastic Bending Test
Authors: Ono T. , Kaji M.
Published: February 2008

Mixed-mode fracture of structural ceramics under a biaxial stress state was investigated by an anticlastic bending test using the controlled surface flaw technique. The stress state of the anticlastic bending specimen is biaxial. This test enables the study of fractures under pure mode I, pure mode II, or any combination of mode I and mode II loading. To discuss the experimental results, a parameter “T” was introduced to the modified maximum hoop stress criterion. This parameter represents frictional effects of crack interfaces on the mixed-mode fracture and can be obtained experimentally. Relative magnitudes of mode I and mode II stress intensity factors and the directions of non-coplanar crack extension angles were predicted using the parameter “T.” Reasonable agreement with the experimental results was obtained.
Dry Ultralow NOx “Green Thumb” Combustor for Allison’s 501-K Series Industrial Engines
Authors: Puri R. , Stansel D. M. , Smith D. A. , Razdan M. K.
Published: February 2008

This paper describes the progress made in developing an external ultralow oxides of nitrogen (NOx) “Green Thumb” combustor for the Allison Engine Company’s 501-K series engines. A lean premixed approach is being pursued to meet the emissions goals of 9 ppm NOx, 50 ppm carbon monoxide (CO), and 10 ppm unburned hydrocarbon (UHC). Several lean premixed (LPM) module configurations were identified computationally for the best NOx–CO trade-off by varying the location of fuel injection and the swirl angle of the module. These configurations were fabricated and screened under atmospheric conditions by direct visualization through a quartz liner; measurement of the stoichiometry at lean blow out (LBO); measurement of the fuel–air mixing efficiency at the module exit; and emissions measurements at the combustor exit, as well as velocity measurements. The influence of linear residence time on emissions was also examined. An LPM module featuring a radial inflow swirler demonstrated efficient fuel-air mixing and subsequent low NOx and CO production in extensive atmospheric bench and simulated engine testing. Measurements show the fuel concentration distribution at the module exit impacts the tradeoff between NOx and CO emissions. The effect of varying the swirl angle of the module also has a similar effect with the gains in NOx emissions reduction being traded for increased CO emissions. A uniform fuel-air mixture (±2.5 percent azimuthal variation) at the exit of the module yields low NOx (5–10 ppm) at inlet conditions of 1 MPa (~10 atm) and temperatures as high as 616 K (650°F). The combustion efficiency at these conditions was also good (>99.9 percent) with CO and UHC emissions below 76 ppm and 39 ppm, respectively. This LPM module was resistant to flashback, and stability was good as LBO was observed below φ = 0.50. Tests with multiple modules in a single liner indicate a strong intermodule interaction and show lower NOx and CO emissions. The close proximity of adjacent modules and lower confinement in the liner most likely reduces the size of the recirculation zone associated with each module, thereby reducing the NOx formed therein. The CO emissions are probably lowered due to the reduced cool liner surface area per module resulting when several modules feed into the same liner.
Non-Random Adaptive Grid Method for High-Speed Optimization of Highly Dimensional, Badly Behaving Real Time Functions
Authors: Shahroudi K. E.
Published: February 2008

The majority of optimization methods lose their applicability when solving highly dimensional functions. The required calculation effort usually becomes enormous as dimensions increase, regardless of the elegance of the method. Most methods concern themselves with finding a single optimum that satisfies the required accuracy, but that provides no quantitative measure (i.e., probability of correctness) indicating whether the true optimum is found. Furthermore, there is usually no exact measure of the calculation effort prior to starting the procedure. There is always an unavoidable coupling (i.e., relation) between the accuracy, probability, and calculation effort of an optimization method, but the exact form of this relation is dependent on the procedures followed to reach optimum. Ideally, an optimization method should facilitate the statement of required accuracy, required probability, and the required calculation effort separately and the method should take care of the rest (i.e., total decoupling of the three requirements). Although this ideal case is generally not possible, it is possible to move toward it by finding procedures that reduce the strength of this unwanted coupling. This report derives simple analytical relations between the required accuracy, probability, and calculation effort of a general multidimensional adaptive grid non-gradient guided (NGG) search method where the search points are generated either decisively or randomly. It is then shown that any adaptive method based on reducing the total solution space is heavily penalized. Further, it is analytically illustrated that if the adaptive grid is randomly generated, it is far less successful than the non-random adaptive grid, because the amount of grid adaptation is less decisive at every step, due to the randomness. As with many optimization techniques, the dimensionality problem limits the application of this method to cases where the function evaluation is real time (~milliseconds) and dimensions are lower than say 25, which occurs in conceptual/preliminary design systems such as CAGED (Shahroudi, 1994b). This method is also particularly useful for problems in which the number of optima is known in advance. In this case the required probability can be set to its minimum value, which is required in order to distinguish an absolute optimum from a known (or likely) number of optima. The coupling relations derived in this report will then provide the minimum calculation effort necessary to satisfy accuracy and probability requirements.
Thermal Cycling Effects on Dynamic Mechanical Properties and Crystallographic Structures of Silicon Nitride-Based Structural Ceramics
Authors: Yang S. , Gibson R. F. , Crosbie G. M. , Allor R. L.
Published: February 2008

Thermal cycling effects on dynamic mechanical properties of hot pressed silicon nitride (HPSN) based structural ceramics were investigated in a simulated thermal cycling environment from room temperature up to 1100°C. Two monolithic silicon nitrides and two silicon nitride composites reinforced with silicon carbide whiskers were studied in such an environment. Experiments show that the dynamic mechanical properties of the tested materials are influenced by thermal cycle. The materials stiffened slightly while damping capacity decreased slightly during each thermal cycle. X-ray diffraction (XRD) was subsequently used to examine the corresponding crystallographic alterations. The XRD patterns show that the amorphous glass phases in the silicon nitride matrix were partially crystallized during thermal cycling.
Modeling Sulfur Dioxide Capture in a Pulverized Coal Combustor
Authors: Nair R. B. , Yavuzkurt S.
Published: February 2008

The formation and capture of sulfur dioxide in a pulverized coal combustor is investigated. A two-dimensional, steady, axisymmetric code, PCGC-2 (Pulverized Coal Gasification and Combustion—two Dimensional), originally developed at Brigham Young University, has been used to simulate combustion of the pulverized coal. This paper represents part of a project to investigate simultaneously enhancing sulfur capture and particulate agglomeration in combustor effluents. Results from the code have been compared to experimental data obtained from MTCI’s (Manufacturing Technology and Conversion International) test pulse combustor, which generates sound pressure levels of ~180 dB. The overall goal behind the pulse combustor program at MTCI is to develop combustors for stationary gas turbines that use relatively inexpensive coal-based fuels. This study attempts to model the capture of sulfur dioxide when injected into a pulse combustor firing micronized coal. While this work does not presume to model the complex gas flow-field generated by the pulsating flow, the effects of the acoustic field are expressed by increased heat and mass transfer to the particles (coal/sorbent) in question. A comprehensive calcination-sintering-sulfation model for single particles was used to model the capture of sulfur dioxide by limestone sorbent. Processes controlling sulfation are external heat and mass transfer, pore diffusion, diffusion through the product layer of CaSO4, sintering, and calcination. The model was incorporated into the PCGC-2 program. Comparisons of exit concentrations of SO2 showed a fairly good agreement (within ~10 percent) with the experimental results from MTCI.
Next-Generation Integration Concepts for Air Separation Units and Gas Turbines
Authors: Smith A. R. , Klosek J. , Woodward D. W.
Published: February 2008

The commercialization of Integrated Gasification Combined Cycle (IGCC) Power has been aided by concepts involving the integration of a cryogenic air separation unit (ASU) with the gas turbine combined-cycle module. Other processes, such as coal-based ironmaking and combined power/industrial gas production facilities, can also benefit from the integration. It is known and now widely accepted that an ASU designed for “elevated pressure” service and optimally integrated with the gas turbine can increase overall IGCC power output, increase overall efficiency, and decrease the net cost of power generation when compared to nonintegrated facilities employing low-pressure ASUs. The specific gas turbine, gasification technology, NOx emission specification, and other site specific factors determine the optimal degree of compressed air and nitrogen stream integration. Continuing advancements in both air separation and gas turbine technologies offer new integration opportunities to improve performance and reduce costs. This paper reviews basic integration principles and describes next-generation concepts based on advanced high pressure ratio gas turbines, Humid Air Turbine (HAT) cycles and integration of compression heat and refrigeration sources from the ASU. Operability issues associated with integration are reviewed and control measures are described for the safe, efficient, and reliable operation of these facilities.
Optimization of Multiple Jets Mixing With a Confined Crossflow
Authors: Doerr Th. , Blomeyer M. , Hennecke D. K.
Published: February 2008

An experimental investigation of a nonreacting multiple jet mixing with a confined crossflow has been conducted. Flow and geometric conditions were varied in order to examine favorable parameters for mixing. The requirement for a rapid and intense mixing process originates from combustion applications, especially the RQL-combustion concept. Thus, the jets were perpendicularly injected out of one opposed row of circular orifices into a heated crossflow in a rectangular duct. Spacing and hole size were varied within the ranges referring to combustor applications. The results presented are restricted to an in-line orientation of opposed jet axis. Temperature distribution, mixing rate, and standard deviation were determined at discrete downstream locations. Best, i.e., uniform mixing can be observed strongly depending on momentum flux ratio. For all geometries investigated, an optimum momentum flux ratio yields to a homogeneous temperature distribution in the flow field downstream of the injection plane. Overly high ratios deteriorate the mixing process due to the mutual impact of the opposed entraining jets along with a thermal stratification of the flowfield. Correlations are introduced describing the dependency of optimum momentum flux ratio on mixing hole geometry. They allow the optimization of jet-in-crossflow mixing processes in respect to uniform mixing.
An Experimental and Numerical Study of the Isothermal Flowfield Behind a Bluff Body Flameholder
Authors: Raffoul C. N. , Nejad A. S. , Gould R. D. , Spring S. A.
Published: February 2008

An experimental and numerical investigation was conducted to study the turbulent velocities and stresses behind a two-dimensional bluff body. Simultaneous three-component laser-Doppler velocimeter (LDV) measurements were made in the isothermal incompressible turbulent flowfield downstream of a bluff body placed at midstream in a rectangular test section. Mean velocities and Reynolds stresses were measured at various axial positions. Spanwise velocity measurements indicated that the flow is three dimensional in the recirculation zone of the bluff body. Confidence in the accuracy of the data was gained by calculating the mass fluxes at each axial station. These were found to agree with each other to within ±3 percent. A parallel Computational Fluid Dynamics (CFD) study was initiated to gage the predictive accuracy of currently available CFD techniques. Three solutions were computed: a two-dimensional steady-state solution using the standard k-ε model, a two-dimensional time-accurate solution using the standard k-ε model, and a two-dimensional time-accurate solution using a Renormalized-Group (RNG) k-ε turbulence model. The steady-state solution matched poorly with the data, severely underpredicting the Reynolds stresses in the recirculation zone. The time-accurate solutions captured the unsteady vortex shedding from the base of the bluff body, providing a source for the higher Reynolds stresses. The RNG k-ε solution provided the best match to the data.
Combustion Oscillation Control by Cyclic Fuel Injection
Authors: Richards G. A. , Yip M. J. , Robey E. , Cowell L. , Rawlins D.
Published: February 2008

A number of recent articles have demonstrated the use of active control to mitigate the effects of combustion instability in afterburner and dump combustor applications. In these applications, cyclic injection of small quantities of control fuel has been proposed to counteract the periodic heat release that contributes to undesired pressure oscillations. This same technique may also be useful to mitigate oscillations in gas turbine combustors, especially in test rig combustors characterized by acoustic modes that do not exist in the final engine configuration. To address this issue, the present paper reports on active control of a subscale, atmospheric pressure nozzle/combustor arrangement. The fuel is natural gas. Cyclic injection of 14 percent control fuel in a premix fuel nozzle is shown to reduce oscillating pressure amplitude by a factor of 0.30 (i.e., −10 dB) at 300 Hz. Measurement of the oscillating heat release is also reported.
“Snapping” Torsional Response of an Anisotropic Radially Loaded Rotor
Authors: Bently D. E. , Goldman P. , Muszynska A.
Published: February 2008

A rotor system with two orthogonal lateral and two angular (torsional) degrees of freedom is considered. The rotor has asymmetry of the lateral stiffness and is laterally loaded with a constant radial force and a rotating unbalance. Constant driving and load torques are applied to the rotor. The important part of the research includes an analysis of “snapping” action, when, during rotation, the rotor experiences a peak of torsional acceleration. This occurs when the “strong stiffness” axis of the anisotropic rotor passes under the axis of the sideload. The numerical simulation of the analytical model exhibits a snapping (accelerated) torsional response of the rotor at twice synchronous frequency (2×), and it is especially pronounced at 1× and 2× torsional resonances. The snapping response can initiate a rotor crack in the area of stress concentration, can stimulate existing crack propagation, and can be a cause of the coupling failure. The analytical results are obtained by the Averaging Method application. They confirm the numerical results and show the possibility of combination resonance occurrences. The synchronous dynamic stiffness for the frequency range around 1× lateral resonance is analytically obtained. The specific shape of the quadrature dynamic stiffness component can serve as a shaft crack indicator and can be used for early detection of a lateral crack on the rotor.
A Numerical Method for the Prediction of Bladed Disk Forced Response
Authors: Berthillier M. , Dhainaut M. , Burgaud F. , Garnier V.
Published: February 2008

A numerical method has been developed to predict the forced response of bladed disks due to a wake excitation from upstream blade rows. The structure is modeled by a three-dimensional finite element mesh of a bladed disk segment. Using cyclic symmetry, this model provides a modal base for the rotating structure. The aerodynamic damping of the vibratory modes and the excitation pressures on the blades due to the propagation of upstream flow defects are computed separately using the same three-dimensional unsteady Euler analysis software. A modal response solution of the aeromechanical system is then performed. This analytical methodology has been used to study the forced response of an experimental high pressure compressor blisk. The results are analyzed and compared with actual rig tests.
Energy Analysis to the Design of Rotor-Bearing Systems
Authors: Chen W. J.
Published: February 2008

In the design of rotating machinery, it is often desirable and necessary to change a subset of system parameters to meet the design requirements. The success in designing rotor-bearing systems and in solving the vibration problems depends heavily upon the understanding of fundamental physical properties and insights of the systems. The modeling improvements and computational techniques have been extensively presented over the years. The design methodologies and fundamental properties have not been widely addressed to assist design engineers in solving their practical problems. The objective of this paper is to relate the various forms of energy and work and their contributions to the system dynamic characteristics. The design strategies and methodologies using the energy approach are also presented and illustrated in a turbine-driven machine.
Comparison of the Rotor Dynamic and Structure Dynamic Calculation of Compressors
Authors: Hohlrieder M. , Irretier H.
Published: February 2008

The paper presents the analysis of a compressor employing the method of cyclic symmetry incorporating gyroscopic effects and geometric nonlinearities of the whole elastic system based on the finite element method. Because of numerical difficulties, the solution of the resulting eigenvalue problem is limited to a small number of DOF’s. For this reason the calculation of the impeller as an elastic model is performed including the prestress and nonlinearities due to rotation. With the knowledge of these frequencies and the mass moment of inertia of the impeller, an equivalent system of rigid disk and speed dependent spring is included in the rotor dynamic model. Further, the gyroscopic effect, speed-dependent bearing coefficients, and the elastic effects due to the rotation of the impeller are included in the rotor dynamic model. For illustration purpose, calculation is performed on a fan rotor and the results are compared with those obtained from experiment.
Modeling and Simulation Methods for MDOF Structures and Rotating Machinery With Impact Dampers
Authors: McElhaney J. M. , Palazzolo A. , Kascak A.
Published: February 2008

Previously published work on applied impact damping typically relates to SDOF models or simple MDOF models such as the classical cantilever beam. Structural models often require an extremely large number of DOF with mode shapes that are generally very complex. Dynamics simulation of these typically becomes both complicated and time consuming. The nonlinear behavior of impact dampers further complicates such simulation in that standard linear solutions are not possible. The primary objective in this research extends previous work by applying impact dampers to MDOF structures that are modeled with general three-dimensional “beam” finite elements. Modal-based models of the MDOF systems and efficient impact damper tracking algorithms were also developed that significantly reduced CPU time for simulation. Significant among the objectives was obtaining an impact damper design for the MDOF casing structure of the Space Shuttle Main Engine (SSME), High-Pressure Oxygen Turbo-Pump (HPOTP), subject to pump rotor shaft unbalance. Impact damper performance is based on suppression of vibration at casing critical frequencies for rotor speed ranges, at rotor full speed, and very high unbalance to simulate a defect such as losing an impeller blade fragment or a cracked bearing [6]. Simulations show significant reductions in vibration at the casing critical frequencies and very high unbalance levels while little or no improvement was observed off resonance. Additionally, the previous work with an experimental rotor bearing system (RBS) and impact damper was modeled using the developed modal-based methods. Simulation of the resulting model response shows remarkable agreement with the experimental. Finally, both the RBS and the HPOTP were modeled and simulated as unstable systems with attached impact dampers. The simulations predict that the impact damper is an excellent stabilizing mechanism for a range of instability driver values. Simulation of the models in this research with the developed modal based algorithms were accomplished with excellent efficiency, and accurate results.
Wave-Rotor-Enhanced Gas Turbine Engines
Authors: Welch G. E. , Jones S. M. , Paxson D. E.
Published: February 2008

The benefits of wave rotor topping in small (300- to 500-kW [400- to 700-hp] class) and intermediate (2000- to 3000-kw [3000- to 4000-hp] class) turboshaft engines, and large (350- to 450-kN [80,000- to 100,000-lbf] class) high-bypass-ratio turbofan engines are evaluated. Wave rotor performance levels are calculated using a one-dimensional design/analysis code. Baseline and wave-rotor-enhanced engine performance levels are obtained from a cycle deck in which the wave rotor is represented as a burner with pressure gain. Wave rotor topping is shown to enhance the specific fuel consumption and specific power of small- and intermediate-sized turboshaft engines significantly. The specific fuel consumption of the wave-rotor-enhanced large turbofan engine can be reduced while it operates at a significantly reduced turbine inlet temperature. The wave-rotor-enhanced engine is shown to behave off-design like a conventional engine. Discussion concerning the impact of the wave rotor/gas turbine engine integration identifies technical challenges.
Distributed Control System for Turbine Engines
Authors: Shaffer P. L.
Published: February 2008

A distributed control system (DCS) for a turbine engine has been demonstrated and tested, consisting of prototype electronic interface units (EIUs) connected to data and power busses. In the DCS, a central control computer communicated with smart sensors and smart actuators via a 2.5 megabit/sec digital data bus, using the Fields protocol. Power was distributed to the smart devices as 100 kHz 100V peak AC, allowing light, simple power converters at each smart device. All smart sensors, smart actuators, and cables were dual redundant. The smart actuators received position demand from the central control computer, exchanged data between channels to provide local redundancy management, closed the position loop locally, and reported actuator position to the central controller. Smart sensors converted sensed signals to digital values in engineering units, and performed local built-in tests. Testing of the DCS was done in a closed-loop simulation with an engine model. Frequency response of the DCS was almost identical with the conventional system.
Conceptual Design of the Cooling System for 1700°C-Class, Hydrogen-Fueled Combustion Gas Turbines
Authors: Kizuka N. , Sagae K. , Anzai S. , Marushima S. , Ikeguchi T. , Kawaike K.
Published: February 2008

The effects of three types of cooling systems on the calculated operating performances of a hydrogen-fueled thermal power plant with a 1,700°C-class gas turbine were studied with the goal of attaining a thermal efficiency of greater than 60 percent. The combination of a closed-circuit water cooling system for the nozzle blades and a steam cooling system for the rotor blades was found to be the most efficient, since it eliminated the penalties of a conventional open-circuit cooling system which ejects coolant into the main hot gas stream. Based on the results, the water cooled, first-stage nozzle blade and the steam cooled first-stage rotor blade were designed. The former features array of circular cooling holes close to the surface and uses a copper alloy taking advantage of recent coating technologies such as thermal barrier coatings (TBCs) and metal coatings to decrease the temperature and protect the blade core material. The later has cooling by serpentine cooling passages with V-shaped staggered turbulence promoter ribs which intensify the internal cooling.
Application of Stress Relaxation Testing in Metallurgical Life Assessment Evaluations of GTD111 Alloy Turbine Buckets
Authors: Daleo J. A. , Ellison K. A. , Woodford D. A.
Published: February 2008

Stress relaxation and constant displacement rate tensile tests were performed on polycrystalline GTD111 alloy material removed from General Electric MS6001B first stage combustion turbine buckets. Samples were examined in the standard heat treated condition, thermally exposed at 900°C for 5000 hours and from service run buckets. Creep rates of the material were measured and evaluated directly in terms of temperature capability at 850°C and 900°C. Stress relaxation tests done at 0.8 percent total strain indicated that the creep rate properties in the service exposed airfoil were an order of magnitude higher than the material properties in the standard heat treated condition measured in the root form. In terms of temperature capability, the creep rate properties of the service run airfoil material had decreased by the equivalent of almost 40°C. The Stress relaxation test method was demonstrated to be a very useful tool in quantifying the degradation of creep properties in service run components. Creep data that would require years to gather using conventional creep tests was generated in a few days. This now makes realistic life assessment and repair/replace decisions possible during turbine overhauls. The test method’s unique ability to measure changes in creep rate over a large stress range, enabled the technique to distinguish between changes in creep strength due to (normal) microstructural evolution from the combined effects of microstructural evolution and strain related creep damage. A method for estimating standard constant load creep rupture life from the stress relaxation creep rate data is also presented along with time-temperature parameter correlations. The data sets examined in this study indicate that creep rupture lives can be estimated within a factor of three from the stress relaxation data. The information and analysis techniques described in this paper are directly applicable to metallurgical life assessment evaluations and the requalification of repaired General Electric buckets in Frame 3, 5, 6, 7, and 9 engine models.
A Test Facility for the Measurement of Torques at the Shaft to Seal Interface in Brush Seals
Authors: Wood P. E. , Jones T. V.
Published: February 2008

An important factor in the performance of brush seals for a wide range of gas turbine applications is the rate of wear at the seal to shaft interface, which is dependent on the contact pressure that exists between the bristles and rubbing surface. This is dependent on a variety of effects. Principally, these are the aerodynamic forces bending the bristles onto the rubbing surface, frictional effects within the bristle pack and at the backing ring that arise with the application of pressure differential, geometrical changes due to centrifugal and thermal growths, and transient differential movements of the rotor that develop in flight manoeuvres. In order to investigate the effect of these phenomena on contact pressure, a test facility has been devised in which the torque exerted by a brush seal on a rotating shaft is used as an indirect measurement of contact pressure. This has necessitated the design of a test facility in which all system torques can be fully calibrated. Consequently, a pressure balanced design has been adopted in which applied seal differential and pressure levels have a minimal effect on axial loads at the rotor bearing assembly. The primary method of torque measurement is the instantaneous deceleration of the rotor. Thus, measurements over a wide speed range are acquired with high frequency instrumentation. The means whereby small parasitic torques are evaluated and corrected is given. Results demonstrating the dependence of contact pressure on seal differential and pressure levels are presented.
Cycle Analyses of 5 and 20 MWe Biomass Gasifier-Based Electric Power Stations in Hawaii
Authors: Ishimura D. M. , Kinoshita C. M. , Masutani S. M. , Turn S. Q.
Published: February 2008

Thermodynamic cycle analyses of biomass gasifier-based electric power stations at two scales, nominally 5 and 20 MWe (net electric power output), were performed to assess process performance and viability. Various configurations (Rankine, simple, steam-injected gas turbine, and combined cycles) of a 5 MW stand-alone power station were modeled and a 20 MW biomass-based integrated gasifier combined-cycle cogeneration facility at a sugar factory was simulated. Information gained from these analyses will be applied to determine whether biomass gasification-based electricity production is practicable in Hawaii and other sugar producing locales.
A Small Scale Biomass Fueled Gas Turbine Engine
Authors: Craig J. D. , Purvis C. R.
Published: February 2008

A new generation of small scale (less than 20 MWe) biomass fueled, power plants are being developed based on a gas turbine (Brayton cycle) prime mover. These power plants are expected to increase the efficiency and lower the cost of generating power from fuels such as wood. The new power plants are also expected to economically utilize annual plant growth materials (such as rice hulls, cotton gin trash, nut shells, and various straws, grasses, and animal manures) that are not normally considered as fuel for power plants. This paper summarizes the new power generation concept with emphasis on the engineering challenges presented by the gas turbine component.
Gas Turbine Cycle Design Methodology: A Comparison of Parameter Variation With Numerical Optimization
Authors: Kurzke J.
Published: February 2008

In gas turbine performance simulations often the following question arises: what is the best thermodynamic cycle design point? This is an optimization task which can be attacked in two ways. One can do a series of parameter variations and pick from the resulting graphs the best solution or one can employ numerical optimization algorithms that produce a single cycle that fulfills all constraints. The conventional parameter study builds strongly on the engineering judgement and gives useful information over a range of parameter selections. However, when values for more than a few variables have to be determined while several constraints are existing, then numerical optimization routines can help to find the mathematical optimum faster and more accurately. Sometimes even an outstanding solution is found which was overlooked while doing a preliminary parameter study. For any simulation task a sophisticated graphical user interface is of great benefit. This is especially true for automated numerical optimizations. It is quite helpful to see on the screen of a PC how the variables are changing and which constraints are limiting the design. A quick and clear graphical representation of trade studies is also of great advantage. The paper describes how numerical optimization and parameter studies are implemented in a Windows-based PC program. As an example, the cycle selection of a derivative turbofan engine with a given core shows the merits of numerical optimization. The parameter variation is best suited for presenting the sensitivity of the result in the neighborhood of the optimum cycle design point.