bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Analysis of Rotordynamic Instabilities in High-Speed Turbomachinery
Authors: Chan D. S. H.
Published: February 2008

A nonlinear approach based on the method of averaging has been developed to study unstable lateral vibrations of rotors in high-speed turbomachinery. The method makes use of an extended concept of bearing dynamic coefficients, which are defined by applying small perturbations to the dynamic equilibrium positions. The approach has been applied to determine the stability threshold of flexible rotors supported on short and tilting-pad journal bearings, respectively. Stability performance of systems supported on short journal bearings is improved by the presence of mass unbalance. However, for flexible rotors supported on tilting-pad journal bearings, increased unbalance can lead to lower rotordynamic stability margins. This has the significant implication that stability estimates from linear analysis are not always conservative. The present method provides a computationally more efficient way to understand the nonlinear vibration behavior of high-speed turbomachinery.
Aircraft Crash Caused by Stress Corrosion Cracking
Authors: Kolkman H. J. , Kool G. A. , Wanhill R. J. H.
Published: February 2008

An aircraft crash in the Netherlands was caused by disintegration of a jet engine. Fractography showed that the chain of events started with stress corrosion cracking (SCC) of a pin attached to a lever arm of the compressor variable vane system. Such a lever arm–pin assembly costs only a few dollars. Investigation of hundreds of pins from the accident and a number of identical engines revealed that this was not an isolated case. Many pins exhibited various amounts of SCC. The failed pin in the accident engine happened to be the first fractured one. SCC requires the simultaneous presence of tensile stress, a corrosive environment, and a susceptible material. In this case the stress was a residual stress arising from the production method. There was a clear correlation between the presence of salt deposits on the levers and SCC of the pins. It was shown that these deposits were able to reach the internal space between the pin and lever arm, thereby initiating SCC in this space. The corrosive environment in Western Europe explains why the problem manifested itself in the Netherlands at a relatively early stage in engine life. The main point is, however, that the manufacturer selected an SCC-prone material in the design stage. The solution has been to change the pin material.
Durability Evaluation of Ceramic Components Using CARES/LIFE
Authors: Nemeth N. N. , Powers L. M. , Janosik L. A. , Gyekenyesi J. P.
Published: February 2008

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Application of this design methodology is demonstrated using experimental data from alumina bar and disk flexure specimens, which exhibit SCG when exposed to water.
Plasticity Considerations in Probabilistic Ceramic-to-Metal Joint Design
Authors: ONeil D. A. , Selverian J. H. , Kim K. S.
Published: February 2008

A new probabilistic failure criterion was developed for the design of high-temperature ceramic-to-metal joints. The essential feature of the theory is the inclusion of the energy dissipated during plastic deformation of the adjacent braze layer in the joint. A large number of bimaterial interface fracture simulations were performed for different crack positions and orientations near the bimaterial interface to determine the effect on stresses in the ceramic near the interface. The effective stress values were then ported to a probabilistic failure analysis code, which permitted simple inclusion of the new failure criterion. Brazed joints were made and failure tested in torsion to verify the failure criterion. Results show that the new failure critertion more closely approximates the failure of the ceramic-to-metal joints over the entire range of ultimate loads, and is a significant improvement in the failures criteria previously used for this type of joint design. Aspects of the failure criterion, material systems, residual stresses, mechanical behavior, and strength predictions will be presented.
High-Enthalpy Extraction Demonstration With Closed-Cycle Disk MHD Generators
Authors: Harada N. , Suekane T. , Tsunoda K. , Yamasaki H. , Shioda S.
Published: February 2008

Recent results of high-enthalpy extraction experiments with closed-cycle MHD disk generators are described. Power generation experiments were carried out with two types of facility: the shock tube facility with the Disk-IV generator and the FUJI-1 blow-down facility. In the shock tube experiments, the effect of channel shape on generator performance was studied using helium seeded with cesium as working fluid. A more divergent channel shape was effective in sustaining a high Hall field throughout the channel and achieving high generator performance even under the strong MHD interaction. High-enthalpy extraction of 27.3 percent was achieved. Furthermore, these experimental results agree well with the results of one-dimensional calculations. In the FUJI-1 blow-down experiments, the effect of stagnation gas pressure on performance was studied with a working gas of seeded argon. The highest enthalpy extraction ratio of 15.7 percent was achieved with the lower stagnation pressure of 0.46 MPa, whereas the largest output power of 516.7 kW and power density of 70 MW/m3 were extracted with the nominal stagnation pressure of 0.6 MPa. This suggested the possibility of a part-load operation without significant degradation of generator performance by reducing stagnation pressure.
Hybrid Bearing Technology for Advanced Turbomachinery: Rolling Contact Fatigue Testing
Authors: Dill J. F.
Published: February 2008

The purpose of this paper is to describe the basic structure and results to date of a major ARPA funded effort to provide a tribological performance database on ceramic bearing materials and their interaction with standard bearing steels. Program efforts include studies of material physical properties, machining characteristics, and tribological performance. The majority of the testing completed to date focuses on rolling contact fatigue testing of the ceramic materials, including efforts to arrive at optimum approaches to evaluating ceramic/steel hybrid combinations in rolling contact fatigue.
Evaluation of Ceramic Rotor Strength by Cold and Hot Spin Tests
Authors: Watanabe M. , Ogita H.
Published: February 2008

Presently in Japan 100 kW ceramic gas turbines (CGT) for automobiles are under development, parts of which include a turbine rotor, scrolls, a combustor, and other parts made of ceramics and ceramic matrix composites. The rotor is designed to rotate at 110,000 rpm, equal to the maximum stress of 300 MPa, and to be exposed to temperatures up to 1350°C. Initially, the strength of ceramic rotors was evaluated by a burst test using a cold spin tester. The burst picture was observed and compared with the 4pt bending strength of the ceramic test specimens. Next, the strength of the rotors was tested by a hot spin test and the burst result of the rotor was evaluated. A high-speed camera was used to observe the rotor at the instant of burst under a high-temperature condition. Applying the result of the cold and hot spin tests, ceramics for turbine rotor were selected and the shape of the rotor was designed.
Control of a Fluidized Bed Combustor Using Fuzzy Logic
Authors: Koffman S. J. , Brown R. C. , Fullmer R. R.
Published: February 2008

Application of fuzzy logic control to a fluidized bed combustor (FBC) is examined. Major aspects of fuzzy control are reviewed, and design of a fuzzy controller for the FBC is described. Selected experimental results are presented, and performance of the fuzzy controller is evaluated through comparisons to results from classical PI control of the combustor.
Functional Forms to Describe Thermodynamic Properties of Gases for Fast Calculations
Authors: Pa´tek J.
Published: February 2008

A simple way to derive physically based functional forms for approximate description of thermodynamic properties of gases is presented. The polynomials in transformed variables obtained are intended for fast industrial calculations. The approach is applied on eleven thermodynamic dependencies with pairs of independent variables most frequently encountered in turbine calculations. These functional forms were originally derived for the description of steam properties, but they are equally applicable to any gas in adequate region of state parameters. Approximation function for the dependence T(h, s) of steam is presented as an example including the values of 18 fitted parameters.
Computational Fluid Dynamics Analysis of a Steam Power Plant Low-Pressure Turbine Downward Exhaust Hood
Authors: Tindell R. H. , Alston T. M. , Sarro C. A. , Stegmann G. C. , Gray L. , Davids J.
Published: February 2008

Computational fluid dynamics (CFD) methods are applied to the analysis of a low-pressure turbine exhaust hood at a typical steam power generating station. A Navier-Stokes solver, capable of modeling all the viscous terms, in a Reynolds-averaged formulation, was used. The work had two major goals. The first was to develop a comprehensive understanding of the complex three-dimensional flow fields that exist in the exhaust hood at representative operating conditions. The second was to evaluate the relative benefits of a flow guide modification to optimize performance at a selected operating condition. Also, the influence of simulated turbine discharge characteristics, relative to uniform hood entrance conditions, was evaluated. The calculations show several interesting and possibly unique results. They support use of an integrated approach to the design of turbine exhaust stage blading and hood geometry for optimum efficiency.
Coadunation of Technologies: Cogeneration and Thermal Energy Storage
Authors: Somasundaram S. , Drost M. K. , Brown D. R. , Antoniak Z. I.
Published: February 2008

Thermal energy storage can help cogeneration meet the energy generation challenges of the 21st century by increasing the flexibility and performance of cogeneration facilities. Thermal energy storage (TES) allows a cogeneration facility to: (1) provide dispatchable electric power while providing a constant thermal load, and (2) increase peak capacity by providing economical cooling of the combustion turbine inlet air. The particular systems that are considered in this paper are high-temperature diurnal TES, and TES for cooling the combustion turbine inlet air. The paper provides a complete assessment of the design, engineering, and economic benefits of combining TES technology with new or existing cogeneration systems, while also addressing some of the issues involved.
Emission and Performance of a Lean-Premixed Gas Fuel Injection System for Aeroderivative Gas Turbine Engines
Authors: Snyder T. S. , Rosfjord T. J. , McVey J. B. , Hu A. S. , Schlein B. C.
Published: February 2008

A dry-low-NOx, high-airflow-capacity fuel injection system for a lean-premixed combustor has been developed for a moderate pressure ratio (20:1) aeroderivative gas turbine engine. Engine requirements for combustor pressure drop, emissions, and operability have been met. Combustion performance was evaluated at high power conditions in a high-pressure, single-nozzle test facility, which operates at full base-load conditions. Single digit NOx levels and high combustion efficiency were achieved. A wide operability range with no signs of flashback, autoignition, or thermal problems was demonstrated. NOx sensitivities to pressure and residence time were found to be small at flame temperatures below 1850 K (2870°F). Above 1850 K some NOx sensitivity to pressure and residence time was observed and was associated with the increased role of the thermal NOx production mechanism at elevated flame temperatures.
Improving Traditional Balancing Methods for High-Speed Rotors
Authors: Ling J. , Cao Y.
Published: February 2008

This paper introduces frequency response functions, analyzes the relationships between the frequency response functions and influence coefficients theoretically, and derives corresponding mathematical equations for high-speed rotor balancing. The relationships between the imbalance masses on the rotor and frequency response functions are also analyzed based upon the modal balancing method, and the equations related to the static and dynamic imbalance masses and the frequency response function are obtained. Experiments on a high-speed rotor balancing rig were performed to verify the theory, and the experimental data agree satisfactorily with the analytical solutions. The improvement on the traditional balancing method proposed in this paper will substantially reduce the number of rotor startups required during the balancing process of rotating machinery.
A Method to Reduce the Rejection Rate for Low Performance at the Acceptance Test of PWC PT6T-6 Overhauled Power Sections
Authors: Colantuoni S. , Mainiero G. , Esposito A.
Published: February 2008

Alfa Romeo Avio is involved in the overhaul process of the Pratt & Whitney of Canada PT6T-6 for the helicopter fleet of the Italian Army and civil services. The overhauled power sections suffered from a high rejection rate (about 40 percent) for low performance at the acceptance test. Alfa Romeo Avio R&D investigated the causes and developed a method to reduce the rejection rate. A first contribution to the decision support method for the selection of the optimal engine configuration can be obtained from engine thermodynamic cycle simulation, which gives indications on the behavior of the average overhauled power section. In this paper the authors also describe a statistical model based on a cause/effect correlation between power section assembly variables and performance parameters. A simulation procedure, based on the statistical model, estimates the influence of the configuration assembly data on the power section performance parameters. A careful application of both statistical and thermodynamic models gives predictions on the optimum matching of turbine nozzle size to reach the target performance at the engine acceptance test. The method has been tested on the field during the last two years and a reduction in the rejection rate at the acceptance test to 18 percent has been obtained.
Mechanisms of Coke Formation in Gas Turbine Combustion Chambers
Authors: Brandauer M. , Schulz A. , Wittig S.
Published: February 2008

New gas turbine combustor designs are developed to reduce pollutant and NOx emissions. In these new combustors, the formation of carbonaceous deposits, especially in prevaporizers, affects the reliability and effectiveness of operation. To avoid deposits, a detailed knowledge of the origins and mechanisms of formation is required. To obtain a deeper insight, the phenomena were studied systematically. The deposits under consideration show differing characteristics suggesting more than one formation mechanism in the combustor. Consequently, the primary goal was to identify the formation mechanisms and, subsequently, to simulate the mechanisms under well-defined conditions in bench tests for determining the relevant parameters of deposit build-up. The mechanisms of formation were identified based on the properties of the deposits in the combustion chamber. In order to characterize the deposits, physical and chemical analysis techniques were utilized. In summary, tests and numerical predictions identified two major paths of formation: a deposit build-up resulting from flame products such as soot or coked droplets and a deposit build-up resulting from liquid fuel impinging the wall accompanied with chemical reactions at the wall. The deposits caused by fuel droplet impingement were intensively studied in bench tests. In analyzing the processes, the influence of wall temperature, fuel composition, and the oxygen content in the environment is shown in detail. In addition, the importance of thermal instabilities of the fuel, previously studied under fuel supply system conditions, is demonstrated for a deposit formation inside a combustion chamber.
Surface Effects on Deposits From Jet Fuels
Authors: Ervin J. S. , Heneghan S. P. , Martel C. R. , Williams T. F.
Published: February 2008

Flow experiments in a single-pass heat exchanger using JP-8 and certain additives were initiated under controlled conditions to explore the effects of a metal surface on deposition. The experimental apparatus permitted a unique viewing of the time evolution of deposits at different axial locations under conditions of limited oxygen availability somewhat similar to those in jet aircraft. Scanning electron microscopy was used to examine deposit microstructure. In addition, x-ray photoelectron spectroscopy and Auger electron spectroscopy determined the chemical composition of the deposits. Oxygen concentration measurements in the bulk flow were also performed, and the observed transient oxidation behavior was related to measured time-dependent changes in the deposit. Increasing dissolved oxygen levels and large changes in deposition were characteristic of the induction time. Mechanisms of fouling in the heated and cooled sections were different. Spectroscopic analysis indicated that deposits formed in the heated section had chemical compositions different from those formed in the cooled section. Scanning electron microscopy revealed differences in microstructure between the heated and cooled sections: More uniform deposits formed in the cooled section as a result of once-soluble species becoming insoluble at low temperatures. In addition, the JP-8 additives significantly reduced fouling in the heated section, but their effectiveness in the cooled section, especially after long periods, was unclear.
Benefits of MS 6001B Gas Turbine in Cogeneration: The UEM Power Plant Case
Authors: Remy P. M. , Boissenin Y. M. , Molie`re M. M.
Published: February 2008

Long before the neologism “Cogeneration” was coined (around 1978), UEM’s Chambie`re Power Plant—which dates back to the turn of the century—was already supplying the city of Metz, east of France, with combined heat and power. In 1992, Chambie`re experienced a major turning point in its history with the installation of a new unit based on one MS 6001B “Heavy Duty” gas turbine. This model, rated 38 MWe-ISO and burning natural gas or fuel oil, has become the core of a new cogeneration unit exhibiting outstanding performance: • efficiency higher than 80 percent (LHV) providing a 20 percent energy saving in comparison to a conventional plant, • low pollutant emissions (NOx, CO, HC) and low contribution to the greenhouse effect (CO2). The gas turbine has been equipped with two steam injection devices, for DeNOx and power augmentation, respectively, resulting in a very flexible system. After describing the power plant and giving its main achievements in the fields of energy and emissions, the paper briefly presents several improvements intended to protect both the turbine and the environment.
Component and Procedural Improvements for the T-62T-40-7 Gas Turbine in the LCAC Fleet
Authors: Ehrhardt J. P. , Spring S. K.
Published: February 2008

The Sundstrand Power Systems T-62T-40-7 Gas Turbine Auxiliary Power Unit (APU) was adapted from an aircraft-borne APU to a marine application on the U.S. Navy’s Landing Craft Air Cushion (LCAC). Although the LCAC APU experienced less operating time than its aircraft version, the environmental conditions that exist cause unusual wear and component failures. Component and procedural improvements have been developed to extend the reliability of the T-62T-40-7 on board the LCAC.
Aero Engine Test Experience With CMSX-4® Alloy Single-Crystal Turbine Blades
Authors: Fullagar K. P. L. , Broomfield R. W. , Hulands M. , Harris K. , Erickson G. L. , Sikkenga S. L.
Published: February 2008

A team approach involving a turbine engine company (Rolls-Royce), its single-crystal casting facilities, and a superalloy developer and ingot manufacturer (Cannon-Muskegon), utilizing the concepts of simultaneous engineering, has been used to develop CMSX-4 alloy successfully for turbine blade applications. CMSX-4 alloy is a second-generation nickel-base single-crystal superalloy containing 3 percent (wt) rhenium (Re) and 70 percent volume fraction of the coherent γ′ precipitate strengthening phase. Its finely balanced composition offers an attractive range of properties for turbine airfoil applications. In particular the alloy’s combination of high strength in relation to creep-rupture, mechanical and thermal fatigue, good phase stability following extensive high temperature, stressed exposure and oxidation, hot corrosion and coating performance, are attractive for turbine engine applications where engine performance and turbine airfoil durability are of prime importance. The paper details the single-crystal casting process and heat treatment manufacturing development for turbine blades in CMSX-4 alloy. Competitive single-crystal casting yields are being achieved in production and extensive vacuum heat treatment experience confirms CMSX-4 alloy to have a practical production solution heat treat/homogenization “window.” The creep-rupture data-base on CMSX-4 alloy now includes 325 data points from 17 heats including 3630 kg (8000 lb) production size heats. An appreciable portion of this data was machined-from-blade (MFB) properties, which indicate turbine blade component capabilities based on single-crystal casting process, component configuration, and heat treatment. The use of hot isostatic pressing (HIP) has been shown to eliminate single-crystal casting micropores, which along with the essential absence of γ/γ′ eutectic phase, carbides, stable oxide, nitride and sulfide inclusions, results in remarkably high mechanical fatigue properties, with smooth and particularly notched specimens. The Re addition has been shown not only to benefit creep and mechanical fatigue strength (with and without HIP), but also bare oxidation, hot corrosion (sulfidation), and coating performance. The high level of balanced properties determined by extensive laboratory evaluation has been confirmed during engine testing of the Rolls-Royce Pegasus turbofan.
Surface Integral and Finite Element Hybrid Method for Three-Dimensional Analysis of Arbitrarily Shaped Surface Cracks
Authors: Keat W. D. , Maybury D. M. , Annigeri B. S.
Published: February 2008

A three-dimensional surface integral and finite element hybrid method has been developed for modeling arbitrarily shaped surface cracks in complex structural components. Accurate stress intensity factors were obtained by decomposing the problem into a surface integral model of the fracture in a domain of infinite extent and a finite element model of the uncracked domain. Boundary conditions were enforced by applying corrective traction to the surfaces of both constituent models. Coupling between the two formulations was minimized by implementing the fundamental solution for a force multipole near a planar free surface. Surface cracks intersecting nonplanar free surfaces were modeled in a piecewise linear fashion by deploying multiple sets of these functions. The effectiveness of this approach was demonstrated for well-documented cases, including a corner crack in a thick plate and a three-dimensional edge crack. The results of these benchmark studies will be used to develop a set of heuristics for assuring suitable finite element mesh densities in the vicinity of the fracture.
Fatigue Cracking in Fiber-Reinforced Metal Matrix Composites Under Mechanical and Thermal Loads
Authors: Bao G. , McMeeking R. M.
Published: February 2008

This article reviews micromechanical models developed for fatigue cracking in fiber-reinforced metal matrix composites under mechanical and thermal loads. Emphasis is placed on the formulae and design charts that can quantify the fatigue crack growth and fiber fracture. The composite is taken to be linear elastic, with unidirectional aligned fibers. Interfacial debonding is assumed to occur readily, allowing fibers to slide relative to the matrix resisted by a uniform shear stress. The fibers therefore bridge any matrix crack that develops. The crack bridging traction law includes the effect of thermal expansion mismatch between the fiber and the matrix and a temperature dependence of the frictional shear stress. Predictions are made of the crack tip stress intensities, matrix fatigue crack growth, and maximum fiber stresses under mechanical or thermomechanical loads. For composites under thermomechanical load, both in-phase and out-of-phase fatigue are modeled. The implications for life prediction for fiber-reinforced metal matrix composites are discussed.
Determination of Blade Stresses Under Constant Speed and Transient Conditions With Nonlinear Damping
Authors: Rao J. S. , Vyas N. S.
Published: February 2008

Determination of resonant stresses is an important step in the life estimation of turbomachine blades. Resonance may occur either at a steady operating speed or under transient conditions of operation when the blade passes through a critical speed. Damping plays a significant role in limiting the amplitudes of vibration and stress values. The blade damping mechanism is very complex in nature, because of interfacial slip, material hysteresis, and gas dynamic damping occurring simultaneously. In this paper, a numerical technique to compute the stress response of a turbine blade with nonlinear damping characteristics, during steady and transient operations of the rotor, is presented. Damping is defined as a function of vibratory mode, rotor speed, and strain amplitude. The technique is illustrated by computing the stress levels at resonant rotor speeds for typical operation of a turbomachine.
Hybrid Ceramic Bearings for Difficult Applications
Authors: Dezzani M. M. , Pearson P. K.
Published: February 2008

The Torrington Company, under contract from the Advanced Research Projects Agency (ARPA), has developed a hybrid bearing with improved properties for difficult applications. M50 and M50 NiL steel rings were nitrided to produce rolling contact raceway surfaces with hardnesses near Rockwell C 70. Rings were assembled with NBD-200 silicon nitride balls. Full-scale bearing tests were run under conditions that included 150°C temperature, surface flaws created by hard particle contamination, partial EHD lubrication, and the sliding action of balls running under thrust loading. The hybrid bearings had longer life than all steel bearings and demonstrated resistance to the surface peeling mode of failure initiation. Higher strength of the rolling contact surfaces, high residual compressive stresses in the nitrided layers, and a more favorable action in ceramic to steel rolling contact are discussed as the reasons for improved performance of the hybrid over all-steel bearings.
Thermodynamic Analysis of New Combination of Supercharged Boiler Cycle and Heat Recovery Cycle for Power Generation
Authors: Akiba M. , Thani E. A.
Published: February 2008

The aim of this paper is to study the performance of a new combination of supercharged boiler–gas turbine cycle, which is expected to reduce the cooling air in the combustor and heat recovery cycle, from a thermodynamic point of view. Two designs of this cycle were adopted and the influences of various operating parameters, such as compressor pressure ratio, ambient temperature, inlet gas temperature of gas turbine, percentage of excess air, and number of feedwater heaters, were studied. Three techniques were applied to increase the overall cycle efficiency: first, increasing the mean temperature of heat supplied by increasing the inlet gas temperature of the gas turbine; second, decreasing the mean temperature of heat rejected through a heat recovery cycle; and third, reducing the percentage of excess air in the supercharged boiler. A performance comparison between the adopted cycles and a conventional heat recovery cycle was made. The results show that there is an improvement in overall cycle efficiency of about 8.5–9.5 percent with the first design of the adopted cycle over the conventional heat recovery cycle, while an improvement of overall cycle efficiency of about 1.0–5.5 percent is obtained for the second design.
Pressure-Gain Combustion: Part II—Experimental and Model Results
Authors: Richards G. A. , Gemmen R. S.
Published: February 2008

An experimental investigation of aerovalve pulse combustion is presented. The experimental measurements compare favorably with model predictions from a control volume analysis of the pulse combustor. Particular emphasis is placed on the mean pressure differences through the combustor as an indicator of the so-called pressure gain performance. Both the operating conditions and combustor geometry are investigated. It is shown that complex fluid/combustion interactions within the combustor make it difficult to isolate the effect of geometric changes. A scaling rule developed from the control-volume analysis is used to produce a combustor geometry capable of producing pressure gain.
Wave Cycle Design for Wave Rotor Gas Turbine Engines With Low NOx Emissions
Authors: Nalim M. R. , Resler E. L.
Published: February 2008

The wave rotor is a promising means of pressure-gain for gas turbine engines. This paper examines novel wave rotor topping cycles that incorporate low-NOx combustion strategies. This approach combines two-stage “rich-quench-lean” (RQL) combustion with intermediate expansion in the wave rotor to extract energy and reduce the peak stoichiometric temperature substantially. The thermodynamic cycle is a type of reheat cycle, with the rich-zone air undergoing a high-pressure stage. Rich-stage combustion could occur external to or within the wave rotor. An approximate analytical design method and CFD/combustion codes are used to develop and simulate wave rotor flow cycles. Engine cycles designed with a bypass turbine and external combustion demonstrate a performance enhancement equivalent to a 200–400 R (110–220 K) increase in turbine inlet temperature. The stoichiometric combustion temperature is reduced by 300–450 R (170–250 K) relative to an equivalent simple cycle, implying substantially reduced NOx formation.
A Conceptual Design Methodology for Predicting Bleed and Horsepower Requirements of Military Aircraft Engines
Authors: Cyrus J. D.
Published: February 2008

Conceptual design codes have been developed to provide conceptual design estimates of bleed and horsepower extraction requirements of advanced military aircraft. This paper describes the methodology for the computer codes. The validity of the models was assessed by generating bleed and horsepower estimates for four advanced air-craft configurations not included in the data base and comparing the model estimates to manufacturer’s estimates.
Development of Ceramic Composite Hot-Gas Filters
Authors: Judkins R. R. , Stinton D. P. , Smith R. G. , Fischer E. M. , Eaton J. H. , Weaver B. L. , Kahnke J. L. , Pysher D. J.
Published: February 2008

A novel type of hot-gas filter based on a ceramic fiber-reinforced ceramic matrix was developed and extended to full-size, 60-mm OD by 1.5-m-long, candle filters. A commercially viable process for producing the filters was developed, and the filters are undergoing testing and demonstration throughout the world for applications in pressurized fluidized-bed combustion (PFBC) and integrated gasification combined cycle (IGCC) plants. Development activities at Oak Ridge National Laboratory (ORNL) and at the 3M Company, and testing at the Westinghouse Science and Technology Center (STC) are presented. Demonstration tests at the Tidd PFBC are in progress. Issues identified during the testing and demonstration phases of the development are discussed. Resolution of the issues identified during testing and the status of commercialization of the filters are described.
Biomass-Gasifier/Aeroderivative Gas Turbine Combined Cycles: Part A—Technologies and Performance Modeling
Authors: Consonni S. , Larson E. D.
Published: February 2008

Gas turbines fueled by integrated biomass gasifiers are a promising option for base load electricity generation from a renewable resource. Aeroderivative turbines, which are characterized by high efficiencies at smaller scales, are of special interest because transportation costs for biomass constrain biomass conversion facilities to relatively modest scales. Commercial development activities and major technological issues associated with biomass integrated-gasifier/gas turbine (BIG/GT) combined cycle power generation are reviewed in Part A of this two-part paper. Also, the computational model and the assumptions used to predict the overall performance of alternative BIG/GT cycles are outlined. The model evaluates appropriate value of key parameters (turbomachinery efficiencies, gas turbine cooling flows, steam production in the heat recovery steam generator, etc.) and then carries out energy, mass, and chemical species balances for each plant component, with iterations to insure whole-plant consistency. Part B of the paper presents detailed comparisons of the predicted performance of systems now being proposed for commercial installation in the 25–30 MWe power output range, as well as predictions for advanced combined cycle configurations (including with intercooling) with outputs from 22 to 75 MWe. Finally, an economic assessment is presented, based on preliminary capital cost estimates for BIG/GT combined cycles.
Specification, Development, and Testing of the FT8-2 Dry Low NOx Control System
Authors: Bell R. C. , Prete T. W. , Stewart J. T.
Published: February 2008

This paper describes the specification, development, and testing of the FT8-2 Dry Low NOx control system, and how the lean burn process requires an integration of the control system and combustion hardware. The FT8-2 digital fuel control system was developed to achieve the precise multizone fuel metering of both gas and liquid fuels, the calculation of combustor air flow necessary to achieve Dry Low NOx and the traditional governing/limiting control loops necessary for safe, stable engine operation. The system design goals were accomplished by the concurrent development of software-based fuel metering algorithms and fuel metering hardware. The fuel metering hardware utilizes an all-electronic valve positioner, employing a combination of feedback and software to achieve closed-loop control of actual fuel flow. Extensive testing under actual gas flow conditions and closed-loop bench testing using a real time engine model and fuel system model was conducted to prove system operation and develop system transient response prior to installation on the test engine. The setup and results of the flow testing and closed-loop testing are described. The paper describes the control scheme used to apportion the gas fuel between combustion zones and how external conditions such as ambient temperature and fuel gas composition affect the apportionment. The paper concludes with a description of the control system installation in the engine test cell and a review of engine test results.
Parametric Modeling of Exhaust Gas Emission From Natural Gas Fired Gas Turbines
Authors: Bakken L. E. , Skogly L.
Published: February 2008

Increased focus on air pollution from gas turbines in the Norwegian sector of the North Sea has resulted in taxes on CO2. Statements made by the Norwegian authorities imply regulations and/or taxes on NOx emissions in the near future. The existing CO2 tax of NOK 0.82/Sm3 (US Dollars 0.12/Sm3) and possible future tax on NOx are analyzed mainly with respect to operating and maintenance costs for the gas turbine. Depending on actual tax levels, the machine should be operated on full load/optimum thermal efficiency or part load to reduce specific exhaust emissions. Based on field measurements, exhaust emissions (CO2, CO, NOx, N20, UHC, etc.) are established with respect to load and gas turbine performance, including performance degradation. Different NOx emission correlations are analyzed based on test results, and a proposed prediction model presented. The impact of machinery performance degradation on emission levels is particularly analyzed. Good agreement is achieved between measured and predicted NOx emissions from the proposed correlation. To achieve continuous exhaust emission control, the proposed NOx model is implemented to the on-line condition monitoring system on the Sleipner A platform, rather than introducing sensitive emission sensors in the exhaust gas stack. The on-line condition monitoring system forms an important tool in detecting machinery condition/degradation and air pollution, and achieving optimum energy conservation.
Optimization of Waste Heat Recovery Boiler of a Combined Cycle Power Plant
Authors: Seyedan B. , Dhar P. L. , Gaur R. R. , Bindra G. S.
Published: February 2008

In the present work a procedure for optimum design of waste heat recovery boiler of a combined cycle power plant has been developed. This method enables the optimization of waste heat recovery boiler independent of the rest of the system and the design thus obtained can directly be employed in an existing plant.
Two-Phase Air/Oil Flow in Aero Engine Bearing Chambers: Characterization of Oil Film Flows
Authors: Glahn A. , Wittig S.
Published: February 2008

For the design of secondary air and lubrication oil systems, a sufficient knowledge of two-phase flow and heat transfer phenomena under bearing chamber flow conditions is required. The characterization of oil film flows at the bearing chamber walls is one of the major tasks for a better understanding of these processes and, therefore, a necessity for improvements of the efficiency of aero engines. The present paper gives a contribution to this subject. Utilizing a fiber-optic LDV setup, measurements of oil film velocity profiles have been performed in our high-speed bearing chamber rig simulating real engine conditions. All data have been compared with different theoretical approaches, which have been derived from a force balance at a liquid film element, including geometric conditions and temperature dependent fluid properties, and by approaches for the eddy viscosity available in the literature.
Phase-Averaged Wall Shear Stress, Wall Pressure, and Near-Wall Velocity Field Measurements in a Whirling Annular Seal
Authors: Morrison G. L. , Winslow R. B. , Thames H. D.
Published: February 2008

The flow field inside a 50 percent eccentric whirling annular seal operating at a Reynolds number of 24,000 and a Taylor number of 6600 has been measured using a three-dimensional laser-Doppler anemometer system. Flush mount pressure and wall shear stress probes have been used to measure the stresses (normal and shear) along the length of the stator. The rotor was mounted eccentrically on the shaft so that the rotor orbit was circular and rotated at the same speed as the shaft (a whirl ratio of 1.0). This paper presents mean pressure, mean wall shear stress magnitude, and mean wall shear stress direction distributions along the length of the seal. Phase-averaged wall pressure and wall shear stress are presented along with phase-averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall, where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure, and wall shear stress are very complex and do not follow simple bulk flow predictions.
Energy Recovery of Blast-Furnace Gas Coke: The Importance of a Correct Regulation System
Authors: Laforgia D. , Ruggiero F.
Published: February 2008

The present work deals with the regulation system of a plant recovering the energy of blast-furnace gas coke residual pressure. Such a plant is equipped with a turbogenerator, which produces electric energy, expanding the gas coke up to the mill pipe network pressure value. Before revamping, the regulation system consisted of an automatic nozzle control of a turbine stator and a throttle valve. Once the system became operative, the regulation system seemed to be inadequate because it caused a significant reduction in energy recovery due to the variation of the gas coke characteristics, compared to the original engineering specifications. A mathematical model for the plant simulation has been developed through the regulation system static and dynamic responses. This simulation, together with a series of experimental tests, identified the causes of the operational problems in the original regulation system. On the basis of the response times of the old regulation system, a value with reduced intervention inertia has been suggested. The regulation logic was also modified: The valve interventions were directly linked to the pressure variations recorded at the blast furnace top, and no longer to the opening variation of the turbine automatic system. A more rational use of the plant components and its control system, together with an increase of the electric energy production, have been demonstrated.
Investigation on Ceramic–Metal Joints for Shaft–Hub Connections in Gas Turbines
Authors: Esebeck G. v. , Kising M. , Neuhof U.
Published: February 2008

This paper shows possibilities for joining ceramic rotors to metal shafts. The investigations presented include exemplary joining methods for shaft–hub connections for ceramic rotors in gas turbines, as positive, permanent locking, or a combination of both. Active brazing as well as the combination of brazing or adhesive bonding and positive locking are discussed. Different shaft–hub connections were tested. The results of experimental investigations as static shear, bending, and torsion tests as well as dynamic torsion tests will be presented. In addition to the experimental investigations, finite-element analyses were made. Elastic calculations on simple geometries have shown the influence of different parameters like the thermal coefficients and the geometry at the joint face. Calculations were done to reduce the induced tensile stress in the joint and to increase carrying capacity. The calculations were also transferred to the shaft–hub connections to optimize the geometry of the joint faces.
Development of an Interactive Electronic Technical Manual
Authors: Masincup W. E. , Bryan J. S. , Ochs L. M.
Published: February 2008

For a number of years, the Navy has been pursuing a means of reducing or eliminating the amount of paper carried on board ship. In particular, technical manuals consume large amounts of storage space. The paper provides a case study of the development of a gas turbine technical manual into an interactive electronic (computerized) format. This paper presents some of the difficulties of the development process, enhancements that have been developed, software selection, graphics complexity, and hardware definition. In addition, a detailed description of a final product will be provided.
Automotive Diesel Fuel Emissions Durability Trends
Authors: Olsen R. E. , Newhall H. K. , Eberhard G. A.
Published: February 2008

Regional mandates for reduced exhaust emissions, sustainable over the useful lives of vehicles or equipment, are influencing diesel fuel compositions and engine designs. Laboratory and real-world examples are provided to illustrate that both fuel composition and engine design can impact injector deposit formation and injector spray-hole corrosion rates, with associated potentials for deterioration of emissions compliance. Potential impacts of poor lubricity fuels are also discussed. A field test in California of a deposit control additive in trucks with Cummins L10 engines is detailed, including measurements of transient cycle emissions performance using conventional and reformulated fuels.
Long-Term Testing of Advanced Ceramics: Concerns, Insights, and Recommendations
Authors: Jenkins M. G.
Published: February 2008

Advanced ceramics have reached a level of material development to warrant serious consideration for use in advanced heat engine designs. Typically, design requirements based on service conditions may include 25,000 h lifetimes under stresses and temperatures of up to 250 MPa and 1370°C, respectively, with probabilities of failure of <0.1 percent. To assure that materials meet these stringent requirements requires long-term testing under the service conditions. Tensile tests at 1370°C in ambient air have been conducted on silicon nitride alloys to 5000 h with reports of 10,000 h tests for silicon carbide. To provide useful data, such long-term tests must incorporate such meticulous attention to detail as: strict temperature control (±5°C); accurate temperature measurement (1 percent of the nominal temperature); close control of grip cooling (±0.1°C) and ambient environment (±0.25°C); stable, high-resolution extensometry (±0.5 μm); reliable heating (MTBF > 10,000 h) and load control (gravity-controlled, dead load), and responsive data acquisition systems (12-bit, digital collection). Data thus obtained can be used as input into design codes such as NASA CARES/LIFE to predict and confirm reliability/durability.
Combined-Cycle Power Stations Using “Clean-Coal Technologies”: Thermodynamic Analysis of Full Gasification Versus Fluidized Bed Combustion With Partial Gasification
Authors: Lozza G. , Chiesa P. , DeVita L.
Published: February 2008

A novel class of power plants for clean conversion of coal into power has been recently proposed, based on the concept of partial coal gasification and fluidized-bed combustion of unconverted char from gasification. This paper focuses on the thermodynamic aspects of these plants, in comparison with full gasification cycles, assessing their performance on the basis of a common advanced power plant technology level. Several plant configurations are considered, including pressurized or atmospheric fluidized-bed, air- or steam-cooled, with different carbon conversion in the gasifier. The calculation method, used for reproducing plant energy balances and for performance prediction, is described in the paper. A complete second-law analysis is carried out, pointing out the efficiency loss breakdown for both technologies. Results show that partial gasification plants can achieve efficiencies consistently higher than IGCC, depending on plant configuration and carbon conversion, making this solution a viable and attractive option for efficient coal utilization.