bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Synthesis and Operation of Thermal Systems by the Thermoeconomic Functional Approach
Authors: Frangopoulos C. A.
Published: April 2008

Methods developed for optimization of thermal systems usually work on a predetermined configuration of the system. Consequently, in order to select the best system, it is necessary to apply the method separately for each possible configuration and compare the results. The designer’s work would be significantly facilitated, if the optimization method could synthesize the optimal configuration of the system automatically. Such a method is presented here, based on the Thermoeconomic Functional Approach (TFA). TFA is a method developed for optimal design or improvement of complex thermal systems. It combines thermodynamic concepts with economic considerations in a systems approach. A thermal system is considered as a set of interrelated units; each unit has one particular function (purpose, or product). The documented determination of the function of the system as a whole and of each unit individually is achieved by functional analysis. The problem is mathematically formulated (objective function, constraints) at two levels: (A) optimization of operation, (B) optimization of the configuration and the design of the system. The solution is obtained by a two-level algorithm. As an example, the method is used to optimize a cogeneration system supplying a process plant with heat and electricity, which are known functions of time.
Thermodynamic Analysis of Four Magnetic Heat-Pump Cycles
Authors: Chen F. C. , Murphy R. W. , Mei V. C. , Chen G. L.
Published: April 2008

Magnetic heat pumps have been successfully used for refrigeration applications at near absolute-zero-degree temperatures. In these applications, a temperature lift of a few degrees in a cryogenic environment is sufficient and can be easily achieved by a simple magnetic heat-pump cycle. To extend magnetic heat pumping to other temperature ranges and other types of application in which the temperature lift is more than just a few degrees requires more involved cycle processes. The possible cycle applications include cooling of superconducting transmission lines, space conditioning, and industrial heating. This paper investigates the characteristics of a few better-known thermomagnetic heat-pump cycles (Carnot, Ericsson, Stirling, and regenerative) in extended ranges of temperature lift. The regenerative cycle is the most efficient one. Cycle analyses were done for gadolinium operating between 0 and 7 Tesla, and with a heat-rejection temperature of 320 K. The analysis results predicted a 42 percent reduction in coefficient of performance at 260 K cooling temperature and a 15 percent reduction in capacity at 232 K cooling temperature for the magnetic Ericsson cycle as compared with the ideal regenerative cycle. Such substantial penalties indicate that the potential irreversibilities from this one source may adversely affect the viability of certain proposed MHP concepts if the relevant loss mechanisms are not adequately addressed.
Mission Design Drivers for Closed Brayton Cycle Space Power Conversion Configuration
Authors: Baggenstoss W. G. , Ashe T. L.
Published: April 2008

Future space power requirements will vary from the subkilowatt range for deep space probes, to the hundreds of kilowatts range for a lunar base, to the multimegawatt range for interplanetary propulsion systems. Closed Brayton cycle (CBC) power conversion has the flexibility to be used in all these power ranges and with a variety of heat source options such as isotope, solar, and nuclear. Each of these types of heat sources has different characteristics that make it more appropriate for particular mission profiles and power output ranges. Heat source characteristics can also be major design drivers in the closed Brayton cycle design optimization process. This paper explores heat source selection and the resulting CBC system designs, and discusses optimization methods as a function of the main design drivers. Such power system requirements as power level, man-rated radiation shielding, fuel costs, eclipse/darkness duration, system mass, radiator area, reliability/mission duration, and insolation level are evaluated through several CBC parametric case studies. These cases include: (1) a 500 We power system for deep space probes; (2) a 50 kWe solar dynamic system for earth orbit and other applications; (3) a 100 kWe man-rated lunar/Mars stationary /rover power system; (4) a 200 to 825 kWe power system for the lunar outpost; and (5) 3300 kWe modules for interplanetary propulsions.
Noise Control Technology With Reference to Natural Gas Compressor Stations Under the Aspect of Investment Costs
Authors: Schneider M. , Mann J.
Published: April 2008

For the conveyance and storage of natural gas, compressor stations are required where the installed power output varies mostly between 1 MW and 20 MW. The noise control measures involved to meet the environmental noise emission regulations in Europe will be presented. The most economical noise control techniques are described particularly for the intake and exhaust systems of gas turbines, the housing of such engines, and peripheral sound sources like gas coolers, oil coolers, and aboveground piping.
Control Systems for the Next Century’s Fighter Engines
Authors: Skira C. A. , Agnello M.
Published: April 2008

The paper describes a conceptual control system design based on advanced technologies currently in the exploratory development phase, and, in some cases, emerging into the advanced development phase. It explores future propulsion control systems that focus on improvements in three areas: (1) significantly reducing control system weight; (2) enhancing engine performance (thrust, sfc, etc.); and (3) improving control system reliability and tolerance to high-threat environments (temperature, vibration, EMI, EMP, etc.). The factors that will influence the design and hardware configuration of future propulsion control systems are described. Design goals for future systems, based on the DOD/NASA IHPTET Initiative, and projections of emerging technology capability (and availability) form the basis for future propulsion control system design requirements and for estimating future hardware configurations.
Optimal State-Space Control of a Gas Turbine Engine
Authors: Watts J. W. , Dwan T. E. , Brockus C. G.
Published: April 2008

An analog fuel control for a gas turbine engine was compared with several state-space derived fuel controls. A single-spool, simple cycle gas turbine engine was modeled using ACSL (high level simulation language based on FORTRAN). The model included an analog fuel control representative of existing commercial fuel controls. The ACSL model was stripped of nonessential states to produce an eight-state linear state-space model of the engine. The A, B, and C matrices, derived from rated operating conditions, were used to obtain feedback control gains by the following methods: (1) state feedback; (2) LQR theory; (3) Bellman method; and (4) polygonal search. An off-load transient followed by an on-load transient was run for each of these fuel controls. The transient curves obtained were used to compare the state-space fuel controls with the analog fuel control. The state-space fuel controls did better than the analog control.
Weak Extinction Limits of Large-Scale Flameholders
Authors: Baxter M. R. , Lefebvre A. H.
Published: April 2008

Weak extinction data obtained from an experimental apparatus designed to simulate the characteristics of practical afterburner combustion systems are presented. The apparatus supplies mixtures of varied composition (equivalence ratio and degree of vitiation), temperature and velocity to Vee-gutter flame holders of various widths and shapes similar to those found in jet engine systems. The fuel employed is a liquid hydrocarbon whose chemical composition and physical properties correspond to those of aviation kerosine, JP5. An equation for predicting weak extinction limits which accounts for upstream vitiation and the chemical characteristics of the fuel is derived from stirred reactor theory. The correlation between the predictions and experimental results indicates that the stirred reactor approach can provide a framework for predicting the lean blowout limits of practical flameholders over wide ranges of engine operating conditions.
Study of External Dynamic Flap Loads on a 6 Percent B-1B Model
Authors: Seiner J. M. , Manning J. C. , Capone F. J. , Pendergraft O. C.
Published: April 2008

The origin of dynamic pressure loads on external divergent engine nozzle flaps of the B-1B aircraft was investigated in the NASA/LaRC 16-ft transonic tunnel using a 6 percent full-span model with powered engine nacelles. External flap dynamic loads and afterbody drag associated with flap removal were measured using this model. Both dry and maximum A/B power nozzles were evaluated in this study. As a result of this study, the principle mechanisms responsible for high dynamic external flap loads were determined along with performance penalty associated with flap removal.
Structural Reliability Analysis of Laminated CMC Components
Authors: Duffy S. F. , Palko J. L. , Gyekenyesi J. P.
Published: April 2008

For laminated ceramic matrix composite (CMC) materials to realize their full potential in aerospace applications design, methods and protocols are a necessity. This paper focuses on the time-independent failure response of these materials and presents a reliability analysis associated with the initiation of matrix cracking. It highlights a public domain computer algorithm that has been coupled with the laminate analysis of a finite element code and which serves as a design aid to analyze structural components made from laminated CMC materials. Issues relevant to the effect of the size of the component are discussed, and a parameter estimation procedure is presented. The estimation procedure allows three parameters to be calculated from a failure population that has an underlying Weibull distribution.
Reliability Analysis of Ceramic Matrix Composite Laminates
Authors: Thomas D. J. , Wetherhold R. C.
Published: April 2008

At a macroscopic level, a composite lamina may be considered as a homogeneous orthotropic solid whose directional strengths are random variables. Incorporation of these random variable strengths into failure models, either interactive or noninteractive, allows for the evaluation of the lamina reliability under a given stress state. Using a noninteractive criterion for demonstration purposes, laminate reliabilities are calculated assuming previously established load sharing rules for the redistribution of load as the failure of laminae occurs. The matrix cracking predicted by ACK theory is modeled to allow a loss of stiffness in the fiber direction. The subsequent failure in the fiber direction is controlled by a modified bundle theory. Results using this modified bundle model are compared with previous models, which did not permit separate consideration of matrix cracking, as well as to results obtained from experimental data.
Stability Analysis of Bridged Cracks in Brittle Matrix Composites
Authors: Ballarini R. , Muju S.
Published: April 2008

The bridging of matrix cracks by fibers is an important toughening mechanism in fiber-reinforced brittle matrix composites. This paper presents the results of a nonlinear finite element analysis of the Mode I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions that resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation, while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack is calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack, results are obtained that highlight the transition from stable to unstable behavior of the propagating crack.
Effect of Cold Work and Aging Upon the Properties of a Ni-Mo-Cr Fastener Alloy
Authors: Rothman M. F. , Srivastava S. K.
Published: April 2008

HAYNES® alloy 242 is a promising new Ni-Mo-Cr alloy for high-strength, high-temperature aerospace fastener applications. Age-hardenable by virtue of a long-range-order strengthening mechanism, 242™ alloy is capable of developing very high strength, particularly in the cold-worked condition. A key difference from other fastener materials is its attendant good ductility. The relationship between the amount of cold work, aging temperature and time, and the properties of this alloy has not been previously explored in detail. In the present work, the nature of the interaction between cold work and aging will be examined, and the properties of the material relevant to aerospace fastener applications will be described.
Application of Flash Welding to a Titanium Aluminide Alloy—Microstructural Evaluations
Authors: Gould J. E. , Stotler T. V.
Published: April 2008

Alpha-two titanium aluminides represent strong candidates for replacing many conventional titanium and nickel-base superalloys for intermediate temperature applications. One potential application of these alloys is turbine engine rings. Nonrotating rings of this type are typically manufactured by flash butt welding. The performance of welds in this alloy is known to be strongly affected by the weld microstructure. Welding processes that result in very slow cooling rates yield relatively coarse Widmanstatten-type microstructure(s), which generally yields acceptable weld performance. Processes that result in intermediate cooling rates, however, result in acicular alpha-two martensite microstructures. These microstructures have very little ductility and lead to reduced weld performance. Finally, for processes where the cooling rate is very rapid, the weld microstructure is a retained ordered beta phase, which apparently results in improved weld properties. In this paper, microstructures of some representative flash welds on T-14Al-21Nb were examined. In addition, flash welding conditions were varied to examine the effects of initial die opening and upset distance. In general, it appears that all the welds included in this study contain the ordered HCP martensite in the weld zone. However, both the scale of the microstructure and the weld hardness seem to depend heavily on the particular set of processing conditions used. These results were then used to estimate the relative cooling rates in these welds, and understand the effects of these processing conditions on the developing microstructures.
Finite Element Simulation of the Upset Welding Process
Authors: Nied H. A.
Published: April 2008

A finite element model of an elevated temperature upset welding process was developed to simulate the process and to study the role and sensitivity of the major process parameters. Particular attention was focused on the deformation characteristics by studying the displacement and stress fields generated for the purpose of obtaining a better understanding of this solidstate welding process. The paper describes the finite element formulation, the experiments used to validate the modeling, and a selected application for upset welding of a titanium alloy.
Status of the Automotive Ceramic Gas Turbine Development Program
Authors: Itoh T. , Kimura H.
Published: April 2008

A seven-year program, designated “Research and Development of Automotive CGT,” commenced in June 1990 with the object of demonstrating the potential advantages of ceramic gas turbine engines for automotive use. This program has been conducted by the Petroleum Energy Center (PEC) with the support of the Ministry of International Trade and Industry. The engine demonstration project in this program is being handled by a team from Japan Automobile Research Institute, Inc. (JARI). This paper describes the activities of the first year of the seven-year program, and includes the project goals and objectives, the program schedule, and the first-stage design of an experimental automotive ceramic gas turbine (CGT) engine and its components. The basic engine is a 100 kW, single-shaft gas turbine engine having a turbine inlet temperature of 1350°C and a rotor speed of 110,000 rpm. The primary engine components including the turbine hot flow path components have been designed using monolithic ceramics and are scheduled to be produced during the second year of the program.
High-Temperature Oxidation and Corrosion of Engineering Ceramics
Authors: Nickel K. G. , Fu Z. , Quirmbach P.
Published: April 2008

The problems of high-temperature oxidation and corrosion of Si3N4 and SiC are discussed. Other ceramics usually do not meet the requirements of structural applications at high temperatures. If the application has to meet very defined limits of size change, it is necessary to specify the exact material composition, as well as the atmosphere composition and physical environment to be able to specify the limits. This is in any case true for extremely reducing conditions or very high temperatures. Under oxidizing conditions, the region between ≈850 and 1100°C should be avoided when salty, sulfurous, and wet fuel conditions are expected. High temperature limits for long-time applications of Si3N4 in oxidizing environments are between 1200 and 1400°C, corresponding to eutectic temperatures of the glass phase. The ultimate limit for long-time use of SiC is likely to be between 1700 and 1800°C, where bubble formation and spallation may become inevitable.
Impact Design Methods for Ceramic Components in Gas Turbine Engines
Authors: Song J. , Cuccio J. , Kington H.
Published: April 2008

Garrett Auxiliary Power Division of Allied-Signal Aerospace Company is developing methods to design ceramic turbine components with improved impact resistance. In an ongoing research effort under the DOE/NASA-funded Advanced Turbine Technology Applications Project (ATTAP), two different modes of impact damage have been identified and characterized: local damage and structural damage. Local impact damage to Si3N4 impacted by spherical projectiles usually takes the form of ring and/or radial cracks in the vicinity of the impact point. Baseline data from Si3N4 test bars impacted by 1.588-mm (0.0625-in.) diameter NC-132 projectiles indicates the critical velocity at which the probability of detecting surface cracks is 50 percent equalled 130 m/s (426 ft/sec). A microphysics-based model that assumes damage to be in the form of microcracks has been developed to predict local impact damage. Local stress and strain determine microcrack nucleation and propagation, which in turn alter local stress and strain through modulus degradation. Material damage is quantified by a “damage parameter” related to the volume fraction of microcracks. The entire computation has been incorporated into the EPIC computer code. Model capability is being demonstrated by simulating instrumented plate impact and particle impact tests. Structural impact damage usually occurs in the form of fast fracture caused by bending stresses that exceed the material strength. The EPIC code has been successfully used to predict radial and axial blade failures from impacts by various size particles. This method is also being used in conjunction with Taguchi experimental methods to investigate the effects of design parameters on turbine blade impact resistance. It has been shown that significant improvement in impact resistance can be achieved by using the configuration recommended by Taguchi methods.
Mechanical Behavior of Fiber-Reinforced SiC/RBSN Ceramic Matrix Composites: Theory and Experiment
Authors: Chulya A. , Gyekenyesi J. P. , Bhatt R. T.
Published: April 2008

The mechanical behavior of continuous fiber-reinforced SiC/RBSN composites with various fiber contents is evaluated. Both catastrophic and noncatastrophic failures are observed in tensile specimens. Damage and failure mechanisms are identified via in-situ monitoring using NDE techniques throughout the loading history. Effects of fiber/matrix interface debonding (splitting) parallel to the fibers are discussed. Statistical failure behavior of fibers is also observed, especially when the interface is weak. Micromechanical models incorporating residual stresses to calculate the critical matrix cracking strength, ultimate strength, and work of pull-out are reviewed and used to predict composite response. For selected test problems, experimental measurements are compared to analytic predictions.
Generalized Polynomial Expansion Method for the Dynamic Analysis of Rotor-Bearing Systems
Authors: Shiau T. N. , Hwang J. L.
Published: April 2008

The determination of critical speeds and modes and the unbalance response of rotor-bearing systems is investigated with the application of a technique called the generalized polynomial expansion method (GPEM). This method can be applied to both linear and nonlinear rotor systems; however, only linear systems are addressed in this paper. Three examples including single spool and dual rotor systems are used to demonstrate the efficiency and the accuracy of this method. The results indicate a very good agreement between the present method and the finite element method (FEM). In addition, computing time will be saved using this method in comparison with the finite element method.
Quality Factors of Rotors With Hydrodynamic Bearings
Authors: Rao J. S.
Published: April 2008

The quality factor of a system is a measure of the maximum amplitude of vibration that occurs at resonance when the frequency of excitation is equal to the undamped natural frequency. This factor can be easily determined for a given mode of vibration, given its equivalent viscous damping ratio, as Q = 1/2ξ. Such a definition becomes complicated for a rotor mounted on hydrodynamic bearings. This note discusses some factors involved in estimating the quality factor of a rotor.
Applications of Sweep Frequency Rotating Force Perturbation Methodology in Rotating Machinery for Dynamic Stiffness Identification
Authors: Muszynska A. , Bently D. E. , Franklin W. D. , Grant J. W. , Goldman P.
Published: April 2008

This paper outlines the sweep frequency rotating force perturbation method for identifying the dynamic stiffness characteristics of rotor/bearing/seal systems. Emphasis is placed on nonsynchronous perturbation of rotating shafts in a sequence of constant rotative speeds. In particular, results of the identification of flexible rotor multimode parameters and identification of fluid forces in seals and bearings are given. These results, presented in the direct and quadrature dynamic stiffness formats, permit the separation of components for easy identification. Another example of the perturbation method application is the identification of the lateral–torsional coupling due to shaft anisotropy. Results of laboratory rig experiments, the identification algorithm, and data processing techniques are discussed.
The Effect of Inlet Swirl on the Rotordynamic Shroud Forces in a Centrifugal Pump
Authors: Guinzburg A. , Brennen C. E. , Acosta A. J. , Caughey T. K.
Published: April 2008

The role played by fluid forces in determining the rotordynamic stability of a centrifugal pump is gaining increasing attention. The present research investigates the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. In particular, the dependency of the rotordynamic characteristics of leakage flows on the swirl at the inlet to the leakage path was examined. An inlet guide vane was designed for the experiment so that swirl could be introduced at the leakage flow inlet. The data demonstrate substantial rotordynamic effects and a destabilizing tangential force for small positive whirl ratios; this force decreased with increasing flow rate. The effect of swirl on the rotordynamic forces was found to be destabilizing.
Optimal Output Feedback Control of Asymmetric Systems Using Complex Modes
Authors: Fan G. W. , Nelson H. D. , Mignolet M. P.
Published: April 2008

A Linear Quadratic Regulator (LQR)-based least-squares output feedback control procedure using a complex mode procedure is developed for the optimal vibration control of high-order asymmetric discrete system. An LQ Regulator is designed for a reduced-order model obtained by neglecting high-frequency complex modes of the original system. The matrix transformations between physical coordinates and complex mode coordinates are derived. The complex mode approach appears to provide more accurate reduced-order models than the normal mode approach for asymmetric discrete systems. The proposed least-squares output feedback control procedure takes advantage of the fact that a full-state feedback control is possible without using an observer. In addition, the lateral vibration of a high-order rotor system can be effectively controlled by monitoring one single location along the rotor shaft, i.e., the number of measured states can be much less than the number of eigenvectors retained in producing the reduced-order model while acceptable performance of the controller is maintained. The procedure is illustrated by means of a 52 degree-of-freedom finite element based rotordynamic system. Simulation results show that LQ regulators based on a reduced-order model with 12 retained eigenvalues can be accurately approximated by using feedback of four measured states from one location along the rotor shaft. The controlled and uncontrolled transient responses, using various numbers of measured states, of the original high-order system are shown. Comparisons of reduced-order model results using normal modes and complex modes are presented. The spillover problem is discussed for both collocated and noncollocated cases based on this same example.
LQR-Based Least-Squares Output Feedback Control of Rotor Vibrations Using the Complex Mode and Balanced Realization Methods
Authors: Fan G. W. , Nelson H. D. , Crouch P. E. , Mignolet M. P.
Published: April 2008

The complex mode and balanced realization methods are used separately to obtain reduced-order models for general linear asymmetric rotor systems. The methods are outlined and then applied to a typical rotor system represented by a 52 degree-offreedom finite element model. The accuracy of the two methods is compared for this model and the complex model method is found to be more accurate than the balanced realization method for the desired frequency bandwidth and for models of the same reduced order. However, with some limitations, it is also shown that the balanced realization method can be applied to the reduced-order complex mode model to obtain further order reduction without loss of model accuracy. A “Linear-Quadratic-Regulator-based least-squares output feedback control” procedure is developed for the vibration control of rotor systems. This output feedback procedure eliminates the requirement of an observer for the use of an LQ regulator, and provides the advantage that the rotor vibration can be effectively controlled by monitoring only one single location along the rotor shaft while maintaining an acceptable performance. The procedures presented are quite general and may be applied to a large class of vibration problems including rotordynamics.
Electromechanical Simulation and Testing of Actively Controlled Rotordynamic Systems With Piezoelectric Actuators
Authors: Lin Reng Rong , Palazzolo A. B. , Kascak A. F. , Montague G. T.
Published: April 2008

Past research on this subject has treated piezoelectric actuators as ideal devices that have tip displacements proportional to their input voltages, at any instant in time. This assumption neglected phase lag and amplitude change at high frequencies. This characteristic of any actuator may lead to coupled control system-structural system instability that limits the amount of active stiffness or active damping that can be obtained. The paper presents a method for simulating the coupled “electromechanical” system to predict rotordynamic stability and unbalance response along with control system stability. The piezoelectric actuators and their amplifiers are represented as equivalent linear electrical circuits. The electromechanical system modeling approach is utilized to correlate test results from a double overhung rotor rig at NASA Lewis. The test results also show the effectiveness of the control system for suppressing the unbalance response of two modes using active stiffness and active damping.
Design of a Hydraulic Actuator for Active Control of Rotating Machinery
Authors: Rashidi M. , Dirusso E.
Published: April 2008

A hydraulic actuator was designed and is described herein. This actuator consists of: a pump, which generates the nominal pressure, a hydraulic servovalve, and a thin elastic plate, which transduces the generated pressure variations into forces acting on a mass, which simulates the bearing of a rotor system. An actuator characteristic number is defined to provide a base for an optimum design of force actuators with combined weight, frequency, and force considerations. This characteristic number may also be used to compare hydraulic and electromagnetic force actuators. In tests this actuator generated 182.3 N force at a frequency of 100. Hz. and a displacement amplitude of 5.8×10−5 m.
Dynamic Force Response of an Open-Ended Squeeze Film Damper
Authors: San Andres L. A. , Meng G. , Yoon S.
Published: April 2008

The effects of whirl frequency and lubricant viscosity on the experimental pressure field and film forces in an open-ended squeeze film damper test rig are presented. The measurements refer to circular centered journal motion of amplitude equal to one half the damper clearance (ε = 0.5). The whirl frequency varied between 16 Hz and 85 Hz, while the lubricant temperature increased from 25°C to 45°C. The damper operated with levels of external pressurization that supressed lubricant cavitation. The experimental results show conclusively that the radial film force is purely an inertial effect, i.e., it depends solely on the fluid density and the second power of the whirl frequency. The tangential film force shows a variation that depends on the viscous and inertial flow conditions in the squeeze film region. Correlation of experimental forces with conventional SFD models shows the radial force to be π times larger than the theoretical prediction, while the tangential force correlates well for low whirl frequencies and large lubricant viscosities.
A Chambered Porous Damper for Rotor Vibration Control: Part II—Imbalance Response and Blade-Loss Simulation
Authors: Walton J. , Martin M.
Published: April 2008

In this paper, results of experimental rotordynamic evaluations of a novel, high load chambered porous damper design are presented. The chambered porous damper concept was evaluated for gas turbine engine application since this concept avoids the nonlinearities associated with high-eccentricity operation of conventional squeeze film dampers. The rotordynamic testing was conducted under large steady-state imbalance and simulated transient bladeloss conditions for up to 0.254 mm (0.01 in.) mass c.g offset or 180 g-cm (2.5 oz-in.) imbalance. The chambered porous damper demonstrated that the steady-state imbalance and simulated blade-loss transient response of a flexible rotor operating above its first bneding critical speed could be readily controlled. Rotor system imbalance sensitivity and logarithmic decrement are presented showing the characteristics of the system with the damper installed. The ability to accommodate high steady-state and transient imbalance conditions makes this damper well suited to a wide range of rotating machinery, including aircraft gas turbine engines.
Performance Characteristics of Brush Seals for Limited-Life Engines
Authors: Chupp R. E. , Dowler C. A.
Published: April 2008

Brush seals are potential replacements for air-to-air labyrinth seals in gas turbine engines. An investigation has been conducted to determine the performance characteristics of brush seals for application in limited-life gas turbine engines. An elevated temperature, rotating test rig was designed and built to test labyrinth and brush seals in simulated subsonic and supersonic engine conditions. Results from initial tests for subsonic applications demonstrated that brush seals exhibit appreciably lower leakage compared to labyrinth seals, and thus offer significant engine performance improvements. Performance results have been obtained showing the effect of various brush seal parameters, including: initial interference, backplate gap, and multiple brush seals in series.
Brush Seal Leakage Performance With Gaseous Working Fluids at Static and Low Rotor Speed Conditions
Authors: Carlile J. A. , Hendricks R. C. , Yoder D. A.
Published: April 2008

The leakage performance of a brush seal with gaseous working fluids at static and low rotor speed conditions was investigated. This report includes the leakage results for air, helium, and carbon dioxide at several bristle/rotor interferences. In addition, the effects of packing a lubricant into the bristles and also of reversing the pressure drop across the seal were investigated. Results were compared to that of an annular seal at similar operating conditions. In order to generalize the results, they were correlated using corresponding state theory. The brush seal tested had a bore diameter of 3.792 cm (1.4930 in.), a fence height of 0.0635 cm (0.025 in.), and 1800 bristles/cm-circumference (4500 bristles/in.-circumference). Various bristle/rotor radial interferences were achieved by using a tapered rotor. The brush seal reduced the leakage in comparison with the annular seal, up to 9.5 times. Reversing the pressure drop across the brush seal produced leakage rates approximately the same as that of the annular seal. Addition of a lubricant reduced the leakage by 2.5 times when compared to a nonlubricated brush seal. The air and carbon dioxide data were successfully correlated using the corresponding state theory. However, the helium data followed a different curve from the air and carbon dioxide data.
A Combined Experimental and Theoretical Study of Flow and Pressure Distributions in a Brush Seal
Authors: Bayley F. J. , Long C. A.
Published: April 2008

A relatively simple theory is presented that can be used to model the flow and pressure distribution in a brush seal matrix. The model assumes laminar, compressible, isothermal flow and requires knowledge of an empirical constant: the seal porosity value. Measurements of the mass flow rate together with radial and axial distributions of pressure were taken on a nonrotating experimental rig. These were obtained using a 122 mm bore brush seal with 0.25 mm radial interference. The experimental data are used to estimate the seal porosity. Measurements of the pressure distributions along the backing ring and under the bristle tips and discussed. Predicted mass flows are compared with those actually measured and there is reasonable agreement considering the limitations of the model.
Unusual Acoustic Vibration in Heat Exchanger and Steam Generator Tube Banks Possibly Caused by Fluid-Acoustic Instability
Authors: Eisinger F. L. , Sullivan R. E.
Published: April 2008

Flow channels of heat exchangers or steam generators containing tube arrays can be subject to acoustic vibration excited by flow of air, gas, or steam tranversely across the tubes. Such vibration occurs when a flow disturbance inside the tube bank excites a strong acoustic (standing wave) mode of the channel. The acoustic modes typically excited are those related to the dimension perpendicular to both the fluid flow direction and the tube axes. Preventive measures taken in the design stage are typically directed against these commonly existing standing waves. Evidence is presented of the unusual occurrence of standing waves that develop in the flow direction and in the tube axial direction. The causes for their development and methods of suppression are discussed.
Development of a Regenerator for an Automotive Gas Turbine Engine
Authors: Sayama J. , Morishita T.
Published: April 2008

It is vital to estimate the temperature effectiveness and pressure loss of the regenerator accurately when designing a gas turbine engine because these characteristics basically determine the size, weight, and fuel consumption of the regenerative gas turbine engine. In operation of an actual engine, regenerators often fail to attain the characteristics predicted by conventional methods, because there are many performance-reducing irregularities such as the nonuniform velocity distribution of gases flowing into the core. In this paper, a prediction method that is based on data from actual engine tests is examined as a way to predict regenerator temperature effectiveness and pressure losses when there are causes for deterioration of these characteristics. This method resulted in a system, taking the deterioration of these characteristics into consideration as they occur in an actual engine, that represents temperature effectiveness and pressure loss as the function of core specifications such as the core size and the core matrix. This prediction method was then used to predict the regenerator characteristics of actual engines with more than satisfactory results (the accuracy is ±1.25 percent for temperature effectiveness and ±4 percent for pressure loss).
Liquid Sheet Disintegration and Atomization Process on a Simplified Airblast Atomizer
Authors: Lavergne G. , Trichet P. , Hebrard P. , Biscos Y.
Published: April 2008

Liquid sheet break-up in coflowing shear flow is the mean by which liquids are atomized in practical injectors for gas turbine combustors. The present study explores experimentally the mechanisms of liquid sheet instabilities and spray formation. Experiments are conducted on four airblast geometries. A high-speed video camera associated with an image processing unit was used to study the liquid sheet instabilities. A microphone and a frequency analyzer were used to track the disintegration frequency. Instability amplitude and disintegration length of the liquid sheet were measured. A two-component Phase Doppler Particle Analyzer was used to characterize the resultant spray. The spatial distribution of the particle size is influenced by the swirling flow field. These experimental results will be used to assess models of fuel sheet instabilities and disintegration.
Particle Diagnostics and Turbulence Measurements in a Confined Isothermal Liquid Spray
Authors: Bren˜a de la Rosa A. , Sankar S. V. , Wang G. , Bachalo W. D.
Published: April 2008

This work reports an experimental study of the behavior and structure of a liquid spray immersed in a strong swirling field. In order to simulate some of the aerodynamic conditions experienced by a spray in a model combustor, an experimental setup using an acrylic chamber, a vane type swirler, and separate air supplies for both the secondary air and the swirl air were integrated to perform the experiments in the wind tunnel. A vane-type swirler exhibiting a high swirl number was used to produce a strong recirculation flow field downstream of a pressure swirl atomizer. Properties of the dispersed phase such as velocity, size distribution, and size-velocity correlation were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. Flow visualization was performed with a laser sheet to gain further understanding of the formation and influence of the recirculation region on the spray. A two-component PDPA system with a frequency-based Doppler signal analyzer was used throughout the measurements, and proved most valuable in the toroidal vortex region where low SNR conditions and nonuniform concentration of seed particles prevail. The results show that flow reversal of the drops is present at this swirl intensity within the recirculation region at distances up to X/D = 2.0. Small variations of drop size distribution within the recirculation region are observed; however, large variations outside of it are also present. Plots of the normal Reynolds stresses and Reynolds shear stresses show double-peak radial distributions, which indicate regions in the flow where high mean velocity gradients and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence.
Modification of Combustor Stoichiometry Distribution for Reduced NOx Emission From Aircraft Engines
Authors: Sturgess G. J. , McKinney R. G. , Morford S. A.
Published: April 2008

Measurements of the emissions from an experimental engine were analyzed to construct a design chart for the reduction of oxides of nitrogen (NOx) in conventional combustors. The design chart was used to reconfigure the stoichiometry distribution of the combustor of a production engine so as to reduce NOx while holding the emissions of carbon monoxide, unburned hydrocarbons, and smoke well below existing regulations. Combustion section pressure loss and combustor outlet temperature distributions were substantially unchanged. The modified design was refined with the aid of computational fluid dynamics calculations to optimize the emissions reduction. Worthwhile reductions in NOx were obtained with combustor modifications that are transparent to the engine user.
Evaluation of Low-NOx Combustor Concepts for Aeroderivative Gas Turbine Engines
Authors: McVey J. B. , Padget F. C. , Rosfjord T. J. , Hu A. S. , Peracchio A. A. , Schlein B. , Tegel D. R.
Published: April 2008

An experimental program was conducted to evaluate low-NOx combustor concepts applicable to natural-gas-burning aeroderivative gas turbine engines operating at a nominal pressure ratio of 20:1. Gas sampling measurements at the exit of the primary zone of high-shear and lean premixed burners were acquired under elevated entrance pressure and temperature conditions over a range of primary zone equivalence ratios. Piloting systems were incorporated in most of the burner designs to achieve satisfactory burner operability. Both swirl stabilized and perforated-plate (grid) stabilized burners were found to produce NOx levels lower than the current engine goal of 25 ppm (15 percent O2).
Carbon Monoxide Emissions From Gas Turbines as Influenced by Ambient Temperature and Turbine Load
Authors: Hung W. S. Y.
Published: April 2008

The emissions of carbon monoxide (CO) from gas turbines are typically below 100 ppmvd at 15 percent O2 at design full-load operating conditions. The use of water/ steam to reduce NOx emissions from gas turbines results in an increase in CO emissions from gas turbines. This is particularly true when increased rates of water/ steam injection are used to meet stringent NOx limits. Regulations limiting CO emissions from stationary gas turbines were first initiated in the late 1980s by the Federal Republic of Germany and the state of New Jersey in the United States. Since these regulations are silent on ambient and load corrections, these CO limits could be the limiting factor in the current development of dry low-NOx combustion systems by gas turbine manufacturers. In addition, since manufacturers are usually quite specific regarding the conditions for CO guarantees, a conflict for the gas turbine user, who is responsible for the permit application, is readily apparent. This paper attempts to characterize the CO emissions from gas turbines as a function of ambient temperature and turbine load. An ambient temperature correction equation for CO emissions, based on previous work, is presented. The intent is to provide more extensive information on CO emissions such that better defined CO limits can be adopted. Ultimately, this should help the combustion design engineers in developing improved dry low-emissions combustion systems for the gas turbine industry.
The Flow Inside a Model Gas Turbine Combustor: Calculations
Authors: McGuirk J. J. , Palma J. M. L. M.
Published: April 2008

The present study assesses the ability of the k-ε turbulence model to calculate the flow inside gas turbine combustors. Results of calculations using a cylindrical system of coordinates, hybrid differencing, and a mesh with about 40,000 nodes are compared with velocity measurements of the flow inside a perspex model of can-type gas turbine combustor. The larger discrepancies between measurements and predictions were found in the primary region. The complexity of the flow near the primary jet impingement led to underprediction of the maximum negative axial velocity and turbulence kinetic energy by about 35 and 20 percent, respectively. The calculated results exhibited higher levels of momentum diffusion compared to the experiments and did not show the two contrarotating vortices created between the primary jets; no qualitative agreement with the azimuthal velocity downstream of the primary jets could be achieved. Despite these deficiencies, the model gave acceptable results in other regions of the combustor and correct prediction of the main features of the combustor flow was possible.
Comparison of Spectrometric Techniques for the Analysis of Liquid Gas Turbine Fuels
Authors: Lukas M.
Published: April 2008

High-temperature corrosion and fuel system fouling are major concerns that confront gas turbine users. Fuel treatment is a critical requirement for gas turbine operators burning alternative fuels, and even so-called “clean fuels.” Spectrometric fuel analysis is used to determine the amount of treatment required as well as the efficiency of the treatment. In most cases, analytical techniques developed by chemists for use in laboratory environments have been adopted for field use. This paper describes the various spectrometric techniques available to the gas turbine user to analyze fuels for contaminants such as sodium, potassium, vanadium, lead, calcium, silicon, etc., and additives such as magnesium compounds. Atomic absorption spectroscopy (AAS) and various atomic emission spectroscopy (AES) techniques will be discussed and compared.
What Affects the Cost of Hot Gas Filter Stations?
Authors: Zievers J. F. , Eggerstedt P. , Zievers E. C. , Nicolai D.
Published: April 2008

This technical paper examines the various aspects of hot gas filter station design that ultimately affect both initial and operational costs. Process conditions such as temperature and pressure, and design constraints such as face velocity, are discussed with respect to their bearing on filter station costs. More subtle parameters, such as pulse gas cleaning requirements and filter element geometry, also directly impact filter design and hence, cost. As all of the information presented is based upon actual filter applications, it will provide useful insight for those involved in filter designing and recommendations.
Development of Hot Gas Cleaning Systems for Advanced, Coal-Based Gas Turbine Cycles
Authors: Lippert T. E. , Newby R. A. , Alvin M. A. , Bachovchin D. M. , Bruck G. J. , Smeltzer E. E.
Published: April 2008

Westinghouse is developing hot gas cleaning systems for advanced, coal-based gas turbine cycles. This paper summarizes the Westinghouse hot gas filter concept and reports on recent in-house and field test programs supporting its design and development. Basic materials issues related to ceramic material stability and hot metals structures are reviewed. Results of recent filter system testing are presented, comparing candle and crossflow designs operating in both “simulated” and actual coal-derived gas streams. Laboratory tests and analysis are reported relating to integrating sulfur and alkali control with the particle filter function.
Ceramic Filters for Hot Gas Cleanup
Authors: White L. R. , Tompkins T. L. , Hsieh K. C. , Johnson D. D.
Published: April 2008

This paper reviews the properties of high-temperature ceramic fibers and relates why strength, thermal shock resistance, chemical inertness, and high-temperature capability are important properties for high-temperature filter media. The use of candle filters, fabric filters, and composite filters will be discussed for removal of particulates from hot gas streams in electrical power generation systems, metal refining, chemical processing, and Diesel engine exhaust applications.