bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comprehensive Model to Predict Simplex Atomizer Performance
Authors: Liao Y. , Sakman A. T. , Jeng S. M. , Jog M. A. , Benjamin M. A.
Published: February 2008

The pressure swirl atomizer, or simplex atomizer, is widely used in liquid fuel combustion devices in the aerospace and power generation industries. A computational, experimental, and theoretical study was conducted to predict its performance. The Arbitrary-Lagrangian-Eulerian method with a finite-volume scheme is employed in the CFD model. Internal flow characteristics of the simplex atomizer, as well as its performance parameters such as discharge coefficient, spray angle and film thickness, are predicted. A temporal linear stability analysis is performed for cylindrical liquid sheets under three-dimensional disturbances. The model incorporates the swirling velocity component, finite film thickness and radius that are essential features of conical liquid sheets emanating from simplex atomizers. It is observed that the relative velocity between the liquid and gas phases, density ratio and surface curvature enhance the interfacial aerodynamic instability. The combination of axial and swirling velocity components is more effective than only the axial component for disintegration of liquid sheet. For both large and small-scale fuel nozzles, mean droplet sizes are predicted based on the linear stability analysis and the proposed breakup model. The predictions agree well with experimental data at both large and small scale.
Inhibition of Interdiffusion From MCrAlY Overlay Coatings by Application of a Ni-Re Interlayer
Authors: Page R. A. , Leverant G. R.
Published: February 2008

The durability of protective coatings on combustion turbine blades and vanes is a critical issue in the power generation industry. Coating life usually dictates the refurbishment intervals for these components, and these intervals have generally been of shorter duration than desired by the operators of the equipment. Both MCrAlY and aluminide type coatings protect against oxidation and hot corrosion by forming a protective Al2O3 surface layer. Degradation of the coatings occurs by depletion of the aluminum content of the coating through interdiffusion with the substrate and through the formation and spallation of an external Al2O3 scale. The results obtained in this study clearly show that the application of a thin interlayer of Ni-Re beneath the MCrAlY coating can significantly decrease the growth rate of the inner β-NiAl depletion zone. Order of magnitude reductions in the inner depletion zone thickness formed at 1000 h were obtained with both the Ni-32 wt.% Re and the Ni-47 wt.% Re interlayer coatings. Since formation of the inner depletion zone is believed to result from interdiffusion with the substrate, these results suggest that the Ni-Re interlayer provided a significant impediment to the inward diffusion of Al into the substrate.
Energy Input of a Centrifugal Stage Into the Attached Piping System During Mild Surge
Authors: Ribi B. , Gyarmathy G.
Published: February 2008

Subjected to an oscillating flow rate, a compressor may feed additional (excitational) energy into the attached piping system. The relation between this additional energy input and the instantaneous behavior of a centrifugal compressor stage is dealt in a first part. Modeling the stage behavior by taking into account either inertia of the enclosed fluid mass or a first-order transient element or transient stall in any component leads to a different energy input. The energy input at a flow rate oscillation of given frequency and amplitude was calculated as a function of the slope of the characteristic and the reduced frequency applying a previously published model to describe the instantaneous behavior of the stage. In this model transient stall in the diffuser is taken into account. At reduced frequencies above unity the energy input of the diffuser was reduced by a considerable amount due to the specified instantaneous behavior of the diffuser. This indicates a potential to reduce the additional energy input of the diffuser either by increasing the time constant of the stall process or by increasing the mild surge frequency. For the investigated diffuser size the required reduced frequencies imply mild surge frequencies in a range being too high for industrial application (>200 Hz). Still, this method turned out to give useful insight into the link between the instantaneous behavior of the compressor and its energy input. In a second part for the same centrifugal compressor the energy contribution of several stage segments during mild surge oscillations was determined from detailed instantaneous measurements. As a result, the contribution of each stage segment to the conservation of the mild surge pulsation emerges. Although at the investigated mild surge frequencies the stage segments no longer behave strictly quasi-steadily, their contribution to the additional energy input is found to be mainly determined by the slope of their quasi-steady characteristic.
Mode Localization of a Cracked Blade Disk
Authors: Kuang J. H. , Huang B. W.
Published: February 2008

In this paper, the effect of blade crack on the mode localization of a rotating blade disk is studied. Pretwisted taper beams are used to simulate blades of a blade disk. The crack on the blade can be regarded as a local disorder of this periodically coupled blades system. An application of Hamilton’s principle and Galerkin’s method is used to formulate the equations of motion of the mistuned system. Effects of pretwisted angle, rotating speed, and crack depth of the blade on the in-plane and off-plane mode localizations of a rotating system are investigated. Numerical results indicate that the increase of rotating speed, pretwisted angle, and crack depth could enhance the localization phenomenon significantly.
A Bulk-Flow Analysis of Multiple-Pocket Gas Damper Seals
Authors: Li J. , San Andre´s L. , Vance J.
Published: February 2008

A bulk-flow model for calculation of the dynamic force characteristics in a single cavity, multiple-pocket gas damper seal is presented. Flow turbulence is accounted for by using turbulent shear stress parameters and Moody’s friction factors in the circumferential momentum equation. Zeroth-order-equations describe the isothermal flow field for a centered seal, and first-order equations govern the perturbed flow for small amplitude rotor lateral motions. Comparisons to limited measurements from a four-pocket gas damper seal show the current model to predict well the mass flow rate and the direct damping coefficient. For a reference two-bladed teeth-on-stator labyrinth seal, the current model predicts similar rotordynamic coefficients when compared to results from a two control volume, bulk-flow model. Force coefficients from a reference single-cavity, four pocket gas damper depend on the rotor speed and pressure drop with magnitudes decreasing as the rotor whirl frequency increases. The multiple-pocket gas damper seal provides substantially more damping than a conventional labyrinth seal of the same dimensions. The damper seal cross-coupled stiffness coefficients are small though sensitive to the inlet circumferential preswirl flow.
High-Speed Rotor Losses in a Radial Eight-Pole Magnetic Bearing: Part 1—Experimental Measurement
Authors: Kasarda M. E. F. , Allaire P. E. , Maslen E. H. , Brown G. R. , Gillies G. T.
Published: February 2008

The continual increase in the use of magnetic bearings in various capacities, including high-speed aerospace applications such as jet engine prototypes, dictates the need to quantify power losses in this type of bearing. The goal of this study is to present experimentally measured power losses during the high-speed operation of a pair of magnetic bearings. A large-scale test rotor has been designed and built to obtain unambiguous power loss measurements while varying a variety of test parameters. The test apparatus consists of a shaft supported in two radial magnetic bearings and driven by two electric motors also mounted on the shaft. The power losses of the spinning rotor are determined from the time rate of change of the kinetic energy of the rotor as its angular speed decays during free rotation. Measured results for the first set of magnetic bearings, a pair of eight-pole planar radial bearings, are presented here. Data from three different parameter studies including the effect of the bias flux density, the effect of the bearing pole configuration, and the effect of the motor stator on the power loss are presented. Rundown plots of the test with the bearings in the paired pole (NNSS) versus the alternating (NSNS) pole configuration show only small differences, with losses only slightly higher when the poles are in the alternating pole (NSNS) configuration. Loss data were also taken with the motor stators axially removed from the motor rotors for comparison with the case where the motor stators are kept in place. No measurable difference was observed between the two cases, indicating negligible windage and residual magnetic effects. Throughout most of the speed range, the dominant loss mechanism appears to be eddy currents.
The Maximum Factor by Which Forced Vibration of Blades Can Increase Due to Mistuning
Authors: Whitehead D. S.
Published: February 2008

In 1966 it was shown that the maximum factor by which the amplitude of forced vibration of blades can increase due to mistuning is, with certain assumptions, 1/2(1+N), where N is the number of blades in the row. This report gives a further investigation of the circumstances when this factor can be obtained. These are small damping, and a relationship must hold between the mistuning distribution γ(s) and the interblade coupling function c(r), where r is the model number. The mistuning distribution must be symmetric about the blade on which maximum amplitude is to occur, s = 0. The coupling function must be symmetric about r = R, where R is the mode number of the excitation. If the coupling is purely mechanical, additional conditions apply. The coupling function c(r) must consist of a number of identical symmetric substrips. A 1976 result for mechanical coupling is amended.
The Effect of Squeeze Film Damper Parameters on the Unbalance Response and Stability of a Flexible Rotor
Authors: Chu F. , Holmes R.
Published: February 2008

There has been much research work carried out on various aspects of individual squeeze-film dampers (SFDs) but very little on the interplay between a damper and the rotating assembly of which it forms a part. In this paper, a flexible rotor-bearing assembly in a configuration, typical of a small centrifugal pump and incorporating an SFD, is investigated theoretically and experimentally from the points of view of forced vibration control and stability control. It is found that change in rotor unbalance, SFD static eccentricity ratio, and SFD supply pressure can cause significant movement of system resonances and vibration resulting from excessive damping. The provision of an SFD also delays the onset of instability and because of its nonlinearity, the SFD contributes more damping than can a linear damper when the vibration amplitude becomes large as instability develops. It is shown that this instability is curbed at some limit cycle, whose frequency is a system natural frequency.
Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)
Authors: Powers L. M. , Jadaan O. M. , Gyekenyesi J. P.
Published: February 2008

The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilizes commercially available finite element packages and takes into of a account the time-varying creep strain distributions (stress relaxation). The creep life of a component is discretized into short time, steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman–Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the CARES/CREEP (Ceramics Analysis and Reliability Evaluation of Structures/CREEP) integrated design program, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benchmark problems and engine components are included.
Radial Turbine Development for the 100 kW Automotive Ceramic Gas Turbine
Authors: Nakazawa N. , Ogita H. , Takahashi M. , Yoshizawa T. , Mori Y.
Published: February 2008

The development of turbine components for the automotive 100 kW ceramic gas turbine has entered the final stage of the seven-year project and is making satisfactory progress toward the goals. We have attained the interim targets of the aerodynamic performances and have been carrying out tests to further improve efficiency. As for ceramic parts, we have changed the material of the turbine rotor to a new one that is excellent in long-sustained and high-temperature strength properties, and have confirmed substantial strength at high temperature through hot-spin tests. After evaluating blade-vibration stress through analyses and experiments, we completed an endurance evaluation at 1200°C (1473 K) TIT (Turbine Inlet Gas Temperature) and a rated speed of 100,000 rpm. We are now carrying out endurance tests at 1350°C (1623 K) TIT. For ceramic stationary parts, we already finished the evaluations at 1200°C TIT and are also conducting an endurance test at 1350°C TIT. Using these parts in a full-assembly test, together with other elements, we confirmed that they cause no functional problem in tests performed at 1200°C TIT level up to the rated speed (100,000 rpm), and are evaluating their performances.
Research and Development of Ceramic Gas Turbine (CGT302)
Authors: Takehara I. , Inobe I. , Tatsumi T. , Ichikawa Y. , Kobayashi H.
Published: February 2008

The ongoing Japanese Ceramic Gas Turbine (CGT) project, as a part of the New Sunshine Project funded by the Ministry of International Trade and Industry (MITI), aims to achieve higher efficiency, lower pollutant emission, and multifuel capability for small to medium sized gas turbine engines to be used in cogeneration systems. The final target of this project is to achieve a thermal efficiency over 42 percent at a turbine inlet temperature (TIT) of 1350°C. Under this project, Kawasaki Heavy Industries (KHI) is developing the CGT302 (a regenerative twin-spool CGT). The CGT302 has several unique features: simple-shaped ceramic components, KHI’s original binding system for turbine nozzle segments, stress-free structure using ceramic springs and rings, etc. In addition to these features, a high turbine tip speed and a metal plate fin recuperator were adopted. At the end of the fiscal year 1994, an intermediate appraisal was carried out, and the CGT302 was recognized to have successfully achieved its target. The CGT302 endurance test at the intermediate stage required 20 hours’ operation of the basic ceramic engine. The actual testing accomplished 40 hours at over 1200°C TIT, which included 30 hours of operation without disassembling. The target thermal efficiency of 30 percent at 1200°C has almost been reached, 29.2 percent having been achieved. In 1995 the CGT302 successfully recorded 33.1 percent at 1190°C of TIT with no trouble. We will introduce the current status of R&D of the CGT302 and its unique features in this paper.
Modeling the Effective Elastic Behavior of a Transversely Cracked Laminated Composite
Authors: Thomas D. J. , Wetherhold R. C.
Published: February 2008

The solution for the stress state present in the vicinity of transverse matrix cracks within a composite laminate is typically obtained by assuming a regular crack spacing geometry for the problem and applying a shear-lag analysis. In order to explore the validity of this underlying assumption, the probability density function for the location of the next transverse matrix crack within a crack bounded region is examined. The regular crack spacing assumption is shown to be reasonable from an engineering point of view. Continuing with this assumption, a generalized shear-lag model for multilayer, off-axis laminates subjected to full in-plane loads is developed. This model is used to quantitatively evaluate the effective elastic properties of the damaged material. The results are applicable to materials such as ceramic matrix or polymer matrix unidirectional fiber systems where damage in the form of transverse matrix cracks arises.
A Mixed Lubrication and Oil Transport Model for Piston Rings Using a Mass-Conserving Algorithm
Authors: Gulwadi S. D.
Published: February 2008

A numerical study of the interactions between hydrodynamic/boundary lubrication, oil transport, and radial dynamics of a piston ring using a mass-conserving (cavitation) algorithm is presented. The scheme outlined in this investigation facilitates the calculation of the volume of oil accumulating at the leading and trailing edges of the piston ring as it scrapes against the line. The calculation of this oil accumulation is important in the estimation of lubricating oil consumption in engines. The numerical procedure employed in this study is capable of depicting the transition between the various modes of piston ring lubrication (hydrodynamic, mixed, and boundary) over an engine cycle, including the detachment of oil film from the ring and its subsequent re-attachment. Additionally, the effects of (a) liner lubricant availability and (b) ring face profiles on the oil accumulation are also discussed.
Toward Automatic Process Simulators: Part I—Modular Numerical Procedures
Authors: Sciubba E.
Published: February 2008

This paper presents a general design approach involving automatic, intelligent process simulation procedures. The aim is to derive a general set of design principles and methodologies that can be developed into computer-assisted procedures. This first part deals with numerical, quantitative calculations, i.e., with what commonly goes under the name of “Numerical Process Simulation.” It is argued that the existing design methods can result in computer codes or packages that perform exactly (and deterministically) the numerical operations an engineer would perform. It is also shown that modularity in these codes is dictated by the necessity of automatically implementing numerical procedures that depend on the structure of the process under examination, rather than by user’s convenience and ease of maintenance. An example of a modular, structure-oriented code (CAMEL) is given and discussed in detail, while numerical applications are discussed elsewhere [4]. The second part deals with the more complex qualitative approach to process design, i.e., with the possibility of implementing automatic “expert” procedures that perform the same conceptual tasks as human process engineers. It is shown that by means of Artificial Intelligence techniques it is possible to mimic (to an extent) the “thinking patterns” of a human expert, and to produce process schemes that are both acceptable and realistic. A general process synthesis package (COLOMBO) is described and some of its applications discussed. The main goal of the two parts of the paper is to show that the very complex activity of process design can be executed automatically, not only in principle, but in actual applications, and that both qualitative synthesis and quantitative calculations are possible with the present state of the art of our computational facilities.
Primary Atomization and Spray Analysis of Compound Nozzle Gasoline Injectors
Authors: Chen J. L. , Wells M. , Creehan J.
Published: February 2008

This work addresses primary atomization modeling, multidimensional spray prediction, and flow characteristics of compound nozzle gasoline injectors. Compound nozzles are designed to improve the gasoline spray quality by increasing turbulence at the injector exit. Under the typical operating conditions of 270-1015 kPa, spray atomization in the compound nozzle gasoline injectors is mainly due to primary atomization where the flow turbulence and the surface tension are the dominant factors. A primary atomization model has been developed to predict the mean droplet size far downstream by taking into account the effect of turbulent intensity at the injector exit. Two multidimensional spray codes, KIVA-2 and STAR-CD, originally developed for high-pressure diesel injection, are employed for the lower-pressure gasoline injection. A separate CFD analysis was performed on the complex internal flows of the compound nozzles to obtain the initial and boundary conditions for the spray codes. The TAB breakup model used in KIVA-2 adequately facilitates the atomization process in the gasoline injection.
A Stability Analysis of a Rotor System With Electromagnetic Control Forces
Authors: Zhu M.
Published: February 2008

The stability analysis of a rotor system with electromagnetic control forces is investigated. The formulas for the electromagnetic forces between the stator and rotor of the electromagnetic actuator are derived with respect to the displacements of the journal center and coil currents. The minimum setting values of the controller, and the relationship between mode shapes at the positions of sensors and actuators of the system, are given by using a perturbation method and Routh–Hurwitz theory.
An Experimental/Computational Study of Airflow in the Combustor–Diffuser System of a Gas Turbine for Power Generation
Authors: Agrawal A. K. , Kapat J. S. , Yang T. T.
Published: February 2008

This paper presents an experimental/computational study of cold flow in the combustor–diffuser system of industrial gas turbines employing can-annular combustors and impingement-cooled transition pieces. The primary objectives were to determine flow interactions between the prediffuser and dump chamber, to evaluate circumferential flow nonuniformities around transition pieces and combustors, and to identify the pressure loss mechanisms. Flow experiments were conducted in an approximately one-third geometric scale, 360-deg annular test model simulating practical details of the prototype including the support struts, transition pieces, impingement sleeves, and can-annular combustors. Wall static pressures and velocity profiles were measured at selected locations in the test model. A three-dimensional computational fluid dynamic analysis employing a multidomain procedure was performed to supplement the flow measurements. The complex geometric features of the test model were included in the analysis. The measured data correlated well with the computations. The results revealed strong interactions between the prediffuser and dump chamber flows. The prediffuser exit flow was distorted, indicating that the uniform exit conditions typically assumed in the diffuser design were violated. The pressure varied circumferentially around the combustor casing and impingement sleeve. The circumferential flow nonuniformities increased toward the inlet of the turbine expander. A venturi effect causing flow to accelerate and decelerate in the dump chamber was also identified. This venturi effect could adversely affect impingement cooling of the transition piece in the prototype. The dump chamber contained several recirculation regions contributing to the losses. Approximately 1.2 dynamic head at the prediffuser inlet was lost in the combustor–diffuser, much of it in the dump chamber where the fluid passed though narrow pathways. A realistic test model and three-dimensional analysis used in this study provided new insight into the flow characteristics of practical combustor–diffuser systems.
Toward Automatic Process Simulators: Part II—An Expert System for Process Synthesis
Authors: Sciubba E.
Published: February 2008

This paper presents an explicit mapping of the conceptual activities that constitute a “process design task” into a series of well-posed, complete, and general formal simulation procedures. Part I of this series of two papers dealt with numerical procedures for process simulation and showed that structure independence and modularity are two prerequisites for a general-purpose simulator. Part II approaches the problem from a completely different point of view and considers the question: Is it possible to derive a general set of design guidelines that can be implemented into a knowledge-based system and result in an automatic, computer-assisted process design procedure? This problem is different in character from that tackled in part I. First, it is by its own nature qualitative, i.e., it requires conceptual rather than numerical answers. Second, it is formulated at a higher level (in Artificial Intelligence terms, at a metalevel). Its solution is clearly in the domain of the logic of process design and, therefore, embeds (contains) all possible quantitative numerical schemes and does not depend on any of them for either its position or its solution. If the answer to this question is affirmative, the resulting code would be a sort of “Expert Assistant” to the engineer in the sense that it would suggest what process can be best suited for the particular application under consideration. The study proceeds by trying to detect conceptual similarities in different design procedures, to construct a suitable knowledge base, and to implement a general macro-procedure that could automatically assist the engineer in the largest possible number of process design operations. The contention here is that the most recent developments of AI-based methods make it possible to extract from human experts all the essential knowledge that pertains to “engineering design,” with the final goal of transferring this body of knowledge—in a form suitable to machine communication—to an “Expert System for Process Design,” which can then be applied (interactively or on a stand-alone basis) with a high degree of confidence to a variety of particular process simulations. A prototype version of an Expert System Assistant is briefly discussed, and an application is analyzed in detail. The code is called COLOMBO and is available as a research tool from the author. Finally, Part II builds on Part I of this series of papers. In particular, it is assumed that a general, modular, numerical Process Simulation Package exists and that it is capable of executing the quantitative mass and energy balance operations described in Part I.
Investigation of Vapor-Phase Lubrication in a Gas Turbine Engine
Authors: Van Treuren K. W. , Barlow D. N. , Heiser W. H. , Wagner M. J. , Forster N. H.
Published: February 2008

The liquid oil lubrication system of current aircraft jet engines accounts for approximately 10–15 percent of the total weight of the engine. It has long been a goal of the aircraft gas turbine industry to reduce this weight. Vapor-Phase Lubrication (VPL) is a promising technology to eliminate liquid oil lubrication. The current investigation resulted in the first gas turbine to operate in the absence of conventional liquid lubrication. A phosphate ester, commercially known as DURAD 620B, was chosen for the test. Extensive research at Wright Laboratory demonstrated that this lubricant could reliably lubricate rolling element bearings in the gas turbine engine environment. The Allison T63 engine was selected as the test vehicle because of its small size and bearing configuration. Specifically, VPL was evaluated in the number eight bearing because it is located in a relatively hot environment, in line with the combustor discharge, and it can be isolated from the other bearings and the liquid lubrication system. The bearing was fully instrumented and its performance with standard oil lubrication was documented. Results of this baseline study were used to develop a thermodynamic model to predict the bearing temperature with VPL. The engine was then operated at a ground idle condition with VPL with the lubricant misted into the #8 bearing at 13 ml/h. The bearing temperature stabilized at 283°C within 10 minutes. Engine operation was continued successfully for a total of one hour. No abnormal wear of the rolling contact surfaces was found when the bearing was later examined. Bearing temperatures after engine shutdown indicated the bearing had reached thermodynamic equilibrium with its surroundings during the test. After shutdown bearing temperatures steadily decreased without the soakback effect seen after shutdown in standard lubricated bearings. In contrast, the oil-lubricated bearing ran at a considerably lower operating temperature (83°C) and was significantly heated by its surroundings after engine shutdown. In the baseline tests, the final bearing temperatures never reached that of the operating VPL system.
Results of Experiments and Models for Predicting Stability Limits of Turbulent Swirling Flames
Authors: Hoffmann S. , Lenze B. , Eickhoff H.
Published: February 2008

Swirling flames are used in many industrial applications, such as process furnaces, boilers, and gas turbines due to their excellent mixing, stability, emission, and burnout characteristics. The wide-spread use of swirl burners in the process and energy industries and, in particular, new concepts for the reduction of NOx emissions, raises the need for simple-to-use models for predicting lean stability limits of highly turbulent flames stabilized by internal recirculation. Based on recently published experimental data of the first author concerning the reaction structures of swirling flames operating near the extinction limit, different methods for predicting lean blow-off limits have been developed and tested. The aim of the investigations was to find stabilization criteria that allow predictions of blow-off limits of highly turbulent recirculating flames without the requirement for measurements in those flames. Several similarity criteria based on volumetric flow rates, burner size, and material parameters of the cold gases were found to be capable of predicting stability limits of premixed and (in some cases) nonpremixed flames at varying swirl intensities, burner scales and fuel compositions. A previously developed numerical field model, combining, a k–ε model with a combined “assumed-shape joint-PDF”/eddy-dissipation reaction model was also tested for its potential for stability prediction.
Developing Centrifugal Compressor Train Optimization Models for Performance Evaluation
Authors: Summers S. M.
Published: February 2008

Recent advances in numerical optimization software now allow problems arising in the evaluation of complex centrifugal compressor train performance to be solved readily by machinery users. Analyses of compressor operations often require consideration of multiple nonlinear constraints involving pressure, temperature, flow rate, composition, and power. Based on these constraints, the operational boundaries of the machinery must be evaluated. Frequently operating points of greatest interest exist where one of the operational variables, such as flow rate, is maximized subject to operational constraints. A methodology is proposed that can be used to apply commercially available optimization software to problems of this type. A review of gas equation of state relationships needed to determine thermodynamic properties is provided, as well as methods for calculating compressor discharge pressure based on polytropic head and efficiency. Recycle control is considered and a model is proposed.
Design of a Semiclosed-Cycle Gas Turbine With Carbon Dioxide–Argon as Working Fluid
Authors: Ulizar I. , Pilidis P.
Published: February 2008

The main performance features of a semiclosed-cycle gas turbine with carbon dioxide–argon working fluid are described here. This machine is designed to employ coal synthetic gas fuel and to produce no emissions. The present paper outlines three tasks carried out. First, the selection of main engine variables, mainly pressure and temperature ratios. Then a sizing exercise is carried out where many details of its physical appearance are outlined. Finally the off-design performance of the engine is predicted. This two-spool gas turbine is purpose built for the working fluid, so its physical characteristics reflect this requirement. The cycle is designed with a turbine entry temperature of 1650 K and the optimum pressure ratio is found to be around 60. Two major alternatives are examined, the simple and the precooled cycle. A large amount of nitrogen is produced by the air separation plant associated with this gas turbine and the coal gasifier. An investigation has been made on how to use this nitrogen to improve the performance of the engine by precooling the compressor, cooling the turbine nozzle guide vanes, and using it to cool the delivery of the low-pressure compressor. The efficiencies of the whole plant have been computed, taking into account the energy requirements of the gasifier and the need to dispose of the excess carbon dioxide. Hence the overall efficiencies indicated here are of the order of 40 percent. This is a low efficiency by current standards, but the fuel employed is coal and no emissions are produced.
Advanced Combined Cycle Alternatives With the Latest Gas Turbines
Authors: Dechamps P. J.
Published: February 2008

The last decade has seen remarkable improvements in industrial gas turbine size and performances. There is no doubt that the coming years are holding the promise of even more progress in these fields. As a consequence, the fuel utilization achieved by combined cycle power plants has been steadily increased. This is, however, also because of the developments in the heat recovery technology. Advances on the gas turbine side justify the development of new combined cycle schemes, with more advanced heat recovery capabilities. Hence, the system performance is spiraling upward. In this paper, we look at some of the heat recovery possibilities with the newly available gas turbine engines, characterized by a high exhaust temperature, a high specific work, and the integration of some gas turbine cooling with the boiler. The schemes range from classical dual pressure systems, to triple pressure systems with reheat in supercritical steam conditions. For each system, an optimum set of variables (steam pressures, etc.) is proposed. The effect of some changes on the steam cycle parameters, like increasing the steam temperatures above 570°C are also considered. Emphasis is also put on the influence of some special features or arrangements of the heat recovery steam generators, not only from a thermodynamic point of view.
Low-Leakage Modular Regenerators for Gas-Turbine Engines
Authors: Kluka J. A. , Wilson D. G.
Published: February 2008

One of the significant problems plaguing regenerator designs is seal leakage resulting in a reduction of thermal efficiency. This paper describes the preliminary design and analysis of a new regenerative heat-exchanger concept, called a modular regenerator, that promises to provide improved seal-leakage performance. The modular regenerator concept consists of a ceramic-honeycomb matrix discretized into rectangular blocks, called modules. Separating the matrix into modules substantially reduces the transverse sealing lengths and substantially increases the longitudinal sealing lengths as compared with typical rotary designs. Potential applications can range from small gas-turbine engines for automotive applications to large stationary gas turbines for industrial power generation. Descriptions of two types of modular regenerators are presented including sealing concepts. Results of seal leakage analysis for typical modular regenerators sized for a small gas-turbine engine (120 kW) predict leakage rates under one percent for most seal-clearance heights.
Oxidation Resistance and Critical Sulfur Content of Single Crystal Superalloys
Authors: Smialek J. L.
Published: February 2008

Single crystal superalloys had greatly improved cyclic oxidation resistance when their sulfur content was reduced from impurity levels, typically 5–10 ppmw in past years, down to 1 ppmw or below currently. Excellent alumina scale adhesion has been documented for PWA 1480, PWA J484, Rene’N5, Rene’N6, and CMSX 4, all without reactive element (Y) additions. Hydrogen annealing was used for effective desulfurization to below 0.1 ppmw, as well as for achieving controlled intermediate levels. This paper summarizes the direct relationship between cyclic oxidation behavior and sulfur content. An adhesion criterion has been proposed based on the concentration of sulfur needed to initiate spallation due to a monolayer of interfacial segregation. This suggests that a level down to ∼0.2 ppmw would be needed to maximize adhesion for a 1 mm thick sample. It is in reasonable agreement with the experimental results.
Prevention of Low-Frequency Vibration of High-Capacity Steam Turbine Units by Squeeze-Film Damper
Authors: Kanki H. , Kaneko Y. , Kurosawa M. , Yamamoto T.
Published: February 2008

The cause of the low-frequency vibration (subsynchronous vibration) of a high-pressure turbine was investigated by the analytical study and vibration exciting test for the actual machine in operation. From the results, it is found that the low-frequency vibration is caused by the decrease of the rotor system damping at high-loading operating conditions. As a countermeasure, a squeeze-film damper is designed in order to increase the damping of the rotor system. After the verification test of the squeeze-film damper’s capability in the workshop, it was installed on the actual turbine. Vibration exciting tests for the high-pressure turbine under the actual operating conditions were carried out. These field tests confirmed that the damping of the rotor system was increased as expected in the design and consequently the low-frequency vibrations disappeared completely under all operating conditions.
Imbalance Response of a Test Rotor Supported on Squeeze Film Dampers
Authors: San Andre´s L. , Lubell D.
Published: February 2008

Squeeze film dampers (SFDs) provide vibration attenuation and structural isolation to aircraft gas turbine engines which must be able to tolerate larger imbalances while operating above one or more critical speeds. Rotor-bearing-SFD systems are regarded in theory as highly nonlinear, showing jump phenomena and even chaotic behavior for sufficiently large levels of rotor imbalance. Yet, few experimental results of practical value have verified the analytical predictions. A test rig for measurement of the dynamic forced response of a three-disk rotor (45 kg) supported on two cylindrical SFDs is described. The major objective is to provide a reliable data base to validate and enhance SFD design practice and to allow a direct comparison with analytical models. The open-ends SFD are supported by four-bar centering structures, each with a stiffness of 3.5 MN/m. Measured synchronous responses to 9000 rpm due to various imbalances show the rotor-SFD system to be well damped with amplification factors between 1.6 and 2.1 while traversing cylindrical and conical modes critical speeds. The rotor amplitudes of motion are found to be proportional to the imbalances for the first mode of vibration, and the damping coefficients extracted compare reasonably well to predictions based on the full-film, open-ends SFD. Tight lip (elastomeric) seals contribute greatly to the overall damping of the test rig. Measured dynamic pressures at the squeeze film lands are well above ambient values with no indication of lubricant dynamic cavitation as simple theoretical models dictate. The measurements show absence of nonlinear behavior of the rotor-SFD apparatus for the range of imbalances tested.
Transient Thermoelastohydrodynamic Study of Tilting-Pad Journal Bearings Under Dynamic Loading
Authors: Monmousseau P. , Fillon M. , Freˆne J.
Published: February 2008

Nowadays, tilting-pad journal bearings are submitted to more and more severe operating conditions. The aim of this work is to study the thermal and mechanical behavior of the bearing during the transient period from an initial steady state to a final steady state (periodic). In order to study the behavior of this kind of bearing under dynamic loading (Fdyn) due to a blade loss, a nonlinear analysis, including local thermal effects, realistic boundary conditions, and bearing solid deformations (TEHD analysis) is realized. After a comparison between theoretical results obtained with four models (ISO, ADI, THD, and TEHD) and experimental data under steady-state operating conditions (static load Ws), the evolution of the main characteristics for three different cases of the dynamic load (Fdyn/Ws < 1, Fdyn/Ws = 1 and Fdyn//Ws > 1) is discussed. The influence of the transient period on the minimum film thickness, the maximum pressure, the maximum temperature, and the shaft orbit is presented. The final steady state is obtained a long time after the appearance of a dynamic load.
Structural Analysis of Cylinder Head Cracking in a Heavy-Duty Diesel Engine
Authors: Luo J.-Y. , Korte C. J.
Published: February 2008

There were fatigue cracking problems at the intake ports of a prototype heavy-duty six-cylinder head. Several proposals of design change were evaluated by finite element and reliability analysis. Constant amplitude loading and monotonic temperature-dependent properties of the head material are assumed. An equivalent stress-strain parameter (ESSP) is proposed to consider multiaxial stress/strain effect on fatigue cracking. A significant reliability improvement was predicted with cost savings and verified by limited engine tests.
Performance and Compatibility of California Reformulated Gasoline in On-Road, Off-Road, and Non-Vehicle Engines
Authors: Bevan A. R. , Nolan K. M.
Published: February 2008

As part of its comprehensive program to reduce air pollution, California has mandated the use of a cleaner burning reformulated gasoline introduced in March 1996. In 1995 the Air Resources Board, with oversight from an industry, public interest, and governmental advisory committee, undertook an extensive study of the performance and compatibility characteristics of California reformulated gasoline in on-road, off-road, and non-vehicle engines. The evaluation included in-use comparison of California reformulated gasoline to conventional gasoline in normal fleet operations. Fleets totaling 829 test and 637 control vehicles were studied. Additionally, off-road and non-vehicle in-use testing was conducted covering engine technologies in the following uses: utility, lawn and garden applications; pleasure craft and small marine vessels; agricultural and industrial engines; and recreational snowmobiles and personal watercraft. California reformulated gasoline was found to perform as well as conventional gasoline in terms of driveability, starting, idling, acceleration, power, and safety.
Black Liquor Gasifier/Gas Turbine Cogeneration
Authors: Consonni S. , Larson E. D. , Kreutz T. G. , Berglin N.
Published: February 2008

The kraft process dominates pulp and paper production worldwide. Black liquor, a mixture of lignin and inorganic chemicals, is generated in this process as fiber is extracted from wood. At most kraft mills today, black liquor is burned in Tomlinson boilers to produce steam for on-site heat and power and to recover the inorganic chemicals for reuse in the process. Globally, the black liquor generation rate is about 85,000 MWfuel (or 0.5 million tonnes of dry solids per day), with nearly 50 percent of this in North America. The majority of presently installed Tomlinson boilers will reach the end of their useful lives during the next 5 to 20 years. As a replacement for Tomlinson-based cogeneration, black liquor-gasifier/gas turbine cogeneration promises higher electrical efficiency, with prospective environmental, safety, and capital cost benefits for kraft mills. Several companies are pursuing commercialization of black liquor gasification for gas turbine applications. This paper presents results of detailed performance modeling of gasifier/gas turbine cogeneration systems using different black liquor gasifiers modeled on proposed commercial designs.
A Direct Coal-Fired Combustion Turbine Power System Based on Slagging Gasification With In-Situ Gas Cleaning
Authors: Newby R. A. , Bannister R. L.
Published: February 2008

Westinghouse began the development of a compact, entrained, slagging gasifier technology utilizing in-situ fuel gas cleaning for combustion turbine power cycles in 1986. The slagging gasifier is air-blown, and produces a hot, low-heating value fuel gas that can be combusted and quenched to combustion turbine inlet temperatures while maintaining low levels of NOx emissions. The U.S. Department of Energy sponsored engineering studies and pilot testing during the period 1986 to 1992. This work has shown that the technology has promise, although performance improvements are required in some key areas. A major challenge has been the development of insitu removal of sulfur, alkali vapor, and particulate to low enough levels to permit its use in combustion turbine power systems without additional, external gas cleaning. This paper reviews the Westinghouse slagging gasifier, direct coal-fired turbine power generation concept; the pilot test results; and the current development activities that Westinghouse is engaged in.
The Meaning of Activation Energy and Reaction Order in Autoaccelerating Systems
Authors: Ervin J. S. , Heneghan S. P.
Published: February 2008

Global reaction mechanisms and rate constants are commonly used in computational fluid dynamics models that incorporate chemical reactions to study aviation fuel thermal and oxidative thermal stability. Often these models are calibrated using one set of conditions, such as flow rate and temperature. New conditions are then calculated by extrapolation using the global expressions. A close inspection of the origin of global oxidation rate constants reveals that in systems that undergo autocatalysis or auto inhibition, a simple overall global activation energy and reaction order are not good descriptors of the reaction process. Furthermore, pseudo-detailed chemical kinetic modeling of a fuel that experiences autocatalysis shows that the observed reaction order for oxygen consumption varies with initial oxygen concentration, extent of reaction, and temperature. Thus, a simple global rate expression used to describe oxygen consumption in an autoaccelerating system is insufficient to allow extrapolation to different temperature or time regimes.
A Semi-Analytical Finite Rate Two-Reactor Model for Gas Turbine Combustors
Authors: Tonouchi J. H. , Held T. J. , Mongia H. C.
Published: February 2008

A gas turbine combustor is modeled using a two-reactor, finite-rate mixing and chemistry gas particle approach. The first reactor, used to simulate combustion in the primary zone, permits independent definition of the rates of macromixing and micromixing within the reactor, and the amount of premixing of fuel and air entering the reactor. Finite-rate macromixing is simulated by consideration of the fluid particle residence time distribution frequency function and the ages of the particles in the reactor. Finite-rate micromixing is simulated using a modified Coalescence-Dispersion (C-D) model. The second reactor model simulates combustion in the dilution zone of the combustor, and is modeled as a plug flow reactor with cross-flowing jets of dilution air and co-flowing streams of cooling film air. The primary zone reactor model predicts physically reasonable trends in mean temperature, and CO and NOx emissions as the macromixing and micromixing parameters are varied with respect to the perfectly stirred reactor limit. The model also has shown to predict the correct trends in modeling NOx and CO emissions from aircraft engine gas turbine combustors.