bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Analysis of the Two-Phase Unsteady Flow in an Aero-Engine LPP Burner
Authors: Caruggi Mario , Canepa Edward , Di Martino Pasquale , Nilberto Alessandro , Ubaldi Marina , Zunino Pietro
Published: November 2008

The present paper reports the results of an experimental investigation on the unsteady flow in a Lean Premixed Prevaporized (LPP) burner for aeronautical applications. The experiments were focused on two main aspects: understanding the effect of the fuel spray on the unsteady air flow field and characterizing the fuel spray under unsteady flow conditions in terms of velocity and spatial distribution of the fuel droplets. The experimental campaign was performed with laser-based instrumentation (LDV, PDA and PIV) on a large-scale model of the LPP burner with air preheating and fuel injection in order to allow detailed measurements of the two-phase unsteady flow. The gas flow field is dominated by a spiral vortex breakdown phenomenon, which results in a complex unsteady flow configuration and an extended recirculation zone near the axis of the burner. The fuel droplets flow field is strongly correlated to the gas flow field. By comparing the results of the present experimental campaign with results obtained without fuel spray, there is evidence of a positive effect of the spray on the air flow field. The spray effect results in a reduction of the recirculation phenomenon in the exit section of the LPP burner. At the LPP burner exit a general satisfactory degree of vaporization is obtained. However, at the periphery of the premixing duct outlet section, a significant concentration of larger droplets of not yet vaporized fuel is present, due to the secondary air blast disintegration of the liquid film formed on the internal surface of the premixer tube. This phenomenon is responsible for lack of homogeneity of the fuel distribution in time and space at the premixer duct exit.
The Evaluation of CFCC Liners After Field Testing in a Gas Turbine: V
Authors: Kimmel Josh , Price Jeffrey , More Karren , Tortorelli Peter , Bhatia Tania , Linsey Gary
Published: November 2008

Under the Ceramic Stationary Gas Turbine (CSGT) and Advanced Material Program sponsored by the U.S. Department of Energy (DOE), a team led by Solar Turbines Incorporated (Solar) has successfully designed engines utilizing SiC/SiC continuous fiber-reinforced ceramic composite (CFCC) combustor liners. Their potential for low NOx and CO emissions was demonstrated in ten separate field-engine tests for an accumulated duration of more than 68,000-hours. In the first four field tests, the durability of the CFCC liners was limited primarily by the long-term stability of SiC in the high-pressure steam environment of the gas turbine combustor. Consequently, the need for an environmental barrier coating (EBC) to meet the 30,000-hour life goal was recognized. An EBC developed under the National Aeronautics and Space Administration (NASA) High Speed Civil Transport, Enabling Propulsion Materials (EPM) program was improved, optimized and applied on the SiC/SiC liners by United Technologies Research Center (UTRC) from the fifth field test onwards. Presented in this paper is the evaluation of the field test with a modified EBC using Strontium Aluminum Silicate (SAS) on SiC/SiC CFCC liners after 8,368-hours.
Exergetic Analysis of the Part-Flow Evaporative Gas Turbine Cycles
Authors: Yari Mortaza , Sarabchi Kazem
Published: November 2008

The evaporative gas turbine cycle is a new high-efficiency power cycle that has reached the pilot plant testing stage. The latest configuration proposed for this cycle is known as part flow evaporative gas turbine cycle (PEvGT) in which humidification is combined with steam injection. Having advantages of both steam injected and humid air cycles, it is regarded as a very desirable plant for future. A mathematical model of the PEvGT cycle was presented in the previous work (Yari and Sarabchi, 2004), in order to do the analysis of the cycles. In this work the exergy equations have been added to the mathematical model. The aim of this work is to investigate the performance of the PEvGT cycles: PEvGT and PEvGT-IC (Intercooled PEvGT cycle), based on the exergy analysis. The results are presented and the influence of the several parameters is discussed: pressure ratio, part-flow humidification rate and the cycle configuration. Also the optimum cycle configuration has been selected from the exergetic point of view.
Performance Evaluation of High Temperature Coatings for Hot Section Turbine Components
Authors: Shifler David A. , Russom Dennis M. , Rodman Bruce E.
Published: November 2008

501-K34 marine gas turbine engines serve as auxiliary power sources for the U.S. Navy’s DDG-51 Class ships. It is desired that 501-K34 marine gas turbine engines have a mean time between removal of 20K hours. While some engines have approached this goal, others have fallen significantly short. A primary reason for this shortfall is hot corrosion (Type I and Type II) damage in the hot section turbine area due to both intrusion of salts from the marine air and from sulfur in the gas turbine combustion fuels. Previous metallographic examination of several unfailed blades removed from a marine gas turbine engine after 18000 operating hours showed that the coating thickness under the platform and in the curved area of transition between the platform to the blade stem was either very thin, porous, and in a few cases, non-existent on each unfailed blade. Type II hot corrosion was evident at these locations under the platform. Corrosion fatigue cracks initiated at several hot corrosion sites and had advanced through the blade stems to varying degrees. Cracking in a few blades had advanced to the point that blade failure was imminent. The objectives of this paper are to: (1) report the hot corrosion results of alternative high temperature coating systems on Alloy M247 and Alloy 792 for hot section components of the 501-K34 gas turbine engine using a low velocity, atmospheric-pressure burner-rig (LVBR), (2) compare and rank hot corrosion performance of these coatings systems to the baseline coating/substrate system (2) down select the best performing coating systems (in terms of LVBR hot corrosion and thermal cycling resistance) to implement on future hot section components in the 501-K34 engine for the Fleet.
Novel CO2 Emissions Reduction Technique for IGCC Plants
Authors: Kakaras E. , Koumanakos A. , Doukelis A. , Giannakopoulos D. , Hatzilau Ch. , Weimer T.
Published: November 2008

Scope of the work presented is to examine and evaluate the state of the art in technological concepts towards the capture and sequestration of CO2 from coal-fired power plants. The discussion is based on the evaluation of a novel concept dealing with the carbonation-calcination process of lime for CO2 capture from coal fired power plants compared to integration of CO2 capture in an Integrated Gasification Combined Cycle power plant. In the novel concept, coal is gasified with steam in the presence of lime. Lime absorbs the CO2 released from the coal, producing limestone. The produced gas can be a low-carbon or even zero-carbon (H2) gas, depending on the ratio of lime added to the process. The produced gas can be used in state-of-the-art combined cycles for electricity generation, producing almost no CO2 emissions or other harmful pollutants. The limestone is regenerated in a second reactor, where pure CO2 is produced, which can be either marketed to industry or sequestered in long term disposal areas. The simulation model of a Combined Cycle power plant, integrating the novel carbonation-calcination process, is based on available data from a typical natural gas fired Combined Cycle power plant. The natural gas fired power plant was adopted to firing with the low-C fuel, maintaining the basic operating characteristics. The performance of the novel concept power plant is compared to that of an IGCC with CO2 removal by means of Selexol absorption. Results from thermodynamic simulation, dealing with the most important features for CO2 reduction, are presented. The operating characteristics, as well as the main figures of the plant energy balances are included. A preliminary economic comparison is also provided, taking into account investment and operating costs, in order to estimate the electricity cost related to the two different technological approaches and the economic constrains towards the potentials for applications are examined. The cycle calculations were performed using the thermodynamic cycle calculation software ENBIPRO (ENergie-BIllanz-PROgram). ENBIPRO is a powerful tool for heat and mass balance calculations, solving complex thermodynamic circuits, calculating the efficiency, and allowing exergetic and exergoeconomic analysis of power plants. The software code models all pieces of equipment that usually appear in power plant installations and can accurately calculate all thermodynamic properties (temperature, pressure, enthalpy) at each node of the thermodynamic circuit, power consumption of each component, flue gas composition etc [1]. The code has proven its validity by accurately simulating a large number of power plants and through comparison of the results with other commercial software.
On the Use of Modal Parameters as Metrics for Condition-Based Monitoring of Rotating Machinery
Authors: Ginsberg Jerry H. , Wagner Benjamin B.
Published: November 2008

Deterioration of a rotordynamic system changes its modal properties. This paper initiates a study of the degree to which such changes can be detected by monitoring modal metrics obtained by a modern technique for experimental modal analysis (EMA). The eigenvalues and residues associated with a complex modal description of the frequency response are identified by processing response data derived from an analytical model. This model, which features an elastic shaft with attached rigid rotor and supported by hydrodynamic bearings, was previously used by Wagner and Ginsberg [Proc. of the 23rd International Modal Analysis Conf. (IMAC), forthcoming, 2005] to explore the merits of using standard or directional frequency response functions to perform EMA. The techniques used there, specfically the original version of the Algorithm of Mode Isolation (AMI) for FRFs and Two-Sided AMI for dFRFs, are used to extract the modal properties from the model’s frequency domain response. The modal eigenvalues and residues are identified for a range of bearing clearances within the limit of acceptable wear. One set of metrics that are considered describes the behavior of the system’s eigenvalues as clearance increases. Another set of metrics describes the modal residue factors, which depend on the drive and response locations. A defect is considered to be detectable if the change in the value of a metric due to deterioration exceeds the uncertainty in that metric’s value associated with the inexact nature of EMA. Although the eigenvalues are identified with great accuracy, they are found to be relatively insensitive to bearing clearance, so that metrics derived from them do not meet the detectability criterion. In contrast, the residue values are identified less accurately, but they are highly sensitivity to the clearance. It is concluded that metrics describing the behavior of the modal residue factors can unambiguously indicate bearing wear that is large, but still acceptable for continued operation. It also is found that it is preferable to monitor the residues obtained by processing standard FRFs using the original AMI version, rather than using Two-Sided AMI to process dFRFs.
Backstepping for Active Control of Surge in Unshrouded Centrifugal Compressors With Magnetic Thrust Bearing Actuation
Authors: Sanadgol Dorsa , Maslen Eric
Published: November 2008

The backstepping method is applied to design a controller which is capable of actively suppressing the oscillations induced by compressor surge using the sensitivity of the centrifugal compressor characteristic to the tip clearance of the unshrouded impeller. This is achieved using a magnetic thrust bearing to modulate the tip clearance of the impeller. The controller is designed with the objective that system trajectories remain on the compressor characteristic curve in the presence of disturbances downstream of the compressor. This ensures zero steady state offset of the impeller, which maintains the efficiency of the compressor. Results from simulation of the nonlinear model for a single stage high speed centrifugal compressor show that using backstepping control, mass flow and pressure oscillations associated with compressor surge are quickly suppressed with acceptable control requirements of typical machines. Further, the stable region of the compressor operation is significantly increased and the compression system will not enter surge cycles for a wide variety of disturbances downstream of the compressor.
Enhancing Flow Field Measurements Through Adaptive Multi-Dimensional Data Sampling
Authors: Franken Arnoud R. C. , Ivey Paul C.
Published: November 2008

A way to gain insights into the flow field conditions in turbomachinery is by carrying out a series of point measurements in a cross-section of the flow, for example, with a miniature multi-hole pressure probe. A problem commonly encountered in situations like these is the selection of a suitable measurement grid layout and density for obtaining all essential information in a cost-effective and timely manner. In order to achieve the latter, a novel adaptive multi-dimensional data sampling technique has been developed at Cranfield University. This paper describes the underlying principles of this technique, the algorithms utilized, and the results obtained during its successful application to data sets of two different flow fields in a high-speed research compressor.
Effects of Transducer Installation on Unsteady Pressure Measurements on Oscillating Blades
Authors: Lepicovsky J.
Published: November 2008

Unsteady pressures were measured above the suction side of a blade that was oscillated to simulate blade stall flutter. Measurements were made at blade oscillation frequencies up to 500 Hz. Two types of miniature pressure transducers were used: surface-mounted flat custom-made, and commercial miniature, body-mounted transducers. The signals of the surface-mounted transducers are significantly affected by blade acceleration, whereas the signals of body-mounted transducers are practically free of this distortion. A procedure was introduced to correct the signals of surface-mounted transducers to rectify the signal distortion due to blade acceleration. The signals from body-mounted transducers, and corrected signals from surface-mounted transducers represent true unsteady pressure signals on the surface of a blade subjected to forced oscillations. However, the use of body-mounted commercial transducers is preferred for the following reasons: no signal corrections are needed for blade acceleration, the conventional transducers are noticeably less expensive than custom-made flat transducers, the survival rate of body-mounted transducers is much higher, and finally installation of body-mounted transducers does not disturb the blade surface of interest.
Carbon Foam: New Generation of Enhanced Surface Compact Recuperators for Gas Turbines
Authors: Yu Q. , Thompson B. E. , Straatman A. G.
Published: November 2008

The potential of porous carbon foam is explored in the context of compact recuperators for microturbine applications. Porous carbon foam has an open, interconnected pore structure and an extremely high solid-phase conductivity, which render the material a viable alternative in compact heat exchanger design. The material is also mechanically stable, non-corrosive and relatively inert to temperatures up to approximately 500°C, which make it particularly attractive for high-temperature non-oxydizing and moderate temperature oxidizing applications. Hydrodynamic and thermal engineering models are proposed based on recent work applied to air-water heat exchangers. The models are developed based on a unit-cube geometric model for carbon foam, a heat transfer model and well-established convective correlations that are extended to account for the effects of the carbon foam. The present calculations suggest that the use of carbon foam in a relatively simple configuration results in a significant reduction in thermal resistance accompanied by a rise in the hydrodynamic resistance. These preliminary results suggest that very compact heat transfer devices could be developed. With further investigation it is felt that the hydrodynamic resistance could be reduced while preserving the heat transfer performance resulting in very high-performance, compact heat transfer devices.
An Integrated Framework for Gas Turbine Power Plant Operational Modeling and Optimization
Authors: Zhao Yongjun , Volovoi Vitali , Waters Mark , Mavris Dimitri
Published: November 2008

The deregulation of the electric power market has introduced strong competition, and as a result, power plant operators strive to develop advanced operational strategies to maximize the profitability given the conditions of the dynamic electric power market. In the deregulated electric power market, the operational strategies should match the evolving electric power market, and be capable of performing an optimization that is specific to a unit operating in a complex environment. A profit based, lifecycle oriented, and unit specific approach is proposed for more effective gas turbine power plant operational optimization, and methodologies for this approach are developed. This paper outlines an integrated, generic environment for unit-specific gas turbine power plant operational modeling and optimization, while several other follow up papers address specific operational optimization problems. The procedure is implemented for a generic combined cycle power plant with single gas turbine with the results demonstrating the feasibility of the proposed approach.
Simulation of Scalar Mixing in Co-Axial Jet Flows Using an LES Method
Authors: Dianat M. , Jiang D. , Yang Z. , McGuirk J. J.
Published: November 2008

The present paper describes a study that is aimed at establishing and quantifying the benefits of the Large Eddy Simulation (LES) method for predicting scalar turbulent transport in a combustor relevant jet-mixing problem. A non-reacting co-annular jet mixing configuration is considered for which comprehensive experimental data for both velocity and scalar fields have recently been obtained. Detailed comparisons are presented for the development of the axial velocity field in terms of both mean and turbulence intensity. Similarly, the mixing between the jets is examined by comparison with measurements for the mean concentration and the variance of concentration fluctuations. Agreement with these statistically averaged fields is demonstrated to be very good, and a considerable improvement over the standard eddy viscosity RANS approach. Illustrations are presented of the time-resolved information that LES provides such as time histories, and also conserved scalar pdf predictions. The LES results are shown, even using a simple Smagorinsky sub-grid-scale model, to predict correctly lower values of the turbulent Prandtl number (∼ 0.6) in the free shear regions of the flow, as well as higher values (∼ 1.0) in the wall-affected regions. The ability to predict turbulent Prandtl number variations (rather than input these as commonly done in most combustor RANS CFD models) is an important and promising feature of the LES approach for combustor simulation since it is known to be important in determining combustor exit temperature traverse.
A Profit Based Approach for Gas Turbine Power Plant Outage Planning
Authors: Zhao Yongjun , Volovoi Vitali , Waters Mark , Mavris Dimitri
Published: November 2008

Traditionally, for complicated systems such as a gas turbine power plant, maintenance cost and on-line availability are two of the most important concerns to the equipment owner. However, in the deregulated electric power market, cost and reliability are not the only concerns. The ultimate goal is to maximize plant profitability, and this requires the evaluation of many different factors including system performance, the aging and reliability of equipment, maintenance practices, and market dynamics accounting for the price and availability of fuel as well as the generation of revenues in competing markets. Thus, gas turbine power plant planning optimization is a complex problem, and comprehensive operational modeling and optimization methods are required. In this paper, a profit based power plant outage planning approach is presented that reflects the new challenges posed by deregulation. Specifically, particular attention is paid to modeling power plant aging, performance degradation, reliability deterioration, and, importantly, the energy market dynamics. A multiple time scale method is developed for coupled short term, long term generation scheduling and outage planning for this profit based outage planning approach. The procedure is implemented for a base load combined cycle power plant with single gas turbine with the results demonstrating the feasibility of the proposed approach.
Simple Model for a Magnetic Bearing System Operating on the Auxiliary Bearing
Authors: Cuesta E. N. , Montbrun N. I. , Rastelli V. , Diaz S. E.
Published: November 2008

The present work studies the behavior of a magnetic bearing supported rotor when the flow of electric current to the magnetic actuator is suppressed In this condition the rotor is supported by the auxiliary bearing, which has looseness with the rotor, generating a series of impacts between these components. For the study of this state, a model of a flexible rotor is proposed, and the impacts are simulated using kinematical restitution coefficient theory. The results obtained from the theoretical model are compared with experimental data taken on a test rig using tools for non linear systems analysis such bifurcation diagrams. The comparison shows that, besides the simplification of the contact, the model predicts ranges chaotic, quasi-periodic, and periodic motions in the test rig.
LPM™ Composite Overlay for Erosion Protection of Turbine Nozzles
Authors: Nagy Doug , Bergstaller Gerry
Published: November 2008

Aircraft turbine engines, particularly those of helicopter and turboprops tend to suffer hot gas path erosion in service. When the service environment includes operation from “un-improved” airstrips, component life is limited by erosion to times well less than the nominal time between overhaul (TBO). In response, an engineered material overlay was applied to the critical areas on turbine nozzles in overhaul. The overlay both “repaired” and “reinforced” the nozzles leading to a longer time on wing and less damage upon removal. No performance penalty was detected during test cell operation or flight service. The engineered material overlay was fabricated by powder metallurgical methods and consisted of a nickel superalloy matrix containing a rigid “skeleton” of chromium carbide hard particles. In the raw form, the overlay material was pliable to allow forming to complex geometries, but after diffusion bonding it was rigid and refractory.
Characteristics and Control of an Unstable Liquid-Fueled Multi-Swirling Combustor
Authors: Yi Tongxun , Gutmark Ephraim J. , Cornwell Michael
Published: November 2008

This paper reports our initial results on active control of combustion instability in a lean direct fuel injection combustor featured with multiple air swirls and distributed fuel injection. Fuel modulation is achieved by “pushing” fuel out of the valve cavity using a magnetostrictive rod that extends or contracts with unsteady currents going through its surrounding coil. To follow the flow commands and quickly reject exogenous disturbances on mean fuel flow rate, an LQG pulse-width modulation controller based on system identification models is developed. As a starting point, we tried a phase shift controller whose optimal control phase is directly obtained from system identification models. Pressure attenuation up to 20 dB is achieved within 150 ms using pressure feedback that achieves more pressure attenuation than optical fiber feedback. It is found that, during unstable combustions, pressure has a higher signal noise ratio than the optical fiber output mainly because the thermoacoustic system has a high gain around its resonant frequencies. Time-varying phase relationship exists between heat release and pressure. Partial blockage of the combustor exit considerably reduces combustion oscillation intensity and postpones the occurrence of unstable combustion to a higher equivalence ratio. This may be because the exit blockage increases the acoustic impedance at the combustor exit and modifies the reacting flow field. With higher preheat temperature, strong combustion oscillations may occur at a lower equivalence ratio. Pressure pulsations may exhibit hysterisis with equivalence ratio, especially at lower preheat temperature.
A Study of Noise Generation by Turbulent Flow Instabilities in a Gas Turbine Model Combustor
Authors: Olbricht Clemens , Flemming Felix , Sadiki Amsini , Janicka Johannes , Bake Friedrich , Michel Ulf , Ro¨hle Ingo
Published: November 2008

Due to successful noise reduction strategies concerning fan- and jet-noise in gas turbine configurations, the relevance of combustion noise is increasing. In order to distinguish between turbulent noise and combustion noise a model gas turbine combustor consisting of a swirl burner and an exit nozzle of Laval-shape is investigated. Because of the instationary character of the flow this configuration is analysed by means of Large Eddy Simulation (LES). Numerical results are first validated by comparison with experimental data. Then a numerical study of noise generated by turbulent flow instabilities is carried out. Providing an extensive temporal and spatial analysis of the isothermal flow length- and timescales as well as vorticitiy are investigated with regard to the formation of rotating flow-instabilities in the recirculating swirling flow. Subsequently a link to the acoustic perturbation equations (APE) is provided, from which the Lamb vector represents the essential noise sources. Therfore noise sources are identified and evaluated by means of LES based on the Lamb vector consideration. It results that the noise sources increase with an increasing swirl number.
Towards an Optimization of Turbulence Effects on Heat and Mass Transfer in Evaporating and Reacting Gas Turbine Sprays
Authors: Sadiki A. , Maneshkarimi M. R. , Chrigui M. , Janicka J.
Published: November 2008

In this paper, the way towards an optimization of turbulence effects on heat and mass transfer in evaporating and reacting GT-sprays is outlined. It is based on an accurate consideration of coupling between turbulence and turbulence modulation, swirl intensity and non-equilibrium effects during the vaporization. This is achieved by including a physically consistent modelling of turbulence modulation phenomena that allows to better retrieve mass and heat transport effects on the droplet surface, and therefore improves the prediction of processes, like evaporation and combustion, which in turn affect the turbulence. For this purpose, an Euler-Lagrangian method in conjunction with advanced models has been used in RANS-context and applied to the numerical study of a single gas turbine combustor configuration. a) To quantify, to control or to optimize the effects of turbulence along with the swirl intensity effects, a mixing parameter has been introduced. b) Under reacting conditions, it is shown how the evaporation characteristics, mixing rate and combustion process are influenced by turbulence. In particular, the turbulence modulation modifies the evaporation rate, which in turn influences the mixing and the species concentration distribution. It is demonstrated that this effect can not be neglected far from the nozzle for low swirl intensities (Sw.Nu.<1) and close to the nozzle for high swirl number intensities. All these findings can well be used to optimize turbulence effects in evaporating and reacting sprays.
Should Biomass Be Used for Power Generation or Hydrogen Production?
Authors: Corradetti Alessandro , Desideri Umberto
Published: November 2008

In the last years gasification has become an interesting option for biomass utilization, since the produced gas can be used as a gaseous fuel in different applications or burnt in a gas turbine for power generation with a high thermodynamic efficiency. In this paper a techno-economic analysis was carried out in order to evaluate performance and cost of biomass gasification systems integrated with two different types of plant, respectively for hydrogen production and for power generation. An indirectly heated fluidized bed gasifier has been chosen for gas generation in both cases and experimental data have been used to simulate the behavior of the gasifier. The hydrogen plant is characterized by the installation of a steam methane reformer and a shift reactor after the gas production and clean-up section; hydrogen is then purified in a pressure swing adsorption system. All these components have been modeled following typical operating conditions found in hydrogen plants. Simulations have been performed to optimize thermal interactions between the biomass gasification section and the gas processing. The power plant consists of a gas-steam combined cycle, with a three pressure levels bottoming cycle. A sensitivity analysis allowed to evaluate the economic convenience of the two plants as a function of the costs of the hydrogen and electrical energy.
An Investigation in Optimal Locations by Genetic Algorithm for Balancing Flexible Rotor-Bearing Systems
Authors: Lin Tsu-Wei , Kang Yuan , Wang Chun-Chieh , Chang Chuan-Wei , Chiang Chih-Pin
Published: November 2008

This study utilizes genetic algorithm to minimize the condition number of Hermitian matrix of influence coefficient (HMIC) to reduce the computation errors in balancing procedure. Then, the optimal locations of balancing planes and sensors would be obtained as fulfilling optimization. The finite element method is used to determine the steady-state response of flexible rotor-bearing systems. The optimization improves the balancing accuracy, which can be validated by the experiments of balancing a rotor kit.
Investigation of the Influence of Aerodynamic Coupling on Response Levels of Mistuned Bladed Discs With Weak Structural Coupling
Authors: Sladojevic´ I. , Petrov E. P. , Sayma A. I. , Imregun M. , Green J. S.
Published: November 2008

The paper summarises the results of a study investigating the correlation between the aerodynamic blade-to-blade coupling in mistuned bladed disc assemblies and the level of forced response. The focus was placed on the torsional mode of vibration, where blades’ coupling through the disc is weak, exposing the effects of aerodynamic coupling. The forced response of a large number of mistuned discs was computed, using whole-annulus finite element (FE) models. The unsteady aerodynamic forces that act upon the disc were calculated using a three-dimensional Reynolds-averaged Navier-Stokes CFD code. The results show the difference in response with and without aerodynamic coupling, exposing higher blade-to-blade interaction in the latter case. The statistical results show the change of the forced response distribution curves with the introduction of aero-coupling and their deviation from Gaussian distribution.
Analysis of Pressure Oscillations Data in Gas Turbine Annular Combustion Chamber Equipped With Passive Damper
Authors: Mastrovito M. , Camporeale S. M. , Forte A. , Fortunato B.
Published: November 2008

Growing environmental awareness, the current legislations, and the increasing competition in the energy market lead gas turbine manufacturers to develop combustion chambers that have to guarantee low NOx emissions, low pressure drop and high combustor outlet temperature. Modern annular and can-type gas turbine combustion chambers, able to work in lean premixed mode, show a remarkable attitude to produce flame instabilities, well known as humming. Many theoretical approaches have been proposed in order to describe the phenomenon and predict the stability margin of the burner. Experimental tests are needed to assess mathematical models and to evaluate the effects of either active or passive methodologies adopted to reduce combustion driven instabilities. Tests have been carried out at the Ansaldo Caldaie test bed on a real-size annular combustion chamber, equipped with a certain number of Helmholtz resonators. The combustion chamber has been instrumented with piezoelectric and opto-electronic transducers in order to determine the pressure field both in proximity of the instability limit and in humming condition. When pressure data are collected before than humming appears, pressure oscillations are much lower than those gathered in humming conditions; therefore, by using sensors designed to work under the pressure levels characterising the humming conditions, difficulties arise in proximity of the stability limit due the low signal-to-noise ratio. In this paper some techniques used to analyse the data gathered from the tests will be shown. Moreover, a simple algorithm capable to analyse a large amount of data and to synthesise them into a few significant parameters useful for the spectral analysis of the pressure field, has been validated by means of both real and simulated signals.
Optical Diagnostics for Characterization of a Full-Size Fighter-Jet Afterburner
Authors: Seyfried H. , Sa¨rner G. , Omrane A. , Richter M. , Schmidt H. , Alde´n M.
Published: November 2008

In the present work the feasibility of using various optical/laser based techniques for characterization of the afterburner of a full-size aircraft engine have been investigated. The tests have been performed on-site at Volvo Aero Corporation and were mainly directed towards surface thermometry using thermographic phosphors and fuel visualization. All applications were studied for different engine running conditions, including various use of the afterburner (A/B). Laser-Induced Fluorescence (LIF) was employed for fuel visualization to investigate to what extent unburned fuel exits the afterburner. Laser-Induced Phosphorescence (LIP) from thermographic phosphors was used to measure two-dimensional surface temperatures on the outlet nozzle of the afterburner. In addition, the spectral characteristics of the burning jet stream were investigated.
Nonlinear Dynamic Analyses of a Gas Turbine Blade for Attainment of Reliable Shroud Coupling
Authors: Szwedowicz J. , Slowik S. , Mahler A. , Hulme C. J.
Published: November 2008

The major objective of this paper is to evaluate a stand-point for integral shroud coupling, regarding the complex problem of nonlinear resonance vibrations of a shrouded blade with friction and impact effects. Following the load sequence in the start-up and further uploading to base load, a nonlinear cyclic FE static computation with friction forces at the shroud interface delivers contact stress results essential for assessment of a reliable shroud coupling. The FE refinement study at the shroud interface proves the reliability of the computed eigenfrequencies with respect to the harmonic engine excitation. Using nonlinear dynamic simulations of the shroud connection with friction forces, contact stiffness, surface roughness and impacts, the decoupling between the static and dynamic motions at the shroud interface is demonstrated. Based on the one-dimensional description of vibration characteristics for the shrouded blade, the resulting normal and tangential contact stiffness are evaluated from the computed 3D FE nodal diameter diagrams. The excitation forces acting on the blade are determined with the stimulus concept, in which an empirical factor is estimated from pulsation measured in the combustor chamber over the frequency range of the blade vibrations. The entire process is illustrated for the redesigned Z-lock interface on the shroud of a gas turbine stage whose contact surfaces had shown fretting problems. The numerical results confirm possible contact failures for the old shroud configuration. The blade calculated with the modified shroud connection shows numerically, stable dynamic behavior and will therefore prevent further fretting contact problems.
Use of Very High Water-Vapor Pressures to Evaluate Candidate Compositions for Environmental Barrier Coatings
Authors: Tortorelli Peter F. , More Karren L.
Published: November 2008

Environmental barrier coatings (EBCs) are used to protect Si-based ceramics from accelerated oxidation and volatilization in the presence of elevated water-vapor pressures at high temperatures and high gas velocities. Previously, an analysis based on mass flux of volatilized species has shown that operating at very high H2O pressures can be used to compensate for the low gas velocities found in many laboratory exposure facilities so as to conduct first-stage screening of EBC compositions for volatility resistance. To test this prediction experimentally, a high-temperature furnace was modified to accommodate gas pressures of up to 20 atm and bulk specimens of barium-strontium aluminosilicate (BSAS), barium aluminosilicate (BAS), and strontium aluminosilicate (SAS), silica (SiO2), and silicon carbide (SiC) were exposed at 1250°C in 90% H2O-10% air. This set of materials provided an adequate spread in susceptibility to volatilization to evaluate the proposed approach because BSAS, BAS, and SAS are significantly more volatilization resistant in water-bearing environments than SiO2 and Si-bearing ceramics (such as SiC) that form silica under these conditions. The gravimetric results provided clear trends in volatilization resistance. The three aluminosilicates exhibited similar kinetic behavior and had significantly lower rates of mass losses than the SiO2 and SiC. These findings provided the experimental proof-of-principle for using high-pressure, low-gas-velocity exposures for qualitative differentiation of degrees of volatilization resistance among different candidate materials being developed for EBC applications.
The High-Temperature Stability of an Oxide/Oxide Composite at High Water-Vapor Pressure
Authors: More Karren L. , Lara-Curzio Edgar , Tortorelli Peter F. , Brummett Tracie M. , Szweda Andy
Published: November 2008

The microstructural and mechanical stabilities of a Nextel 720 (alumina+mullite) fiber-reinforced, alumina matrix composite were evaluated following exposure of the material to a high H2O pressure (to simulate a gas turbine combustor environment) in Oak Ridge National Laboratory’s (ORNL’s) high temperature, high pressure facility (Keiser Rigs). Coupons were exposed at 1135°C and 1200°C in a high-pressure (10 atm) furnace containing 10% water vapor for 1000, 2000, and 3000 h. Extensive microstructural characterization was conducted after each exposure to evaluate fiber and matrix stabilities as a function of exposure time and temperature. Retained tensile strengths were also measured and compared to baseline properties following each exposure. It was found that there was no significant change in the composite microstructure or tensile strength after long-term exposure in the Keiser Rig at 1135°C, whereas significant Nextel 720 fiber degradation (grain growth and increased surface roughness) occurred during exposure for 3000 h at 1200°C. Statistical variations in the mean strength values between the as-processed and exposed composites indicated little change in strength, however. The composite degradation was primarily thermal and the addition of H2O had little effect on changing or accelerating these effects.
Aircraft Gas Turbine Engines’ Technical Condition Identification System
Authors: Abdullayev P. S. , Pashayev A. M. , Askerov D. D. , Sadiqov R. A.
Published: November 2008

In this paper is shown that the probability-statistic methods application, especially at the early stage of the aviation gas turbine engine (GTE) technical condition diagnosing, when the flight information has property of the fuzzy, limitation and uncertainty is unfounded. Hence is considered the efficiency of application of new technology Soft Computing at these diagnosing stages with the using of the Fuzzy Logic and Neural Networks methods. Training with high accuracy of fuzzy multiple linear and non-linear models (fuzzy regression equations) which received on the statistical fuzzy data basis is made. Thus for GTE technical condition more adequate model making are analysed dynamics of skewness and kurtosis coefficients’ changes. Researches of skewness and kurtosis coefficients values’ changes show that, distributions of GTE work parameters have fuzzy character. Hence consideration of fuzzy skewness and kurtosis coefficients is expedient. Investigation of the basic characteristics changes’ dynamics of GTE work parameters allows to draw conclusion on necessity of the Fuzzy Statistical Analysis at preliminary identification of the engines’ technical condition. Researches of correlation coefficients values’ changes shows also on their fuzzy character. Therefore for models choice the application of the Fuzzy Correlation Analysis results is offered. At the information sufficiency is offered to use recurrent algorithm of aviation GTE technical condition identification (Hard Computing technology is used) on measurements of input and output parameters of the multiple linear and non-linear generalised models at presence of noise measured (the new recursive Least Squares Method (LSM)). The developed GTE condition monitoring system provides stage-by-stage estimation of engine technical conditions. As application of the given technique the estimation of the new operating aviation engine D-30KU-154 technical condition was made.
Upgrading the LCAC APU System
Authors: Hillen Michelle M. , Hampshire James D.
Published: November 2008

The Navy’s Landing Craft Air Cushion (LCAC) hovercraft vehicles use two Auxiliary Power Unit (APU) engines to provide AC power to the craft and bleed air to start the main engines. The APU Engine Sequencing Unit (ESU) and bleed air valve have consistently been high failure items. NAVSEA Philadelphia and Hamilton-Sundstrand have developed a Component Improvement Program (CIP) to increase the APU reliability and reduce repair/replacement cost by upgrading the ESU and bleed air valve. This paper will document and outline the APU CIP development effort, along with the installation, testing, and operation of the new APU components.
Development of a 3 MW High Speed Generator and Turbine Drive for a Hybrid Vehicle Propulsion System
Authors: Herbst John D. , Thelen Robert , Cook Kathleen , Bigley Drew , Ranero Joe
Published: November 2008

This paper reports on the development of a 3 MW gas turbine generator set developed as the prime mover for a hybrid-electric locomotive propulsion system. The lightweight turbine generator set described in the paper is also suitable for marine power generation applications. The paper describes the direct drive, high-speed generator and the lightweight skid-mounted turbine/alternator package developed by the program as well as plans for both laboratory and field testing of the system. Critical technical challenges and the solutions developed by the program are also presented in the paper.
Mechanism and Impact of Damper Seal Clearance Divergence on the Rotordynamics of Centrifugal Compressors
Authors: Eldridge Thom M. , Soulas Thomas A.
Published: November 2008

Damper seals (such as honeycomb and hole pattern seals) have been widely used in the turbomachinery industry to counterbalance destabilizing aerodynamic forces acting on the rotor system and to provide the necessary amount of damping for stable operation of the machine. Recent experience and research developments have focused the interest of the turbomachinery community on the dynamic characteristics of the divergent-taper damper seal. In addition to offering a review of the current literature on the subject of interest (in order to provide a comprehensive vision of the overall phenomenon), this paper extends the discussion for a better understanding of the mechanism and impact of damper seal clearance divergence on the rotordynamics of a rotor-bearing-seal system (as applied to centrifugal compressors). The analysis of a damper seal alone is insufficient to assess the influence of this component on the rotordynamic stability of a turbocompressor. This paper will show the variation of a complete rotor-bearing-seal system’s logarithmic decrement as a function of the hole pattern seal clearance divergence for a sample centrifugal compressor application, as analyzed with the proprietary, state-of-the-art rotordynamic software suite from the author’s company. This divergence-based transition of system logarithmic decrement from positive to zero (thereby implying the onset of instability) leads to the definition of a “damper seal divergence stability threshold.” Divergence in a damper seal can originate from numerous sources, including taper produced during manufacture, and pressure or thermal-driven distortion of the seal under operation. While small damper seal divergence may first produce an increase of the system logarithmic decrement, additional seal divergence has a dramatic effect on the first forward whirling mode natural frequency, as well as on the logarithmic decrement of that mode. This paper describes the analytical methods used to derive the stability of the rotor-bearing-seal system. It also presents a practical experience that stresses the necessity for a sound approach to properly evaluate the impact of a divergent damper seal on the stability of centrifugal compressors.
Engine Design and Operational Impacts on Particulate Matter Precursor Emissions
Authors: Lukachko Stephen P. , Waitz Ian A. , Miake-Lye Richard C. , Brown Robert C.
Published: November 2008

Aircraft emissions of trace sulfur and nitrogen oxides contribute to the generation of fine volatile particulate matter (PM). Resultant changes to ambient PM concentrations and radiative properties of the atmosphere may be important sources of aviation-related environmental impacts. This paper addresses engine design and operational impacts on aerosol precursor emissions of SOx and NOy species. Volatile PM formed from these species in the environment surrounding an aircraft is dependent on intra-engine oxidation processes occurring both within and downstream of the combustor. This study examines the complex response of trace chemistry to the temporal and spatial evolution of temperature and pressure along this entire intra-engine path, after combustion through the aft combustor, turbine, and exhaust nozzle. Low-order and higher fidelity tools are applied to model the interaction of chemical and fluid mechanical processes, identify important parameters, and assess uncertainties. The analysis suggests intra-engine processing is inefficient. For engine types in-service in the large commercial aviation fleet, mean conversion efficiency (ε) is estimated to be 2.8% to 6.5% for sulfate precursors and 0.3% to 5.7% for nitrate precursors at the engine exit plane. These ranges reflect technological differences within the fleet, the variation in oxidative activity with operating mode, and modeling uncertainty stemming from variance in rate parameters and initial conditions. Assuming sulfur-derived volatile PM is most likely, these results suggest emission indices of 0.06–0.13 g/kg-fuel assuming particles nucleated as 2H2SO4·H2O for a fuel sulfur content of 500 ppm.