bluuebunny/crossref_metadata_2025 huggingface dataset:
Metallic Alloys for Primary Surface Recuperators
Authors: Rakowski James M. , Stinner Charles P. , Lipschutz Mark , Montague J. Preston
Published: September 2008

The efficiency of small and intermediate-size gas turbine engines can be significantly increased by the use of a primary surface recuperator, which uses waste heat from the exhaust gas to preheat the compressor discharge air before it enters the combustor. The result is lower fuel consumption to reach a particular firing temperature. The construction and operation of a primary surface recuperator present numerous challenges in the area of materials selection. Experiences with stainless steels and nickel-base alloys in construction and application in Solar Turbines’ Mercury 50 gas turbine will be presented, along with the results of extensive laboratory creep and oxidation testing and post-test evaluation. Oxidation testing in humidified air has been carried out on a variety of commercially available stainless steel and nickel-base alloy thin foils considered as materials of construction for primary surface recuperators. Two predominant degradation modes have been identified. The active mode generally depends on the exposure conditions and the alloy composition. Alloys which are rich in iron tend to suffer from accelerated oxidation, while alloys with higher chromium and nickel contents tend to exhibit oxide scale evaporation via the formation of volatile chromium-bearing species. The active mechanism is evident in the oxidation kinetics, the oxide scale morphology and composition, and in observations of compositional changes in the metal alloy substrate.
Lifetime Prediction of Components Including Initiation Phase
Authors: Besel Michael , Brueckner-Foit Angelika
Published: September 2008

The lifetime distribution of a component subjected to fatigue loading is calculated using a micro-mechanics model for crack initiation and a fracture mechanics model for crack growth. These models are implemented in a computer code which uses the local stress field obtained in a Finite Element analysis as input data. Elemental failure probabilities are defined which allow to identify critical regions and are independent of mesh refinement. An example is given to illustrate the capabilities of the code. Special emphasis is put on the effect of the initiation phase on the lifetime distribution.
Swedish Navy YS2000 Visby Class Propulsion System Refinements
Authors: Braccio Kenneth M. , Ranero Joe , Nilsson Peter B. , Olsson Magnus , Slogar Gerrick
Published: September 2008

The YS2000 program is a 73 meter length and 10.5 meter width all composite Corvette class vessel. It displaces 640 metric tons when fully equipped and drafts 2.5 meters. It is to be crewed by 18 officers and 25 enlisted men. It is a CODOG propulsion system supplied by Vericor Power Systems, with two MTU 16V 2000 M90 diesels and four TF50A gas turbine engines. Both the diesels and gas turbines are connected to a pair of MA-107 SBS gearboxes that run two 125 SII KaMeWa waterjets. The Visby is designed to be difficult to detect by enemy using radar, infrared, hydro-acoustic monitoring or any other sensor system. The Visby has been in development In Sweden since 1999. To date, four craft have been constructed and sea trailed out of the five totals. The fifth ship is on schedule to complete construction and sea trials later in the 2006 year. Many refinements to the overall propulsion package and related supporting systems have been incorporated since the first ship “Visby” has been sea trailed and since put in service. This paper will review various areas of the propulsion package, explaining the challenges that had to be overcome. The areas of interest will include: the FADEC digital engine control, the exhaust & inlet systems, the turbine engine and starting system, engine room cooling and turbine engine enclosures. The paper will focus on some of the before and after results and attempts to highlight the specific challenges that had to be overcome.
A Dynamic Model of a Shipboard PEM Fuel Cell Reformer System With an Integrated Gas Turbine
Authors: Miller Steven P. , Heinzel John M. , Kuseian John H. , Hoffman Donald J. , House Edward M. , Nickens Anthony , Tsourapas Vasilis
Published: September 2008

A dynamic model is presented that predicts the transient characteristics of an integrated autothermal fuel reformer and gas turbine engine for extracting a high purity stream of hydrogen from logistical fuels such as F76 marine diesel or JP-5 for use in a shipboard proton exchange membrane (PEM) fuel cell power plant. The model incorporates a water-gas shift reactor for increasing hydrogen yield, and a separation membrane for extracting a pure stream of hydrogen gas from the reformer output. Compressed air supply and energy recovery is achieved by an integrated gas turbine generator. The dynamic model serves as a testing ground for the development of control methodologies and to predict limitations in transient response during electrical load variations.
Marine Gas Turbine Propulsion System Applications
Authors: Bricknell David J.
Published: September 2008

Within the marine world gas turbines operate in niche ship types only, but why is this? This paper considers the ship types that have adopted marine gas turbines and the ship characteristics that determine the choice of the propulsion system and prime mover type. Ship determined characteristics include; speed, power density, general arrangements, operating profile, fuel type, fuel consumption, maintenance opportunity, manpower and others. Gas turbine characteristics derived from their parentage — either aero or industrial — influence the characteristics available from the marine gas turbine. Historical marine applications are reviewed and new marine applications, influenced by developments with new marine gas turbines are considered both in the developed but evolving naval markets and within the growing but focused commercial marine sector. Propulsion system selection is also influenced by the prevailing and emerging propulsion system technologies, particularly with transmission systems which influence the choice of the prime mover, their number and specific power, and their disposition in the ship.
Experimental Characterization of Contact Hysteresis at High Temperatures
Authors: Filippi Sergio , Rodrigues Esequiel B. , Gola Muzio M.
Published: September 2008

The current paper presents a measurement system for the experimental determination of contact hysteresis cycles at temperatures up to 800° C. A test rig was designed to conduct experiments in a wide range of temperatures, with different combinations of normal and tangential load, frequencies and contacting materials. An induction system supplies the heat for measurements of hysteresis cycles at the required temperatures. Measurements show the dependence of the friction coefficient on temperature.
An Experimental Method for the Measurement of Blade-Root Damping
Authors: Allara Marco , Filippi Sergio , Gola Muzio M.
Published: September 2008

Stresses produced by vibrations reduce the life of turbo engine blades. The design of disk assemblies requires the capability to predict their dynamic behavior. In order to achieve this objective, knowledge of damping associated with the contact between blade and disk is fundamental. This paper proposes a technique to measure the influence of blade-disk attachment on the dynamics of turbo engine blades. Moreover, experimental values of damping and resonance frequencies are presented as a function of the amplitudes of vibration and of centrifugal load at the attachment.
A Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals
Authors: Childs Dara W. , Shin Yoon-Shik , Seifert Brent
Published: September 2008

Predictions are presented for hole pattern seals for which the hole depth is varied axially, showing that various depth patterns can significantly improve damping performance in terms of both increasing the seal’s effective damping and reducing its cross-over frequency — the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable hole depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant hole depth (CHD) design, versus predictions of 2.7. The cross over frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor jump phenomena, not flow path divergence. The VHD seal leaks less than a comparable CHD design.
Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical Seal: Part I — Unidirectional Load Tests
Authors: San Andre´s Luis , Delgado Adolfo
Published: September 2008

Squeeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus not generating enough damping capability. Single frequency, unidirectional load tests were conducted on a SFD test rig replicating a commercial jet-engine configuration. The damper journal is 2.54 cm in length and 12.7 cm in diameter, with nominal clearance of 0.127 mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports, and a mechanical seal ring in contact with the damper journal. A wave spring pushes the ring ensuring tight sealing to prevent gas ingestion. The mechanical seal also serves to contain the lubricant within the squeeze film land for extended periods of time and; while in operation, to prevent contamination of the ball bearing cartridge. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and motion amplitude dependent, albeit decreasing rapidly as the motion parameters increase. Identified squeeze film force coefficients, damping and added mass, agree well with predictions based on the full film, short length damper model.
Small Gas Turbine Engine Operating With High-Temperature Foil Bearings
Authors: Heshmat Hooshang , Tomaszewski Michael J. , Walton James F.
Published: September 2008

A 134 Newton thrust class, 120,000 rpm turbojet was redesigned to incorporate a high-temperature compliant foil bearing aft of the turbine rotor and a compliantly mounted ball bearing forward of the centrifugal compressor–cold section. Two rotor-bearing system configurations were evaluated, one for operation above the bending critical speed and one for rigid rotor operation. Required characteristics for the foil bearing and ball bearing equipped with compliant foil damper mount were determined through a series of design tradeoff studies evaluating critical speeds and system stability. Following the design studies, the necessary hardware was fabricated, the engine assembled and operation to full speed achieved. Engine speed, rotor vibrations, compressor discharge pressure, exhaust gas temperature, thrust and fuel consumption were all recorded for both a baseline fluid lubricated ball bearing supported engine and the new turbojet engine using the hybrid foil bearing support system. Issues related to high-speed operation above the bending critical speed are identified and recommendations offered. Engine test data show that approximately 10% less fuel is consumed by the hybrid foil bearing mount system than the baseline conventional design. It is also shown that the foil bearing life was longer than the ball bearing life even though the foil bearing operated in the exhaust gas stream at temperatures exceeding 800°C. The results of this program demonstrate the feasibility of developing a completely oil-free foil bearing gas turbine engine.
Effect of Misalignment on the Characteristics of Journal Bearings
Authors: Ahmed A. M. , El-Shafei A.
Published: September 2008

Due to the renewed interest in the effect of misalignment on the dynamic characteristics of journal bearings, this paper presents a study of the effect of misalignment on the dynamic characteristics of journal bearings. A 2D finite difference program is developed and used for this study. The results show that there are a total of 16 stiffness and 16 damping coefficients considering horizontal and vertical displacements and rotations. The variation of these coefficients with journal tilting (i.e. angular misalignment) is illustrated. It is shown that misalignment can have a significant effect on the bearings’ dynamic characteristics.
Probabilistic Treatment of Crack Nucleation and Growth for Gas Turbine Engine Materials
Authors: Enright M. P. , McClung R. C. , Hudak S. J. , Francis W. L.
Published: September 2008

The empirical models commonly used for probabilistic life prediction do not provide adequate treatment of the physical parameters that characterize fatigue damage development. For these models, probabilistic treatment is limited to statistical analysis of strain-life regression fit parameters. In this paper, a model is proposed for life prediction that is based on separate nucleation and growth phases of total fatigue life. The model was calibrated using existing smooth specimen strain-life data, and has been validated for other geometries. Crack nucleation scatter is estimated based on the variability associated with smooth specimen and fatigue crack growth data, including the influences of correlation among crack nucleation and growth phases. The influences of crack nucleation and growth variability on life and probability of fracture is illustrated for a representative gas turbine engine disk geometry.
Analytical Maps of Aerodynamic Damping as a Function of Operating Condition for a Compressor Profile
Authors: Petrie-Repar Paul J. , McGhee Andrew , Jacobs Peter A. , Gollan Rowan
Published: September 2008

In this paper, analytical maps of aerodynamic damping for a two-dimensional compressor cascade (Standard Configuration 10) are presented. The maps are shown as contour plots of the aerodynamic damping as a function of operating condition. The aerodynamic dampings were calculated by a linearized Navier-Stokes flow solver. The flutter boundaries over a wide range of operating conditions are clearly shown on the damping maps and were found to be strongly dependent on the mode frequency and the mode shape. Extremely low values of negative aerodynamic damping were predicted for some off-design operating conditions where flow separation occurred. A damping map was also constructed based on inviscid flow simulations. There were differences in the viscous and inviscid flutter boundaries particularly at off-design inflow angles. The extremely low values of negative aerodynamic damping were only predicted by the viscous simulations and not the inviscid simulations.
Compressor Rubbing Risk Analyses for Combustion Turbine Using Thermomechanical and Dynamical FE Modeling
Authors: Meissonnier Franck T. , Stoisser Carlo M.
Published: September 2008

Combustion Turbines operators have recently experienced compressor rubbing related problems during Hot Restart transients. Based on maintenance feedback from in-service combustion turbine, some turbo machinery designers have imposed Hot Restart Restriction and have considered prudent to increase the rotor-to-stator clearances. Combustion Turbines operators have recently experienced compressor rubbing related problems during Hot Restart transients. Based on maintenance feedback from in-service combustion turbine, some turbo machinery designers have imposed Hot Restart Restriction and have considered prudent to increase the rotor-to-stator clearances. Hot Restart has a significant impact on compressor clearances since temperature distribution hasn’t reach its steady-state condition due to heat conduction. When Hot-Restart occurs, thermal distortions of the casing and the bladed rotor are indeed continually evolving. The resulting rotor-to-stator clearances may become extremely low while the rotor expands rapidly due to inertial body forces generated by rotor speed up and vibrates due to mass-unbalance. As a consequence, clearances may dramatically decrease until rubbing occurs. A Finite Element-based analysis has been developed for simulating the time-transient thermo mechanical and the vibratory motion responses of a F-Class combustion turbine. The thermo mechanical responses enable to calculate thermal distortions of the casing and the bladed rotor as well as the rotor expansion due to the inertial body forces generated by rotor speed up. The dynamical responses enable to calculate the amplitude of the shaft line vibration due to mass-unbalance. The approach developed by EDF R&D relies on a 3D thermo mechanical modeling of the compressor rotor/casing and a 1D beam-type modeling of the whole combustion turbine shaft line using Finite Element Code Code_Aster® and Rotor Dynamics Code CADYAC, respectively, developed by EDF R&D. The FE-Models have been validated by comparing compressor tip clearance measurements published by a F-Class manufacturer and FE calculations during a typical start-stop cycle. The FE-predictions obtained with such models are in acceptable agreement with measurements data. The FE models are then used to predict the evolution of the rotor-to-stator clearances and to evaluate the compressor rubbing risk during Hot Restart. The results are then compared with Hot Restart time-restriction imposed by the turbo machinery designer.
The Development of Anomaly Distributions for Machined Holes in Aircraft Engine Rotors
Authors: Corran Richard , Gorelik Michael , Lehmann Darryl , Mosset Stephane
Published: September 2008

The Aerospace Industries Association (AIA) Rotor Integrity Sub-Committee (RISC) has proposed an enhanced damage tolerance design strategy for critical rotating parts intended to reduce the rate of uncontained rotor events. Building upon the industry committee’s experience in developing a probabilistic relative risk assessment methodology for hard alpha anomalies in titanium rotors, a similar probabilistic approach has been proposed for induced anomalies along machined hole surfaces in engine rotors. Key inputs to this strategy are the development of a surface anomaly distribution for machined holes and the benchmark of design target risk (DTR). The DTR is an FAA/industry agreed upon design target value of relative risk against which the results of the probabilistic risk assessment are compared.
Probabilistic Flutter Analysis of a Mistuned Bladed Disks
Authors: Kielb Robert E. , Hall Kenneth C. , Hong Esther , Pai Shantaram S.
Published: September 2008

This paper presents the results of a probabilistic flutter study of a mistuned bladed disk using a high fidelity model including both structural and aerodynamic coupling. The approach used in this paper is relatively fast because it does not require any additional information than that required of a tuned flutter analysis, with the exception of the mistuned blade frequencies. The case study shows that the stability of the fleet can be significantly affected by the standard deviation of blade frequencies and the pattern in which they are arranged in the wheel. A method for understanding and identifying the beneficial patterns is presented.
Design of a Highly Offset Pipe-to-Annular Flow Inlet
Authors: Zausner Jack
Published: September 2008

Conceptual design and CFD analysis of an inlet to a compressor is undertaken. In this design the inlet transitions pipe flow to annular flow and provides for a mechanical device to be mounted in centerline and in front of the compressor. The solution to this constraint along with the constraints of uniform outlet flow and low weight, size, and total pressure drop consists of: a highly offset transition region, where pipe flow is transitioned into annular flow, and a nozzle region, with the goal of delivering uniform flow to the compressor at minimal pressure drop. The design approach consists of utilizing CFD to guide the overall shape of the inlet toward desirable regions of the design space, then examining specific parameters and optimizing these to meet the constraints. A final analytical inlet design, optimized in the regions of interest, is selected for experimental work.
A Virtual Tool for Prediction of Turbocharger Nonlinear Dynamic Response: Validation Against Test Data
Authors: San Andres Luis , Rivadeneira Juan Carlos , Gjika Kostandin , Groves Christopher , LaRue Gerry
Published: September 2008

Advances on the modeling of nonlinear rotor-bearing models for prediction of the dynamic shaft response of automotive turbochargers (TCs) supported on floating ring bearings (FRBs) are presented. Comprehensive test data for a TC unit operating to a top speed of 65 krpm serves to validate the model predictions. The static forced performance of the support FRBs considers lubricant thermal effects, thermal expansion of the shaft and bearings, and entrance pressure losses due to centrifugal flow effects. The bearing analysis also yields linearized rotordynamic force coefficients for the inner and outer lubricant films. These coefficients are used with the rotor model to predict the synchronous response to imbalance and the system natural frequencies and stability. A method renders an accurate estimation of the test rotor imbalance by using the actual vibration measurements and influence coefficients derived from predictions using linearized bearing force coefficients. Predicted ring rotational speeds, operating radial clearances and lubricant viscosities for the inner and outer films are the main input to the nonlinear time transient analysis. The nonlinear response model predicts the total shaft motion, with FFTs showing the synchronous response, and amplitudes and whirl frequencies of subsynchronous motions. The predicted synchronous amplitudes are in good agreement with the measurements, in particular at high shaft speeds. The nonlinear analysis predicts multiple frequency subsynchronous motions for speeds ranging from 10 krpm to 55 krpm (maximum speed 70 krpm), with amplitudes and frequencies that correlate well with the test data. The comparisons validate the comprehensive rotor-bearings model whose ultimate aim is to save TC design time and accelerate product development.
Numerical Investigation of the Effect of Tip Clearance to the Performance of a Small Centrifugal Compressor
Authors: Tang Jin , Turunen-Saaresti Teemu , Reunanen Arttu , Honkatukia Juha , Larjola Jaakko
Published: September 2008

Numerical analysis is conducted for the 3-dimensional impeller and vaneless diffuser of a small centrifugal compressor. The influence of impeller tip clearance is investigated. A Navier-Stokes flow solver Finflo has been applied for the simulation. A practical real gas model has been generated for the calculation. Simulations with different sizes of tip clearance at different mass flow rates have been made. The results are compared to experimental results at a certain tip clearance and one operating point. Reasonable agreement has been obtained. The ideal gas model has also been applied to compare with the real gas model. The numerical results show that tip clearance has a significant effect on the performance of a small centrifugal compressor. As the size of tip clearance increases, both the pressure ratio and the efficiency decrease. The decreasing rate of efficiency is higher at higher mass flow rates and lower at lower mass flow rates. The input power of the compressor hardly changes with different sizes of tip clearance, but increases as the mass flow rate increases. The incidence of impeller and flow angle at the exit of the impeller increase as the size of tip clearance increases. Correlations of the size of tip clearance with the efficiency drop and change of flow angle at the exit of impeller are given. The detailed flow distribution shows that as the size of tip clearance increases, the tangential leaking flow at the tip clearance makes the low velocity flow region grow larger and move from the suction-shroud corner to the center of the flow channel. The main flow at the pressure side is compressed and accelerated. Therefore the uniformity of the flow in the whole channel decreases. The detailed flow distribution also shows that the leaking flow is stronger at higher mass flow rates.
Development and Testing of a Low Power Gas Turbine Alternator: The ACL-GTA
Authors: Timbrell Ian , Thouvenot Jean-Luc , Poumare`de Vincent , McCallum Neil
Published: September 2008

In 2000 the UK Ministry of Defence (MoD) placed a contract on Turbomeca Limited to develop a 1.8 MW advanced cycle gas turbine alternator that could compete directly with comparable diesel generators in terms of performance and cost. The Advanced Cycle Low power Gas Turbine Alternator (ACL GTA) has been designed with simplicity in mind and utilises a revolutionary high-speed alternator and heat recuperator to realise the project aspirations. Development and evaluation testing commenced on this engine in 2004 at Turbomeca’s facility in Pau. This paper will provide a brief overview of the design of the complete gas turbine alternator concentrating on innovative characteristics. It will then continue by presenting in detail the component testing and data obtained followed by system testing results of the gas turbine and gas turbine alternator. Conclusions will be drawn detailing the benefits and suitability of this novel gas turbine alternator within modern Naval platforms and some comparisons with in-service diesel generators.
Use of Restoring Moment on Main Shaft Thrust Bearings for Turboprop Engines With High Predicted Values of Misalignment
Authors: Castillo Javier , Cristobal Erlantz , Lang Robin
Published: September 2008

During the optimization of the TP400D6 turboprop engine (powering A400M military transport aircraft), the mechanical design of the main thrust bearing has proven to be one of the most challenging topics. Main problem of this bearing has been the high misalignment values combined with the high axial load (over 17000 lbs) to which it has been designed. The scope of this paper is to go through the details of the aforementioned misalignment problem focusing on the adopted solution. This is based on deeper understanding of the internal bearing kinematics and the application of the restoring moments in mechanical calculations during the design stage. The restoring moment is the reaction force due to the change in operation contact angle because of the increase in contact pressure of the balls onto the races under a high relative rotation of the inner with respect to the outer race. It is therefore translated into a rotational stiffness function, dependant on the thrust force and misalignment. Although normally the rotational stiffness is not considered in aero engines application since values are not significant due to low value of misalignment, when misalignment is high, restoring moments together with the dependency on the flight thrust condition, must be considered as a mean of improving the analytical model predictions.
Numerical and Experimental Damping Assessment of a Thin-Walled Friction Damper in the Rotating Set-Up With High Pressure Turbine Blades
Authors: Szwedowicz J. , Gibert C. , Sommer T. P. , Kellerer R.
Published: September 2008

Under-platform friction dampers are preferably solutions for minimizing vibrations of rotating turbine blades. Solid dampers, characterized by their compact dimensions, are frequently used in real applications and often appear in patents in different forms. A different type of the friction damper is a thin-walled structure, which has larger dimensions and smaller contact stresses on a wider contact area in relation to the solid damper. The damping performance of a thin-walled damper, mounted under the platforms of two rotating, freestanding high pressure turbine blades is investigated numerically and experimentally in this paper. The tangential and normal contact stiffness, that are crucial parameters in optimal design of each friction damper, are determined from three-dimensional finite element (FE) computations of the contact behaviour of the thin-walled damper on the platform including friction and centrifugal effects. The computed contact stiffness values are applied to non-linear dynamic simulations of the analysed blades with the friction damper of a specified mass. These numerical analyses are performed in the modal frequency domain with a code, which is based on the Harmonic Balance Method (HBM) for the complex linearisation of friction forces. The blade vibrations are characterised by a set of the lowest FE mode shapes of one freestanding blade without damper. The dynamic results of the calculated blades with the damper are in good agreement with the measured data of the real mistuned system. In the analysed excitation range, the numerical performance curve of the thin-walled damper is obtained within the scatter band of the experimental results. For the known friction coefficients and available FE and HBM tools, the described numerical process confirms its usability in the design of under-platform dampers.
Numerical and Experimental Study of Ventilation for Gas Turbine Package Enclosure
Authors: Vahidi Daniel , Bagheri Hamid , Glezer Boris
Published: September 2008

The presented paper provides details of the enclosure design validation practice that combines a CFD and experimental study using an engine enclosure subscale model. The main features from the actual engine package were included in geometrically similar experimental model and represented in detail in the CFD model. Performance of ventilation was studied for both cold and heated engine surfaces. A number of experimental techniques, including flow visualization, flow-velocity, temperature measurements, and infrared thermal imaging have been applied in the study. A potential methane leakage was emulated with CO2 and was combined with CO2 sampling and concentration measurements in various locations within the enclosure. Numerical predictions were then compared to experimental data allowing to fine tune the model and applied boundary conditions. Based on presented study certain improvements in design of the enclosure were recommended and described in the paper.
A New Foil Gas Bearing With Compression Springs as Compliant Structure for Microturbomachinery Applications
Authors: Song Ju-Ho , Kim Daejong
Published: September 2008

A new foil gas bearing is introduced in this paper. This foil gas bearing uses series of compression springs as a compliant structure instead of expensive corrugated bump foils. The new foil gas bearing is very simple in structure and easy to manufacture. A theoretical model to estimate stiffness and damping of the spring bump was developed. Measured stiffnesses of individual spring bump agree well with predictions. Load capacity was measured up to 62.5 N at 20,000rpm with both cooled and uncooled bearings. Initial selection of spring geometry rendered rather soft supports compared to other bump foil bearings, and allowed only limited load during the test. Developed cooling method using direct air supply holes machined on the bearing sleeve was very effective to cool the test bearing because the spring bumps are not connected along the circumferential direction, and allow very effective circumferential distribution of cooling air. A series of orbit simulation was performed to estimate critical speed and onset speed of instability. Bump dynamics was directly coupled with the orbit simulation. Critical speed was estimated at around 7500 rpm due to relatively soft support structure. Hydrodynamic instability with WFR 0.5 could be predicted at around 15,000 rpm. The rotor instability is predicted even under the equivalent viscous damping extracted from bump dynamics, implying the viscous damping alone within the bump cannot suppress hydrodynamic instability of foil bearings.
Traction Characteristics of a Rolling Element Bearing Under Rapid Acceleration and Implications for Auxiliary Operation in Magnetic Bearing Systems
Authors: Cole Matthew O. T. , Wongratanaphisan Theeraphong
Published: September 2008

The application of rolling element bearings for auxiliary operation in magnetic bearing systems is quite common, yet such operation is very different to that for which standard bearings are designed. During initial touchdown of a spinning rotor with an auxiliary bearing, rapid acceleration of the bearing inner race results in large inertial and friction forces acting on the rolling elements. Complex dynamic behavior of the bearing assembly and resulting traction forces are difficult to predict but, nonetheless, have important implications for both rotor dynamic behavior and thermo-elastic behavior of the bearing components. The aim of this work is to obtain an insight into bearing behavior by analyzing component interaction forces that would arise based on the assumption that the overall bearing traction torque is dependent only on instantaneous load, speed and acceleration. How such an analysis can be verified by experimental measurements of traction during rapid acceleration is discussed and some initial experimental results are presented. The implications for modeling and prediction of rotor-magnetic bearing system behavior during touchdown are also discussed.
Development of a Design Methodology for Ducted Fan Systems Used in Micro Unmanned Air Vehicle Propulsion
Authors: Engeda Abraham
Published: September 2008

This paper presents an aerodynamic loss prediction and design methodology that has been developed for ducted-fan system of a vertical takeoff and landing Micro Unmanned Air Vehicle (Micro UAV). The method is based on a parametric geometry model and semi-empirical aerodynamic methods. The developed loss correlation method was applied to an initial sizing attempt of a ducted fan system.
A Revised Compressor Polytropic Performance Analysis
Authors: Hundseid O̸yvind , Bakken Lars E. , Helde Tor
Published: September 2008

The compressor polytropic head and efficiency analysis are based on the assumption that the compression process follows the path of a constant polytropic exponent n. Both the ASME PTC10-97 and the ISO 5389 refer to the polytropic analysis by John M. Schultz. The procedure utilizes a head correction factor and two compressibility functions to obtain a solution of the integral Δhp = ∫vdp. Present computer technology renders possible a direct integration of the compression path where the variation in actual gas properties along the path is included. This method eliminates the averaging of gas properties which the Schultz procedure includes. This paper reports deviation in compressor performance using the Schultz procedure with different average gas properties. The implementation of a direct integration procedure, employing actual gas properties from the new GERG-2004 equation of state, is given. The GERG-2004 equation of state has proven to give accurate density values both in the vapour and liquid phases. Depending on how the polytropic compression analysis is implemented, the work has revealed up to 4% deviation in polytropic head and efficiency for some specific compressors. This adds an extra uncertainty in compressor performance verification. Even though the API 617 allows up to 4% deviation, some compressors have to meet a more stringent demand, for instance 2% at the Sno̸hvit LNG plant. Future challenges within oil and natural gas production are related to wet gas compressors. The present paper points out the advantages in using a direct integration method for wet gas performance predictions as this takes phase changes along the compression path into account.
Technology Insertion in the U.S. Navy
Authors: Quin˜ones Martin , Fauvell Kevin
Published: September 2008

With a new perspective on how to conduct business through acquisition reform, the Navy faces infrastructure challenges that are not necessarily in sync with acquisition principles. Historically, the U.S. Navy (Navy hereinafter) has always spearheaded the means of developing design for form, fit, and function of Navy machinery. This leadership role has its roots on the unique requirements that the U.S. Navy has to fulfill its mission. Unfortunately, this process does not always prove to be cost effective since its implementation normally carries heavy restrictions, unique applications, and little competition. This is commonplace for most technology insertion efforts into Navy Ships.
Comparison of Transient Modeling Techniques for a Micro Turbine Engine
Authors: Davison Craig R. , Birk A. M.
Published: September 2008

A large number of papers have been published on transient modeling of large industrial and military gas turbines. Few, however, have examined micro turbines. The decrease in size affects the relative rates of change of shaft speed, gas dynamics and heat soak. This paper compares the modeled transient effects of a micro turbojet engine comprised of a single stage of radial compression and a single stage of axial expansion, with a diameter of 12cm. The model was validated with experimental data. Several forms of the model were produced starting with the shaft and fuel transients. Conservation of mass, and then energy, was subsequently added for the compressor, combustor and turbine, and a large inlet plenum that was part of the experimental apparatus. Heat soak to the engine body was incorporated into both the shaft and energy models. Heat soak was considered in the compressor, combustor and turbine. Since the engine diameter appears in the differential equations to different powers, the relative rates of change vary with diameter. The rate of change of shaft speed is very strongly influenced. The responses of the different transient effects are compared. The relative solution times are also discussed, since the relative size of the required time steps changes when compared to a large engine.
Impact of Manufacturing Variability on Combustor Liner Durability
Authors: Bradshaw Sean D. , Waitz Ian A.
Published: September 2008

This paper presents a probabilistic model that quantifies the impact of manufacturing variability on combustor liner temperature and low cycle fatigue life. This model is applied to a gas turbine engine combustor for a commercial aircraft and assessed using combustor liner wall temperature and outlet gas temperature measurements. A probabilistic analysis shows that the model estimates cup-to-cup outlet temperature variations and liner wall temperature variations consistent with these measurements. Furthermore, this analysis shows that the typical liner life is 25 percent less than the life estimated using deterministic methods. In addition, approximately 99 percent of the combustors designed using deterministic methods will fail earlier than predicted. A sensitivity analysis shows that the variability in combustor unmixedness is the key driver of liner life.
Neural Network Models for Usage Based Remaining Life Computation
Authors: Parthasarathy Girija , Menon Sunil , Richardson Kurt , Jameel Ahsan , McNamee Dawn , Desper Tori , Gorelik Michael , Hickenbottom Chris
Published: September 2008

In engine structural life computations, it is common practice to assign a life of certain number of start-stop cycles based on a standard flight or mission. This is done during design through detailed calculations of stresses and temperatures for a standard flight, and the use of material property and failure models. The limitation of the design phase stress and temperature calculations is that they cannot take into account actual operating temperatures and stresses. This limitation results in either very conservative life estimates and subsequent wastage of good components, or in catastrophic damage because of highly aggressive operational conditions which were not accounted for in design. In order to improve significantly the accuracy of the life prediction, the component temperatures and stresses need to be computed for actual operating conditions. However, thermal and stress models are very detailed and complex, and it could take on the order of a few hours to complete a stress and temperature simulation of critical components for a flight. The objective of this work is to develop dynamic neural network models, that would enable us to compute the stresses and temperatures at critical locations, in orders of magnitude less computation time than required by more detailed thermal and stress models. This work expands on the work done previously [1] where a linear system identification approach was developed. The current paper describes the development of a neural network model and the temperature results achieved in comparison with the original models for Honeywell turbine and compressor components. Given certain inputs such as engine speed and gas temperatures for the flight, the models compute the component critical location temperatures for the same flight in a very small fraction of time it would take the original thermal model to compute.
Reconstruction of the Control Systems of 6MW Turbosets in Compressor Stations Kralice and Kourim
Authors: Kyncl Jiri , Patocka Jindrich
Published: September 2008

The RWE Transgas, a.s., was challenged with the reconstruction of the control system of 6 MW turbosets installed in compressor stations Kralice and Kourim (Czech Republic) in late 1970’s. The control of the turbosets was formerly performed by the compressor station personnel by means of a relay-based control system. The reconstruction has been completed in 2004. In this contribution, some new functions of the modified control system are analyzed in greater detail with special emphasis on the surge identification and protection.
Structural Synthesis and Enumeration of Epicyclic Gear Mechanisms Up to 12-Links Using Acyclic Graph Method
Authors: El-Gayyar M. S. , El-Eashy H. M. , Zaki M.
Published: September 2008

In this paper, a new approach for graphical enumeration of epicyclic gear mechanisms is presented using the concept of acyclic graph. A new graphical code has been introduced to specify the priorities of all vertices of associated displacement graph. This graphical code is used to identify open graph, redundant links and isomorphic graphs. A computer program has been developed for automatic enumeration of displacement graphs as well as automatic detection of isomorphic graphs and open graphs and graphs with a redundant link without using adjacency matrices. This simplified methodology has been applied for the enumeration of epicyclic gear mechanisms with up to 12-links having up to 9 coaxial links. An atlas for 11 and 12-link mechanisms has been constructed using the proposed methodology.
The Lomakin Effect in Annular Gas Seals Under Choked Flow Conditions
Authors: Arghir Mihai , Defaye Cyril , Freˆne Jean
Published: September 2008

The paper deals with the static stability of annular gas seals under choked flow conditions. For a centered straight annular seal choking can occur only in the exit section because the gas is constantly accelerated by friction forces. From the mathematical standpoint, the flow choking corresponds to a singularity that was never dealt with numerically. The present work introduces an original numerical treatment of this singularity that is validated by comparisons with the analytical solution for planar channel flow. An interesting observation stemming from these results is that the usual hypothesis of considering the flow as being isothermal is not correct anymore for a gas accelerated by a pressure gradient; the characteristics of the flow are the same but the quantitative results are different. The analysis of eccentric annular seals then shows that choked flow conditions produce a change in the static stiffness. For a subsonic exit section the Lomakin effect is represented by a centering radial force opposed to the rotor displacement. For a choked exit section the radial force stemming from an eccentricity perturbation has the same direction as the rotor displacement. The annular seal becomes then statically unstable. From the physical standpoint this behaviour is explained by the modification of the Lomakin effect that changes sign. The pressure and Mach number variations along the seal depict the influence of high compressible flow regimes on the Lomakin effect. This characteristic has never been depicted before.
“SMART ENGINE”: A Gas Turbine Fault Diagnostics and Life Management Tool
Authors: Sampath Suresh , Marinai Luca , Singh Riti , Gulati Ankush
Published: September 2008

Given the maturity of the gas turbine user industry, and the quality of the original equipment manufactured, the field experience of these machines has been broadly very good. Nonetheless, there can be difficulties in managing availability and reliability, and the costs of unscheduled shut downs can be extremely large. Advanced gas turbine performance management offers opportunities in improving availability, reliability and productivity, driving down life cycle costs as well as adding to safety and compliance. This paper describes in detail the development of an engine fault diagnostics tool by the authors. The authors focus on structure, functionality as well as possible benefits of its use. The first part describes the structure and various methodologies adopted in the development of the system and the second part of the work describes the system and its salient features. The primary goal at this point of time was to test the utility, functionality and robustness of the presented tool, interesting and relevant results are obtained. Due to space limitations we restrict ourselves to discussing the system and not go into the details of actual simulation runs.
Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions
Authors: San Andre´s Luis , Rubio Dario , Kim Tae Ho
Published: September 2008

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e. simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10 mm. Coast down rotor responses from 25 krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5 krpm to 15 krpm with a whirl frequency at ∼ 50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5 krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Post-test inspection reveal wear spots on the top foils and rotor surface.