bluuebunny/crossref_metadata_2025 huggingface dataset:
Active Suppression of Cascade Flutter With Piezoelectric Device
Authors: Kazawa Junichi , Watanabe Toshinori
Published: September 2008

Possibility of active control on cascade flutter with piezoelectric device was both experimentally and numerically studied under a subsonic condition. A blade on which a piezoelectric device was glued was installed in the test cascade. When AC voltage was provided on the device, the blade could be actively oscillated. The unsteady aerodynamic work induced by the active oscillation was measured on the cascade blades. From the results, the active oscillation of the piezo-blade was found to generate sufficiently large unsteady aerodynamic work for changing instability of blade vibration. The active control was effective for flutter suppression if the phase difference between the unstable blade vibration and the active oscillation was adequately selected. The numerical results also showed effectiveness of the piezoelectric device, and the active oscillation was observed to change the unsteady aerodynamic work distribution on blade surfaces, which change should cause the stabilization effect. By a developed numerical method with flow-structure coupling, a suppression method for instability with a control rule was tested numerically to confirm its effectiveness.
Effect of Bleed Flows on Flutter and Forced Response of Core Compressors
Authors: di Mare Luca , Simpson George , Mueck Bernhard , Sayma Abdulnaser I.
Published: September 2008

This paper presents a methodology for the modeling of flutter and forced response in axial compressors while taking into account the effect of bleed off-takes. Usually, aeroelasticity analyses are performed assuming smooth solid end walls. This type of analysis has two main shortcomings. Firstly, it does not account for the change in the aerodynamic speed of the stages downstream of the bleed off-take, so that aeroelasticity analyses are not performed at the correct aerodynamic conditions. Secondly, bleed off-takes influence the flow pattern particularly in the stages around or close to the bleed off-take, thus leading to possibility of obtaining the wrong aeroelastic response. Another objective of this paper is to present a methodology for the accurate prediction of the flow in a compressor with bleed off-take, by both including the geometry of the bleed off-take and performing the calculations on the entire compressor, thus eliminating errors resulting from prescribing boundary conditions at inter-blade row boundaries. It is concluded that bleed off-takes could influence significantly the aeroelastic response of the blades.
Fan Forced Response Due to Ground Vortex Ingestion
Authors: di Mare Luca , Simpson George , Sayma Abdulnaser I.
Published: September 2008

This paper presents a computational study of the formation and ingestion of ground vortices and resulting fan forced response levels in a large turbofan operating near the ground. The model is based on an integrated aeroelasticity numerical method; the aerodynamic part is based on a 3D unstructured Reynolds-Averaged Naveir-Stokes solver. The mechanical model uses linear modal model for the structure, allowing for the direct computation of the structural response during the unsteady simulations. The analysis shows that under certain fan speed and mass flow rate conditions, for a given fan and intake combination, situated at a fixed distance from the ground, an inlet vortex can form near the ground. This inlet vortex is drawn into the intake causing inlet distortions that could excite several low engine order harmonics of the fan. Predictions are compared with measured data showing good agreement in general. Ability to predict the level of response at the design stage allows for implementing design solutions preventing possible failure due to high cycle fatigue.
Development, Testing, and Qualification of the Marine LM6000 Gas Turbine
Authors: Sidenstick David , McAndrews Glenn , Tanwar Ravi , Farley Scott
Published: September 2008

In 1990, GE announced it would begin development of the first-ever gas turbine with output greater than 40MW and a thermal efficiency above 40%. It was designated the LM6000, and was first introduced as the -PA model in December 1992. This turbine used a single annular combustion system with relatively few changes from the successful aircraft engine — the CF6-80C2. At the same time, GE began development of Dry Low Emissions (DLE) combustion technologies, culminating in the LM6000-PB model being introduced in December 1994. As the LM6000 fleet approached the 1 million-hour point, with an installed base of over 100 units, the next step — the development of a turbine with greater power and efficiency — was initiated, creating the LM6000-PC and -PD models. The launch of GE’s LM6000-PC/PD aero-derivative gas turbine was announced in 1996 and the first unit went into commercial operation in a power generation application in late 1997. The mechanical drive version of this gas turbine has been available as a product since early 1998. This machine opens an entirely new market segment, with interest being paced by the development of this segment requiring variable speed drivers with outputs greater than 50,000 shaft horsepower. Although some exploratory interest for mechanical drive applications was generated when the product was first announced, significantly greater interest within both gas pumping, and marine applications has been expressed recently especially considering changes in the global environmental regulations, energy prices, larger ships moving at greater speeds. Typical applications are new designs of large oil and gas production facilities — for gas pumping, processing, and natural gas liquefaction, as well as large marine and naval applications requiring high power-weight densities. GE is currently supporting several ongoing application studies using the LM6000 gas turbine as the driver of choice. This document provides the highlights of the development, testing and qualification of the LM6000 by General Electric as well as the certification program by the American Bureau of Shipping (ABS). Notable engineering accomplishments during this development include part power NOX abatement, auto-throttles, and cubic loading using a generator.
Gas Turbine Propulsion for LNG Transports
Authors: Ellington Louis , McAndrews Glenn , Harsema-Mensonides Alexander , Tanwar Ravi
Published: September 2008

GE aero-derivative gas turbines were first introduced into marine operations during the late 1960’s and early 1970’s. GE is now leveraging its many years of proven marine experience and offshore dual-fuel experience to offer dual-fuel gas turbines for LNG Carrier (LNGC) propulsion and electric power. With building of new larger LNGC’s now beginning, the industry is seriously considering a change to gas turbine based systems in order to capitalize on their many advantages. CoGES (combined gas turbine — steam generator electric) plants for LNGC’s consist of dual-fueled gas-turbine-generator (GTG) set(s) and auxiliaries, heatrecovery steam generator (HSRG), a steam-turbine-generator set, feed-water, steam and condensate systems. Leveraging cruise-ship reliability programs, the GTG instrumentation and control systems are single-point fault tolerant. Gas turbine power plants offer many additional advantages, including but not limited to: Use of boil-off gas as a cost-effective and environmentally friendly fuel (slow speed diesel ships require complex on-board reliquifaction of boil-off gas). When installed on deck, CoGES plants provide high power-volume density that translates into increased cargo revenue and deferred capital cost. Gas turbines ease of maintenance and quick changeout. Developed to meet the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC) and classification society standards for marine applications, GE’s 2 X LM2500 CoGES plant is a very simple and reliable solution. Dry-run capable HRSG’s are used in lieu of exhaust damper and by-pass systems. Outage of any one prime mover leaves the plant with nominally 50% power remaining. Common spares are inherent. Established as having an equivalent level of safety as traditional LNGC propulsion systems via FMECA type studies, the 2 x dual-fueled LM2500 CoGES plant has been “Approved in Principle” by Class for use on LNG Carriers. Alternatively, GE’s 1 X dual-fueled LM6000 or 1 X LM2500+/G4 CoGES plant addresses capital & operating cost pressures via reduced equipment costs and improved fuel economy. Redundancy and simplicity are achieved via a dry-run capable HRSG and an STG, combined with auxiliary diesel generator sets. Both the LM2500 family and LM6000 CoGES plants offer viable alternatives to traditional steam turbine and slow-speed-diesel propulsion. Gas-fuel, liquid-fuel, and bi-fuel operation provide flexibility and redundancy to ship owners who must safely and reliably deliver cargo at the lowest possible cost per MMBTU throughout a fleet life cycle.
A Design to Increase the Static Stiffness of Hole Pattern Stator Gas Seals
Authors: Childs Dara W. , Shin Yoon-Shik , Wade John
Published: September 2008

An analysis is presented which shows that a deep groove located at about 60% along the axial length from the inlet will approximately double the static stiffness of a hole-pattern-stator, annular gas seal. Test results for a seal using this geometry generally confirm the correctness of this prediction. The groove also produces an increase in leakage by about 4% and a modest decrease in effective damping.
Application of Nonparametric Methods to Rainflow Stress Density Estimation of Gas Turbine Engine Usage
Authors: Enright M. P. , McClung R. C. , Hudak S. J. , Millwater H. R.
Published: September 2008

The risk of fracture associated with high energy rotating components in aircraft gas turbine engines can be sensitive to small changes in applied stress values which are often difficult to measure and predict. Although a parametric approach is often used to characterize random variables, it is difficult to apply to multimodal densities. Nonparametric methods provide a direct fit to the data, and can be used to estimate the multimodal densities often associated with rainflow stress data. In this paper, a comparison of parametric and nonparametric methods is presented for density estimation of rainflow stress profiles associated with military aircraft gas turbine engine usages. A nonparametric adaptive kernel density estimator algorithm is illustrated for standard parametric probability density functions and for rainflow stress pairs associated with F-16/F100 engine usages. The kernel estimates are compared to parametric estimates, including a hybrid approach based on separate treatment of maximum stress pairs. The results provide some insight regarding the strengths and weaknesses of parametric and nonparametric density estimation methods for gas turbine engines, and can be used to develop improved stress estimates for probabilistic life predictions.
Forced Response of Bladed Disks in Cyclic Symmetry With Underplatform Dampers
Authors: Zucca Stefano , Borrajo Juan , Gola Muzio M.
Published: September 2008

In this paper a methodology for forced response calculation of bladed disks with underplatform dampers is described. The FE disk model, supposed to be cyclically symmetric, is reduced by means of Component Mode Synthesis and then DOFs lying at interfaces are further reduced by means of interface modes. Underplatform dampers are modeled as rigid bodies translating both in the radial and in the tangential direction of the engine. Contacts between blade platforms and damper are simulated by means of contact elements characterized by both tangential and normal contact stiffness, allowing partial separation of contact surfaces. Differential equilibrium equations are turned in non-linear algebraic equations by means of the Harmonic Balance Method (HBM). The methodology is implemented in a numerical code for forced response calculation of frictionally damped bladed disks. Numerical calculations are performed to evaluate the effectiveness of both the reduced order model and the underplatform model in simulating the dynamic behavior of bladed disks in presence of underplatform dampers.
On the Development of an Oil-Free Electric Turbocharger for Fuel Cells
Authors: Walton James F. , Tomaszewski Michael J. , Heshmat Crystal A. , Heshmat Hooshang
Published: September 2008

Proton Exchange Membrane, fuel cells intended for automotive applications require widely varying flows of contaminant free air for high efficiency and successful longterm operation. One machine being considered for this application is the oil-free electric turbocharger, which combines a centrifugal compressor, radial inflow turbine, permanent magnet electric motor and air lubricated compliant foil bearings. In this paper the results of a preliminary system design study integrating a motor, foil bearings and aerodynamic wheels, as well as performance testing of a crucial element, the compliant foil thrust bearing, are presented. Several different thrust bearings were tested in sizes suitable for operation to speeds over 250,000 rpm and operating thrust loads greater than 98 Newtons. Additional tradeoff studies are presented for a preliminary design of 12 kW permanent magnet motor driven, 120,000 rpm motorized turbocompressor operating above its bending critical speed.
Resolving Landing Craft Air Cushion Main Engine Starter Valve Corrosion Issues
Authors: Hampshire James D. , Myers Lee
Published: September 2008

The Navy’s Landing Craft Air Cushion (LCAC) hovercraft vehicles use two Auxiliary Power Units (APUs) to provide bleed air to start the main propulsion TF40B or ETF40B engines. Each main propulsion engine is assigned a normally closed starter shutoff valve to permit APU bleed air to pass to the main propulsion engine air starters. These starter shutoff valves are seizing due to corrosion and prohibit airflow needed to start the main engines. This paper will describe the planned study to identify and resolve starter shutoff valve failures.
High-Pressure Pocket Damper Seals: Leakage Rates and Cavity Pressures
Authors: Gamal Ahmed M. , Ertas Bugra H. , Vance John M.
Published: September 2008

The turbomachinery component of interest in this paper, the pocket damper seal, has the dual purpose of limiting leakage and providing an additional source of damping at the seal location. The rotordynamic coefficients of these seals (primarily the direct stiffness and damping) are highly dependent on the leakage rates through the seals and the pressures in the seals’ cavities. This paper presents both numerical predictions and experimentally obtained results for the leakage and the cavity pressures of pocket damper seals operating at high pressures. The seals were tested with air, at pressures up to 1000 Psi (6.92 MPa), as the working fluid. Earlier flow-prediction models were modified and used to obtain theoretical reference values for both mass flow-rates and pressures. Leakage and static pressure measurements on straight-through and diverging-clearance configurations of eight-bladed and twelve-bladed seals were used for code validation and for calculation of seal discharge coefficients. Higher than expected leakage rates were measured in the case of the twelve-bladed seal, while the leakage rates for the eight-bladed seals were predicted with reasonable accuracy. Differences in the axial pitch lengths of the cavities and the blade profiles of the seals are used to explain the discrepancy in the case of the twelve-bladed seal. The analysis code used also predicted the static cavity pressures reasonably well. Tests conducted on a six-bladed pocket damper seal to further investigate the effect of blade profile supported the results of the eight-bladed and twelve-bladed seal tests and matched theoretical predictions with satisfactory accuracy.
The Method of Accounting for Loading Cycle Asymmetry in Gas Turbine Engine Components’ Cyclic Durability Analysis
Authors: Muratov R. H.
Published: September 2008

The proposed method has been demonstrated on the universal slopes equation (Manson 1965) and the modified universal slopes equation (Muralidharan & Manson 1998). New equations take into account independence of the transient strain range from the cycle mean stress, define more precisely the impact of the cycle mean stress upon the durability, take into account the impact of cycle mean strain plastic component upon the durability. The resulted equations have been validated with finite element analyses of smooth samples and full-scale parts, for which the results of cyclic tests in the conditions of asymmetric loading are available. The analyses have been performed employing an elastic-plastic approach using cyclic strain curves taken from original durability equations. The use of new equations ensured a good match between design and experimental durability values. Also, the new equations were used to plot Smith and Hay diagrams for low, mean and high durability. The resulted analytical diagrams represent a high quality illustration of the experimental diagrams found in the publications. The presented approach to the accounting for cycle mean stress and strain will also apply when using experimental cyclic durability curves specific for the material.
Electric Start and Generation Systems for Gas Turbines: A Means to Self Sustainability
Authors: Timbrell Ian , Mason Steve , Green Alan , McCallum Neil
Published: September 2008

Following the design shift in Naval ship architecture from conventional mechanical through hybrid to Integrated Electric Propulsion (IEP), the starting philosophy of prime movers needs to be rationalised so as to interact and augment the propulsion configuration and electrical distribution whilst remaining cost effective. To fulfil this requirement the UK Ministry of Defence contracted Ultra Electronics (PMES) to work in partnership to develop and demonstrate a gas turbine Electric Start and Generation System (ESGS). The undertaken programme is to demonstrate full control over the gas turbine starting system and associated maintenance features together with generating sufficient electrical power that can be used to supply all the gas turbine alternator auxiliaries. This paper will give an overview of such requirements together with the design of the basic system and the challenges to ‘navalise’ such a product and install it on a marine gas turbine. The paper will continue by reviewing data obtained from factory acceptance testing and on-engine testing with the Marine Trent MT-30. It is hoped to further compare and analyse these results with future planned testing scheduled in late 2005. Conclusions will be drawn from the initial results, the design of the proposed ESGS system and comparisons with existing in-service gas turbine start systems.
Model Reduction of Large Rotor-Bearing-Foundation Systems
Authors: Zhang N. , Hu W. , Hahn E. J.
Published: September 2008

Finite element models of mechanical or structural systems contain too many degrees of freedom (dofs) for dynamic analysis, particularly if the system is nonlinear. This paper presents an investigation on the performance of nonlinear rotor-bearing-foundation systems with reduced rotor models obtained by the Guyan and the mode superposition methods. A simple unbalanced rotor-bearing-foundation system wherein the rotor is supported via four hydrodynamic journal bearings; i.e. a nonlinear statically indeterminate system, was selected for numerical evaluation purposes. The steady state responses obtained using the reduced rotor models were compared with the responses of the original unreduced system. The results show that whereas the Guyan rotor model provides good accuracy in low frequency range, the mode superposition rotor model is capable of good accuracy in the high frequency range as well. It is concluded that the mode superposition method is preferable to the Guyan reduction method for mechanical systems, such as turbo generator units, that operate over a wide speed range.
Forced Response Variation of Aerodynamically and Structurally Mistuned Turbo-Machinery Rotors
Authors: Sladojevic´ I. , Petrov E. P. , Imregun M. , Sayma A. I.
Published: September 2008

The paper presents the results of a study looking into changes in the forced response levels of bladed disc assemblies subject to both structural and aerodynamic mistuning. A whole annulus FE model, representative of a civil aero-engine fan with 26 blades was used in the calculations. The forced response of all blades of 1000 random mistuned patterns was calculated. The aerodynamic parameters, frequency shifts and damping, were calculated using a three-dimensional Reynolds-averaged Navier-Stokes aero-elasticity code. They were randomly varied for each mistuning pattern, with the assumption that the system would remain stable, i.e. flutter would not occur due to aerodynamic mistuning. The results show the variation of the forced response with different types of mistuning, with structural mistuning only, with aerodynamic mistuning only and with both structural and aerodynamic mistuning.
Uncertainty Analysis of Centrifugal Compressor Aero-Performance Test Data: Effects of Correlated Systematic Error
Authors: Gilarranz R. Jose´ L.
Published: September 2008

This paper presents the continuation of the work performed during the development of an uncertainty analysis method for estimating error levels in data gathered during factory aero-performance acceptance tests of centrifugal compressors. The previous work incorporated the effects of the variation and uncertainty levels associated with every parameter used in the calculation of centrifugal compressor aero-thermal performance. The work discussed herein focuses on the effects of the variation and uncertainty levels associated with the key measured variables, which are the parameters identified as having the greatest effect on the uncertainty of the performance measurements. Also included in this work is an evaluation of the effects of the correlated bias uncertainty components associated with said key variables, as well as comments on how these effects can be harnessed to reduce the uncertainty of the test data. The evaluation is performed via parametric studies, which present the test uncertainty levels achievable as a function of different correlation levels between the systematic uncertainty components of the measured data. Two different methods are used for the analysis of data measured for several machines. The first method is based on the direct use of the Monte Carlo simulation technique combined with real gas equations of state. The second method employs uncertainty propagation equations and the methodology included in the ASME PTC-19.1(1998) test code. Both approaches use the polytropic compression model and equations for performance evaluation included in the ASME PTC 10 (1997) Power Test Code. Data gathered during an on-site acceptance test of a centrifugal gas compression package are used to illustrate the effects of the uncertainty in the knowledge of the gas composition handled by the compressor over the uncertainty levels that can be obtained with this type of tests.
Analysis of Leakage Flow and Dynamic Characteristics in Floating Ring Seals for High Pressure Turbopump
Authors: Lee Yong-Bok , Kim Chang-Ho , Duan Wenbo , Chu Fulei
Published: September 2008

Because the solutions based on the numerical integration of the complete Navier-Stokes equations can be very time-consuming, the bulk-flow model was used for calculating the static and the dynamic characteristics of floating ring seals. The bulk-flow model is governed by three partial differential equations on eccentric working conditions with steepest descent method to find the seal’s equilibrium position efficiently. A finite difference scheme has been used to solve the nonlinear governing equations. Compared to Nelson and Nguyen’s Fast Fourier Transform Method, this scheme has better consistency. Perturbation analysis of the flow variables yields a set of zeroth and first-order equations. The SIMPLE algorithm is used to integrate the system of bulk-flow equations. Comparisons of the numerical predictions (lock-up eccentricity ratio, leakage flow rate and rotordynamic coefficients) with Ha’s results, which were formulated using the Fourier series, and experimental data are presented subsequently.
DACE Based Probabilistic Optimization of Mechanical Components
Authors: Ramanath Vinay , Wiggs Gene E.
Published: September 2008

Application of DACE (Design and Analysis of Computer Experiments) methods for probabilistic design space exploration and optimization to the design of a mechanical component is demonstrated. The key part of the paper is focused on the problem formulation and process flow for performing a probabilistic optimization. The authors have shown that for computationally intensive problems, probabilistic optimization can be carried out efficiently within a DACE framework. For problems that are not costly to compute, direct probabilistic optimization can be carried out by the efficient integration of probabilistic analysis and global optimization (such as Genetic Algorithms). The strategy in the paper proves to be especially beneficial for those organizations that are reluctant to move to probabilistic methods and also for the current practitioners of probabilistics. The methodology is illustrated with examples from both simple and computationally intensive engineering problems.
Wet Gas Performance Analysis
Authors: Hundseid O̸yvind , Bakken Lars E.
Published: September 2008

The growing interest in wet gas compressors calls for accurate methods for performance prediction. Present evaluation methods for compressor and pump performance fail when evaluating the compression of gases containing liquid. Gas compression performance predictions given in ASME PTC-10-97 and ISO 5318 are based on the method John M. Schultz proposed in 1962. This method assumes a polytropic compression path and is based on averaged gas properties of inlet and outlet condition. The polytropic compression path is defined by keeping pvn constant, where n is constant along the compression path. When employing the Schultz method there is a challenge in defining the polytropic constant. This is seen in cases where dry gas compressors are exposed to wet components and compressor efficiency estimates exceed 100%. Today’s computer technology makes a direct integration of the polytropic head (∫vdp) possible where actual fluid properties along the compression path are included. Phase changes along the compression path are included with this method. This enables a detailed prediction to be made of the actual volumetric flow rate for the various compressor stages. This paper reports the implementation of the direct integration procedure for wet gas performance prediction. The procedure enables generic wet gas compression to be studied which forms the foundation for performance analysis with variations in operation at conditions and fluid components and properties.
Analysis of the Pollutant Formation in the FLOX® Combustion
Authors: Schu¨tz H. , Lu¨ckerath R. , Kretschmer T. , Noll B. , Aigner M.
Published: September 2008

FLOX® — or flameless combustion is characterized by ultra-low NOx emissions. Therefore the potential for its implementation in gas turbine combustors is investigated in recent research activities. The major concern of the present paper is the numerical simulation of flow and combustion in a FLOX®-combustor [1, 2] at high pressure operating conditions with emphasis on the pollutant formation. FLOX®-combustion is a highly turbulent and high-velocity combustion process, which is strongly dominated by turbulent mixing and chemical non-equilibrium effects. By this means the thermal nitric oxide formation is reduced to a minimum, because even in the non-premixed case the maximum combustion temperature does not or rather slightly exceed the adiabatic flame temperature of the global mixture due to almost perfectly mixed reactants prior to combustion. In a turbulent flow the key aspects of a combustion model are twofold, i) chemistry and ii) turbulence/chemistry interaction. In the FLOX®-combustion we find that both physical mechanisms are of equal importance. Throughout our simulations we use the complex finite rate chemistry scheme GRI3.0 for methane and a simple partially stirred reactor (PaSR) model to account for the turbulence effect on the combustion. The computational results agree well with experimental data obtained in DLR test-facilities. For a pressure level of 20 bar, a burner load of 417 kW and an air to fuel ratio of λ = 2.16 computational results are presented and compared with experimental data.
Rotordynamic Force Coefficients of Pocket Damper Seals
Authors: Ertas B. , Gamal A. , Vance J.
Published: September 2008

This paper presents measured frequency dependent stiffness and damping coefficients for 12 and 8 bladed pocket damper seals (PDS) subdivided into 4 different seal configurations. Rotating experimental test are presented for inlet pressures at 69 bar (1,000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the 8 bladed PDS. Results of the frequency dependent force coefficients for the 4 PDS designs are compared. The conclusions of the test show that the 8 bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12 bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a de-stabilizing influence on rotor-bearing systems.
Experimental Measurement of a Three Lobe Air Bearing Rotordynamic Coefficients
Authors: Ruiz Rafael O. , Di Liscia Marcelo H. , Di´az Sergio , Medina Luis
Published: September 2008

This work presents direct experimental measurements of air film rotordynamic coefficients on a three lobe bearing. The test rig uses two magnetic bearing actuators to impose desired test orbits to the journal. Tests are conducted at several rotating speeds up to 12,000rpm. Journal whirling excitation is independent of the rotating speed, thus allowing asynchronous excitations. One-dimensional orbits in the horizontal and vertical axes are applied as excitations at each rotating speed. The experimental results show the behavior of the rotordynamic coefficients of the air film bearing under synchronous and asynchronous excitation. The synchronous experimental results are compared to numerical estimation of the bearing force coefficients through solution of the isotropic ideal gas journal bearing Reynolds equation coupled with the pressure drop through the feeding holes. The results of this work prove the suitability of the rig to identify both the synchronous and nonsynchronous response of air fluid film bearings.
A Fracture Mechanics Based Methodology for Fatigue Life Prediction of Single Crystal Nickel Based Superalloys
Authors: Ranjan Srikant , Arakere Nagaraj K.
Published: September 2008

A comprehensive fracture mechanics based life prediction methodology is presented for FCC (Face Centered Cubic) single crystal components, based on computation of stress intensity factors (SIFs), and modeling the crystallographic fatigue crack growth process, under mixed-mode loading conditions. The 3D finite element numerical procedure presented for computing SIFs for anisotropic materials under mixed-mode loading is very general, and not just specific to FCC single crystals. Stress intensity factors for a Brazilian Disc (BD) specimen are presented for the crack on the {111} plane in the 〈101〉 and 〈121〉 directions, which represent the primary and secondary slip directions. Variation of SIFs as a function of thickness is also presented. Modeling of the crystallographic fatigue crack growth (FCG) behavior is performed by using the resolved shear stress intensity coefficient (RSSIC), Krss. This parameter is sensitive to the grain orientation and is based on the resolved shear stresses on the slip planes at the crack tip, which is useful in identifying the active crack plane as well as predicting the crack growth direction. A multiaxial fatigue crack driving force parameter, ΔKrss, was quantified, which can be used to predict the FCG rate and hence life in single crystal components subject to mixed mode fatigue loading.
System Identification of a Rotor System With Hydrodynamic Bearing by Eigensystem Realization Algorithm (ERA) With an Optimum Doping Signal
Authors: Shiau T. N. , Cheng C. H. , Tsai M. S.
Published: September 2008

This paper proposes a system identification methodology by using eigensystem realization algorithm (ERA) with doping an optimum signal such that the noise effect can be attenuated and more accurate identification results of y-direction dynamics of a hydrodynamic bearing can be obtained. The technique of optimum doping signal integrates the optimization process with singular value decomposition (SVD) technique to achieve nice removal of the noise. Theoretical derivation is given to interpret the function of the optimum signal and explain the relationship between SVD and optimum signal. Simulation result shows that this proposed ERA with a novel optimum signal is more accurate as compared to the case without optimum signal.
Feasibility Study of an Innovative Micro Gas Turbine With a Swiss-Roll Recuperator
Authors: Shih Hsin-Yi , Wang David , Kuo C.-Ron
Published: September 2008

Feasibility of an innovative micro gas turbine with heat recuperation has been studied. The proposed core engine has back-to-back rotor configuration formed by a centrifugal-flow compressor and an axial-flow turbine. A newly Swiss-roll recuperator is wrapped around a can-type combustor to recover the exhaust heat, thus reducing the fuel consumption rate and improving the engine thermal efficiency. From the recuperated cycle analysis, thermodynamic requirements at both inlet and outlet of each component were predetermined to evaluate the engine performance. The conceptual design and preliminary analysis to achieve these requirements were made, component-by-component. The thermal design of the Swiss-roll recuperator was also carried out by theoretical analysis, which gives the thermal characteristics of the recupeator, including the trend of effectiveness, thermal requirement of number-of-transfer-unit (NTU) and the preliminary sizing with the number of turns and the width of the flow channels be determined. The characteristics of Swiss-roll recuperator resemble the counter-flow spiral plate heat exchanger and basically have the excellent performance with high effectiveness and low pressure loss. The performance of the proposed micro gas turbine was investigated, and potentially a compact micro gas turbine with thermal efficiency higher than 20% is possible for the power output less than 10 kW.
Mitigation of Marine Gas Turbine Water Wash Risks
Authors: Shappell Lance , Myers Lee , Hunter Jason
Published: September 2008

The US Navy Landing Craft, Air Cushion (LCAC) engines, like all marine gas turbines, use water washes to preserve performance and increase reliability by removing salt and other contaminants from the compressor. Due to the severity of the operating environment and unfavorable operations base, water washing can pose risks to the LCAC engines. Galvanic corrosion, crevice corrosion, insufficient contaminant removal and incompatibility among seal materials, contaminants and wash solvents can outweigh the benefits of water wash. The US Navy has incorporated water wash procedures and materials such as silicon rubber seals and glass fiber and Teflon bushings to mitigate these risks.
Experimental Investigation of Mode Shape Sensitivity of an Oscillating LPT Cascade at Design and Off-Design Conditions
Authors: Vogt Damian M. , Fransson Torsten H.
Published: September 2008

The effect of negative incidence operation on mode shape sensitivity of an oscillating low pressure (LP) turbine rotor blade row has been studied experimentally. An annular sector cascade has been employed in which the middle blade has been made oscillating in controlled three-dimensional rigid-body modes. Unsteady blade surface pressure data were acquired at midspan on the oscillating blade and two pairs of non-oscillating neighbor blades and reduced to aeroelastic stability data. The test program covered variations in reduced frequency, flow velocity and inflow incidence; at each operating point a set of three orthogonal modes was tested such as to allow for generation of stability plots by mode recombination. At nominal incidence it has been found that increasing reduced frequency has a stabilizing effect on all modes. The analysis of mode shape sensitivity yielded that the most stable modes are of bending type with axial to chordwise character whereas high sensitivity has been found for torsion-dominated modes. Negative incidence operation caused the flow to separate on the fore pressure side. This separation was found to have a destabilizing effect on bending modes of chordwise character whereas an increase in stability could be noticed for bending modes of edgewise character. Variations of stability parameter with inflow incidence have hereby found being largely linear within the range of conditions tested. For torsion-dominated modes the influence on aeroelastic stability was close to neutral.
Development, Testing and Implementation of a Gas Turbine Starting Clutch With Manual Turning Feature for U.S. Navy Ships
Authors: Hendry Morgan L. , Hoffman Matthew G.
Published: September 2008

Most gas turbine generators rely on an automatic-engaging, free-wheel clutch to connect a starting motor to accelerate the gas turbine generator from zero to some intermediate speed to enable ignition and then provide torque assistance to a higher speed until the gas turbine is self-sustaining. The U.S. Navy has used various designs of starter motors and clutches for its gas turbine fleet. In addition, there has been a requirement to periodically borescope each gas turbine and this has necessitated removal of the starting system and clutch assembly in each instance. This paper examines the U.S. Navy experience with starting clutches and provides details of the development and testing of a synchronous-self-shifting clutch with an additional, stationary, manual turning feature to provide very slow and precise gas turbine rotor rotation for borescope purposes. This paper also gives details of the installation of the first two prototype clutches on the USS Ramage, DDG 61, operating experience for approximately four years, and possible future installations of this type of clutch in U.S Navy gas turbine generator sets.
Analyzing the Impact of Using Biodiesel in the Parameters of a 30 kW Micro-Turbine Control Model
Authors: Rendo´n Manuel A. , Do Nascimento Marco A. R. , Mendes Pedro P. C.
Published: September 2008

This work presents the modifications in a 30 kW gas micro-turbine speed control model, when it was supplied with castor bean biodiesel in several proportions. The concern about using biodiesel as an alternative fuel is increasing in the Brazilian distributed generation market. For this analytics, a complete study was developed considering the effects of using this new fuel. Characteristics like chemical composition, physical and chemical properties of the different mixtures were analyzed, especially focusing on the kinematic viscosity of the fuel. The tests results performed with the micro-turbine, originally projected for diesel, are shown. Mixtures of 5, 10, 15, 20, 25, 30, 50 e 100% of biodesel were used, and several variables were measured in the whole range of power. The influence of the biodiesel characteristics in the model parameters are commented in the conclusions. The possible application of the proposed model in studies of electrical power network is suggested in the end of the article.
Experimental Results of a Novel Integrated Energy System Formed by a Microturbine and an Exhaust Fired Single-Double Effect Absorption Chiller
Authors: Nogue´s Miquel , Mauzey Josh , Freeman Aaron , McDonell Vincent , Samuelsen Scott
Published: September 2008

Integrated Energy Systems (IES) combine a distributed power generation (DG) system such as a microturbine generator (MTG) or a fuel cell with thermally activated technologies (TAT) such as absorption cooling. This integration maximizes the efficiency of energy use by on-site utilization of most of the waste heat generated by the DG system, and thus reduces harmful emissions to the environment. This study shows experimental results of a real IES commercial unit that has been tested in the Advanced Power and Energy Program (APEP) DG testing facility at the University of California, Irvine. The system consists of an MTG with an internal recuperator that provides a maximum electrical power generation capacity of 28 kW, and a novel absorption cooling cycle. The absorption cycle is a single effect-double effect exhaust fired cycle, which increases the heat exchange from the MTG exhaust gases using two generators at two different temperature levels. With this combination, the maximum cooling capacity of the absorption machine is nominally 14 refrigeration tons (49.2 kW), which represents 25% more cooling capacity than a double effect absorption machine could provide with the same heat source. The results will show the electrical and thermal performance of this system, both at full load and partial load, for different cooling temperatures, and the relationship between the electrical load and the performance of the absorption unit.
The Evolution of Gas Turbine Generator Set Reliability in the U.S. Navy
Authors: Russom Dennis M. , Pin˜eiro Ivan
Published: September 2008

This paper looks back at the evolution of the Gas Turbine Generator sets (GTGs) in the U.S. Navy’s DDG 51 Class, reviewing lessons learned, successes and areas where work is still required. Topics are discussed in the context of Mean Time Between Failure (MTBF) Total Ownership Cost (TOC) and maintainability. It reviews changes that resulted in MTBF increasing by a factor of five and TOC dropping by a factor of four. It also looks to the future, identifying potential areas of further improvement.
Role of Quantitative NDE Techniques in Life Management of Gas Turbine Components
Authors: Gorelik Michael , Hassan Waled T. , Kington Harry
Published: September 2008

A number of earlier publications discussed the benefits of probabilistic analysis and probabilistic lifing in application to critical rotating engine components. One of the important variables in both probabilistic and deterministic lifing analysis is the level of residual stress in the component. Near surface residual stresses directly influence the fatigue life of critical engine rotating components. Depending on sign and magnitude a near surface residual stress gradient can either inhibit or accelerate fatigue initiation and crack propagation. A major barrier to introducing subsurface residual stress information into the life calculation process is the necessity to make accurate and reliable nondestructive measurements on as produced hardware. The paper reviews several NDE technologies that could be candidates for both production and in-service non-destructive residual stress measurements. The importance of having accurate residual stress information and its use in the probabilistic design and life management process is illustrated on several examples. A linkage with several ongoing industry R&D programs is discussed.
Probabilistic Prediction of Aviation Engine Critical Parts Lifetime
Authors: Nozhnitski Y. A. , Lokshtanov E. A. , Dolgopolov I. N. , Shashurin G. V. , Volkov M. E. , Tsykunov N. V. , Ganelin I. I.
Published: September 2008

Lifetime of disks and other aviation engine parts critical for safe operation is currently probabilistically predicted using mainly two methods. One method to predict lifetime is to confirm lifetime to low-cycle fatigue (LCF) cracking of a part without initial defects. The other method to predict lifetime is to confirm lifetime for safe propagation of a crack from initial defects available in a part. Combination of the above stated methods along with usage of margins on cyclic durability that ensure the required nonfracture probability presents another more conservative approach. Confirmation of lifetime to LCF cracking of a part without initial defects is usually performed based on results of cyclic tests of parts. The safe life determination algorithms were developed in Central Institute of Aviation Motors (CIAM) that take into account a difference in test outcome (“failure”–“no failure”). The developed software makes possible to consider the admissible failure probability, use the actual cyclic durability spread characteristics of the parts involving both lognormal and Weibull durability distributions. This paper discusses the examples of application of the elaborated methods and software. To confirm lifetime for safe propagation of a crack from defects available in a part, a program of statistical determination of durability of powder alloy disks with random fields of ceramic inclusions was developed in CIAM. This program allows performing the partition of disks into typical elements, the generation of realizations of initial defects for each typical disk element and calculation of life realizations corresponding to them, the statistical processing of the obtained data made with usage of asymptotic theory of extreme values, and the determination of technical risk functions for a disk as a whole. While developing the software, the problems of crack initiation and its stable propagation from ceramic inclusions were sequentially decided. Example of the calculation made according to the developed program is given in this paper. The probabilistically-justified approaches to determine the safe life shall be supplemented with the methods of economical and ecological risk analysis. In this case these approaches may become a good support for arranging the engine service to Reliability Centered Maintenance.
Linear Motif Atlas for Phosphorylation-Dependent Signaling
Authors: Miller Martin Lee , Jensen Lars Juhl , Diella Francesca , Jørgensen Claus , Tinti Michele , Li Lei , Hsiung Marilyn , Parker Sirlester A. , Bordeaux Jennifer , Sicheritz-Ponten Thomas , Olhovsky Marina , Pasculescu Adrian , Alexander Jes , Knapp Stefan , Blom Nikolaj , Bork Peer , Li Shawn , Cesareni Gianni , Pawson Tony , Turk Benjamin E. , Yaffe Michael B. , Brunak Søren , Linding Rune
Published: September 2008

Created with both in vitro and in vivo data, NetPhorest is an atlas of consensus sequence motifs for 179 kinases and 104 phosphorylation-dependent binding domains and reveals new insight into phosphorylation-dependent signaling.
The Extracellular Calcium-Sensing Receptor (CaSR) Is a Critical Modulator of Skeletal Development
Authors: Chang Wenhan , Tu Chialing , Chen Tsui-Hua , Bikle Daniel , Shoback Dolores
Published: September 2008

The extracellular calcium-sensing receptor (CaSR) is essential for embryonic and postnatal skeletal development.