bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer in Rotating Rectangular Cooling Channels (AR=4) With Dimples
Authors: Griffith Todd S. , Al-Hadhrami Luai , Han Je-Chin
Published: February 2009

As the world of research seeks ways of improving the efficiency of turbomachinery, attention has recently focused on a relatively new type of internal cooling channel geometry, the dimple. Preliminary investigations have shown that the dimple enhances heat transfer with minimal pressure loss. An investigation into determining the effect of rotation on heat transfer in a rectangular channel (aspect ratio = 4:1) with dimples is detailed in this paper. The range of flow parameters includes Reynolds number (Re = 5000–40000), rotation number (Ro = 0.04–0.3) and inlet coolant-to-wall density ratio (Δρ/ρ = 0.122). Two different surface configurations are explored, including a smooth duct and dimpled duct with dimple depth-to-print diameter (δ/Dp) ratio of 0.3. A dimple surface density of 10.9 dimples/in2 was used for each of the principal surfaces (leading and trailing) with a total of 131 equally spaced hemispherical dimples per surface; the side surfaces are smooth. Two channel orientations of β = 90° and 135° with respect to the plane of rotation are explored to determine channel orientation effect. Results show a definite channel orientation effect, with the trailing-edge channel enhancing heat transfer more than the orthogonal channel. Also, the dimpled channel behaves somewhat like a 45° angled rib channel, but with less spanwise variations in heat transfer.
Numerical Investigation of Heat Transfer in Turbine Cascades With Separated Flows
Authors: de la Calzada P. , Alonso A.
Published: February 2009

Modern design of turbine blades usually requires highly loaded very thin profiles in order to save weight and cost. If local leading edge incidence is kept close to zero, then flow separation might occur on the pressure side. Although, it is known that flow separation, flow reattachment and the associated zones of re-circulation have a major impact on the heat transfer to the wall, the turbomachinery community needs an understanding of the heat transfer mechanisms in separated flows as well as models and correlations to predict it. The aim of the present investigation is a detailed study by means of an in-house CFD code, MU2 S2T, of the heat transfer mechanisms in separated flows, in particular in separation and reattachment point regions. Furthermore, an attempt is made to identify a limited number of parameters (i.e. Re, M, inlet flow angle, etc.) whose influence on the heat flux would be critical. The identification of these parameters would be the starting point to develop special correlations to estimate the heat transfer in separated flow regions.
A Prediction Method for the Local Entropy Generation Rate in a Transitional Boundary Layer With a Free Stream Pressure Gradient
Authors: Walsh Ed , Myose Roy , Davies Mark
Published: February 2009

To design an aerodynamically efficient blade the distribution of entropy generation on the blade surface should be known. Having only knowledge of the integrated loss, makes the task of improving the efficiency of a blade extremely difficult. A method to predict the entropy generation rate in steady, two-dimensional, incompressible, adiabatic boundary layer flows is presented, which gives both the distribution and magnitude of the entropy generation rate. This prediction method is based upon five correlations which are used to determine the: 1. entropy generated in the laminar region; 2. entropy generated in the turbulent region; 3. location of transition; 4. length of transition; 5. entropy generated in the transition region. These are then used to predict the entropy generation rate on the suction surface of a turbine rotor blade at a moderate Reynolds number; comparisons are then drawn with past measurements. The aim is to develop a quick, simple and relatively accurate method for the prediction of entropy in the boundary layers of turbomachines, although the method is not confined to this application. The only information required to implement this prediction method is the boundary layer edge velocity distribution and the turbulence intensity. A benefit of this method is that it does not rely upon dissipative CFD predictions, which are both slow to use in a design process and not yet sufficiently trustworthy. The dissipation coefficient and entropy generation rate predicted for this test case compare well to experimental measurements, with the percentage difference between the integrated entropy measured and predicted being approximately 13%. However, the difference in the turbulent region is found to be as high as 30%.
The Nonstationary Behaviour of Stator Profile Boundary Layer Excited by Periodic Upstream Wakes
Authors: Elsner Witold , Stanisław Drobniak
Published: February 2009

The paper presents an experimental analysis of the interaction between wakes and boundary layers on aerodynamic profiles. The experiment performed on the model linear stator cascade revealed that incoming wakes cause the significant increase of velocity fluctuations in the boundary layer. It was proved that wakes generated upstream the cascade distinctly shift the transition zone towards the leading edge of the profile what results in the increase of profile losses.
On the Numerical Difficulties in Calculating Laminar Separation Bubbles
Authors: Sanz Wolfgang , Platzer Max F.
Published: February 2009

Behaviour of laminar separation bubbles on the surfaces of compressor and turbine blades has increasingly attracted the attention of researchers and designers of turbomachinery in the last years. For the numerical investigation of laminar separation bubbles transition models are implemented into Navier-Stokes flow solvers to predict their location, extent and behaviour accurately. Several researchers conducted comparative studies to investigate the applicability of different transition models for separated-flow transition. In this work a comprehensive numerical study is carried out to investigate not only the influence of the transition model, but of the solution method in general on laminar separation bubble prediction. The flow around a NACA 0012 airfoil at different angles of attack where laminar separation bubbles were observed in experiments is chosen as test case. Different flow solvers (Osher and Roe scheme), different turbulence models as well as different solution procedures were applied together with transition models. The results show that besides the transition model other parameters like the discretisation scheme of the turbulence model or the flow solver have a comparably large influence on the computational result.
Separated Flow Transition Under Simulated Low-Pressure Turbine Airfoil Conditions: Part 2 — Turbulence Spectra
Authors: Volino Ralph J.
Published: February 2009

Spectral analysis was used to investigate boundary layer separation, transition and reattachment under low-pressure turbine airfoil conditions. Cases with Reynolds numbers ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) have been considered at low (0.5%) and high (9% inlet) free-stream turbulence levels. Spectra of the fluctuating streamwise velocity and the turbulent shear stress are presented. The spectra for the low free-stream turbulence cases are characterized by sharp peaks. The high free-stream turbulence case spectra exhibit more broadband peaks, but these peaks are centered at the same frequencies observed in the corresponding low turbulence cases. The frequencies of the peaks suggest that a Tollmien-Schlichting instability mechanism drives transition, even in the high turbulence cases. The turbulent shear stress spectra proved particularly valuable for detection of the early growth of the instability. The predictable nature of the instability may prove useful for future flow control work.
Predicting Transition Without Empiricism or DNS
Authors: Johnson Mark W.
Published: February 2009

A numerical procedure for predicting the receptivity of laminar boundary layers to freestream turbulence consisting of vortex arrays with arbitrary orientation has been developed. Results show that the boundary layer is most receptivity to those vortices which have their axes approximately in the streamwise direction and vortex wavelengths of approximately 1.2 δ. The computed near wall gains for isotropic turbulence are similar in magnitude to previously published experimental values used to predict transition. The new procedure is therefore capable of predicting the development of the fluctuations in the laminar boundary layer from values of the freestream turbulence intensity and length scale and hence determining the start of transition without resorting to any empirical correlation.
Measurement and CFD Prediction of the Flow Within an H.P. Compressor Drive Cone
Authors: Long Christopher A. , Turner Alan B. , Kais Guven , Tham Kok M. , Verdicchio John A.
Published: February 2009

In some gas turbine aeroengines, the H.P. compressor is driven by the H.P. turbine through a conical shaft or drive cone. This drive cone is enclosed by a stationary surface that forms the supporting material for the combustion chambers. Air used to cool the turbine blades is directed into the space around the drive cone, and a major concern to an engine designer is the temperature rise in this air due to frictional dissipation and heat transfer. This paper presents results from a combined experimental and CFD investigation into the flow within an engine representative H.P. compressor drive cone cavity. The experimental results show similarities in flow structure to that found in classic rotor-stator systems. Both 2D and 3D CFD simulations were carried out using the FLUENT/UNS code. The 3D model which included the actual compressor blade tip clearance gave the best agreement with the experimental data. However, the computational resource required to run the 3D model limits its practical use. The 2D CFD model, however, was found to give good agreement with experiment, providing care was exercised in selecting an appropriate value of initial tangential velocity.
Development of Diagnostic Tools for Real Time Assessment of Gas Turbine Hot Gas Path Component Temperatures: A Preliminary Study
Authors: Carcasci Carlo , Facchini Bruno , Grillo Francesco , Benvenuti Erio , Mochi Gianni
Published: February 2009

This paper outlines a part of the work under way at GE Oil and Gas – Nuovo Pignone to develop advanced diagnostic tools to evaluate gas turbine hot gas path components life on the basis of actual operating data continuously recorded by remote monitoring systems. The system aims at correlating component metal temperatures and stresses as a function of operating performance data measured through standard machine instrumentation. Monitored data is processed by a new inverse-cycle algorithm to evaluate gas-path temperatures and pressures. The generated gas path information needs then to be correlated to metal temperatures and stresses with precision suitable for input to algorithms evaluating creep, oxidation and hot corrosion damage. Typically, calculations of gas path data to metal temperatures and stresses are performed at the design stage for a limited number of critical operating conditions by using complex and sophisticated CFD and structural/thermal analysis computer codes. For applications to diagnostic, direct use of such tools for any monitored sets of data would be impracticable. On the other hand, they represent the most effective means for assessing hot gas path component temperatures with adequate accuracy, particularly on last generation engines with substantial turbine blade and nozzle cooling. The approach chosen and described herein consists in extensively using high level design tools over a wide range of turbine operating conditions and use the results to produce equations and maps linking field monitored data to component temperatures suitable for easy implementation into a life evaluation system. In the paper major aspects of the above work are reviewed and synthesized, and significant steps in the first application to a turbine first stage cooled blade are illustrated.
GT10C: 30 MW Gas Turbine for Mechanical Drive and Power Generation
Authors: Hellberg Anders , Norden Georg , Shukin Sergey
Published: February 2009

ALSTOM Power has launched the GT10C a 30 MW industrial gas turbine (see figure 1) upgraded from the 25 MW GT10B. The thermal efficiency of the new gas turbine is 37.3% (shaft) and 36% electrical at ISO inlet conditions with no losses. The new GT10C has a Dry Low Emission (DLE) combustor for both natural gas and diesel oil fuel; it has NOx emissions at 15 ppmv on gas and 42 ppmv on oil fuel (15% O2 dry). The first GT10C is now manufactured and assembled, and has been under testing since October 2001. For this purpose a new test rig has been built in Finspong, Sweden, in order to verify performance and reliability. GT10C will be available to the market mid-2002 and manufactured in parallel with GT10B. The general design is based on the GT10B and measures have been taken for maximum reliability and maintenance in order to keep operation costs to a minimum. Improvements for GT10C are mainly derived from GT10B or taken from ALSTOM Power GTX100 (43 MW gas turbine), as described herein.
Design, Development and Operational Experience of the ALSTOM’s 13.4MW Cyclone Gas Turbine
Authors: Igoe Brian M. , McGurry Martin
Published: February 2009

The Cyclone industrial gas turbine was launched in 1997 and entered commercial operation in 2000. Rated at 13.4MW and with a thermal efficiency in excess of 35% (at ISO operating conditions), the Cyclone was configured as a twin-shaft engine derivative of the Tempest Gas turbine, to meet both power generation and mechanical drive applications. This paper describes the design, development and early operational experience of the Cyclone gas turbine. The design aspects include features, which are common with other products within the ALSTOM product range, those that have been developed out of technology programmes, and those scaled from existing parts. Details are presented of the compressor construction, where a “zero” stage has been added to the Tempest rotor, and coupled with an increase in firing temperature, has resulted in the increase in power output. A two stage overhung compressor turbine, includes cooled blading technology to both stages. A separate free power turbine is based on a scale version of the Typhoon twin-shaft power turbine. The Cyclone includes the ALSTOM, Dry Low Emissions combustion system as standard and is able to operate on a wide range of fuels, in single or dual fuel configurations. The combustion system is based on the proven, generic system first introduced into the Typhoon. The result of engine testing has resulted in the release of both the Cyclone, and the Tempest, with sub 10ppmvd NOx (corrected to 15% O2). The first Cyclone engines entered service in the autumn of 2000, in a co-generation facility in Australia. Described in this paper are the early operating experiences, and the evaluation of a large amount of site data that has been recorded. Included in this section is information on issues that have had to be addressed during the first 8000 hours of operation.
Initial Operation and Analysis of a Cogeneration Laboratory
Authors: Banta Andrew
Published: February 2009

California State University, Sacramento, has constructed and put into service a stand alone cogeneration laboratory. The major components are a 75 kW gas turbine and generator, a waste heat boiler, and a 10 ton absorption chiller. Initial testing has been completed with efforts concentrating on the gas turbine engine and the absorption chiller. A two part thermodynamic performance analysis procedure has been developed to analyze the cogeneration plant. A first law energy balance around the gas turbine determines the heat into the engine. A Brayton cycle analysis of the gas turbine engine is then compared with the measured performance. While this engine is quite small, this method of analysis gives very consistent results and can be applied to engines of all sizes. Careful attention to details is required to obtain agreement between the calculated and measured outputs; typically they are within 10 to 15 percent. In the second part of the performance analysis experimental operation of the absorption chiller has been compared to that specified by the manufacturer and a theoretical cycle analysis. While the operation is within a few percent of that specified by the manufacturer, there are some interesting differences when it is compared to a theoretical analysis.
Gas Turbines Design and Off-Design Performance Analysis With Emissions Evaluation
Authors: Andreini Antonio , Facchini Bruno
Published: February 2009

Many gas turbines simulation codes have been developed to estimate power plant performance both in design and off-design conditions in order to establish the adequate control criteria or the possible cycle improvements; estimation of pollutant emissions would be very important using these codes in order to determine the optimal performance satisfying legal emission restrictions. This paper present the description of a 1-D emission model to simulate different gas turbine combustor typologies, such as conventional diffusion flame combustors, Dry-Low NOx combustors (DLN) based on lean-premixed technology (LPC) or Rich Quench Lean scheme (RQL) and the new catalytic combustors. This code is based on chemical reactor analysis, using detailed kinetics mechanisms, and it is integrated with an existing power plant simulation code (ESMS Energy System Modular Simulator) to analyze the effects of power plant operations and configurations on emissions. The main goal of this job is the study of the interaction between engine control and combustion system. This is a critical issue for all DLN combustors and, in particular, when burning low-LHV fuel. The objective of this study is to evaluate the effectiveness of different control criteria with regard to pollutant emissions and engine performances. In this paper we present several simulations of actual engines comparing the obtained results with the experimental published data.
Incremental Cost of CO2 Reduction in Power Plants
Authors: Narula Ram G. , Wen Harvey , Himes Kenneth
Published: February 2009

Carbon dioxide (CO2) emissions from fossil-fueled power plants contribute to more than one-third of all CO2 emissions in the U.S. [1]. Any effort to curtail greenhouse gases should therefore include the reduction of this emission source. Methods of CO2 reduction include (1) use of alternative fuels with lower CO2 emissions and (2) CO2 scrubbing and sequestration to prevent its release to the atmosphere. The cost of CO2 reduction varies with the selected technology. This paper compares (1) the cost of electricity (COE) without and with CO2 removal/avoidance and (2) the impact of the incremental cost of CO2 reduction on COE for different technology options, including replacing existing coal plants with natural-gas-fired combined cycle (NGCC), integrated gasification combined cycle (IGCC) with and without CO2 removal, pulverized coal (PC) with CO2 scrubber, and nuclear plants. Full and partial compliance with the Kyoto Protocol are addressed.
Evaluation of At Sea Tested LM2500 Rainbow Rotor Blade Coatings
Authors: Driscoll Matthew , McFetridge Eric , Arseneau William
Published: February 2009

This paper discusses the performance of various high pressure turbine (HPT) blade coatings applied to refurbished LM2500 components that were operated in a frigate class marine application. In the early 1990s, an LM2500 propulsion gas turbine engine was removed from the Australian Navy ship HMAS DARWIN for overhaul. In an effort to reduce the cost of overhaul, it was proposed to refurbish the HPT blades instead of the standard practice of replacing the blades with new parts. Included in the proposal to replace the blades with refurbished parts, various coatings were applied in order to evaluate the cost effectiveness of refurbishing blades during overhaul vice replacing with new components. The HPT “Rainbow” Rotor is a paired blade configuration and was built up in 1991 using refurbished blades coated with the standard BC 21 (overlay CoCrAlY) and an industrial standard platinum aluminide (diffusion) coating. In addition, BC 23 coating was applied to several new production blades and installed in the Rainbow Rotor as a control to evaluate the refurbished parts performance. In May 2000, the Rainbow Rotor set of LM2500 blades was removed from service after having accumulated in excess of 11,500 operating hours. This paper details the coating compositions tested and the resultant metallurgical analysis of these blades/coatings.
The WR-21 Intercooled Recuperated Gas Turbine Engine: Operation and Integration Into the Royal Navy Type 45 Destroyer Power System
Authors: McCarthy Steven J. , Scott Ian
Published: February 2009

The WR-21 gas turbine engine will be employed by the Royal Navy and potentially by the United States and French Navies in their future Integrated Full Electric Powered Surface Combatants. The Intercooled Recuperated (ICR) advanced cycle means that in a Warship power system a single WR-21 engine sits on the throne of the realm that traditionally would have been occupied by two gas turbine engines, one for ‘cruise’ and one for ‘boost’; not forgetting that it is also doing the job of at least two diesel generators in our traditional example. This performance will provide Warship operators with an unprecedented opportunity to configure the Warship propulsion plant to return exceptional Platform Life Cycle Cost reductions in peacetime while retaining warfighting operational capability in time of conflict. The Royal Navy is the first user of the WR-21 ICR gas turbine engine in its Type 45 Air Defense destroyer, an artists impression of which is shown in Figure 1. The vessel is a 7500 tonne monohull, fitted with an integrated electric propulsion plant comprising two WR-21 Gas Turbine Alternators (GTAs), the prime mover side of which is capable of delivering 25 MW (ISO) and the Alternator side of which is rated at 21.6 MWe (0.9 pf lagging), 4.16KV. These GTAs in combination with a pair of diesel generators rated at around 2 MWe (0.9 pf lagging) will provide electrical power to two 20 MWe (0.9 pf lagging) 4.16 KV electric propulsion motors and to the ship’s non propulsion consumer electrical distribution system. Any combination of generator set can provide any consumer with electrical power. In their crudest form any generator set that forms part of the Type 45 power system may be simply regarded as Mega Watts towards the installed power total. The division of priority and delivery of power to meet the Command’s requirements will require skilful and subtle engineering of the control systems that will be used to operate the power system and precise definition of the operating philosophy and principles for the platform. In a Warship that has only four sources of electrical power the principles of survivability and prime mover independence are fundamental. The limitations of operating electrical generation machinery are established. This paper examines how the WR-21 will be capable of providing power to the Command of the Type 45 as an integral part of the Warship power system in all states of operational readiness for war.
Application of Diagnostic Algorithms for Maintenance Optimization of Marine Gas Turbines
Authors: Orsagh Rolf F. , Kacprzynski Gregory J. , Roemer Michael J. , Scharschan John W. , Caguiat Daniel E. , McGroarty Jack J.
Published: February 2009

As part of the Naval gas turbine CBM effort, diagnostic and prognostic algorithms that utilize state-of-the-art probabilistic modeling and analysis technologies are being developed and implemented onboard Navy ships. The algorithms under development and testing will enhance gas turbine preventative maintenance in such areas as compressor on-line/crank wash and fuel nozzle replacement. In one application, the prognostic module assesses and predicts compressor performance degradation due to salt ingestion. From this information, the optimum time for on-line water washing or crank washing can be determined from a cost/benefit standpoint. A second application diagnoses the severity of fuel nozzle fouling in real-time during startup. This paper discusses the diagnostic and prognostic modeling approaches to these maintenance issues and their implementation for an Allison 501-K34 gas turbine engine onboard a DDG 51 class guided missile destroyer.
Using a Digital Fuel Control System and Digital Engine Controller for U.S. Navy LM2500 Engines
Authors: Calabrese Marc A. , Skarbek Lee F. , Shah Parag H. , Yassine Mazen K.
Published: February 2009

All United States Navy LM2500 gas turbine engines use a hydromechanical Main Fuel Control to meter the amount of fuel and air introduced into the engine based upon power demand and ambient conditions. The Main Fuel Control is one of the highest failure items on the LM2500 engine and is frequently the cause of costly high-speed engine stalls resulting from mis-rigged throttle or stator vane positioning linkages. Efforts are underway to upgrade the LM2500 with Woodward Governor Company’s state-of-the-art Digital Fuel Control system, subsequent to successful integration testing. The system consists of an off-engine fuel metering valve/actuator, a hydraulic pump/servo valve, and Variable Stator Vane hydraulic actuators equipped with electronic positioning feedback devices. The system will be controlled via one of two engine controllers; the Woodward MicroNet for CG-47 class ships and the Lockheed Martin Universal Engine Controller (UEC) “Plus” for DDG-51 class ships. This paper covers the development, land-based testing, shipboard testing, and fleet implementation of the Digital Fuel Control system in addition to associated engine controllers on the LM2500 engine.
Intrinsic and Extrinsic Variable Effects on Thermal Barrier Coatings Life
Authors: Mutasim Zaher
Published: February 2009

Thermal barrier coating life is dependent on many intrinsic and extrinsic variables within the environment that they operate within. Intrinsic variables include material composition, mechanical and thermal properties, microstructure and ceramic coating thickness. On the other hand, extrinsic variables include cycle time, interface and top surface temperatures, and the gaseous environment, among others. Laboratory testing was conducted to determine the effects of these variables on TBC life. This paper addresses TBC life as a function of microstructure, thickness, and interface temperature.
Gas Turbine Health Indices Determination by Using Neural Networks
Authors: Bettocchi R. , Spina P. R. , Torella G.
Published: February 2009

Recently, diagnostic approaches based on Artificial Intelligence have become very attractive. In particular Neural Networks (NNs) seem to have suitable characteristics for gas turbine diagnostics. This paper deals with the activities carried out for: • selecting the most appropriate NN structure for gas turbine diagnostics; • developing a NN for the detection, isolation and assessment of single and combined causes of performance degradation in a two shaft industrial gas turbine; • testing both the NN performance in recognizing causes of performance degradation and robustness in presence of scarce and/or wrong input data. The data used in all these phases in order to train and test the NN have been generated using a non-linear Cycle Program. So, the Cycle Program becomes a data generator, which may be integrated with data derived from field experience, while the diagnostic function is performed by the NN.
Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes
Authors: Pawloski J. , Ching C. , Shoukri M.
Published: February 2009

The flow regimes and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. The current flow regime data show significant differences in the transitional boundaries from the flow regime maps of Mandhane et al. (1974), Taitel and Dukler (1974) and Spedding and Nguyen (1980). The pressure drop measurements were compared to the predictions from four existing pressure drop models: Homogeneous, Martinelli (1948), Chisolm (1973) and Olujic (1985). The Chisolm and Martinelli models were found to be the most accurate, with an average error of about 35 percent. A capacitance sensor for instantaneous void fraction measurement was developed. Results indicate the data from the sensor could be used to identify the different flow regimes.
Remote Diagnostics of the Alliance Gas Pipeline System Architecture and Initial Operating Experience
Authors: Mochi Gianni , Benvenuti Erio , Baldocci Roberto , Bianucci David
Published: February 2009

Alliance Pipeline Limited (APL) pipeline is a 1850 miles transmission line delivering natural gas from British Columbia (Canada) to Chicago (Illinois USA). The Pipeline crosses remote areas and is subject to adverse winter weather conditions that may temporarily limit accessibility to sites where boosting stations are located. By considering APL requirements in terms of turbo compressor maintenance and operation level, a system providing real time and historical monitoring capabilities was designed to support pipeline operation with the newest available analysis techniques. Thanks to current communication technologies the system allows for a stable link between equipment and OEM (Original Equipment Manufacturer - GE Oil&Gas - O&G) that is operating the system since pipeline commissioning in November 2000. This paper describes the system architecture and processes to deliver advanced condition monitoring and proactive maintenance planning for the APL turbo compressing fleet.
A Bulk-Flow Model of Angled Injection Lomakin Bearings
Authors: San Andre´s Luis , Soulas Thomas , Challier Florence , Fayolle Patrice
Published: February 2009

The paper introduces a bulk-flow model for prediction of the static and dynamic force coefficients of angled injection Lomakin bearings. The analysis accounts for the flow interaction between the injection orifices, the supply circumferential groove, and the thin film lands. A one control-volume model in the groove is coupled to a bulk-flow model within the film lands of the bearing. Bernoulli-type relationships provide closure at the flow interfaces. Flow turbulence is accounted for with shear stress parameters and Moody’s friction factors. The flow equations are solved numerically using a robust computational method. Comparisons between predictions and experimental results for a tangential-against-rotation injection water Lomakin bearing show the novel model predicts well the leakage and direct stiffness and damping coefficients. Computed cross-coupled stiffness coefficients follow the experimental trends for increasing rotor speeds and supply pressures, but quantitative agreement remains poor. A parameter investigation evidences the effects of the groove and land geometries on the Lomakin bearing flowrate and force coefficients. The orifice injection angle does not influence the bearing static performance, although it largely affects its stability characteristics through the evolution of the cross-coupled stiffnesses. The predictions confirm the promising stabilizing effect of the tangential-against-rotation injection configuration. Two design parameters, comprising the feed orifices area and groove geometry, define the static and dynamic performance of Lomakin bearing. The analysis also shows that the film land clearance and length have a larger impact on the Lomakin bearing rotordynamic behavior than its groove depth and length.
Deterministic Micro Asperities on Bearings and Seals Using a Modified LIGA Process
Authors: Stephens Lyndon Scott , Siripuram Ravi , Hayden Matthew , McCartt Bianca
Published: February 2009

Deterministic micro asperities show potential for enhancement of lubrication in conformal contacts as found in many bearing and seal designs. Several manufacturing methods have been proposed for deterministic micro asperities. Of these, laser texturing has emerged as the most viable option. This paper proposes the LIGA MEMs manufacturing method as an alternative. Using LIGA, surfaces with patterned micron sized surface features of arbitrary cross section (cylindrical, hex, triangular, etc.) can be fabricated from electroplated nickel, gel-cast silicon nitride or plastic. The resulting asperities can be positive (protuberances) or negative (recesses) and can have heights (depths) from 1–1000 microns and be patterned over surface areas up to about 150 mm × 150 mm. In this paper, the LIGA method is used to fabricate a sample thrust bearing surface with a hexagonal array of positive asperities. The resulting asperities are 550 μm in average diameter, 165 μm in edge-to-edge spacing and have heights of 3–100μm. Surface metrology indicates sub-micron accuracy of form and 13 nm Ra roughness on the asperity tops (land). Tribology testing in a non-pressurized oil bath indicates full film conditions and shows a 14–22% reduction in friction coefficient for a thrust surface covered with the micro asperities. A model confirms the experimental trends and indicates the potential to further reduce the friction coefficient by about 60% through optimization of the asperity geometry and layout.
Measurement of Oil Aeration Effects in Journal Bearings
Authors: Nikolajsen J. L. , Dong D. , Goodwin M. J.
Published: February 2009

Preliminary measurements have been conducted to determine the effect of oil aeration on journal bearing performance. Oil aeration was observed to reduce the bearing load capacity and to increase the bearing stiffness. Also, the bearing damping capacity was improved significantly by oil aeration.
Oil-Free Foil Bearings as a Reliable, High Performance Backup Bearing for Active Magnetic Bearings
Authors: Swanson E. E. , Heshmat H.
Published: February 2009

Gas turbine engines and other high speed rotating machinery supported by magnetic bearings require some form of backup bearing to ensure reliable and safe operation. To date, this backup capability has been provided by either rolling element bearings or solid lubricated bushings. Both of these solutions have drawbacks — must notably limited life and uncertain dynamic performance. In many cases, the backup bearing system requires substantial maintenance following an activation event. An alternative approach investigated in this work is the use of a compliant foil bearing as a backup bearing. This work discusses tests of this concept on a test rig with a 63 kg rotor. In this application, the foil bearing demonstrated smooth, stable operation during a variety of simulated magnetic bearing failure events, and allowed for continued operation of the rotor following the simulated failures.
Non-Linear Behaviors in the Motion of a Magnetically Supported Rotor on the Catcher Bearing During Levitation Loss: An Experimental Description
Authors: Cuesta E. N. , Rastelli V. R. , Medina L. U. , Montbrun N. I. , Diaz S. E.
Published: February 2009

Recent developments improving load capacity foretell the practical implementation of Active Magnetic Bearings (AMB) on industrial level, pushed by the advantages of reduced wear and higher speeds that they make available. However, the possibility of an eventual power failure forces the use of back-up (catcher) bearings, which usually are of the ball bearing type. The back-up bearings present a clearance between the shaft and the inner race, such that there is not contact during normal operation. On a power failure or an emergency stop, the rotor is only supported by the catcher bearings. Thus, the rotor motion within the clearance results on a succession of impacts, contact and non-contact intervals producing a non-linear behavior of the system. The complexity of this non-linear behavior prevents the use of traditional methods for the design of the catcher bearings, calling for the need of extensive experimentation and previous experience in their dimensioning process. Here, the response of a rigid rotor, supported by a pivot on the drive side and a magnetic bearing on the other side, is measured during the emergency stop from several operating speeds. Non-linear analysis tools, such as Poincare´ Maps and Bifurcation Diagrams, are employed to demonstrate the non-linear characteristics of the motion, which in some conditions is shown to become chaotic with a vibration limit cycle. The rotor motion on the catcher bearings (with the magnetic bearing deactivated) is measured at constant running speeds. The limit cycles and chaotic attractors are described, showing the relation of the non-linear effects to the rotational speed.
Neural Network Emulation of a Magnetically Suspended Rotor
Authors: Escalante A. , Guzma´n V. , Parada M. , Medina L. , Diaz S. E.
Published: February 2009

The use of magnetic bearings in high speed/low friction applications is increasing in industry. Magnetic bearings are sophisticated electromechanical systems, and modeling magnetic bearings using standard techniques is complex and time consuming. In this work a Neural network is designed and trained to emulate the operation of a complete system (magnetic bearing, PID controller and power amplifiers). The neural network is simulated and integrated into a virtual instrument that will be used in the laboratory both as a teaching and a research tool. The main aims in this work are: 1-Determining the minimum amount of artificial neurons required in the neural network to emulate the magnetic bearing system. 2-Determining the more appropriate ANN training method for this application. 3-Determining the errors produced when a neural network trained to emulate system operation with a balanced rotor is used to predict system response when operating with an unbalanced rotor. The neural network is trained using as input the position data from the proximity sensors; neural network outputs are the control signals to the coil amplifiers.
A Simple Method for Estimating the Parameters of the Beta Distribution Applied to Modeling Uncertainty in Gas Turbine Inlet Temperature
Authors: Holland Frederic A.
Published: February 2009

The beta distribution is a particularly convenient model for random variables when only the minimum, maximum and most likely values are available. It is also very useful for estimating the mean and standard deviation given this information. In this paper a simple method is proposed to estimate the beta parameters from these three values. The proposed method has advantages over the conventional approach. In the conventional approach, the four parameters of the beta distribution are determined from only three values by assuming a standard deviation that is one-sixth the range. In contrast, the new method assumes a value for one of the beta shape parameters based on an analogy with the normal distribution. This new approach allows for a very simple algebraic solution of the beta shape parameters in contrast to the simultaneous solution required by the conventional method. The results of the proposed method are very similar to the conventional method. However, the proposed method generally gives a slightly higher (more conservative) estimate of the standard deviation when the distribution is skewed. In addition, the new approach allows the standard deviation to vary as the shape or skew of the distribution varies. Both methods were applied to modeling the probability distribution of temperature.
A Review of Damage Accumulation Rules Applied to Maintenance Scheduling of Advanced Industrial Gas Turbines
Authors: Soechting Friedrich O. , Kallianpur Vinod , Koff Steven G. , Lee Jun-Hee , Tomita Yasuoki
Published: February 2009

Land based gas turbines are utilized to provide electric power on a continuous basis or just to satisfy peak consumer demand for a short operating period during each day. A unit that is operating on a continuous basis will incur few start and stop thermal cycles, and is typically referred to running in a baseload mode (BL). However, a unit that is operating to meet daily peak loads will accumulate an increased number of start and stop thermal cycles, and is typically referred to as operating in a daily start and stop mode (DSS). Gas turbine units are also operated with a weekly start and stop (WSS) cycle due to a different customer power demand. Hot parts in engines running in BL, WSS and DSS accumulate different levels of fatigue damage because thermal cycles vary significantly within the same actual operating hour period; e.g., the DSS engine will accumulate the most fatigue damage during the same operating hour period. Material testing has shown that an interaction of creep and fatigue damage produces a reduction in the fatigue life of a component. Different criteria and maintenance scheduling philosophy are used within the industrial gas turbine industry to account for the interaction of the creep and fatigue damage in engines. The purpose of this paper is to document how a maintenance scheduling philosophy has been developed that takes into account actual differences in engine usage on the capability of gas turbine hot parts and how current maintenance schedule intervals are being revised for Mitsubishi’s customers.
Load History Effects on Fretting Contacts of Isotropic Materials
Authors: Rajeev P. T. , Murthy H. , Farris T. N.
Published: February 2009

The load history that blade/disk contacts in jet engine attachment hardware are subject to can be very complex. Using Finite Element Method (FEM) to track changes in the contact tractions due to changing loads can be computationally very expensive. For 2D plane strain contact problems with friction involving similar/dissimilar isotropic materials, the contact tractions can be related to the initial gap function and the slip function using coupled Cauchy Singular Integral Equations (SIEs). The effect of load history on the contact tractions is illustrated by presenting results for an example fretting “mission”. For the case of dissimilar isotropic materials the misson results show the effect of the coupling between the shear traction and the contact pressure.
Stress Analysis of Turbomachinery Discs Having Complex Bolted Flange Design Features
Authors: Warikoo R. , Beaulieu R. , Mason B.
Published: February 2009

Mating flanges of two rotating discs with dissimilar materials were stress analysed by 3D Finite Elements using a contact algorithm to simulate the relative motion between the flanges. All the hardware associated with the flanges (bolts, nuts, bushings and washers) were also modelled. The difference in radial growths of the two flanges, hereby called “slip”, produces high cyclic stresses in the bolt holes leading to Low Cycle Fatigue (LCF) and premature cracking. Design changes were studied where the slip was minimised by changing the thermal and centrifugal response of the mating flanges. In order to substantiate the LCF life of a rotating part, spin pit testing is carried out. In the spin pits available for testing the temperature remains constant while the speed is cycled. So in order to simulate the engine duty cycle which includes thermal stresses, the spin pit test conditions are modified. The procedure adopted in this case is explained in the paper.
An Empirical Model for Predicting Crack Growth Behavior of Gas Turbine Stage 1 Nozzles
Authors: Yau Jenfu , Kuang Hui
Published: February 2009

Expenditure of maintenance cost for gas turbines can be greatly reduced if the parts can be well managed during the service to avoid excessive fallout rate or unplanned forced outage. In order to achieve the optimum part life management plan, the ability to accurately predict the life capabilities and fallout rates of the life limiting components becomes very important. An empirical model for the stage 1 nozzle of F-class frame 9 GE gas turbine has been developed based on Weibull statistic analysis of measured crack dimensions at observed critical locations of the nozzle. The crack measurements were taken during the hot gas path inspections and data from several different machine units which had different operating histories were used to establish relationship between Weibull parameters and elapsed operation histories. The fallout rate as function operation history is predicted by performing a Monte Carlo analysis to account for the combined effects of multiple cracks.
A New Tool for Design and Certification of Aircraft Turbine Rotors
Authors: Leverant Gerald R. , McClung R. Craig , Millwater Harry R. , Enright Michael P.
Published: February 2009

This paper summarizes recent enhancements to a probabilistic damage tolerance software code, DARWIN™, that can be used for design certification of aircraft jet engine titanium disks/rotors that may contain melt-related anomalies. Evaluations of DARWIN™ by engine manufacturers are also discussed, including comparisons with existing codes for accuracy and time efficiency. In addition, relevant test results, including various fatigue tests on material containing melt-related anomalies, are summarized.
Fatigue Crack Growth Life Prediction for Surface Crack Located in Stress Concentration Part Based on 3D-FEM
Authors: Yamashita Youichi , Shinozaki Masaharu , Ueda Yuusuke , Sakano Kenji
Published: February 2009

Fatigue crack growth prediction methods using three dimensional finite element analyses were investigated to improve the predictability of part-through surface crack growth life. First, a direct analysis method of cyclic finite element analysis was adopted. Fatigue crack growth was predicted on a step by step basis from the Paris’ law using stress intensity factor range (ΔK) calculated by 3D-FEM. This method takes the procedure of cyclic operation of FE-analysis modeled with crack tip elements, crack growth increment calculation and remeshing of FE-model. Second, a method based on influence function method for ΔK calculation directly using 3D-FE-analysis result has been developed and applied. It was found that crack growth prediction based on step by step finite element method and the method based on the influence function method showed good correlation with the experimental results if Paris’ law coefficient C determined by CT specimen was appropriately used for semi-elliptical surface crack.
On the Three-Dimensional Finite Element Analysis of Dovetail Attachments
Authors: Beisheim J. R. , Sinclair G. B.
Published: February 2009

The stress analysis of dovetail attachments presents some challenges. These stem from the high stress gradients at the edges of contact. They also stem from the nonlinearities accompanying conforming contact. Even with two-dimensional analysis, obtaining converged peak stresses is not trivial. With three-dimensional analysis, convergence can be expected to be more difficult to achieve because of the added computational costs of refinement in three dimensions. To meet these challenges, this paper describes a submodeling procedure with finite elements. The submodeling approach features bicubic surface fits to displacements for submodel boundary conditions. The approach also features a means of verifying these boundary conditions have converged: This is crucial to obtaining accurate converged peak stresses. The approach is applied to a three-dimensional test piece used to simulate a dovetail attachment. This application leads to converged three-dimensional stresses. These stresses serve to quantify the sort of increases in contact stresses in attachments due to three-dimensional effects.
Optimum Strain Gauge Application to Bladed Assemblies
Authors: Szwedowicz J. , Senn S. M. , Abhari R. S.
Published: February 2009

Optimum placements of the strain gauges assure reliable vibration measurements of structural components such as rotating blades. Within the framework of cyclic vibration theory, a novel approach has been developed for computation of the optimum gauge positions on tuned bladed discs regarding the determined sensitivity, orthogonality, gradient and distance criteria. The utilized genetic algorithm optimization tool allows for an effective numerical search of suitable solutions of the defined optimization function. A rotating impeller disc represented by a cyclic finite element model demonstrates the application of this method. The present technique can be easily applied to other structural components requiring optimal strain gauge instrumentation.