bluuebunny/crossref_metadata_2025 huggingface dataset:
Failures of the High Energy, High Pitch Velocity Gear Boxes
Authors: Ingistov Steve
Published: November 2008

This Paper describes the on-going efforts of finding the root-cause for the failures of high-energy (over 30,000 HP), high-pitch velocity (over 30,000 FPM) gear elements. These gear elements are presently operating in Oil and Gas Production Facilities. They are installed between the GT drivers and turbo-compressors. Turbo-compressors deliver high-pressure gas into the underground oil fields to enhance the oil production. The oldest Gas Compression Units were commissioned in 1995 and the latest in 1998. Since installation in 1995 at least 6 gear boxes experienced failures of the pinion (high speed gear) teeth. The Mean Time Between Failures (MTBF) of the pinion teeth was estimated around 34,000 operating hours. The costly shutdown of Gas Compression Units forced the management to seek advice within the company. The intent of this Paper is to share some field experiences and to present some corrective actions. The intent of this Paper is also to help Original Equipment Manufacturers (OEMs) in this case gear elements Manufacturers to develop better balance between cost, life and reliability. Sometimes the balance between these three parameters is difficult to maintain. Too often the gear elements Manufacturers are forced to compete on the price basis and as result the quality of the gear elements are sometimes compromised. In addition, several well-known gear elements Manufacturers stopped offering high energy, high-pitch velocity gear elements because they suffered serious failures of the gear elements on the test stand and also in the field.
Experimental Sector and Flame-Tube Evaluations of a Multipoint Integrated Module Concept for Low Emission Combustors
Authors: Tacina Robert , Mansour Adel , Partelow Leonard , Wey Changlie
Published: November 2008

Emissions from a low-NOx combustor concept were measured in a flame-tube (uncooled, ceramic lined) combustor and a three-module sector combustor. The low-NOx concept used in both the flame-tube and sector tests is a multipoint, lean-direct injection concept. The multipoint modules have 12, 13 or 20 fuel injectors in place of a conventional fuel injector. An integrated-module approach is used for the construction, where chemically etched laminates are diffusion bonded and combine the fuel injectors, air swirlers and fuel manifold into a single module. Test conditions include inlet temperatures up to 810K, inlet pressures up to 2760 kPa, and equivalence ratios up to 0.6 using Jet-A fuel. The NOx emissions from the sector tests are similar to those from the flame-tube tests when the difference in liner cooling is accounted. The NOx emissions are correlated to the inlet temperature, inlet pressure, and fuel-air ratio. The goal of at least 70% reduction from the 1996 ICAO standard using a 20:1 pressure-ratio engine cycle was met. The range of low-power operability using circumferential fuel staging was near the goal, but fuel staging within the module did not improve the operability range.
Characterising the Aerodynamic and Aeroacoustic Performance for a Small Axial-Flow Fan
Authors: Cao Renjing , Lee Duck-Joo
Published: November 2008

This study aims to predict the unsteady aerodynamic performance and the tonal noise radiation from a small axial flow fan. The computation is divided into two stages: (a) the computation of the unsteady flow field at design and off-design working conditions, and (b) detailed analysis of acoustic field. A dual-time approach and finite volume control method is applied for the unsteady solution involving the whole flow passages of the axial flow fan, and the pressure rise against volume flow rate is obtained and shown to be in good agreement with experimental data. The interaction of the rotor wake and the downstream struts has been simulated by investigating the effects of source distribution over the whole blades. And the tonal noise is then predicted based on Lowson theory. The unsteady force is divided into thrust in the rotational axis direction and drag in the rotational direction for rotor and strut. It is demonstrated that the unsteady forces acting on rotor and strut are produced by the interaction between rotor and strut, and has close relationship with the rotor wake structure and strut alignment. In the rotor near wake, both the viscous and potential flow is dominant not only to aerodynamic forces but also to interaction noise. The present study shows that the higher leaned angle of struts can gain about 4 dB reduction of overall sound power level compared to the smallest one.
Tuning Your Fuel-Gas Delivery System
Authors: Newbound T. D. , Al-Showiman K. S.
Published: November 2008

Saudi Aramco has focused more attention in recent years on fuel gas conditioning for land-based industrial and aeroderivative combustion gas turbines CGTs. Hydrocarbon dew points and entrained solids are two important fuel quality issues that frequently trouble CGT operators, partly because they cannot be guaranteed by the fuel suppliers and they are rarely monitored by the operators. This paper addresses these issues and offers some practical advice to optimize the design and operation of fuel gas delivery systems. Saudi Aramco has been testing an automated on-line dew point monitor capable of detecting both hydrocarbon and aqueous dew points in natural gas. Dew point monitoring conducted at three locations on the fuel gas grid revealed wide variations in the hydrocarbon and aqueous dew points due to a variety of conditions. Gas production and pipeline operations were responsible for the most dramatic variations in dew points, but exposure of pipelines to the weather can also be important. Measurement of pipeline solids for the purpose of sizing and placement of particle filters have also been explored. Pipeline scraping, gas velocities, length of pipeline span, pipeline junctions and control valves are all considerations for solid control strategies. The optimized design and operation of a CGT fuel system is highly dependent on dew point control and efficient removal of entrained pipeline solids. Practical experience in monitoring hydrocarbon and aqueous dew points, pipeline solids control, and optimizing fuel conditioning equipment will be presented.
Separated Flow Transition Mechanism and Prediction With High and Low Freestream Turbulence Under Low Pressure Turbine Conditions
Authors: Volino Ralph J. , Bohl Douglas G.
Published: November 2008

A correlation for separated flow transition has been developed for boundary layers subject to initial acceleration followed by an unfavorable pressure gradient. The correlation is based on the measured growth of small disturbances in the pre-transitional boundary layer. These disturbances were identified and quantified through spectral analysis of the wall normal component of velocity. Cases typical of low pressure turbine airfoil conditions, with Reynolds numbers (Re) ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) were considered at low (0.5%) and high (8.7% inlet) freestream turbulence levels. In some cases, two-dimensional rectangular bars were placed at the beginning of the adverse pressure gradient region as passive flow control devices. The dimensionless magnitude of the initial disturbance which begins to grow at the suction peak depends on the freestream turbulence level and the size of any bar applied to the surface. The growth rate depends on the Reynolds number. When the pre-transitional disturbances grow to a sufficient magnitude, transition begins. The new correlation is based on the physics observed in the turbulence spectra, but allows transition prediction using only the Reynolds number, freestream turbulence level and bar height. The correlation has been checked against experimental data from the literature, and allows transition location prediction to within the uncertainty of the experimental measurements. The correlation represents an improvement over previous correlations which accounted for Reynolds number or freestream turbulence effects, but not both.
Quantitative Determination of Methane, Ethene, Ethyne, and Benzene From Within the Sector of a Gas Turbine Combustor
Authors: Miller M. N. , Wilson C. W. , Hilton M. , Marston G.
Published: November 2008

This paper describes experimental work undertaken in the quantitative measurement of specific hydrocarbons found at different axial locations within a gas turbine combustor. The motivation for this work was to gain a greater understanding of the combustion process and obtain data which could be used to provide validation for computational fluid dynamic and chemical kinetic models. Chemical species routinely measured using the QinetiQ internal traversing facility are: H2, O2, NO, NO2, THC, CO2, CO and smoke. For this work, a Fourier Transform Infrared spectrometer (FTIR) was added to the suite of gas analysers to measure the concentration of individual hydrocarbons in real time. Gaseous samples were also acquired in pressurised stainless steel cylinders and analysed for individual hydrocarbons using Gas Chromatography Mass Spectrometry (GCMS), thus providing validation for the FTIR methodology. A “water cooled” gas-sampling probe was utilised to perform the measurements at realistic operating conditions within a generic gas turbine combustor sector. Heated sample lines were used to convey the sample from the probe to a heated, variable-pathlength sample cell incorporated into the optical path of the FTIR analyser. FTIR spectra were acquired in the mid-infrared region between 400 to 4000 cm−1. H2O and CO2 have absorption bands that overlap with some of the hydrocarbons of interest in this spectral region: it was therefore necessary for spectral subtraction to be undertaken. The predominant hydrocarbons found at all axial locations within the combustor were CH4, C2H2, and C2H4. Benzene was found in the primary zone but not at other axial locations. Simultaneous measurements made using a total hydrocarbon analyser compared favourably with total hydrocarbon values obtained using GCMS and FTIR. This suggests that the majority of the unburned hydrocarbons were accounted for.
Investigation of Turbulent Combustion in Humid Air Using a Level-Set Flamelet Library Approach
Authors: Engdar Ulf , Hermann Fredrik , Nilsson Per , Klingmann Jens
Published: November 2008

To meet the demands of high electrical efficiencies in combination with low emissions for gas turbine-based power plants, wet cycles have gained new interest. The combustion chamber is a key component in such a power plant. Detailed investigations are necessary to gain insight into the formation of hazardous emissions such as CO and NOx. In this paper, computational fluid dynamics (CFD) has been employed to perform the investigations. To examine the influence of humidity content in the inlet air stream on the mean flame position and CO and NOx emissions, the humidity content was varied from 0 to 31%. The CO emissions are a measure of incomplete combustion. The inlet temperature and the maximum flame temperature were held constant for all computations. The influence of different combustor loads was also investigated. This will influence the flame position, which is important for emission formation. The flame under investigation is a lean premixed propane flame, stabilized by a bluff body. The turbulent combustion has been modeled with the level-set flamelet library approach (FLA). This model includes a detailed chemical mechanism, which is of great importance when emissions are to be predicted. To illustrate this importance, the FLA model is compared with a simple eddy break-up model and validated against known experimental data at dry condition. The level-set flamelet library method shows very good agreement with the experimental data for both the temperature profile and the CO and NOx emissions. The simple eddy break-up model is only able to predict the temperature profile fairly well while the important emissions are being greatly overestimated. The computations have shown that the flame position, and hence the residence time, is most sensitive to the change in combustor load-while the degree of humidification appears to be of less importance. The CO emissions rise with an increase in the degree of humidification at constant load, while the opposite behavior is true for NOx emissions. At a constant level of humidification, the CO emissions fall with an increase in load and again, the opposite behavior is observed for NOx emissions. A map of emission indices for CO and NOx under different load conditions as a function of humidification can be generated. This map shows an operation window within which both the CO and NOx emissions are quite low.
Optimisation of the Arrhenius Parameters in a Semi-Detailed Mechanism for Jet Fuel Thermal Degradation Using a Genetic Algorithm
Authors: Wade A. S. , Ingham D. B. , Kyne A. G. , Mera N. S. , Pourkashanian M. , Wilson C. W.
Published: November 2008

This paper presents a novel way to determine new reaction rate parameters (A’s and Ea’s in the Arrhenius expression) in a semi-detailed reaction mechanism for the thermal degradation of aviation fuel and surface fouling. The technique employed is a specialised optimisation procedure, namely a genetic algorithm (GA), which utilises an abstraction of the Darwinian principle of survival of the fittest in order to “breed” good solutions over a predefined number of “generations”. Deposition rates for a given fuel which have been measured experimentally over a range of conditions are reproduced by solving the conservation equations of mass, momentum, energy and species using a CFD code and the optimised set of rate constants obtained using a genetic algorithm inversion process. The new set of rate constants lie within predefined boundaries based upon previous values found in the literature for the mechanism being used. In addition, this powerful technique promises the ability to develop reaction mechanisms whose newly optimised rate constants reproduce closely all the experimental data available, enabling a greater confidence in their predictive capabilities. The process is also shown to be an effective tool to facilitate the elucidation of shortcomings in current global chemistry models of fuel degradation. Therefore, the results of this study demonstrate that the genetic algorithm inversion process may be used to develop and calibrate more detailed models for the thermal stability behaviour of aviation fuels than have been seen previously and, subsequently, accurately predict the locations and rates of deposit build-up in fuel handling systems. Furthermore, it has been demonstrated that, modern high speed computers allow for evaluation of increasingly complex and expensive GA objective functions.
The Aerodynamic Interaction of Tip Leakage and Mainstream Flows in a Fully-Ducted Axial Fan
Authors: Corsini Alessandro , Rispoli Franco , Sheard Geoff , Kinghorn Iain
Published: November 2008

The three dimensional structures of the blade tip vortical flow field is herein discussed for an axial fan in a fully-ducted configuration. The investigation has been carried-out using an accurate in-house developed multi-level parallel finite element RANS solver, with the adoption of a non-isotropic two-equation turbulence closure. Due to the fully-ducted configuration the fan has a complex vortical flow field near the rotor tip. The tip clearance flows have been detected for operating conditions near peak efficiency and near stall, with multiple vortex formations being identified in both cases. The nature of the flow mechanisms in the fan tip region is correlated to the specific blade design features that promote reduced aerodynamic noise. It was found that the blade lean at the higher radii attenuates the sensitivity to leakage flow effects. Consequently, the rotor operates efficiently and with nearly unchanged noise emission approaching its throttling limit. The rotor loss behaviour, within the passage and downstream of it, is also discussed at both near design and part-load conditions.
Dynamic Modeling and Simulation of Saturators for Humid Air Turbine Cycle
Authors: Liu Yongwen , Su Ming
Published: November 2008

This paper describes the dynamic modeling and simulation of spray tower saturator using one-dimensional flow control volume method, as a part of study for dynamic modeling of the humid air turbine cycle. The mass, energy and momentum exchanges between gas flow and water flow, as well as their conservations, are taken into consideration. Separate modules are built for gas flow and water flow, and are put into an application library of EASY5, which is general-purpose simulation software. Modular structure and mathematical causality needed by explicit modeling are maintained for the modules in the application library. Then spray tower saturators can be divided into arbitrary number of segments, and each one is modeled by a gas flow module and a water flow module. To exemplify the modeling method, two dynamic models with different number of segments are built for a spray tower saturator. For steady state analysis, quantity variations with tower height at design point are illustrated, and the results of the two models are compared. For dynamic analysis, two dynamic simulations are run to obtain response to 10% step increase of the gas and water inlet temperature respectively. Estimation of the dominant time constants by linearized model is also discussed.
Shock Induced Flutter of Turbomachinery Blade Row
Authors: Srivastava R. , Keith Theo G.
Published: November 2008

This paper describes the influence and effect of a normal shock wave on the flutter characteristics of a turbomachine blade row. High fidelity numerical analysis is used to calculate the energy exchange for a vibrating blade row in the presence of an oscillating normal shock wave. The 3-D Tenth Standard Cascade is used in the present study to calculate the influence of a shock on the energy exchange of blades undergoing a torsional vibration and to correlate the observations with an algebraic model. Effect of three parameters-distance of shock from elastic axis, inter-blade phase angle and vibration frequency are investigated. The results indicate that the three parameters strongly influence the flutter characteristics. The distance between shock location and elastic axis was found to have a linear effect on stability. Moving the elastic axis from downstream of the shock to upstream changes the sign of the stability characteristics as well. It was found that the shock induced energy exchange varied harmonically with inter-blade phase angle indicating the phase between shock motion and blade motion to be independent of inter-blade phase angle. The influence of vibration frequency on work done by the shock was found to be harmonic for reduced frequencies up to 2. The results also showed that either a positive or negative energy exchange could be induced by a shock depending upon the frequency of vibration. The influence of the shock wave on the unsteady flowfield was found to be linear for small amplitude blade oscillation. It was also found that the region of influence of the shock on the work could be divided into primary and secondary regions with work in the primary region being influenced directly by the shock motion. The work in the secondary region was found to be influenced by flow variations induced by shock motion downstream of the shock.
Comparing Turbine Gaspath Component Alternatives
Authors: Willett Fred T. , Anderson Rodger O. , Pothier Michael R.
Published: November 2008

The large installed base of large frame industrial gas turbines has prompted a number of replacement part offerings, in addition to the replacement parts offered by the OEM. The quality and rigor of the offerings varies considerably. The replacement parts can be broken down into three categories: replicated parts, reverse-engineered parts, and re-engineered parts. The processes of replication, reverse engineering, and re-engineering are examined in detail. Specific differences between the three approaches are identified and discussed. The economic model presented by Willett and Pothier [2003] is used to examine the potential economic benefits of replacement parts and quantify differences in potential benefits as a function of engineering approach. The benefits of each approach depend not only on the engineering process, but also on the customer (power plant operator) profile. Base load, cyclic duty, and peaking operation, along with risk tolerance, influence the predicted benefit and determine the most effective engineering approach.
CFD: Analysis of the Influence of Modified Tangential Air Inlets on the Combustion Behavior of a Two-Stage Combustion Chamber
Authors: Hoerzer Klaus , Haselbacher Hermann
Published: November 2008

At the Institute of Thermal Turbomachines and Powerplants at the Vienna University of Technology, a two-stage combustion chamber was designed and constructed to directly drive a gas turbine by combustion of wood dust. A commercial CFD-solver was applied to examine the effects of modifications of the geometry on the combustion performance. Since this parameter study was done with the same operation parameters and the same boundary conditions, the computational results represent the influence of the different flow fields caused by the modified combustion chamber. The particle gasification time, the temperature, and the chemical composition of the flue gas at the combustion chamber exit have been used for the assessment of the combustion performance.
An Integrated Design System for Fans, Compressors, and Turbines: Part 1 — Overview
Authors: Miller Max J. , Durschmidt Don F. , Medlock Allen , Sandel Wolfgang A.
Published: November 2008

In the early 1990s, a team of Honeywell fan, compressor, and turbine aerodynamic designers concluded that major savings in design time and cost could be achieved with a new aero design system. The range of turbomachinery in company engines, the manufacturing methods used for airfoils, and the different design activities set the scope of the new aerodynamic design system. Emphasis was placed on making the system general, flexible, and easy to use. The end result was a new aero design system with a lot of functionality packed into a single, easy to use program. The new system contains both geometry generators and a 2-D through-flow solver. The system has many special features that have provided savings from productivity improvements and reductions in design cycle time. Overall, use of the system has provided a net cumulative savings of over $6 million since 1992.
Effects of Swirler Configurations on Flow Structures and Combustion Characteristics
Authors: Li Guoqiang , Gutmark Ephraim J.
Published: November 2008

Modern gas turbine combustion technologies are driven by stringent regulations on pollutant emissions such as CO and NOx. A combustion system of multiple swirlers coupled with distributed fuel injection was studied as a new concept for reducing NOx emissions by application of Lean Direct Injection (LDI) combustion. The present paper investigates the effects of swirler configurations on the flow structures in isothermal flow and combustion cases using a multiple-swirlers fuel injector at atmospheric conditions. The swirling flow field within the combustor was characterized by a central recirculation zone formed after vortex breakdown. The differences between the tangential and axial velocity profiles, the shape of the recirculation zones and the turbulence intensity distribution for the different fuel injector configurations impacted the flame structure, the temperature distribution and the emission characteristics both for gaseous and liquid fuels. Co-swirling configuration was shown to have the lowest NOx emission level compared with the counter-swirling ones for both types of fuels with lower inlet temperature. In contrast to this, the swirl configuration had less effect on the combustion characteristics in the case of gaseous fuel with high air inlet temperature. The differences in NOx emissions were shown to be closely related to the Damkohler number or the degree to which the flame resembled well-mixed combustion, which is the foundation for LDI combustion.
Advanced H2/Air Cycles Based on Coal Gasification
Authors: Gambini M. , Guizzi G. L. , Vellini M.
Published: November 2008

In this paper the overall performance of a new advanced mixed cycle (AMC), fed by hydrogen-rich fuel gas, has been evaluated. Obviously, hydrogen must be produced and here we have chosen the coal gasification for its production, quantifying all the thermal and electric requirements. At first, the thermodynamic performance of this cycle has been investigated in comparison with that attainable by combined cycle power plants (CC). Then, the power plants have been integrated with the fuel production system. Including all the material and energy flows, the overall performance has been evaluated. The main result of the performed investigation is that the two power plants attain the same efficiency level with and without H2 production requirements (over 60% and over 34% without and with hydrogen production respectively). The final carbon dioxide emissions are about 0.123 kg/kWh both for AMC and CC. It is important to underline that the “clean” use of coal in new power plant types must be properly investigated because it is the most abundant and the cheapest fossil fuel available on earth; moreover, hydrogen production, by using coal, is an interesting prospect because hydrogen has the potential to become the main energy carrier in a future sustainable energy economy.
Influence of the 180° Bend Geometry on the Pressure Loss and Heat Transfer in a High Aspect Ratio Rectangular Smooth Channel
Authors: Pape Detlef , Jeanmart Herve´ , von Wolfersdorf Jens , Weigand Bernhard
Published: November 2008

An experimental and numerical investigation of the pressure loss and the heat transfer in the bend region of a smooth two-pass cooling channel with a 180°-turn has been performed. The channels have a rectangular cross-section with a high aspect ratio of H/W = 4. The heat transfer has been measured using the transient liquid crystal method. For the investigations the Reynolds-number as well as the distance between the tip and the divider wall (tip distance) are varied. While the Reynolds number varies from 50’000 to 200’000 and its influence on the normalized pressure loss and heat transfer is found to be small, the variations of the tip distance from 0.5 up to 3.65 W produce quite different flow structures in the bend. The pressure loss over the bend thus shows a strong dependency on these variations.
Making Use of Labyrinth Interaction Flow
Authors: Pfau A. , Kalfas A. I. , Abhari R. S.
Published: November 2008

It is the aim of this publication to attract the designers attention to the end wall flow interactions of shrouded high pressure turbines. One of the key issue for designing better turbines is the understanding of the flow interactions set up by the presence of labyrinth seals. Those interaction flows are carefully examined in this publication using the control volume analysis and the radial equilibrium of forces acting on streamlines. The consequences on secondary flow development and mixing losses are discussed and quantified. Out of this insight, design recommendations are derived, which attempt to make use of the nature of the labyrinth interaction flow. The open labyrinth cavities are classified in a systematic way. The aim of this approach is to work out the characteristic differences between hub and tip cavities and those having a leakage jet or sucking main flow fluid into the labyrinth. The influence on the main flow is discussed in terms of the incidence flow angle of downstream blade rows and the associated loss production mechanisms. The design strategies presented in this paper follow two paths: (a) Optimization of the mixing losses of the leakage jets at hub and tip is estimated to result in an efficiency increase of up to 0.2%. (b) The non-axisymmetric shaping of the labyrinth interaction flow path aims at the secondary flow control in downstream blade rows. This approach might contribute in the same magnitude of order as reduction in the mixing losses.
Instrumentation Selection and Uncertainty Analysis for Performance Test of Small Centrifugal Compressors
Authors: Al-Qutub Amro M. , Al-Sulaiman Fahad A.
Published: November 2008

In the design phase of centrifugal compressors, it is essential to have some experimental results on performance. The extent of usefulness of the experiments depends on quality and accuracy of the results. Part of proper experimental procedure is the correct selection of instrumentation leading to lower uncertainty in the final results. ASME PTC 10 (Performance Test Code on Compressors and Exhausters) requires fluctuation limits on the measured performance parameters. This does not guarantee limits for accuracy of performance parameters. Also, different experimental setup will affect uncertainty of the results, even with similar instrumentation accuracy. The present research deals with uncertainty analysis for performance evaluation of small-scale centrifugal compressor. The instrumentation errors are accommodated in the relation to ASME PTC 19.1 (test uncertainty). The analysis takes into consideration the correlated bias limits. Selection of proper type of instruments for measuring associated parameters is based on literature review. A case study is included as an example to illustrate the selection on instrumentation accuracy and preferred bias correlations. The analysis is a useful tool in designing experiments for testing compressor and optimizing accuracy of results.
Performance of a Small Reheat Gas Turbine System as a Cogeneration System
Authors: Iki Norihiko , Takahashi Sanyo , Furutani Hirohide
Published: November 2008

We proposed the concept of a small reheat gas turbine system. This reheat gas turbine consists positive-pressure part (Brayton cycle), negative-pressure part (inverted Brayton cycle) and heat exchangers. The system components are interchangeable with the micro gas turbine. This system can supply hot water and steam. However, we focused on the electric efficiency in the previous paper. This paper describes the performance of a small reheat gas turbine system from a point of view as a cogeneration system. The efficiency of electric power output is over 32% and the efficiency of heat output is only 15–20%. So overall, efficiency is about 50%. Therefore, we improved the heat recovery system of a small reheat gas turbine system. As a result, the overall efficiency becomes over 60% and consumption of cooling water reduces extremely. PURPA is over 50% when TIT is over 1573K.
Evaluating the Stability of BSAS-Based EBCs in High Water-Vapor Pressure Environments
Authors: More Karren L. , Tortorelli Peter F. , Bhatia Tania , Linsey G. D.
Published: November 2008

Barium Strontium Aluminosilicate (BSAS)-based environmental barrier coatings (EBCs) have been used successfully to protect the surface of Si-based fiber-reinforced ceramic-matrix composite (CMC) combustor liners in Solar Turbines Centaur 50S gas turbine engines. Two such EBC/CMC combustor liner sets were engine-exposed for times > 14,000h. However, extensive microstructural characterization of the EBC/CMC liners after the long-term engine exposures showed a significant loss/recession of the BSAS-based EBC. The mechanisms by which BSAS recession occurs and the rate at which the BSAS recesses as a function of pressure, gas velocity, temperature, etc. are not fully understood but such information will be necessary for improving the life to >15,000h in order for the materials to be acceptable for use in an engine application. To this end, the thermochemical stabilities of candidate EBCs are being evaluated analytically and experimentally at very high H2O pressures in a high-temperature, high-pressure furnace (Oak Ridge National Laboratory’s “Keiser Rig”). Calculations based on generalized volatility reactions and mass flux of volatilized species have shown that high H2O pressures can be used to compensate for the low gas-flow velocities in the Keiser Rig. An examination of the phase stability/volatilization of state-of-the-art EBC compositions (Ba- and Sr-based aluminosilicates) has been conducted through equilibrium thermodynamic calculations and initial experiments to validate assumptions via Keiser Rig exposures of the same EBC formulations conducted at 1250°C and 20 atm H2O.
Unsteady Load of Partial Admission Control Stage Rotor of a Large Power Steam Turbine
Authors: Lampart Piotr , Szymaniak Mariusz , Rza˛dkowski Romuald
Published: November 2008

Partial admission flow in the control stage of a 200MW steam turbine is investigated with the help of a RANS solver with k-ω SST turbulence model in the code Fluent. A 2D model of flow at the mid-span section of the full annulus is assumed. The results exhibit interesting details of the process of expansion in the control stage. Unsteady forces acting on the single rotor blades of the control stage are calculated, and are subject to Fourier analysis. Single blade forces are summed up to obtain the unsteady load at the rotor (forces acting at the rotor disc are neglected due to the assumed 2D model). The calculations take into account pressure pulsations at the entry to the nozzle boxes and rotor blade mistuning / geometrical imperfections.
Steady-State and Transient Compressor Surge Behavior Within a SOFC-GT-Hybrid System
Authors: Hildebrandt Andre , Genrup Magnus , Assadi Mohsen
Published: November 2008

Future pressurized Solid Oxide Fuel Cell (SOFC) Gas Turbine Hybrid Systems (HS) promise high efficiency at both full- and part-load on account of the upper and lower SOFC temperature limit and the compressor surge line [1]. The compressor surge constraint is also evident in transient HS operation, caused by the slow transients of SOFC temperature imposed by large SOFC plenum, and fast turbo-machinery transients. This paper presents steady-state and unsteady-state HS modeling and calculation results with regard to surge. The transient compressor and SOFC models have been validated against literature. Calculation results of the coupled SOFC-GT-HS reveal a small operational window in case of unmatched turbine and the critical transient characteristics for HS shut-down.
A Wall Function for Calculating the Skin Friction With Surface Roughness
Authors: Shabbir Aamir , Turner Mark G.
Published: November 2008

Wall functions are used in CFD to provide skin friction values and hence the boundary conditions for flow variables along solid surfaces. In this paper the effect of surface roughness on skin friction is incorporated in a wall function approach which uses Spalding’s formula. The use of Spalding’s formula extends the method to a wider range of wall distance than the logarithmic friction law. For CFD applications the results are then re-formulated for explicit calculation throught the use of an additional variable — the ratio of the surface roughness height to the distance from the solid surface. For a given computational grid this information is readily available in a CFD calculation. This methodology is applied to a linear compressor cascade that has been experimentally measured for different roughness values. The comparison of the simulation followed the same trends as the experiment, but with less overall effect.
An Integrated Fault Diagnostics Model Using Genetic Algorithm and Neural Networks
Authors: Sampath Suresh , Singh Riti
Published: November 2008

This paper presents the development of an integrated fault diagnostics model for identifying shifts in component performance and sensor faults using Genetic Algorithm and Artificial Neural Network. The diagnostics model operates in two distinct stages. The first stage uses response surfaces for computing objective functions to increase the exploration potential of the search space while easing the computational burden. The second stage uses concept of a hybrid diagnostics model in which a nested neural network is used with genetic algorithm to form a hybrid diagnostics model. The nested neural network functions as a pre-processor or filter to reduce the number of fault classes to be explored by the genetic algorithm based diagnostics model. The hybrid model improves the accuracy, reliability and consistency of the results obtained. In addition significant improvements in the total run time have also been observed. The advanced cycle Intercooled Recuperated WR21 engine has been used as the test engine for implementing the diagnostics model.
Ignition Delay Time Measurements of C2HX Fuels and Comparison to Several Detailed Kinetics Mechanisms
Authors: Petersen Eric L. , Hall Joel M. , Kalitan Danielle M. , Rickard Matthew J. A.
Published: November 2008

Recent results from experiments and modeling by the authors are reviewed for the ignition of acetylene, ethylene, and ethane in oxygen/argon mixtures at temperatures between 1000 and 2300 K and pressures near 1 atm. The ignition measurements were obtained behind reflected shock waves using emission from electronically excited OH and CH radicals to monitor the reaction progress. While many discrepancies exist amongst previous studies for these lower-order hydrocarbons, the accuracy afforded by the present experiments provides conclusive evidence verifying the trends seen in certain studies from the literature. Several modern, detailed chemical kinetics mechanisms were compared to the new results with some models showing quite good agreement with both ignition delay times and species profiles, particularly for stoichiometric mixtures. However, improvement is still required to match the entire range of fuel concentrations, temperatures, and mixture ratios, particularly for fuel-rich mixtures.
Using “Design Envelopes” to Aid in the Preliminary Design of Rotating Turbomachinery
Authors: Byerley Aaron R. , Boyer Keith M. , Halliwell Ian
Published: November 2008

This paper describes a systematic and graphical approach for leading undergraduates or other inexperienced designers through the preliminary design process of rotating turbomachinery. It is based upon the general principles of classic thermal system design and optimization. The paper explains the steps required to arrive at a combination of design variables that yield a “design envelope” or workable domain of aerodynamic and mechanical solution space. Once the “design envelopes” for both the compressor and the turbine have been identified, the rotor angular velocities are matched. The students are introduced to the design concept of moving from the workable to the optimal using two Mathcad®11 worksheets described in the paper. The process begins with obtaining the performance requirements and operating conditions form cycle analysis which leads to the selection of the aerodynamic design point. A system of equations based upon aerodynamic and mechanical principles is then optimized for both the compressor and the turbine. Two animated surface plots allow the designer to keep track of three independent design variables as they influence the value of an objective function that represents how close each design alternative is to achieving the target values of several important stage properties. Constraint maps reveal the range of acceptable rotor angular velocities for both the compressor and the turbine which enables a match to be made. The design approach is explained using a descriptive example of a multistage compressor and turbine operating on a high pressure spool. This paper provides a clear roadmap for systematically arriving at the correct combination of multiple design inputs that yield the appropriate multiple outputs required in the preliminary design of rotating turbomachinery.
Unsteady Aerodynamics and Aeroacoustics of a High-Bypass Ratio Fan Stage
Authors: Prasad Anil , Prasad Dilip
Published: November 2008

A numerical investigation of the unsteady aerodynamics of a fan stage comprised of a transonic rotor, swept fan exit guide vane (FEGV) and low-pressure compressor inlet guide vane (IGV) is described, with emphasis on acoustics. It is shown that the effects of the two downstream stator rows on the time-mean blade flow field are negligible, permitting its investigation using isolated rotor calculations. Simulations of this type are carried out along the engine operating line to quantify the acoustic sources associated with the upstream shock field and wake turbulence-stator interaction. The shock noise achieves its maximum value near the flyover acoustic certification condition, while the wake turbulence is least at this condition owing to its proximity to the design point. The behavior of these noise sources is explained physically by carrying out a detailed examination of the rotor flow field. The unsteady interaction between the rotor and stator rows at a high-power setting is investigated next. It is shown that the time-mean IGV flow is significantly affected by this interaction. Moreover, the unsteady loading on the IGV is found to be large. The behavior of the upstream-propagating acoustic field generated by rotor-IGV interaction is examined. The interaction between the rotor and FEGV is found to be linear in nature. The FEGV surface unsteady pressure and far-field acoustic field behavior are investigated.
A Comprehensive Prognostics Approach for Predicting Gas Turbine Engine Bearing Life
Authors: Orsagh Rolf , Roemer Michael , Sheldon Jeremy , Klenke Christopher J.
Published: November 2008

Development of practical and verifiable prognostic approaches for gas turbine engine bearings will play a critical role in improving the reliability and availability of legacy and new acquisition aircraft engines. In addition, upgrading current United States Air Force (USAF) engine overhaul metrics based strictly on engine flight hours (EFH) and total accumulated cycles (TAC) with higher fidelity prognostic models will provide an opportunity to prevent failures in engines that operate under unusually harsh conditions, and will help avoid unnecessary maintenance on engines that operate under unusually mild conditions. A comprehensive engine bearing prognostic approach is presented in this paper that utilizes available sensor information on-board the aircraft such as rotor speed, vibration, lube system information and aircraft maneuvers to calculate remaining useful life for the engine bearings. Linking this sensed data with fatigue-based damage accumulation models based on a stochastic version of the Yu-Harris bearing life equations with projected engine operation conditions is implemented to provide the remaining useful life assessment. The combination of health monitoring data and model-based techniques provides a unique and knowledge rich capability that can be utilized throughout the bearing’s entire life, using model-based estimates when no diagnostic indicators are present and using the monitored features such as oil debris and vibration at later stages when failure indications are detectable, thus reducing the uncertainty in model-based predictions. A description and initial implementation of this bearing prognostic approach is illustrated herein, using bearing test stand run-to-failure data and engine test cell data.
Wet Compression System Stability Analysis: Part I — Wet Compression Moore Greitzer Transient Model
Authors: Li Minghong , Zheng Qun
Published: November 2008

Wet compression Moore-Greitzer stability model is established in this paper. Transient performances of wet compression system are investigated and discussed. The model can be used for instabilities analyses of wet compression gas turbine, and be used for active control of compression system instabilities. The simulation results indicate that water injection is not only a technique to improve the thermodynamic performance of gas turbine, but also be an effective method to stabilize the instabilities of the compression system, surge and rotating stall.
Frequency Response Analysis of an Actively Lubricated Rotor/Tilting-Pad Bearing System
Authors: Nicoletti Rodrigo , Santos Ilmar Ferreira
Published: November 2008

In the present paper, the dynamic response of a rotor supported by an active lubricated tilting-pad bearing is investigated in the frequency domain. The theoretical part of the investigation is based on a mathematical model obtained by means of rigid body dynamics. The oil film forces are inserted into the model by using two different approaches: (a) linearized active oil film forces and the assumption that the hydrodynamic forces and the active hydraulic forces can be decoupled; (b) equivalent dynamic coefficients of the active oil film and the solution of the modified Reynolds equation for the active lubrication. The second approach based on the equivalent dynamic coefficients leads to more accurate results since it includes the frequency dependence of the active hydraulic forces. Theoretical and experimental results reveal the feasibility of reducing resonance peaks by using the active lubricated tilting-pad bearing. By applying a simple proportional controller, it is possible to reach 30% reduction of the resonance peak associated with the first rigid body mode shape of the system. One of the most important consequences of such a vibration reduction in rotating machines is the feasibility of increasing their operational range by attenuating resonance peaks and reducing vibration problems.
Thermal Improvement of Coal and Cooking Oil Wastes Mixtures in a Fluidised-Bed Gasifier
Authors: Franco Carlos , Andre´ Rui , Pinto Filomena , Gulyurtlu Ibrahim , Cabrita Isabel
Published: November 2008

The objective of co-gasiication of edible oil wastes with coal or biomass, could, on one hand, lead to improvement of characteristics of final product, benefiting from complementary natures of different fuels and could simultaneously contribute to resolving the environmental problem of disposing used edible oils. This work also aims at providing potential new applications for law rank coals including those from marginal reserves. Co-gasification studies of mixtures of coal or biomass wastes with small amounts of waste edible oils (WEO) were carried out in an atmospheric bench-scale fluidised bed gasifier. The gasification medium was both steam and air-steam mixtures. The experimental trials were undertaken to understand the behaviour of these mixtures and to optimize the range of operating conditions, like gasification temperature, air-steam/fuel ratio and oil content in the feedstock.
Condition-Based Maintenance for Aircraft Engines
Authors: Rajamani Ravi , Wang Jihua , Jeong Ki-Young
Published: November 2008

In this paper we describe how a condition-based maintenance (CBM) system might be operated for operators of assets such as aircraft engines. We show that merely having a monitoring and diagnostics system in place is not enough to derive the full, or even the majority of the, benefit from CBM. Our investigations show that to maximize the benefits from CBM for the enterprise, it is as important to focus on the aftermarket supply chain — i.e. the back-end of the process — as it is to develop better data gathering, diagnostics, and prognostics techniques. Via simulation, we show that optimizing the value chain results in lower costs and turn around times, and higher asset availability, spare part availability, and fill rates. For individual equipment operators the benefits could be substantial, depending on the size of their fleets and nature of their equipment usage. Providers of maintenance services, increasingly the original equipment manufacturers, stand to gain as well. As the demands on the aftermarket supply chain become more predictable, they can service the same asset base with lower spares inventory, while meeting increasingly aggressive turn-around-time targets, thus improving the bottom line and customer satisfaction.