bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Healing Technology for Compressor and Turbine Blades
Authors: Guntur Krishna , Amano R. S. , Lucci Jose Martinez , Rohatgi P. K. , Schultz Ben
Published: February 2010

The problem of cracking in steam turbines and compressor blades is one of the major problems associated with their design. Not only in these areas, but many other parts are suffering from the same problem of cracking due to excess stress, fatigue and high temperatures. One of the recent solutions to this is the use of specialized alloys, ceramics and metal matrix composites with improved high temperature strength and fatigue limits, but these materials will also suffer from cracking. Another potential method of improving the fatigue life of steam turbine and compressor blades is through the use of self-healing metals. There has been a recent interest in making self-healing metal composites that heal any cracks with little or no human interaction. One of the ways to achieve this is to send a healing agent (generally a low melting alloy or uncured resin) through hollow passages made in the matrix. When a crack appears, the healing agent flows into the crack, solidifies and closes the crack, effectively healing it. Recently, researchers at UW-Milwaukee have extended the concept of self-healing to metals, and have synthesized self-healing aluminum and solder alloys. This method may be used for the blades of steam turbines and compressors. The hollow passages can be made in a similar method that cooling passages of the gas turbine blades are made. Proper material choice will result in good bonding between the healing agent and the walls of a crack. This study deals with the advantages, ease of use and other considerations for this method to be used in practice. The main problems that need to be over come are materials selection, loss of strength due to addition of hollow channels, and the need to develop methods to initiate healing by flow of the healing agent into a crack. Plausible solutions to these are also discussed.
Heat-Exchanged Propulsion Gas Turbines: A Candidate for Future Lower SFC and Reduced-Emission Military and Civil Aeroengines
Authors: McDonald Colin F. , Rodgers Colin
Published: February 2010

After seven decades of service the evolution of simple cycle propulsion gas turbines continues with emphasis now being placed on reduced fuel burn, lower emissions, and less noise. With compressor and turbine efficiencies near plateauing, and turbine inlet temperatures paced by materials and blade cooling technologies, improvements in SFC, specific power and weight for conventional engines (including small turboprop, and turboshaft engines and larger turbofans) will likely be incremental compared with the past. With retention of the simple cycle both evolutionary and revolutionary approaches are being taken by the aeroengine industry to improve performance, particularly reduced fuel burn in an era of high fuel cost. In this paper a further step is suggested, that is in concert with meeting performance, economic, and environmental goals of future aeroengines, namely the use of a more complex thermodynamic cycle involving recuperation for turboprop and turboshaft engines, and intercooling together with recuperation for higher pressure ratio turbofan engines. The idea of heat exchanged propulsion gas turbines is not new, but the many concepts identified from studies done periodically over the last 65 years, including the few engines that were static tested and one test flown, didn’t find acceptance in an era of low fuel cost and concerns about recuperator integrity and reliability. With today’s very high fuel cost there is current interest in this type of engine because of its potential for low SFC and reduced emissions. In this paper potential applications are summarized and the features of various heat exchanged aeroengine design concepts together with projected performance are presented. Included is a discussion on the various issues that must be resolved before they enter service. A postulated deployment scenario is suggested with engines initially developed to meet military aviation needs, such as recuperated turboprop and turbofan engines for extended range UAV’s, followed by a recuperated turboshaft engine for a helicopter. Operational experience and demonstrated reliability from these would pave the way for high efficiency ICR turbofan engines for military and civil aircraft service sometime after the year 2020.
Effects of a Reacting Cross-Stream on Turbine Film Cooling
Authors: Anderson Wesly S. , Polanka Marc D. , Zelina Joseph , Evans Dave S. , Stouffer Scott D. , Justinger Garth R.
Published: February 2010

Film cooling plays a critical role in providing effective thermal protection to components in modern gas turbine engines. A significant effort has been undertaken over the last 40 years to improve the distribution of coolant and to ensure that the airfoil is protected by this coolant from the hot gases in the freestream. This film, under conditions with high fuel air ratios, may actually be detrimental to the underlying metal. The presence of unburned fuel from an upstream combustor may interact with this oxygen rich film coolant jet resulting in secondary combustion. The completion of the reactions can increase the gas temperature locally resulting in higher heat transfer to the airfoil directly along the path line of the film coolant jet. This secondary combustion could damage the turbine blade, resulting in costly repair, reduction in turbine life, or even engine failure. However, knowledge of film cooling in a reactive flow is very limited. The current study explores the interaction of cooling flow from typical cooling holes with the exhaust of a fuel-rich well-stirred reactor operating at high temperatures over a flat plate. Surface temperatures, heat flux, and heat transfer coefficients are calculated for a variety of reactor fuel-to-air ratios, cooling hole geometries, and blowing ratios. Emphasis is placed on the difference between a normal cylindrical hole, an inclined cylindrical hole, and a fan shaped cooling hole. When both air and nitrogen are injected through the cooling holes, the changes in surface temperature can be directly correlated to the presence of the reaction. Photographs of the localized burning are presented to verify the extent and locations of the reaction.
The Application of Time-Frequency and Phase Diagram Analyses for the Early Detection of Faulty Roller Bearing
Authors: Jauregui Juan C. , Gonzalez Oscar , Rubio Eduardo
Published: February 2010

There are many systems that monitor and analyze machinery conditions, but there is a lack on monitoring techniques that are able to identify early faults. This is critical since faulty roller bearings cause most of the problems in rotating machinery. Two major difficulties limit the early prediction of roller bearing failures: The acquisition of high frequency data, and the low energy levels emitted by surfaces cracks on rollers or tracks. Early fault detection requires adequate instrumentation and signal analysis. Therefore, it is important to identify its nonlinear response, and to be able to detect low energy signals in order to detect early faults. The vibration characteristics of the bearing depend on the rotational speed, clearance, radial load, rolling element stiffness, and the surface waviness. Additionally, they generate transient vibrations due to stiffness nonlinearities and structural defects. We present in this work a technique for the detection of early faults. The technique is based on the derivation of the rolling bearing nonlinear stiffness as a function of the roller translation and roller deformation. For the deformation, we determine the relative displacement of the roller tracks and we apply Hertz’s contact stress function. With this formulation we identify the nonlinear response to the external excitation forces. Then, the results are analyzed with a time-frequency map and the phase diagram; the two analyses are compared in order to determine the best signal procedure to identify early failures.
Modelling and Performance Analysis of the Rolls-Royce Fuel Cell Systems Limited: 1 MW Plant
Authors: Trasino Francesco , Bozzolo Michele , Magistri Loredana , Massardo Aristide F.
Published: February 2010

This paper is focused on the performance of the 1MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector and off gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the components is complex and the system behaviour is determined by many parameters. In particular two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole and each physical component is modelled in detail as a sub-system. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the SOFC stack and reformer. In order to characterise the system behaviour, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure as described in the paper. Given the complexity of the system various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.
Investigation of Trailing Edge Cooling Concepts in a High Pressure Turbine Cascade: Analysis of the Adiabatic Film Cooling Effectiveness
Authors: Dannhauer Axel
Published: February 2010

Within a European research project experimental studies were performed concerning the determination of the film cooling efficiency on the pressure side of trailing edges of high pressure turbine blades. The experiments were carried out at the linear cascade wind tunnel (EGG) of the German Aerospace Center (DLR), Go¨ttingen. The thermodynamic investigations were performed using the same cascade geometries and trailing edge configurations as for the aerodynamic measurements. Two different trailing edge geometries with coolant ejection were investigated. The first configuration was equipped with a pressure side cutback while for the second configuration the pressure side film cooling was realized by a row of cylindrical holes. The determination of the surface temperatures was done by using a combination of IR-thermography and thermocouples. Preliminary studies showed the feasibility to use metallic surfaces of the suction side of the adjacent blade as a mirror for IR-thermography. Thus it is possible to observe the pressure side near the trailing edge of interest by means of an infrared camera. The camera was mounted outside of the cascade’s free stream ensuring no influence to the aerodynamic boundary conditions. Up to seven flush mounted thermocouples on each side of the trailing edge were used for an in-situ calibration of the infrared pictures and thermal loss calculations. The distributions and averaged values of the film cooling efficiency are in agreement with aerodynamic measurements [9]. The results for the cutback configuration with 0.5% mass flow rate ejected show an accumulation of coolant just behind the coolant slot which is caused by a vortex in the dead region of the cutback. In case of 1.0% mass flow rate a refilling of this region with coolant is indicated. For higher mass flow rates the distributions of the film cooling efficiency looses it’s homogeneity due to flow separations on some ribs of the pin fin array inside of the slot. For the configuration with pressure side bleeding the best coverage could be obtained applying 1.0% mass flow rate.
CFD Assisted Design of Micro GT Combustor
Authors: Levy Yeshayahou , Erenburg Vladimir , Goldman Yakov , Sherbaum Valery , Ovcharenko Vitaly
Published: February 2010

The work presents the development of a micro-combustor design, where the combustion process was simulated by CFD and tested experimentally. The inner diameter of the first model was 5.5 mm, the exit diameter 2.5 mm, and the length 24.5 mm. The designed heat release was 200W. Some modifications of the microcombustor were studied. Three-dimensional model for combustion simulations was used. The ‘conjugate heat transfer’ methodology, based on a simultaneous solution of the heat transfer equations for gas and combustor walls, coupled with equations for the working fluid, enabled the prediction of the combustor wall temperatures. To check model convergence 2 simulations with different number of cells were carried out. Effect of heat radiation was also studied by the CFD simulation. The fuel is methane and stoichiometric ratio was simulated. Reactive flow calculations were carried out with a two-step reaction. The analysis of the simulated results was based on the obtained velocity profiles, concentration and temperature distributions within the liner. Preliminary simulations showed that the first combustor design had inefficient combustion. The reason was poor mixing of methane and air inside the mixing chamber and deterioration of the combustion by dilution holes. Consequently, the combustor design was modified and simulated. The simulation showed that the modification significantly improved mixing and combustion process and better combustion was provided. Due to complexity associated with performing combustion experiments in such small dimensions, only limited data could be recorded. A small combustor was manufactured and tests and demonstrated its successful operation. Measurements of temperature and optical UV-VIS-IR - emissions at the combustor exit were obtained. The experimental and simulation results are compared and a good qualitative agreement was found between the experiments and the predicted values.
Active Control of Noise in Supersonic Jets Using Plasma Actuators
Authors: Samimy Mo , Kim Jin-Hwa , Kearney-Fischer Martin
Published: February 2010

Noise mitigation has been in the forefront of research and development since the advent of jet engines. Supersonic commercial and especially supersonic military aircraft cannot take the advantages offered by large bypass ratio engines due to significant drag penalty and performance degradation. Therefore, other control techniques must be utilized to reduce noise and satisfy the more recent and looming future stringent noise regulations. A class of plasma actuators has recently been developed at the Ohio State University that offers a significant promise. These actuators possess a wide bandwidth and can provide large amplitude perturbations enabling manipulation of various instabilities in high Reynolds number subsonic and supersonic jets for noise mitigation as well as mixing enhancement. A brief overview of the actuators and some results are presented in perfectly-expanded Mach 1.3 axisymmetric unheated and heated jets.
The Effect of Side Wall Mass Extraction on Pressure Loss and Heat Transfer of a Ribbed Rectangular Two-Pass Internal Cooling Channel
Authors: Schu¨ler Marco , Zehnder Frank , Weigand Bernhard , von Wolfersdorf Jens , Neumann Sven Olaf
Published: February 2010

Gas turbine blades are often cooled by using combined internal and external cooling methods, where for internal cooling purposes usually serpentine passages are applied. In order to optimize the design of these serpentine passages it is inevitable to know the influence of mass extraction due to film cooling holes, dust holes or due to side walls for feeding successive cooling channels as for the trailing edge on the internal cooling performance. Therefore, the objective of the present study was to analyse the influence of side wall mass extraction on pressure loss and heat transfer distribution in a two-pass internal cooling channel representing a cooling scheme with flow towards the trailing edge. The investigated rectangular two-pass channel consisted of an inlet and outlet duct with a height-to-width ratio of H/W = 2 connected by a 180° sharp bend. The tip-to-web distance was kept constant at Wel/W = 1. The mass extraction was realized using several circular holes in the outlet pass side wall. Two geometric configurations were investigated: A configuration with mass extraction solely in the outlet pass, and a configuration with mass extraction in the bend region and outlet pass. The extracted mass flow rate was 0%, 10%, and 20% of the inlet channel mass flow. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Pressure losses were determined in separate experiments by local static pressure measurements. Furthermore, a computational study was performed solving the Reynolds-Averaged Navier-Stokes equations (RANS method) using the commercial Finite-Volume solver FLUENT. The numerical grids were generated using the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f model. The experimental data of the investigation of side wall ejection showed that the heat transfer in the bend region slightly increased when the ejection was in operation, while the heat transfer in the section of the outlet channel with side wall ejection was nearly not affected. After this section a decrease in heat transfer was observed which can be attributed to the decreased mainstream mass flow rate.
Combustor Design for Low Emissions and Long Lifetime Requirements
Authors: Eroglu Adnan , Flohr Peter , Brunner Philipp , Hellat Jaan
Published: February 2010

Advanced combustor design for gas turbines in power generation is driven by reliability, lifetime and emission requirements, by needs for fuel flexible operation, and minimization of cost of electricity. The present paper explains in detail the basic design principles of the annular combustors, as implemented in the most recent upgrades of the GT13E2 and GT24/GT26 engine families. One fundamental principle is the choice of a premix burner system with low pressure drop, allowing serial combination of a convective cooling scheme by fuel-air premixing with almost all available air. This allows operating at the lowest possible flame temperature, for a given hot gas temperature, thus assuring the minimum NOx emissions. Introduction of advanced seals reduce the leakage of air, helping further to reduce the flame temperature and improve burnout and stability. A second distinct feature of annular combustors is the possibility of single- and multiple-row burner arrangements for optimized operational flexibility. Burner arrangements are further optimized to yield the best stability with low heat loads to combustor walls and more uniform exit temperature distribution over the entire engine load range. Another feature of the modular combustion chambers is the separation of cold load-carrying structures and hot heat-shielding elements, which allows for easy maintenance and minimization of air leakages. Examples for the most recent component upgrades will be given in the full paper, with a focus on the reheat (SEV) combustor improvements for increased robustness and life-time, whilst maintaining combustion performance and minimizing cost. Field-feedback has proven to be an important element to understand and exploit the full lifetime potential of this design concept. A comprehensive account of field data from both EV and SEV combustors are presented, accounting more than one and a half decade long operation experience with annular combustors.
Application of the SAS Turbulence Model to Buoyancy Driven Cavity Flows
Authors: Smirnov Pavel E. , Kapetanovic Semir , Braaten Mark E. , Egorov Yuri , Menter Florian R.
Published: February 2010

The SST-SAS model has been applied to compute variable-density flow and heat transfer in cavities subjected to intensive rotation. To validate the model, a benchmark test case was simulated first and numerical solutions were compared with the measurements at different mass flow rates and rotation rates. A fairly good agreement with the experiment is demonstrated compared with the characteristic flow features observed in the experiments (e.g., two counter-rotating vortices of global circulation and a radial arm flow) as well as for the trends in disk heat transfer. This justified the application of the model to a rotor cavity of a real aircraft engine. The simulations performed indicate that the SST-SAS model captures the large-scale vortical structures developing in the cavity and predicts measured temperature difference between the cavity inlet and outlet within the experimental uncertainty limits. For both considered flows, a grid sensitivity study has been performed confirming a sufficient accuracy of the numerical solutions obtained on the baseline grids.
Local Thermal Buckling Analysis Method of Combustor Liner
Authors: Hong Jie , Gao Jinhai , Ma Yanhong , Chen Meng
Published: February 2010

Aero-engine combustor liners are always plagued by local thermal buckling failure problems because of complex thermal and mechanical loading conditions caused by the continuously increasing thrust-to-weight ratio and turbine gas temperature. Traditional theoretical methods focus on simple plate and shell structures, and the numerical methods are not applicable in local thermal buckling analysis of complex structures and loading conditions. As a result, it is necessary to establish a local thermal buckling analysis method in which the failure mechanism must be taken into account. Firstly, the discriminant of thin-wall structure thermal buckling instability boundary is derived from governing equations of plates in which the stress function and deflection function are two variables, and the two buckling factors which are local temperature and compressive stress are included in the equations. Secondly, the three dimensional temperature distribution of a combustor liner is captured by the numerical simulation of an annular return-flow combustion chamber with ANSYS/CFX based on the thermal-fluid-solid coupling finite element (FE) method. The calculation includes the effect of heat source and heat radiation, the influence of variable flow field on heat transfer and variation of properties with temperature of the gas, kerosene, and the solid. In addition, the resultant imposed thermal load and design pressure load are used to capture the critical locations in the combustor liner through static analysis considering thermal buckling instability factors. The critical temperature and critical compressive stress which are the defining parameters of local thermal buckling discriminant are calculated with FE and the sub-model method. Then a judgment of local thermal buckling is performed through the discriminant. Analysis results for an example combustion chamber calculated by the method in this paper are compared with the experimental data. It is concluded that the local thermal buckling analysis method is accurate and valid.
Ignition and Oxidation of 50/50 Butane Isomer Blends
Authors: Donato Nicole , Aul Christopher , Petersen Eric , Zinner Christopher , Curran Henry , Bourque Gilles
Published: February 2010

One of the alkanes found within gaseous fuel blends of interest to gas turbine applications is butane. There are two structural isomers of butane, normal butane and iso-butane, and the combustion characteristics of either isomer are not well known. Of particular interest to this work are mixtures of n-butane and iso-butane. A shock-tube experiment was performed to produce important ignition delay time data for these binary butane isomer mixtures which are not currently well studied, with emphasis on 50–50 blends of the two isomers. These data represent the most extensive shock-tube results to date for mixtures of n-butane and iso-butane. Ignition within the shock tube was determined from the sharp pressure rise measured at the endwall which is characteristic of such exothermic reactions. Both experimental and kinetics modeling results are presented for a wide range of stoichiometry (φ = 0.3–2.0), temperature (1056–1598 K), and pressure (1–21 atm). The results of this work serve as validation for the current chemical kinetics model. Correlations in the form of Arrhenius-type expressions are presented which agree well with both the experimental results and the kinetics modeling. The results of an ignition-delay-time sensitivity analysis are provided, and key reactions are identified. The data from this study are compared with the modeling results of 100% normal butane and 100% iso-butane. The 50/50 mixture of n-butane and iso-butane was shown to be more readily ignitable than 100% iso-butane but reacts slower than 100% n-butane only for the richer mixtures. There was little difference in ignition time between the lean mixtures.
Fundamental Differences Between Conventional and Geared Turbofans
Authors: Kurzke Joachim
Published: February 2010

The potential for improving the thermodynamic efficiency of aircraft engines is limited because the aerodynamic quality of the turbomachines has already achieved a very high level. While in the past increasing burner exit temperature did contribute to better cycle efficiency, this is no longer the case with today’s temperatures in the range of 1900...2000K. Increasing the cycle pressure ratio above 40 will yield only a small fuel consumption benefit. Therefore the only way to improve the fuel efficiency of aircraft engines significantly is to increase bypass ratio — which yields higher propulsive efficiency. A purely thermodynamic cycle study shows that specific fuel consumption decreases continuously with increasing bypass ratio. However, thermodynamics alone is a too simplistic view of the problem. A conventional direct drive turbofan of bypass ratio 6 looks very different to an engine with bypass ratio 10. Increasing bypass ratio above 10 makes it attractive to design an engine with a gearbox to separate the fan speed from the other low pressure components. Different rules apply for optimizing turbofans of conventional designs and those with a gearbox. This paper describes various criteria to be considered for optimizing the respective engines and their components. For illustrating the main differences between conventional and geared turbofans it is assumed that an existing core of medium pressure ratio with a two stage high pressure turbine is to be used. The design of the engines is done for takeoff rating because this is the mechanically most challenging condition. For each engine the flow annulus is examined and stress calculations for the disks are performed. The result of the integrated aero-thermodynamic and mechanical study allows a comparison of the fundamental differences between conventional and geared turbofans. At the same bypass ratio there will be no significant difference in specific fuel consumption between the alternative designs. The main difference is in the parts count which is much lower for the geared turbofan than for the conventional engine. However, these parts will be mechanically much more challenging than those of a conventional turbofan. If the bypass ratio is increased significantly above 10, then the geared turbofan becomes more and more attractive and the conventional turbofan design is no longer a real option. The maximum practical bypass ratio for ducted fans depends on the nacelle drag and how the installation problems can be solved.
A Novel Coal-Based Hydrogen Production System With Low CO2 Emissions
Authors: Xu Gang , Jin Hongguang , Yang Yongping , Duan Liqiang , Han Wei , Gao Lin
Published: February 2010

In this paper, we have proposed a novel coal-based hydrogen production system with low CO2 emission. In this novel system, a pressure swing adsorption H2 production process and a CO2 cryogenic capture process are well integrated to gain comprehensive performance. In particular, through sequential connection between the PSA H2 production process and the CO2 capture unit, the CO2 concentration of PSA purge gas that entering the CO2 capture unit can reach as high as 70%, which results in as much as 90% of CO2 to be separated from mixed gas as liquid at temperature of −55°C. This will reduce the quantity and quality of cold energy required for cryogenic separation method, and the solidification of CO2 is avoided. The adoption of cryogenic energy to capture CO2 enables direct production of liquid CO2 at low pressure, and thereby saves a lot of compression energy. Besides, partial recycle of the tail gas from CO2 recovery unit to PSA inlet can help to enhance the amount of hydrogen product and lower the energy consumption for H2 production. As a result, the energy consumption for the new system’s hydrogen production is only 196.8 GJ/tH2 with 94% of CO2 captured, which is 9.2% lower than that of the coal-based hydrogen production system with Selexol CO2 removal process, and is only 2.6% more than that of the coal-based hydrogen production system without CO2 recovery. What’s more, the energy consumption of CO2 recovery is expected to be reduced by 20–60% compared to that of traditional CO2 separation processes. Further analysis on the novel system indicates that synergetic integration of the H2 production process and cryogenic CO2 recovery unit, along with the synthetic utilization of energy, plays a significant role in lowering energy penalty for CO2 separation and liquefaction. The promising results obtained here provide a new approach for CO2 removal with low energy penalty.
Flow Field Derived Equivalent Reactor Networks for Accurate Chemistry Simulation in Gas Turbine Combustors
Authors: Drennan Scott A. , Chou Chen-Pang , Shelburn Anthony F. , Hodgson Devin W. , Wang Cheng , Naik Chitralkumar V. , Meeks Ellen , Karim Hasan
Published: February 2010

A method has been developed in which the flow field predicted by Computational Fluid Dynamics (CFD) is automatically condensed into an Equivalent Reactor Network (ERN), composed of well stirred reactors, allowing rapid and accurate analysis of emissions. This paper presents the effectiveness of utilizing an ERN that is a direct abstraction of the computational flow field for combustion analysis. The CFD results are divided into reactors using various filters on flow-field variables to construct an ERN that represents the 3-D combustor flow field and flame structure. Detailed kinetics can then be used in ERN simulations to analyze effects of fuel composition and operating condition on emissions. The technique is applied to a commercial industrial gas turbine combustor fuel injector and compared against experimental emissions results. Sensitivity of emissions predictions to different parameters in the network extraction is also presented. Parameter variations in fuel flow rate are applied to the ERN to obtain relative impacts of fuel-air ratio on the emissions of NOx without requiring new CFD solutions. This automatic approach has been found to reduce the time required to construct and analyze flow field derived ERNs with detailed chemistry by 90%. A local calculation of Damko¨hler number, important for stability analysis, is also presented. This calculation also uses abstracted information from the CFD flow field and detailed-kinetics simulations for more accurate, cost-effective analysis.
Gas Turbine Compressor Performance Characteristics During Wet Compression: Influence of Polydisperse Spray
Authors: Bhargava Rakesh K. , Bianchi Michele , Chaker Mustapha , Melino Francesco , Peretto Antonio , Spina Pier Ruggero
Published: February 2010

The available literature shows that there exists a lack of understanding about the impact of wet compression, involving two-phase flow, on the physics of flow in the compressor stages of a gas turbine engine. In recent years, analytical models have been proposed which provide effects of wet compression on the overall compressor performance and in few studies on the stage-by-stage performance. In spite of the fact that the wet compression technology for power augmentation has been commercially implemented on numerous gas turbines from all the major gas turbine manufacturers, many issues such as, effects of polydisperse spray, droplets dynamics, influence on the performance characteristics of individual stages, stage and overall surge margin, etc., remain not completely understood. This investigation clearly shows importance of considering effects of polydisperse spray on the overall and stage-by-stage compressor performance characteristics. The presented results show that for a given droplets distribution and ambient condition, later stages of a compressor are prone to reduced surge margin under wet compression process due to redistribution of stage loading. Moreover, the study shows that smaller distributions allow the achievement of higher performance, but the compressor surge is reached with a lower amount of injected water.
An Experimental Study on the Coupling of Combustion Instability Mechanisms in a Lean Premixed Gas Turbine Combustor
Authors: Lee Hyung Ju , Kim Kyu Tae , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A.
Published: February 2010

An experimental study was conducted to characterize the combined effects of flame-vortex interactions and equivalence ratio fluctuations on self-excited combustion instabilities in a swirl-stabilized lean premixed gas turbine combustor. The combustor was designed so that the fuel injector location and the combustion chamber length could be independently varied. In addition, the fuel and air could be mixed upstream of the choked inlet to the combustor, thereby eliminating the possibility of equivalence ratio fluctuations. Experiments were performed over a broad range of operating conditions and at each condition both the combustor length and the fuel injection location were varied. Dynamic pressure in the combustor, acoustic pressure and velocity in the mixing section, and the overall rate of heat release were simultaneously measured at all operating conditions. Two distinct instability regimes were observed; one near 220 Hz and the other near 345 Hz. It was also found that the strength of the instability changed significantly as the fuel injection location was varied, while the phase of the acoustic pressure and velocity fluctuations in the mixing section did not change. A time series of pressure and CH* chemiluminescence signals confirmed constructive or destructive coupling of the two instability mechanisms; the flame-vortex interaction and the equivalence ratio fluctuation interact each other and determine the instability characteristics in partially premixed conditions.
U.S. Navy Experiences Coking of Lube Oil Purifier Heaters
Authors: Rauf Walter , Philipp Russell
Published: February 2010

Normally U.S. Navy ships operate their lubricating oil systems with oil that is clear to light amber in color. Recently, many ships have reported the presence of dark oil and, in some cases, burgundy colored oil. Laboratory analysis of the affected oil has shown that the lube oil has been stressed due to heat. In at least three cases, the flashpoint and the viscosity of the oil were significantly reduced as compared to the samples analyzed from ship’s storage tanks. In one particular case volatile aromatics were discovered possibly indicating that pyrolysis is taking place. In an effort to determine the cause of the heat stress a hand-over-hand tracing of the system was accomplished. Subsequently, the lube oil purifier heater was inspected and coking of the heating elements was discovered. Approximately 65% of the ships inspected have reported fouling of the heating elements ranging from a tar-like substance to severe coking. A land-based lube oil purifier heater was configured to operate in the same manner as a shipboard unit. This unit was instrumented to collect oil and sheath temperature data to aid in determining the temperature within the heater that may cause the lubricating oil to form coke. In addition, laboratory testing is also being conducted to determine the oil’s tendency to coke and at what temperatures the pyrolysis will begin to take place. The purpose of this paper is to discuss the ongoing investigation, results of data collected, the laboratory testing and engineering solutions to minimize or eliminate lube oil coking.
Hybrid Fault Diagnosis: Application to a Gas Turbine Engine
Authors: Mohammadi Rasul , Hashtrudi-Zad Shahin , Khorasani Khashayar
Published: February 2010

This paper presents a hybrid framework for fault diagnosis of complex systems that are modeled by hybrid automata. A bank of residual generators is constructed based on the continuous models of the system. Each residual generator is modeled by a discrete-event system (DES). Next, the DES models of the residual generators and the DES model of the hybrid plant are combined to build an “extended DES” model. A hybrid diagnoser is constructed based on the extended DES model. The hybrid diagnoser effectively combines the readings of discrete sensors and the information supplied by the residual generators (which is based on continuous sensors) to determine the health status of the hybrid plant. The hybrid diagnosis approach is employed to investigate faults in the fuel supply system and the nozzle actuator of a single-spool turbojet engine with an afterburner.
Effects of Combustion Chamber Geometry Upon Exit Temperature Profiles
Authors: Kotzer Clayton , LaViolette Marc , Allan William
Published: February 2010

The purpose of this research was to investigate the effects of combustion chamber geometry on exit temperature fields using an ambient pressure test rig. The apparatus contained a 120° sector of a combustion section of a Rolls Royce (previously Allison) T56-A-15 gas turbine engine. A thermocouple rake acquired high-resolution temperature measurements in the combustion chamber exit plane. Rig test conditions were set to simulate an engine operating condition of 463 km/h (250 knots) at 7620 m (25000ft) by matching the Mach number, the equivalence ratio and the Sauter mean diameter of the fuel spray. To quantify the geometric deviations of the combustion chamber specimens, which varied in service conditions, a three-dimensional laser scanning system was used. Combustion chamber geometric deviations were extracted through comparison of the scanned data to a reference model using the selected software. The relationship between combustion chamber exit temperature profile and geometric deviation was then compared. The main conclusion of this research was that small deviations from nominal dimensions in the dilution zone of the combustion chamber correlated to an increase in pattern factor. A decrease in the mixing of the products of combustion and dilution air was observed as damage in the dilution zone increased. This reduction in mixing created a more compact, higher temperature core flow. The results obtained from this research were compared to past studies.
Ignition Triggering of Afterburner Fuel Using Partial Oxidation Mixtures
Authors: Cutright John T. , Neumeier Yedidia , Zinn Ben T. , Shahid Emad , Birmaher Shai
Published: February 2010

This study is the first of a three-part investigation into the feasibility of a practical augmentor operating without flame holders. The preliminary study presented herein investigated the enhancing effect that Partial Oxidation (POx) mixtures have on the ignition of propane, which simulated the Jet A fuel used in practical augmentors. The study used “synthetic” POx comprising a cold mixture of hydrogen, carbon monoxide and nitrogen. This allowed adjustments in the POx mixture composition to simulate the effect of short residence times in a partial oxidation reactor that could be used in practical applications to form the POx. The experimental setup used in this study consisted of a methane burning combustor whose products were further diluted with air to generate vitiated air with properties (e.g., temperature) simulating those that would be encountered in practical augmentor inlets subsequent to the expansion in the turbine. A secondary injector that was located downstream the main combustor was used to inject propane fuel with or without POx mixture into a simulated augmentor section. The secondary injection was performed so that the flame could not be readily stabilized by “conventional” flame holding processes. Instead, combustion occurred when the temperature of the vitiated air was sufficiently high to cause autoignition. The temperature of the vitiated air was controlled by the amount of the diluting air. The compositions of the gases upstream and downstream of the secondary injector were measured by a gas analyzer. The study used the autoignition limit of the augmentor fuel/POx mixture as a metric for the reaction kinetics responsible for the complete combustion of fuel in a realistic augmentor. The results indicate that a small amount of POx, with a composition that can be achieved in a reactor with 0.2 ms residence time, significantly enhanced the ignition process in the augmentor simulator. Specifically, the results showed that the ignition temperature of a mixture of propane and small amount of POx was nearly 100C lower than that of propane alone. Moreover, POx by itself had a nearly 200C lower ignition temperature than propane. This suggests that with proper design of the injection system even greater benefits could be obtained.
Novel Turbine Rotor Shroud Film-Cooling Design and Validation: Part 1
Authors: Chana K. S. , Haller B.
Published: February 2010

This paper is part one of a two part paper which considers a shroud film-cooling system designed using a two-dimensional approach. Heat transfer to rotor-casings has reached levels that are causing in-service difficulties to be experienced. Future designs are likely to need to employ film-cooling of some form. There is currently very little information available for film-cooling on shroudless turbine rotor-casing liners. Heat transfer literature on uncooled configurations is not extensive and in particular, spatially-detailed, time-accurate data are rare. This paper describes the aero-thermodynamic design and validation of a rotor casing film-cooling system for a transonic, high-pressure shroudless turbine stage. The design was carried out using a boundary layer code with the film-cooling hole geometry representative of an engine configuration and, has been subjected to mechanical constraints similar to those for an engine component. The design consists of two double rows of cooling holes and two ‘cooling-hole’ shape configurations, cylindrical and fan shaped. The design was tested in the QinetiQ short duration turbine test facility (TTF). Measurements taken include casing heat transfer using thin film gauges and stage exit total pressure, Mach number and flow angle using a three-hole pressure probe. Results showed that while the cooling produced a reduction in the heat transfer rate close to the injection point, the film was stripped off the casing and entrained in nozzle guide vane secondary and rotor overtip flow, where it was transported spanwise towards the hub in the rotor passage. Using the results obtained from this deign a second cooling design was carried out, using a three-dimensional approach this gave significantly better cooling performance. The thee-dimensional design and validation is reported in GT2009-60246 as part 2 of this paper.
Alkali Control for Gas Turbines by a Combined Hot Gas Clean-Up Approach
Authors: Schofield Keith
Published: February 2010

Gas turbines require very clean fuels if they are to avoid high temperature corrosion due to alkali sulfates and chlorides. Indications are that the alkali (sodium and potassium) salt levels need to be well below parts per million by volume in the hot gases and probably no more than 50 parts per billion by volume (0.01 mg/m3) for maintenance free operation. Moreover, it is the alkali that is the dominant factor and the actual concentrations of sulfur or chlorine are of minor relevance. Recently, numerous studies have shown that by using inexpensive absorbent type clay materials such as kaolin, bentonite, emathlite, or even bauxite and boehmite that these can reduce the alkali content very significantly (≥ 90%) in the hot gases. Coupled now to a final polishing method to remove the remainder, a new viable two step approach appears technically and economically feasible. This polishing method involves adding traces of either ammonium paramolybdate or ammonium metatungstate, both of which are water soluble, as a dilute aerosol into the hot gases. The ratio of molybdenum, or tungsten, to alkali needs to be in a ratio of about two to one on an atomic basis. This modifies the deposition process and alkali polymolybdate or polytungstate bronzes are preferentially produced. These are low melting point molecules that are benign and create with any remaining alkali a protective coating on the blades. They are thermodynamically more stable and rank above the sulfates and chlorides for formation. Also, being added in quantities of only parts per million or less there are no repercussions on NOX emissions or performance and remain cost effective at these levels. This coupling of the two complimentary approaches now appears feasible for final developmental testing to permit the use of alternate fuels without a need for cool-down cleaning cycles.
The Effect of Size on Optimisation of Solid Oxide Fuel Cell/Gas Turbine Hybrid Cycles
Authors: Brear Michael J. , Dunkley Michael J.
Published: February 2010

The integration of high temperature solid oxide fuel cells with gas turbines to form high efficiency, hybrid generators is receiving significant attention within both the academic and industrial communities. Various systems have been proposed or demonstrated, and which cover a range of sizes from low power generators suitable for domestic power generation through to larger systems in the megawatt size range. The performance of such hybrid systems depends on the matching of the fuel cell and gas turbine through optimisation of the system pressure ratio and reactant flow rates. Losses associated with non-ideal cycle components are significant and vary with component size, and must be taken into account if optimal performance is to be achieved. This paper presents an intentionally very simple numerical model of the hybrid system, so that the effect of key component efficiencies on the overall cycle efficiency can be examined easily. These component efficiencies of course scale with size, and the results presented suggest that hybrid cycles with total power output of order several MW are preferable.