bluuebunny/crossref_metadata_2025 huggingface dataset:
Retinal Microvascular Signs: A Key to Understanding the Underlying Pathophysiology of Different Stroke Subtypes?
Authors: Lindley Richard I. ,   and The Multi-Centre Retinal Stroke Study Collaborative
Published: September 2008

Background

The heterogeneity of the pathology of stroke has been a major difficulty in assessing new treatments for acute stroke, and contributes to the complexity of stroke medicine. Some underlying mechanisms are poorly understood, such as small vessel (lacunar) disease. New technology such as advanced brain imaging has transformed our knowledge of large vessel disease and we suggest that other new technology such as detailed analysis of retinal vessels may provide new insights into the pathology of small vessel (lacunar) stroke disease. We hypothesise that retinal microvascular signs differ by pathological stroke subtype, and we plan to test this hypothesis in over 1000 acute stroke patients.

Eligible patients undergo a standardised neurological assessment followed by digital retinal photography. At a consensus meeting, an anatomical and aetiological classification is determined. Retinal photographs will be assessed qualitatively (e.g. retinal emboli, arteriovenous nicking) and quantitatively (arteriolar/venule ratio). Six-month vascular event rates together with disability and vital status are collected.

Conclusion

Retinal vessel appearances may provide a ‘window’ to the brain and help determine the important underlying pathophysiological mechanisms of small vessel disease stroke.
Just War Theory and the Privatization of Military Force
Authors: Pattison James
Published: September 2008

The use of private military companies (PMCs) has become increasingly prevalent, with such firms as Blackwater, MPRI, and DynCorp taking over a growing number of roles traditionally performed by the regular military. This article uses the framework of just war theory (JWT) to consider the central normative issues raised by this privatization of military force. In particular, I first examine the claim that private contractors are inappropriate actors to wage war because they contravene the JWT principle of right intention. The next section asserts that the use of PMCs is largely consistent with the application of the principle of legitimate authority but undermines two of its central rationales. In the third section, I apply the jus in bello principle of discrimination to PMC personnel. Overall, I argue that JWT needs to be updated and extended to respond to the issues raised by the privatization of military force.
Incidence of open‐angle glaucoma in central Sweden
Authors: Ekström Curt
Published: September 2008

Purpose:  To estimate the incidence rate of open‐angle glaucoma (OAG) in a population in which pseudoexfoliation is a common finding.

Methods:  A population‐based survey of 760 people aged 65–74 years was conducted in the municipality of Tierp, in central Sweden, during 1984−86. Visual fields (VFs) were tested with the Competer 350 automated perimeter. The present report concerns 711 people, all of whom participated in the survey and were not diagnosed with glaucoma. Since 1988, a follow‐up study of the 530 individuals in this cohort with normal and reliable VFs has been in progress. Incident cases of OAG were identified among study participants and patients seeking medical attention at the Eye Department in Tierp. Records of prescriptions for anti‐glaucoma drugs were used to search for unidentified patients. A time‐weighted mean intraocular pressure (IOP) for all visits was calculated.

Results:  By the end of the study in May 2006, 51 new cases of definite OAG had been identified, 31 with capsular and 20 with chronic simple glaucoma. Of these, 46 cases were detected in the follow‐up study, corresponding to an incidence of 7.11 (95% confidence interval 5.06–9.17) per 1000 person‐years. Twelve of the 51 cases were classified as normal‐tension glaucoma, all of which were found in the follow‐up study. Open‐angle glaucoma with a mean IOP ≥ 23 mmHg tended to emerge closer to the baseline examination than OAG with a mean IOP < 23 mmHg.

Conclusions:  The incidence of OAG was high compared with that reported for other studies conducted in White populations.
Ejector Model for High Temperature Fuel Cell Hybrid Systems: Experimental Validation at Steady-State and Dynamic Conditions
Authors: Ferrari Mario L. , Pascenti Matteo , Massardo Aristide F.
Published: September 2008

The aim of this work is the experimental validation of a steady-state and transient ejector model for high temperature fuel cell hybrid system applications. This is a mandatory step in performing the steady state and the transient analysis of the whole plant to avoid critical situations and to develop the control system. The anodic recirculation test rig, developed at TPG-University of Genoa, and already used in previous works to validate the ejector design models (0D and computational fluid dynamics), was modified and used to perform tests at transient conditions with the aim of ejector transient model validation. This ejector model, based on a “lumped volume” technique, has been successfully validated against experimental data at steady-state and transient conditions using air or CO2 at room temperature and at 150°C in the secondary duct inlet. Then, the ejector model was integrated with the models of the connecting pipes, and with the volume simulation tool, equipped with an outlet valve, in order to generate an anodic recirculation model. Also in this case, the theoretical results were successfully compared with the experimental data obtained with the test rig. The final part of the paper is devoted to the results obtained with square wave functions generated in the ejector primary pressure. To study the effects of possible fast pressure variations in the fuel line (ejector primary line), the test rig was equipped with a servo-controlled valve upstream of the ejector primary duct to generate different frequency pressure oscillations. The results calculated with the recirculation model at these conditions were successfully compared with the experimental data too.
Biomass Solid Oxide Fuel Cell-Microgas Turbine Hybrid System: Effect of Fuel Composition
Authors: Sucipta Made , Kimijima Shinji , Song Tae Won , Suzuki Kenjiro
Published: September 2008

Performance analysis of the solid oxide fuel cell-microgas turbine (SOFC-MGT) hybrid system has been made. We assume a fuel composition that is methane based with varying concentrations of other species that are expected to be present in biomass-derived gas streams in preparation for the study of biomass fueled SOFC-MGT hybrid system. This is based on the fact that the chemical composition of biomass fuel produced from different fuel production processes is diversified, i.e., in one case one chemical species rich in concentration and in another case another chemical species rich. In the analysis, the multistage model for internal reforming SOFC module developed previously with some modification is used. With this model, studies cover not only the performance of the hybrid system but also the spatial distributions of temperature and concentration of some chemical species inside the module, namely, in the cell stack and in the internal reformer.
On-Demand Hydrogen via High-Pressure Water Reforming for Military Fuel Cell Applications
Authors: Oster Benjamin G. , Timpe Ronald C. , Aulich Ted R. , Lin Mike C. J. , Holcomb Franklin H.
Published: September 2008

Researchers have developed a high-pressure water-reforming (HPWR) process that produces high-pressure hydrogen from a jet fuel feedstock. Converting petroleum-based fuels to hydrogen for fuel cell use is a unique approach to reducing military petroleum consumption by improving petroleum utilization efficiency. HPWR is an attractive option because, unlike traditional steam methane reforming, it does not require postreformer hydrogen compression and storage. A HPWR apparatus was designed and manufactured. Several catalysts were tested for their ability to produce high-pressure hydrogen from jet fuel. S-8, which is a jet fuel derived from natural gas, was used as a model feedstock for initial experiments because the fuel is sulfur and aromatics free. After optimizing with S-8, JP-8 will be utilized for future experiments. The most promising catalyst produced a 4000psi(gauge) product gas stream that contained 54mol% hydrogen. These experimental results show that HPWR is a promising solution for high-pressure hydrogen production as a key step toward reducing military petroleum use.
A Simplified Method for Optimal Sensor Distribution for Process Fault Diagnosis in Multistation Assembly Processes
Authors: Xinmin Lai , Zhaoqing Tian , Zhongqin Lin
Published: September 2008

The fault diagnosis plays an important role for product quality improvement in the multistation assembly processes (MAPs) and the efficiency of diagnosis significantly depends on the sensor distribution strategy, such as the number and location of the sensor. The diagnosis-oriented sensor distribution optimization in MAP has been studied for the purpose of a full diagnosis of the process faults with the minimum sensing stations number as well as the minimum sensor number. However, the existing studies are time consuming with the complex analysis and calculation processes, and no intuitive principles are given directly according to the process configuration. In this paper, a simplified method for the optimal sensor distribution is presented for a fully diagnosis of the process faults. First, two different types of assembly modes are defined and the variation transmissibility ratios for these two assembly modes are discussed based on the process configuration. Then, the conditions for between-station diagnosability and within-station diagnosability are analyzed, respectively. Based on the results, the optimal sensor distribution method is derived finally. After comparing with the former methods, the optimal sensor distribution in this paper is based only on the process configuration without using for model-based matrix computation. Therefore, the proposed method greatly simplified the process.
Benchmark Experimental Data for Fully Stalled Wide-Angled Diffusers
Authors: Kibicho K , Sayers A. T.
Published: September 2008

Due to adverse pressure gradient along the diverging walls of wide-angled diffusers, the attached flow separates from one wall and remains attached permanently to the other wall in a process called stalling. Separated diffuser flows provide a classical case of pressure driven flow separation. Such flows present a very serious challenge to fluid dynamics modelers. This paper provides a data bank contribution for the streamwise mean velocity field and pressure recovery data in wide-angled diffusers. Turbulent mean flow measurements were carried out at Reynolds numbers between 1.07×105 and 2.14×105 based on inlet hydraulic diameter and centerline velocity for diffusers whose divergence angles were between 30 deg and 50 deg. The results presented provide a reliable validation data bank for computational fluid dynamics studies for pressure driven flow separation studies.
Influence of Torque on the Lift and Drag of a Particle in an Oscillatory Flow
Authors: Fischer Paul F. , Leaf Gary K. , Restrepo Juan M.
Published: September 2008

In the work of Fischer et al. (2002, “Forces on Particles in an Oscillatory Boundary Layer,” J. Fluid Mech., 468, pp. 327–347, 2005; “Influence of Wall Proximity on the Lift and Drag of a Particle in an Oscillatory Flow,” ASME J. Fluids Eng., 127, pp. 583–594) we computed the lift and drag forces on a sphere, subjected to a wall-bounded oscillatory flow. The forces were found as a function of the Reynolds number, the forcing frequency, and the gap between the particle and the ideally smooth rigid bounding wall. Here we investigate how the forces change as a function of the above parameters and its moment of inertia if the particle is allowed to freely rotate. Allowing the particle to rotate does not change appreciably the drag force, as compared to the drag experienced by the particle when it is held fixed. Lift differences between the rotating and nonrotating cases are shown to be primarily dominated in the mean by the pressure component. The lift of the rotating particle varies significantly from the fixed-particle case and depends strongly on the Reynolds number, the forcing frequency, and the gap; much less so on the moment of inertia. Of special significance is that the lift is enhanced for small Reynolds numbers and suppressed for larger ones, with a clear transition point. We also examine how the torque changes when the particle is allowed to rotate as compared to when it is held fixed. As a function of the Reynolds number the torque of the fixed sphere is monotonically decreasing in the range Re=5 to Re=400. The rotating-sphere counterpart experiences a smaller and more complex torque, synchronized with the lift transition mentioned before. As a function of the gap, the torque is significantly larger in the fixed particle case.
Extended Angular Range of a Three-Hole Cobra Pressure Probe for Incompressible Flow
Authors: Argüelles Díaz Katia María , Fernández Oro Jesús Manuel , Blanco Marigorta Eduardo
Published: September 2008

This paper analyzes the operative characteristics of a three-hole cobra type probe especially designed to attain an angular range higher than 180deg for planar turbulent flows. A new calibration and data reduction method are also introduced, discriminating three different zones inside the angular range of the calibration. This methodology improves the probe performance, extending its operative angular range from the typical ±30degto±105deg. In addition, the transmission of the uncertainty—from the pressure measurements to the flow variables—is estimated, showing reasonably low levels for the whole angular range. Furthermore, the sensibility of the probe calibration to the Reynolds number and the pitch angle is considered, and the influence of the turbulence level is outlined. Regarding these factors, the probe precision in the extended angular range is found to be similar to that of the traditional range. Finally, the probe is tested in a flow field with large variations of the incidence angle, and the results obtained with the new method are compared to those given by the traditional calibration.
A General Macroscopic Turbulence Model for Flows in Packed Beds, Channels, Pipes, and Rod Bundles
Authors: Nakayama A. , Kuwahara F.
Published: September 2008

This study focuses on Nakayama and Kuwahara’s two-equation turbulence model and its modifications, previously proposed for flows in porous media, on the basis of the volume averaging theory. Nakayama and Kuwahara’s model is generalized so that it can be applied to most complex turbulent flows such as cross flows in banks of cylinders and packed beds, and longitudinal flows in channels, pipes, and rod bundles. For generalization, we shall reexamine the extra production terms due to the presence of the porous media, appearing in the transport equations of turbulence kinetic energy and its dissipation rate. In particular, we shall consider the mean flow kinetic energy balance within a pore, so as to seek general expressions for these additional production terms, which are valid for most kinds of porous media morphology. Thus, we establish the macroscopic turbulence model, which does not require any prior microscopic numerical experiments for the structure. Hence, for the given permeability and Forchheimer coefficient, the model can be used for analyzing most complex turbulent flow situations in homogeneous porous media without a detailed morphological information. Preliminary examination of the model made for the cases of packed bed flows and longitudinal flows through pipes and channels reveals its high versatility and performance.
A Theoretical Solid Oxide Fuel Cell Model for System Controls and Stability Design
Authors: Kopasakis George , Brinson Thomas , Credle Sydni
Published: September 2008

As the aviation industry moves toward higher efficiency electrical power generation, all electric aircraft, or zero emissions and more quiet aircraft, fuel cells are sought as the technology that can deliver on these high expectations. The hybrid solid oxide fuel cell system combines the fuel cell with a microturbine to obtain up to 70% cycle efficiency, and then distributes the electrical power to the loads via a power distribution system. The challenge is to understand the dynamics of this complex multidiscipline system and the design distributed controls that take the system through its operating conditions in a stable and safe manner while maintaining the system performance. This particular system is a power generation and a distribution system, and the fuel cell and microturbine model fidelity should be compatible with the dynamics of the power distribution system in order to allow proper stability and distributed controls design. The novelty in this paper is that, first, the case is made why a high fidelity fuel cell model is needed for systems control and stability designs. Second, a novel modeling approach is proposed for the fuel cell that will allow the fuel cell and the power system to be integrated and designed for stability, distributed controls, and other interface specifications. This investigation shows that for the fuel cell, the voltage characteristic should be modeled, but in addition, conservation equation dynamics, ion diffusion, charge transfer kinetics, and the electron flow inherent impedance should also be included.
Modeling of a Proton Exchange Membrane Fuel Cell With a Large Active Area for Thermal Behavior Analysis
Authors: Jung Dohoy , Yu Sangseok , Assanis Dennis N.
Published: September 2008

A numerical model of a proton exchange membrane fuel cell has been developed to predict the performance of a large active area fuel cell with the water cooling thermal management system. The model includes three submodels for water transport, electrochemical reaction, and heat transfer. By integrating those submodels, local electric resistance and overpotential depending on the water and temperature distribution can be predicted. In this study the effects of the inlet gas temperature and humidity on the fuel cell performance are explored, and the effect of the temperature distribution at different coolant temperatures is investigated. The results show that the changes in local electric resistance due to temperature distribution cause fuel cell power decrease. Therefore, the coolant temperature and flow rate should be controlled properly depending on the operating conditions in order to minimize the temperature distribution while maximizing the power output of the fuel cell.
Influence of Air and Fuel Mass Flow Fluctuations in a Premix Swirl Burner on Flame Dynamics
Authors: Auer M. P. , Hirsch C. , Sattelmayer T.
Published: September 2008

This paper discusses the structural changes observed in oscillating premixed turbulent swirling flames and demonstrates the influence of modulated mass flows on the flame dynamics in a preheated atmospheric test rig with a natural gas fired swirl burner. The experimentally investigated self excited and forced combustion oscillations of swirl stabilized premixed flames show varying time delays between the acoustically driven mass flow oscillations and the integral heat release rate of the flame. High speed films of the OH*-chemiluminescence reveal how the flame structure changes with the oscillation frequency and the phase angle between the fuel mass flow oscillation and the total mass flow at the burner exit. These parameters are found determine the spatial and temporal heat release distribution and thus the net heat release fluctuation. Therefore, the spatial and temporal heat release distribution along the flame length has an influence on the thermoacoustic coupling, even in the case of acoustically compact flames. The observed phenomena are discussed further using an 1-d analytical model. It underscores that for swirl stabilized premixed turbulent flames the dynamics of the flow field perturbation play a major role in creating the effective heat release fluctuation.
Ceramic Composite Development for Gas Turbine Engine Hot Section Components
Authors: DiCarlo James A. , van Roode Mark
Published: September 2008

The development of ceramic materials for incorporation into the hot section of gas turbine engines has been ongoing for about fifty years. Researchers have designed, developed, and tested ceramic gas turbine components in rigs and engines for automotive, aero-propulsion, industrial, and utility power applications. Today, primarily because of materials limitations and/or economic factors, major challenges still remain for the implementation of ceramic components in gas turbines. For example, because of low fracture toughness, monolithic ceramics continue to suffer from the risk of failure due to unknown extrinsic damage events during engine service. On the other hand, ceramic matrix composites (CMC) with their ability to display much higher damage tolerance appear to be the materials of choice for current and future engine components. The objective of this paper is to briefly review the design and property status of CMC materials for implementation within the combustor and turbine sections for gas turbine engine applications. It is shown that although CMC systems have advanced significantly in thermo-structural performance within recent years, certain challenges still exist in terms of producibility, design, and affordability for commercial CMC turbine components. Nevertheless, there exist some recent successful efforts for prototype CMC components within different engine types.
Nozzle Guide Vane Static Strip Seals
Authors: Farahani Arash , Childs Peter
Published: September 2008

Sealing of components where there is no relative motion between the elements concerned remains a significant challenge in many gas turbine engine applications. Loss of sealing and cooling air from the internal air system through seals impacts on specific fuel consumption and can lead to undesirable flow interactions with resultant cost implications. For gas turbines, various strip seal types have been developed for use between Nozzle Guide Vanes in order to limit the flow of gas between the main stream annulus and the internal air system. Many different types of design have been proposed for overcoming strip seal problems such as misalignment of the grooves due to manufacturing and assembly constraints. In this paper various methods, with a particular focus on patents, for minimising the amount of leakage caused by such problems for strip seals between nozzle guide vanes are reviewed. By considering the advantages and disadvantages of each technique it is concluded that although apparently new strip seal designs for NGVs have improved performance, none of them can be considered to be ideal. This paper reviews the techniques and makes recommendations for future designs.
Active Control of Combustion Instabilities in Gas Turbine Burners
Authors: Paschereit Christian Oliver , Gutmark Ephraim
Published: September 2008

This paper gives an overview of open and closed loop active control methodologies used to suppress symmetric and helical thermoacoustic instabilities in an experimental low-emission swirl-stabilized gas turbine combustor. The controllers were based on fuel (or equivalence ratio) modulations in the main pre-mixed combustion or alternatively in secondary pilot fuel. For the main premix fuel supply two methods of fuel injection modulations were tested: symmetric and asymmetric injection. The tests showed that the closed loop asymmetric modulations were more effective in the suppression of the symmetric mode instability than symmetric fuel excitation. Symmetric excitation was quite efficient in abating the symmetric mode as well, however, at a certain range of phase shift the combustion was destabilized to an extent that caused blow out of the flame. Using premixed open loop fuel modulations the symmetric instability mode responded to symmetric excitation only when the two frequencies matched. The helical fuel injection affected the symmetric mode only at frequencies that were much higher than that of the instability mode. The asymmetric excitation required more power to obtain the same amount of reduction as that required by symmetric excitation. Unlike the symmetric excitation which destabilized the combustion when the modulation amplitude was excessive, the asymmetric excitation yielded additional suppression as the modulation level increased. The NOx emissions were reduced to a greater extent by the asymmetric modulation. Secondary fuel injection in a pilot flame was used to control low frequency symmetric instability and high frequency helical instability. Adding a continuous flow of fuel into the pilot flame controlled both instabilities. However, modulating the fuel injection significantly decreased the amount of necessary fuel. The reduced secondary fuel resulted in a reduced heat generation by the pilot diffusion flame and therefore yielded lower NOx emissions. The secondary fuel pulsation frequency was chosen to match the time scales typical to the central flow recirculation zone which stabilizes the flame in the burner. Suppression of the symmetric mode pressure oscillations by up to 20 dB was recorded.
Parts Life Management: Essential for Minimizing Life Cycle Costs
Authors: DellaVilla Salvatore A. , Steele Robert F.
Published: September 2008

This paper will review the issues associated with parts tracking and critical parts life management, discussing the need to implement accurate and efficient processes to develop meaningful and accurate empirical observations.
New Attempt for Diagnostics of the Geometry Deterioration of the Power System Based on Thermal Measurement
Authors: Gluch Jerzy , Krzyzanowski Jerzy
Published: September 2008

The authors developed the bi-modular thermal diagnostic system for power cycles, [1]. The task of the systems is not only search for inefficient components of the complex power cycle, [2], and determination of the type of its deterioration, [3], but also recognition of the geometry degradation of its faulty components, [4], based on thermal and flow measurements, which is the novelty of the presented diagnostic system. The paper summarises the developed procedure based on previous authors’ publications as indicated above and illustrates it with the flow diagram attached, Fig.1.
Prediction of Combustor Liner Cooling
Authors: Yuan Jiankun , Dede Mehmet , Buyukisik Osman , Xiong Yuexi
Published: September 2008

Effective cooling of combustor liners is an important and integrated part of jet engine combustor design, as the liner temperature directly impacts the durability of the combustor. Cooling air jet, usually around 1000–1200 °F, is inserted into slots at the onset of each liner panel. These slots and feedholes are together called nuggets. The discrete air jets are expected to coalesce and form a cooling film with uniform velocity at the exit of the slots. This paper presents results of CFD analysis using realizable k–ε turbulence model in a commercial CFD software FLUENT®. For accurate analysis of different nugget feedhole configurations, an appropriately selected turbulent model is crucial for flow and heat transfer analysis. Special care is given to the coefficient of destruction term related to the turbulent decay exponent of the dissipation rate in transport equation. Validation is achieved by comparison of predicted and measured liner cooling film effectiveness from experimental tests conducted under various blowing ratios. Mass transfer analogy method is used to measure cooling film effectiveness, represented by mass fraction of CO2 along combustor liner. Reasonably good agreement is obtained between the CFD analysis results and the experimental data.
Effects of Combustor Exit Profiles on High Pressure Turbine Vane Aerodynamics and Heat Transfer
Authors: Barringer M. D. , Thole K. A. , Polanka M. D.
Published: September 2008

The goal of this work was to investigate the effects of different profiles representative of those exiting aero-engine combustors on high pressure turbine vane aerodynamics and heat transfer. The various profiles were produced using the non-reacting, inlet profile generator in the Turbine Research Facility (TRF) located at the Air Force Research Laboratory (AFRL). This paper reports how the pressure loading and heat transfer along the vane surface is affected by different turbine inlet pressure and temperature profiles at several different span locations. The results indicate that the different inlet total pressure profiles affected the aerodynamic loading by as much as 10%. The results also reveal that the combination of different total pressure and total temperature profiles significantly affected the vane heat transfer for a baseline test with relatively uniform inlet total pressure and total temperature profiles. Near the ID endwall, the baseline heat transfer was reduced 30 to 40% over the majority of the vane surface. Near the OD endwall, it was found that certain inlet profiles could increase the baseline heat transfer by 20 to 30%, while other profiles resulted in a decrease of the baseline heat transfer by 30 to 40%.
Gas Turbine Off-Design Performance Adaptation Using a Genetic Algorithm
Authors: Lo Gatto E. , Li Y. G. , Pilidis P.
Published: September 2008

Gas turbine gas path diagnostics is heavily dependent on performance simulation models accurate enough around a chosen diagnostic operating point, such as design operating point. With current technology, gas turbine engine performance can be predicted easily with thermodynamic models and computer codes together with basic engine design data and empirical component information. However the accuracy of the prediction is highly dependent on the quality of those engine design data and empirical component information such as component characteristic maps but such expensive information is normally exclusive property of engine manufacturers and only partially disclosed to engine users. Alternatively, estimated design data and assumed component information are used in the performance prediction. Yet, such assumed component information may not be the same as those of real engines and therefore poor off-design performance prediction may be produced. This paper presents an adaptive method to improve the accuracy of off-design performance prediction of engine models near engine design point or other points where detailed knowledge is available. A novel definition of off-design scaling factors for the modification of compressor maps is developed. A Genetic Algorithm is used to search the best set of scaling factors in order to adapt the predicted off-design engine performance to observed engine off-design performance. As the outcome of the procedure, new compressor maps are produced and more accurate prediction of off-design performance is provided. The proposed off-design performance adaptation procedure is applied to a model civil aero engine to test the effectiveness of the adaptive approach. The results show that the developed adaptive approach, if properly applied, has great potential to improve the accuracy of engine off-design performance prediction in the vicinity of engine design point although it does not guarantee the prediction accuracy in the whole range of off-design conditions. Therefore, such adaptive approach provides an alternative method in producing good engine performance models for gas turbine gas path diagnostic analysis.
Film Cooling Effectiveness Distribution on a Gas Turbine Blade Platform With Inclined Slot Leakage and Discrete Film Hole Flows
Authors: Wright Lesley M. , Gao Zhihong , Yang Huitao , Han Je-Chin
Published: September 2008

A five blade, linear cascade is used to experimentally investigate turbine blade platform cooling. A 30° inclined slot upstream of the blades is used to model the seal between the stator and rotor, and 12 discrete film holes are located on the downstream half of the platform for additional cooling. The film cooling effectiveness is measured on the platform using pressure sensitive paint (PSP). The mainstream Reynolds number is 3.1*105 based on the inlet velocity and the chord length of the scaled high pressure turbine blade. The upstream slot covers 1.5 passages with the coolant exiting the slot at the leading edge of the rotor blades. The length-to-width ratio (ls/w) of the slot is 5.7, and the slot flowrate varies from 0.50% to 2.0% of the mainstream flow. The discrete film cooling holes also have an inclination of 30°, so the length-to-diameter (lf/d) ratio of each hole is 10. The blowing ratio of the coolant through the holes varies from 0.5 to 2.0, based on the mainstream exit velocity. Using PSP it is clear that the film cooling effectiveness on the blade platform is strongly influenced by the platform secondary flow through the passage. Increasing the slot injection rate weakens the secondary flow and provides more uniform film coverage. Increasing the freestream turbulence level was shown to increase film cooling effectiveness on the endwall, as the increased turbulence also weakens the passage vortex. However, downstream, near the discrete film cooling holes, the increased turbulence decreases the film cooling effectiveness (as reported for flat plate film cooling studies). Finally, combining upstream slot flow with downstream discrete film holes should be done cautiously to ensure coolant is not wasted by overcooling regions on the platform.
Enhanced Gas Turbine Performance Simulation Using CFD Modules in a 2D Representation of the Low-Pressure System for a High Bypass Turbofan
Authors: Mund Friederike C. , Doulgeris Georgios , Pilidis Pericles
Published: September 2008

The improvement of performance simulation for gas turbines has been approached in very different ways. In particular for high bypass turbofans, efforts have been made to investigate radial flow distributions. The aim of the presented study was to combine a conventional characteristics based performance code using a 2d representation of the fan with 2d representations of the adjoining intake and bypass system. Computational Fluid Dynamics was the chosen tool to generate modules for the intake, bypass duct and bypass nozzle. This approach required geometry data. A design procedure to generate these components in an axi-symmetric meridional fashion and the numerical requirements for the CFD modules were developed. Typical component performances were predicted and the combined use of CFD and the performance code showed that in terms of performance, the inclusion of intake and bypass losses and the radial inlet distribution was worth considering. In particular however, the required numerical effort was significant.
The Effects of Obstructions on Film Cooling Effectiveness on the Suction Side of a Gas Turbine Vane
Authors: Demling Patricia , Bogard David G.
Published: September 2008

The effects of obstructions on film cooling performance on a scaled-up 1st stage turbine vane will be discussed. Experimental results show that obstructions located upstream or inside of a film cooling hole will degrade adiabatic effectiveness up to 80% of the levels found with no obstructions. Downstream obstructions had little effect on performance. The location where the upstream obstructions ceased to degrade adiabatic effectiveness was determined and temperature profiles were constructed to determine how the upstream obstructions were affecting the mainstream and coolant flow.
Biomass Gasification for Syngas Production
Authors: Zhang Xiaodong , Xu Min , Sun Li , Sun Rongfeng , Cai Feipeng , Guo Dongyan
Published: September 2008

For the concern with environment protection and energy security, much attention has been paid to alternative fuels from renewable resources in modern times, among which liquid fuel production from biomass gasification has aroused much enthuasitics. One two-stage gasification technology is proposed to promote the produciton of syngas suitable for F-T synthesis. The novel technology combines moving-bed pyrolysis, the secondary reinforcement decomposition, and reduction of pyrolysis intermediates. With the addition of certain amount of oxygen in the reaction scheme, large portion of large molecular hydrocarbons and some methane in the pyrolysis gas are reformed into hydrogen and carbon monoxide, and downstream reduction process also helps the mitigation of carbon dioxide emission. The secondary gasification stage proves to be effective in adjusting the product syngas composition to accommodate the requirment of the succeeding synthesis process. From preliminary test on pilot scale experimental facility, syngas with about the same content of hydrogen and carbon monoxide was achieved, with little content of tar. With water gas shift reaction, hydrogen content can be further increased to above 45 percent, resulting suitable H2/CO for downstream synthesis process.
Development of Elemental Technologies for Advanced Humid Air Turbine System
Authors: Kuroki Hidetoshi , Shibata Takanori , Koganezawa Tomomi , Kizuka Nobuaki , Hatamiya Shigeo , Marushima Shinya
Published: September 2008

The Advanced Humid Air Turbine (AHAT) system improves the thermal efficiency of gas turbine power generation by using a humidifier, a Water Atomization Cooling (WAC) system, and a heat recovery system, thus eliminating the need for an extremely high firing temperature and pressure ratio. The following elemental technologies have been developed to realize the AHAT system: (1) a broad working range and high-efficiency compressor that utilizes the WAC system to reduce compression work, (2) turbine blade cooling techniques that can withstand high heat flux due to high-humidity working gas, and (3) a combustor that achieves both low NOx emissions and a stable flame condition with high-humidity air. A gas turbine equipped with a two-stage radial compressor (with a pressure ratio of 8), two-stage axial turbine, and a reverse-flow type of single-can combustor has been developed based on the elemental technologies described above. A pilot plant that consists of a gas turbine generator, recuperator, humidification tower, water recovery system, WAC system, economizer, and other components is planned to be constructed, with testing slated to begin in October 2006 to validate the performance and reliability of the AHAT system. The expected performance is as follows: thermal efficiency of 43% (LHV), output of 3.6 MW, and NOx emissions of less than 10 ppm at 15% O2. This paper introduces the elemental technologies and the pilot plant to be built for the AHAT system.
Development of a Pressurized MCFC/MGT Hybrid System
Authors: Azegami Osamu , Hamai Michihiko , Itou Kazuhiko , Higuchi Shinichiro
Published: September 2008

A pressurized molten carbonate fuel cell (MCFC) and a micro gas turbine (MGT) hybrid power system has been developed to demonstrate high power generation efficiency (target of 55%), very low NOx emissions, and the operation using high-temperature gasification gas (biogas) as its fuel. The MCFC generator is pressurized, and is operating on process air supplied by the compressor of the MGT and reformed fuel. The power system achieves increased power output and higher efficiency thanks to its utilization by the gas turbine generator of thermal energy from the pressurized MCFC exhaust gas. The MGT is a single-shaft gas turbine that powers a high-speed direct-drive alternator. A heat recovery steam generator (HRSG) and the low-temperature heat exchanger of a hot water driven absorption refrigeration machine are also equipped using the heat recovered from the MGT exhaust gas. The MGT combustor plays an important role during system start-up. But the system is able to operate with no combustor firing in the range of 75% to 100% load. Therefore the NOx emissions are almost zero. The demonstration of this system was carried out at the 2005 World Exposition, Aichi, Japan. Wood waste that had to be cut during the construction of the EXPO 2005 site and waste plastic bottles at 1200°C in a high-temperature gasifier produce hydrogen and carbon monoxide. The MCFC/MGT hybrid system can use both high-temperature gasification gas (biogas) as well as Town Gas as its fuel. This system was started in February 22nd, and was operated by controlling from Distributed Power Supply Management System. A maximum efficiency was 52% at 300kW, and the total on-site operating time reached about 5200 hours with no failures. After the end of the half-year term of Aichi Expo., this system will be located to Central Japan Airport City, and the endurance test of next phase will be continued there.
Study of Two Miniature Air-Assist Atomizers With Radial and Axial Air Swirlers
Authors: Levy Y. , Sherbaum V. , Ovcharenko V. , Nadvani V.
Published: September 2008

The performances of two types of miniature air-assist atomizers were investigated; one with air being directed to the liquid spray through radial-tangential air channels and the other with air supplied through a small axial swirler. The study has shown that droplet size is reduced significantly when the air velocity increases up to about 50 m/s. However, further increase in air velocity has only a weak effect on the droplet size. In the absence of air supply, elevating the liquid pressure causes a reduction in the droplet diameter. The maximum values of the droplet mass flux shifts to the spray periphery with increasing of air velocity. In the air-assist operational regime, the liquid pressure has a slight effect on SMD however; the spray cone angle is increased significantly and can achieve values of up to 120 degrees for low liquid pressure drop. The larger spray angle at comparable droplet size distribution makes the atomizers with the radial air swirlers more favorable for small jet engines.
A Generalized Fault Classification for Gas Turbine Diagnostics on Steady States and Transients
Authors: Loboda Igor , Yepifanov Sergey , Feldshteyn Yakov
Published: September 2008

Gas turbine diagnostic techniques are often based on the recognition methods using the deviations between actual and expected thermodynamic performances. The problem is that the deviations depend on real operating conditions. However, our studies show that such a dependency can be reduced. In this paper, we propose the generalized fault classification that is independent of the operating conditions. To prove this idea, the averaged probabilities of the correct diagnosis are computed and compared for two cases: the proposed classification and the traditional one based on the fixed operating conditions. The probabilities are calculated through a stochastic modeling of the diagnostic process, in which a thermodynamic model generates deviations that are induced by the faults. Artificial neural networks recognize these faults. The proposed classification principle has been realized for both, steady state and transient operation of the gas turbine units. The results show that the acceptance of the generalized classification practically does not reduce the diagnosis trustworthiness.
The Effect of Liquid-Fuel Preparation on Gas Turbine Emissions
Authors: Nakamura Sosuke , McDonell Vince , Samuelsen Scott
Published: September 2008

The emissions of liquid-fuel fired gas turbine engines are strongly affected by the fuel preparation process that includes atomization, evaporation and mixing. In the present paper, the effects of fuel atomization and evaporation on emissions from an industrial gas turbine engine were investigated. In the engine studied, the fuel injector consists of a co-axial plain jet airblast atomizer and a premixer, which consists of a cylindrical tube with four mixing holes and swirler slits. The goal of this device is to establish a fully vaporized, homogeneous fuel/air mixture for introduction into the combustion chamber and the reaction zone. In the present study, experiments were conducted at atmospheric pressure and room temperature as well as at actual engine conditions (0.34MPa, 740K) both with and without the premixer. Measurements included visualization, droplet size and velocity. By conducting tests with and without the premixing section, the effect of the mixing holes and swirler slit design on atomization and evaporation was isolated. The results were also compared with engine data and the relationship between premixer performance and emissions was evaluated. By comparing the results of tests over a range of pressures, the viability of two scaling methods was evaluated with the conclusion that spray angle correlates with fuel to atomizing air momentum ratio. For the injector studied, however, the conditions resulting in superior atomization and vaporization did not translate into superior emissions performance. This suggests that, while atomization and the evaporation of the fuel are important in the fuel preparation process, they are of secondary importance to the fuel/air mixing prior to, and in the early stages of the reaction, in governing emissions.
A Multidisciplinary Aero-Engine Exhaust Emission Study
Authors: Shakariyants Savad A. , van Buijtenen Jos P. , Visser Wilfried P. J. , Tarasov Alexander
Published: September 2008

The paper illustrates an aero-engine exhaust emission study, which involves successive simulation procedures for aircraft flight, engine, combustor operation and exhaust emissions. It reveals a generic approach to analyze the effect of changes in flight conditions, power settings and combustor parameters on exhaust gas composition. Using reference measurement data at given engine operating points, pollutant models can be tuned to predict absolute concentration values at altered conditions. Emission formation processes were analyzed in the study using multi-reactor combustor models. The so-called principal pollutants of NOx, UHC, CO and soot were modeled over a broad range of engine power settings at static sea-level conditions. Modeling results were benchmarked against and tuned to emission certification data for a large commercial turbofan. CFD methods were employed to cross-check solution procedures for the engine combustor at the design operating point. Pollutants were also simulated in cruse conditions. Different flight conditions were considered using cross-linked engine and aircraft performance models.
CFD Analysis of Hot Gas Ingestion Mechanisms for the Vertical Descent Phase of a Harrier Aircraft
Authors: Richardson G. A. , Dawes W. N. , Savill A. M.
Published: September 2008

Hot Gas Ingestion (HGI) can be a problematic feature of STOVL aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows. As a partner in the PUMA DARP (Unsteady Methods Focus Group), the Cambridge University Engineering department CFD Lab are trying to model this flow-field in order to validate the Rolls-Royce HYDRA CFD code against experimental data obtained from detailed Rolls-Royce HGI tests. The HYDRA code has been developed to include a suitable mesh deformation technique for the descending aircraft configuration. The code is applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. Based on these computational results, this paper studies the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake. The trends in experimental engine intake temperature profiles are explained by analysis of these mechanisms. Following a more thorough validation of these results, the HYDRA code will provide a valuable tool for predicting the occurrence of HGI. The CFD method can then be used for the analysis of other STOVL aircraft as well as configuration changes aimed at preventing HGI.