bluuebunny/crossref_metadata_2025 huggingface dataset:
Platelet distribution width and mean platelet volume in the interpretation of thrombocytopenia in dogs
Authors: Bommer N. X. , Shaw D. J. , Milne E. M. , Ridyard A. E.
Published: September 2008

Objectives:To investigate the use of platelet volume indices in the interpretation of thrombocytopenia in dogs with systemic disease.

Methods:Case records of 80 control dogs and 159 thrombocytopenic dogs with systemic disease were reviewed retrospectively. The relationships between mean platelet volume, platelet distribution width and platelet count in systemically well dogs were established. Knowledge of these relationships was used to interpret thrombocytopenia in terms of the underlying disease process.

Results:There was a positive relationship between platelet distribution width and mean platelet volume. Both platelet distribution width and mean platelet volume varied in a negative relationship with platelet count, which was unaffected by signalment, underlying disease, variations in haematological parameters or serum proteins.

ClinicalSignificance:The interpretation of mean platelet volume and platelet distribution width in dogs requires simultaneous reference to the platelet count. Platelet volume indices did not aid interpretation of thrombocytopenia in terms of underlying pathological processes in the population studied.
Applications of Shuttle Radar Topography Mission Elevation Data
Authors: Zandbergen Paul
Published: September 2008

The Shuttle Radar Topography Mission (SRTM) was flown in February 2000 and collected the first ever high‐resolution near‐global digital elevation data. The final SRTM data have become widely available at 1 arc‐second resolution for the United States and 3 arc‐second resolution for other areas. This article reviews the background of the SRTM mission, the data quality characteristics of the SRTM elevation data, and the many applications of SRTM elevation data that have emerged in recent years, including forest ecology, volcanology, glaciology, geomorphology, and hydrology. SRTM data have been particularly useful for areas where previously limited topographic data were available, but results from STRM data also compare reasonably well with those obtained from other high‐resolution digital elevation models.
Transmural variation in myosin heavy chain isoform expression modulates the timing of myocardial force generation in porcine left ventricle
Authors: Stelzer Julian E. , Norman Holly S. , Chen Peter P. , Patel Jitandrakumar R. , Moss Richard L.
Published: September 2008

Recent studies have shown that the sequence and timing of mechanical activation of myocardium vary across the ventricular wall. However, the contributions of variable expression of myofilament protein isoforms in mediating the timing of myocardial activation in ventricular systole are not well understood. To assess the functional consequences of transmural differences in myofilament protein expression, we studied the dynamic mechanical properties of multicellular skinned preparations isolated from the sub‐endocardial and sub‐epicardial regions of the porcine ventricular midwall. Compared to endocardial fibres, epicardial fibres exhibited significantly faster rates of stretch activation and force redevelopment (ktr), although the amount of force produced at a given [Ca2+] was not significantly different. Consistent with these results, SDS‐PAGE analysis revealed significantly elevated expression of α myosin heavy chain (MHC) isoform in epicardial fibres (13 ± 1%) versus endocardial fibres (3 ± 1%). Linear regression analysis revealed that the apparent rates of delayed force development and force decay following stretch correlated with MHC isoform expression (r2= 0.80 and r2= 0.73, respectively, P < 0.05). No differences in the relative abundance or phosphorylation status of other myofilament proteins were detected. These data show that transmural differences in MHC isoform expression contribute to regional differences in dynamic mechanical function of porcine left ventricles, which in turn modulate the timing of force generation across the ventricular wall and work production during systole.
Selective Coating of Anatase and Rutile TiO2 on Carbon via Ultrasound Irradiation: Mitigating Fuel Cell Catalyst Degradation
Authors: George P. P. , Pol V. G. , Gedanken A. , Gabashivili A. , Cai M. , Mance A. M. , Feng L. , Ruthkosky M. S.
Published: September 2008

Before mass produced automotive fuel cell technology can be made practical, the oxidative instability of the carbons currently, used as the catalyst support at the oxygen electrode, must be addressed. This article describes a method for coating carbon (Vulcan XC-72) with protective barriers of titanium dioxide (titania) and provides the results of physical characterization tests on those materials. By combining the sol-gel coating process with high intensity ultrasonication and choosing the appropriate precursor, either the anatase or rutile phases of titania can be produced. More complete coverage of the carbon was provided by the anatase process. Accelerated gas-phase oxidation tests showed that platinized, anatase-coated carbon oxidized at 1∕5 the rate of untreated carbon while the rutile phase showed a mass loss of 1∕3 that of untreated carbon.
Optimal Design of Hybrid Fuel Cell Vehicles
Authors: Han Jeongwoo , Kokkolaras Michael , Papalambros Panos Y.
Published: September 2008

Automotive use of fuel cells has received increased attention due to clean and efficient power generation. Successful vehicular applications require careful balance of design and control trade-offs. This article presents a model-based vehicle design capability with sufficient fidelity and efficiency to perform design and power management optimization using quasisteady fuel cell performance maps. Optimized fuel cell systems demonstrate a trade-off between power density and efficiency depending on compressor size. Vehicle performance can be improved significantly when the fuel cell system is designed to balance this trade-off.
Virtual Simulation and Optimization of Milling Operations—Part I: Process Simulation
Authors: Merdol S. Doruk , Altintas Yusuf
Published: September 2008

The ultimate aim of the manufacturing is to produce the first part correctly and most economically on the production floor. This paper presents computationally efficient mathematical models to predict milling process state variables, such as chip load, force, torque, and cutting edge engagement at discrete cutter locations. Process states are expressed explicitly as a function of helical cutting edge-part engagement, cutting coefficient, and feed rate. Cutters with arbitrary geometry are modeled parametrically, and the intersection of their helical cutting edges with workpiece features are evaluated either analytically or numerically depending on the geometric complexity. Process variables are computed for each cutting edge-part engagement feature and summed to predict the total force, torque, and power generated at each feed rate interval. The proposed algorithms are experimentally verified in simulating milling of a gear box cover, and integrated to the virtual milling process system, which is capable of predicting cutting forces, torque, power, and vibrations within CAM environment.
Virtual Simulation and Optimization of Milling Applications—Part II: Optimization and Feedrate Scheduling
Authors: Merdol S. Doruk , Altintas Yusuf
Published: September 2008

The ultimate goal of future manufacturing is to design, test, and manufacture parts in a virtual environment before they are sent to the shop floor. While Part I of this paper presents the modeling of process simulation in a virtual environment, this second part presents computationally efficient algorithms for optimal selection of depth of cut, width of cut, speed, and feed while considering process constraints and variation of the part geometry along the tool path. The objective function is selected as the material removal rate (MRR), and optimization of milling processes is based on user defined constraints, such as maximum tool deflection, torque/power demand, and chatter stability. The MRR is maximized by optimal selection of cutting speed, feed rate, depth, and width of cut. Two alternative optimization strategies are presented. Preprocess optimization provides allowable depth and width of cut during part programming at the computer aided manufacturing stage using chatter constraint, whereas the postprocess optimization tunes only feed rate and spindle speed of an existing part program to maximize productivity without violating torque, power, and tool deflection limits. Optimized feed rates are filtered by considering machine tool axis limitations, and the algorithms are tested in machining a helicopter gear box cover.
Modeling of Polymer Electrolyte Membrane Fuel Cell Stack End Plates
Authors: Karvonen Suvi , Hottinen Tero , Ihonen Jari , Uusalo Heidi
Published: September 2008

Good thermal and electric contacts of gas diffusion layers (GDLs) with electrode surface and flow-field plates are important for the performance of a polymer electrolyte membrane fuel cell (PEMFC). These contacts are dependent on the compression pressure applied on the GDL surface. The compression also affects the GDL porosity and permeability, and consequently has an impact on the mass transfer in the GDL. Thus, the compression pressure distribution on the GDL can have a significant effect on the performance and lifetime of a PEMFC stack. Typically, fuel cell stacks are assembled between two end plates, which function as the supporting structure for the unit cells. The rigidity of the stack end plates is crucial to the pressure distribution. In this work, the compression on the GDL with different end plate structures was studied with finite element modeling. The modeling results show that more uniform pressure distributions can be reached if ribbed-plate structures are used instead of the traditional flat plates. Two different materials, steel and aluminum, were compared as end plate materials. With a ribbed aluminum end plate structure and a certain clamping pressure distribution, it was possible to achieve nearly uniform pressure distribution within 10–15bars. The modeling results were verified with pressure-sensitive film experiments.
Flexible Coproduction of Hydrogen and Power Using Internal Reforming Solid Oxide Fuel Cells System
Authors: Hemmes Kas , Patil Anish , Woudstra Nico
Published: September 2008

Within the framework of the Greening of Gas project, in which the feasibility of mixing hydrogen into the natural gas network in the Netherlands is studied, we are exploring alternative hydrogen production methods. Fuel cells are usually seen as the devices that convert hydrogen into power and heat. It is less well known that these electrochemical energy converters can produce hydrogen, or form an essential component in the systems for coproduction of hydrogen and power. In this paper, the coproduction of hydrogen-rich syngas (that can be converted into hydrogen) and power from natural gas in an internal reforming fuel cell is worked out by flow sheet calculations on an internal reforming solid oxide fuel cell system. The goal of this paper is to study the technical feasibility of such a system and explore its possibilities and limitations for a flexible coproduction. It is shown that the system can operate in a wide range of fuel utilization values at least down to 60% representing highest hydrogen production mode up to 95% corresponding to standard FC operation mode.
A Machining-Dimension-Based Approach to Locating Scheme Design
Authors: Qin Guo-Hua , Zhang Wei-Hong , Wan Min
Published: September 2008

In traditional and modern manufacturing systems, how to plan the workpiece holding is the first issue of the machining operation to be confronted for the fixture design. To ensure the machining accuracy of specific dimensions, it is necessary to develop a proper fixture locating scheme to constrain correctly the degrees of freedom (DOFs) of a workpiece with respect to the cutting tool. In this paper, a machining-dimension-based locating scheme design approach is developed and partitioned into two main parts for the study. First, the relationship is established between the machining dimensions and the DOFs to be constrained theoretically. Second, the fixture locating scheme is established to characterize the practical constrained DOFs of a workpiece in terms of the known locator number and positions. As a result, judgment criteria are formulated quantitatively for the first time to verify not only the locating scheme correctness but also to identify the cause of locating scheme incorrectness. Finally, two test examples are illustrated to show the proposed locating scheme.
Modeling of Manufacturing Complexity in Mixed-Model Assembly Lines
Authors: Zhu Xiaowei , Hu S. Jack , Koren Yoram , Marin Samuel P.
Published: September 2008

Mixed-model assembly lines have been recognized as a major enabler to handle product variety. However, the assembly process becomes very complex when the number of product variants is high, which, in turn, may impact the system performance in terms of quality and productivity. This paper considers the variety induced manufacturing complexity in manual mixed-model assembly lines where operators have to make choices for various assembly activities. A complexity measure called “operator choice complexity” (OCC) is proposed to quantify human performance in making choices. The OCC takes an analytical form as an information-theoretic entropy measure of the average randomness in a choice process. Meanwhile, empirical evidences are provided to support the proposed complexity measure. Based on the OCC, models are developed to evaluate the complexity at each station and for the entire assembly line. Consequently, complexity can be minimized by making system design and operation decisions, such as error-proof strategies and assembly sequence planning.
Effect of Slip on the Entropy Generation From a Single Rotating Disk
Authors: Arikoglu Aytac , Komurgoz Guven , Ozkol Ibrahim
Published: September 2008

In this study, it is the first time that the effect of slip on the entropy generation is investigated for the flow over a rotating single free disk. The problem is considered for steady and axially symmetrical case in a Newtonian ambient fluid. The classical approach introduced by Von Karman is followed to reduce nonlinear flow and heat field equations to ordinary differential equations. Then these equations are solved by using differential transform method. Entropy generation equation for this system is then derived and nondimensionalized. This equation, which has never been introduced for such a geometry and boundary conditions before in open literature, is interpreted for various physical cases by using nondimensional parameters of fluid and heat fields. It is observed that the effects of slip are to reduce the magnitude of entropy generation and to reduce the total energy in the system by reducing velocities and velocity gradients. Also, while entropy generation reduces, Bejan number converges to 1 with increasing slip factor.
The Influence of Viscous Effects and Physical Scale on Cavitation Tunnel Contraction Performance
Authors: Brandner P. A. , Roberts J. L. , Walker G. J.
Published: September 2008

The general performance of an asymmetric cavitation tunnel contraction is investigated using computational fluid dynamics (CFD) including the effects of fluid viscosity and physical scale. The horizontal and vertical profiles of the contraction geometry were chosen from a family of four-term sixth-order polynomials based on results from a CFD analysis and a consideration of the wall curvature distribution and its anticipated influence on boundary layer behavior. Inviscid and viscous CFD analyses were performed. The viscous predictions were validated against boundary layer measurements on existing full-scale cavitation tunnel test section ceiling and floor and for the chosen contraction geometry against model-scale wind tunnel tests. The viscous analysis showed the displacement effect of boundary layers to have a fairing effect on the contraction profile that reduced the magnitude of local pressure extrema at the entrance and exit. The maximum pressure gradients and minimum achievable test section cavitation numbers predicted by the viscous analysis are correspondingly less than those predicted by the inviscid analysis. The prediction of cavitation onset is discussed in detail. The minimum cavitation number is shown to be a function of the Froude number based on the test section velocity and height that incorporate the effects of physical scale on cavitation tunnel performance.
Prediction of Dynamic Stall Onset for Oscillatory Low-Speed Airfoils
Authors: Sheng W. , Galbraith R. A. McD. , Coton F. N.
Published: September 2008

This research presents some common features of oscillatory airfoils, and the method for indicating dynamic stall onset for the unsteady process. Under deep stall conditions, the stall-onset angle in oscillation is independent of the mean angle of the oscillatory motion, and by combining the reduced frequency and the amplitude of the oscillatory motion, the equivalent reduced pitch rate is an analog of this motion to the constant reduced pitch rate of the ramp-up motion. By correlating with the measured data, and with the ramp-up results, the equivalent reduced pitch rate can be defined as a representation for the oscillatory motion. Accordingly, the triple-parameter problem of an oscillation (mean angle, reduced frequency, and amplitude) degrades into the single-parameter problem (equivalent reduced pitch rate). Based on these foundations, an extension of the stall-onset criterion is then made for oscillatory airfoils: a method of extracting the stall-onset parameters directly from oscillatory test data, and an indication of stall onset for the oscillatory airfoils. The results from the new proposed method have shown the consistency with the data of Glasgow University and the public data.
Pressure Drop Through Anisotropic Porous Mediumlike Cylinder Bundles in Turbulent Flow Regime
Authors: Kim Tongbeum , Lu Tian Jian
Published: September 2008

Pressure drop through anisotropic porous mediumlike cylinder bundles is experimentally examined in turbulent flow regime. Three porosities, ε=0.66, 0.82, and 0.90, are considered. The flow blockage by the cylinder bundles is varied, with the yaw angle (α) used as an anisotropic measure. When the yaw angle is fixed while the porosity is varied, the pressure drop behaves as predicted by the force balance model, consistent with the classic observation: The pressure drop is proportional to the square of the flow velocity with the empirical proportionality as a function of (1−ε1∕2)∕ε2 obtained from the force balance model compared to that of (1−ε)∕ε3 from the hydraulic radius theory. On the other hand, for a given porosity, topological anisotropy of the cylinder bundles causes the sinusoidal response of the pressure drop to the variation of yaw angle. At α=0deg with a 60deg period, the lowest pressure drop occurs from the most open configuration of the cylinder bundle whereas the largest flow blockage at α=30deg causes the highest pressure drop. This variation appears to result from an increase in the drag coefficient of each cylinder element in a harmonic manner.
Microscale Flow Through Channels With a Right-Angled Bend: Effect of Fillet Radius
Authors: Raghavan V. , Premachandran B.
Published: September 2008

Microscale gas flow through channels with a right-angled bend has been numerically analyzed to study the effect of the fillet radius on flow characteristics. The flow is assumed to be incompressible, laminar, and hydrodynamically developing. The fillet radius has been varied from zero, representing a sharp corner, to 0.6 times the height of the channel. The Knudsen number has been varied from zero, representing no-slip at the boundary, to 0.1, which is the limiting case for the slip-flow regime. A low Reynolds number of value 1 has been considered in the present study, which makes the flow to be within the incompressible slip-flow regime. The flow characteristics in terms of velocity profiles, velocity vectors, and the pressure ratio between the inlet and outlet of the channel have been presented for several cases. Results show that for the case of the fillet radius equal to zero, the flow separation occurs after the bend and due to this, the exit velocity profile changes significantly. The highest pressure ratio between the inlet and the outlet is required to maintain a specific mass flow rate for this case. The cases with a nonzero fillet radius exhibit exit velocity profiles identical to that of a straight channel. The pressure ratio decreases when the fillet radius and the Knudsen number are increased.
Large Eddy Simulation of Flow Past Free Surface Piercing Circular Cylinders
Authors: Yu G. , Avital E. J. , Williams J. J. R.
Published: September 2008

Flows past a free surface piercing cylinder are studied numerically by large eddy simulation at Froude numbers up to FrD=3.0 and Reynolds numbers up to ReD=1×105. A two-phase volume of fluid technique is employed to simulate the air-water flow and a flux corrected transport algorithm for transport of the interface. The effect of the free surface on the vortex structure in the near wake is investigated in detail together with the loadings on the cylinder at various Reynolds and Froude numbers. The computational results show that the free surface inhibits the vortex generation in the near wake, and as a result, reduces the vorticity and vortex shedding. At higher Froude numbers, this effect is stronger and vortex structures exhibit a 3D feature. However, the free surface effect is attenuated as Reynolds number increases. The time-averaged drag force on the unit height of a cylinder is shown to vary along the cylinder and the variation depends largely on Froude number. For flows at ReD=2.7×104, a negative pressure zone is developed in both the air and water regions near the free surface leading to a significant increase of drag force on the cylinder in the vicinity of the free surface at about FrD=2.0. The mean value of the overall drag force on the cylinder increases with Reynolds number and decreases with Froude number but the reduction is very small for FrD=1.6–2.0. The dominant Strouhal number of the lift oscillation decreases with Reynolds number but increases with Froude number.
Solid Oxide Fuel Cell System Configurations for Distributed Generation
Authors: Verda Vittorio
Published: September 2008

This paper deals with the determination of the optimal configuration of two integrated systems for distributed energy generation, based on solid oxide fuel cells. Both systems are obtained starting from the Siemens CHP100 generator. The first system is obtained by recovering some of the heat flux available from the fuel cell to feed an organic Rankine cycle. The second system is obtained by installing the fuel cell generator instead of the combustion chamber of a micro-gas-turbine. The fuel cell produces about 100kW of electricity. The integrated systems allow to increase of about 30% the electricity production. Pinch analysis is then applied in order to analyze the theoretical improvements and to rearrange the location of the heat recovery devices, without modifying the temperature conditions of the main processes. The optimal structure, according to a thermodynamic criterion, is obtained and discussed.
An Experimental Investigation of the Effects of the Environmental Conditions and the Channel Depth for an Air-Breathing Polymer Electrolyte Membrane Fuel Cell
Authors: Park Yong Hun , Caton Jerald A.
Published: September 2008

The effects of the environmental conditions and the channel depth for an air-breathing polymer electrolyte membrane fuel cell were investigated experimentally. The fuel cell used in this work included a membrane and electrode assembly, which possessed an active area of 25 cm2 with Nafion® 117 membrane. Triple serpentine designs for the flow fields with two different flow depths were used in this research. The experimental results indicated that the relative humidity and temperature play an important role with respect to fuel cell performance. The fuel cell needs to be operated at least 20 min to obtain stable performance. When the shallow flow field was used, the performance increased dramatically for low humidity and slightly for high humidity. The current density was obtained around only 120 mA/cm2 at 30°C with an 80% relative humidity, which was nearly double the performance for the deep flow field. The minimum operating temperature for an air-breathing fuel cell would be 20°C. When it was 10°C at 60% relative humidity, the open circuit voltage dropped to around 0.65 V. The fuel cell performance improved with increasing relative humidity from 80% to 100% at high current density.
A Cutting Rate Model for Reciprocating Sawing
Authors: Domblesky Joseph P. , James Thomas P. , Widera G. E. Otto
Published: September 2008

In the present paper, the reciprocating sawing process is analyzed, and a model for linear cutting rate is developed. The resulting model is based on an orthogonal approximation of cutting at individual teeth and accounts for elastic and plastic indentation. Cutting rates obtained from an instrumented sawing fixture show good agreement with predicted results for the range of conditions considered. Cutting rate was found to be proportional to thrust force and reciprocating rate though this behavior is influenced by edge radius and flow stress at higher levels. While it was not possible to decouple the effect of pitch and blade set, it was confirmed that coarser pitch blades do provide higher cutting rates.
Evaluation of the Performance of CBN Tools When Turning Austempered Ductile Iron Material
Authors: Aslantas K. , Ucun İ. , Gök K.
Published: September 2008

The study deals with the machinability properties of austempered ductile iron using cubic boron nitride cutting tools. To emphasize the role of the austempering process, ductile iron specimens were first austenitized in salt bath at 900°C for 60min, after which they were quenched in a salt bath at 250°C and 325°C for 60min. Machining tests were carried out at various cutting speeds under the constant depth of cut and the feed rate. Tool performance was evaluated based on the workpiece surface roughness and flank wear. The influence of the austempering temperature and cutting speed on the chip form was also studied. The results point out that the lower austempering temperature results in the increase in the cutting forces, while better surface roughness is attained.
Expanding the Reliability Process to More Accurately Assess Business Risks and Opportunities Associated With Long-Term Maintenance Contracts
Authors: Burkett Michael A.
Published: September 2008

Many aerospace manufacturers, including Rolls -Royce, have expanded beyond direct product sales into a variety of aftermarket services. Long-term maintenance agreements are a prime example, where the customer pays an agreed monthly fee and the manufacturer takes responsibility for all covered repairs and maintenance. The company’s obligation to cover future repair costs brings with it the need to accurately predict those costs years into the future. This infers a need for detailed and accurate service data, advanced analysis methods and tools, and effective communication of analysis results. Recognizing this, Rolls-Royce formed a cross-functional team to assess these needs and to design an improved reliability process that meets them. This paper describes the improved process recommended by the team, along with the rationale supporting this recommendation.
Film-Cooling Effectiveness on a Rotating Blade Platform
Authors: Suryanarayanan A. , Mhetras S. P. , Schobeiri M. T. , Han J. C.
Published: September 2008

Film cooling effectiveness measurements under rotation were performed on the rotor blade platform using a pressure sensitive paint (PSP) technique. The present study examines, in particular, the film cooling effectiveness due to purging of coolant from the wheel-space cavity through the circumferential clearance gap provided between the stationary and rotating components of the turbine. The experimental investigation is carried out in a new three-stage turbine facility, recently designed and taken into operation at the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. This new turbine rotor has been used to facilitate coolant injection through this stator-rotor gap upstream of the 1st stage rotor blade. The gap was inclined at 25° to mainstream flow to allow the injected coolant to form a film along the passage platform. The effects of turbine rotating conditions on the blade platform film cooling effectiveness were investigated at three speeds of 2550 rpm, 2000 rpm and 1500 rpm with corresponding incidence angles of 23.2°, 43.4° and 54.8° respectively. Four different coolant-to-mainstream mass flow ratios varying from 0.5% to 2.0% were tested at each rotational speed. Aerodynamic measurements were performed at the 1st stage stator exit using a radially traversed five-hole probe to quantify the mainstream flow at this station. Results indicate that film cooling effectiveness increases with an increase in the coolant-to-mainstream mass flow ratios for all turbine speeds. Higher turbine rotation speeds show more local film cooling effectiveness spread on the platform with increasing magnitudes.
RANS Modelling of Wake Induced Transition With the Dynamic Intermittency Concept
Authors: Lodefier Koen , Dick Erik
Published: September 2008

A transition model for describing wake-induced transition is presented based on the SST turbulence model by Menter and two dynamic equations for intermittency: one for near-wall intermittency and one for free-stream intermittency. In the Navier-Stokes equations, the total intermittency factor, which is the sum of the two, multiplies the turbulent viscosity computed by the turbulence model. The quality of the transition model is illustrated on the T106A test cascade for different levels of inlet free-stream turbulence intensity. The unsteady results are presented in space-time diagrams of shape factor, wall shear stress, momentum thickness and intermittency on the suction side. Results show the capability of the model to capture the physics of unsteady transition. Inevitable shortcomings are also revealed.
Very Rough Grid Approach for CFD Modelling of Thermoacoustic Oscillations Inside an Annular Premixed Combustor
Authors: Tiribuzi Stefano
Published: September 2008

Large pressure oscillations due to thermoacoustic instabilities may occur in the modern gas turbine equipped with lean premixed burners. The Research Department of ENEL is studying this phenomenon using research methods that include plant supervision, laboratory experiments and modelling. This paper presents a new CFD modelling approach capable of simulating the time evolution of thermofluiddynamic fields during thermoacoustic instabilities in a whole annular combustor. Its peculiarity consists in the adoption of a very rough computational mesh. The use of the Very Rough Grid (VRG) approach allows all the resonant cavities involved in the acoustic oscillations to be considered, as well as to prolonging the computed transient until spontaneous thermoacoustic oscillations onset, with affordable computation time. The rationale of this approach is that thermoacoustic instabilities are more affected by acoustics than by fluiddynamics. KIEN, an in-house low diffusive URANS code capable of simulating 3D reactive flows, has been used. A 3D structured monoblock computational grid of an industrial annular combustor has been set up. It goes from the compressor outlet to the turbine inlet, including both the annular plenum and the annular combustion chamber, and extends over the entire circumferential angle. The results obtained by an exemplifying computed case are illustrated. They appear to be congruent with the real behaviour of thermoacoustic oscillation reported in literature. The type of information that can be extracted directly or by suitable post-processing from these results is shown and their usefulness in interpreting the real data obtained from functioning plants or experimental facilities is demonstrated.
3-Dimensional Pressure Driven Temperature Field in a Gas Turbine Combustion Chamber
Authors: Sierra Fernando Z. , Uribe Areli , Kubiak Janusz , Lara Hugo , Urquiza Gustavo , Nebradt Jesu´s
Published: September 2008

In this work the temperature field in a gas turbine combustion chamber is investigated through numerical computations. The combustion chamber under study is part of a 70 MW gas turbine from an operating combined cycle power plant. The simulation of combustion and flow dynamics is fully 3-dimensional. It addresses complex turbulence structure and temperature distribution inside the combustion chamber. The swirling effect is taken into account using a detailed gas-fuel-air mixing swirler. The combustion was simulated with proper gas-fuel-air flow ratio assuming stoichiometric equilibrium conditions. Based on previous results, pressure imbalance conditions of air flow between primary and secondary inlets is used to perturb the temperature distribution. In this work, a periodic function was used to produce pressure variation in the air flow, which in turn alter the temperature field and turbulence structures. First, characteristic temperature and pressure fields were obtained using steady state boundary conditions. The steady state solutions were perturbed using a periodic boundary condition (6 kPa per short periods of time) resulting in different results. The results are discussed and confirm previous 2-dimesional computations where excessive heating in regions other than the combustion chamber core occurred. The investigation is aimed to explain why overheating occurs, since it causes burning out of pipe materials, producing permanent damage to auxiliary cross flame pipes.
University Turbine Systems Research Program
Authors: Day William H. , Wenglarz Richard A. , Golan Lawrence P.
Published: September 2008

The University Turbine Systems Research (UTSR) Program, developed by the National Energy Technology Laboratory of the US Department of Energy, supports research in gas turbines which is performed at universities. An Industrial Review Board (IRB), consisting of gas turbine OEM’s, users, and suppliers of gas turbine components and technologies recommends topics for the research to DOE. They also review the universities’ proposals and recommend a short list of proposals from each solicitation for funding. Since the program’s inception in 1992 a total of 101 research projects have been awarded. There are 110 universities participating in the program and eligible to compete for UTSR research awards. The research is mostly in three areas: Combustion, Materials (mostly thermal barrier coatings) and Aerodynamics / Heat Transfer. The program has produced significant benefits for the gas turbine industry in these fields. This paper provides several examples of the most significant research results.
The Effects of Varying the Combustor-Turbine Gap
Authors: Cardwell N. D. , Sundaram N. , Thole K. A.
Published: September 2008

To protect hot turbine components, cooler air is bled from the high pressure section of the compressor and routed around the combustor where it is then injected through the turbine surfaces. Some of this high pressure air also leaks through the mating gaps formed between assembled turbine components where these components experience expansions and contractions as the turbine goes through operational cycles. This study presents endwall adiabatic effectiveness levels measured using a scaled up, two-passage turbine vane cascade. The focus of this study is evaluating the effects of thermal expansion and contraction for the combustor-turbine interface. Increasing the mass flow rate for the slot leakage between the combustor and turbine showed increased local adiabatic effectiveness levels while increasing the momentum flux ratio for the slot leakage dictated the coverage area for the cooling. With the mass flow held constant, decreasing the combustor-turbine interface width caused an increase in uniformity of coolant exiting the slot, particularly across the pressure side endwall surface. Increasing the width of the interface had the opposite effect thereby reducing coolant coverage on the endwall surface.
Derivation of Diagnostic Requirements for a Distributed UAV Turbofan Engine Control System
Authors: Hannius Olof , Ring Dan , Karlsson Johan
Published: September 2008

This paper presents a method to derive the efficiency of diagnostic functions so that consistency with safety requirements is met. The method is applied to a distributed UAV engine control system, but could as well be applicable to any other mechatronic system. A control system architecture is proposed with a minimum of hardware redundancy for lowest cost and simple design. Efficient diagnostic functions (executable assertions in software) are used to detect and isolate errors. The goal is to completely recover from any transient error and reconfigure the system after a permanent error so that engine thrust remains unaffected. Given the requirement that an engine failure due to the control system is not allowed to occur more than 10 times per million hours, any permanent or transient error must be correctly handled with 99% certainty on node level and 90–95% on system level. The high error coverage figures are much driven by the assumption that a transient error occurs 1 time per 1000 hours in any control system node. The high number used for transient errors are due to the concern about Single Event Upsets (SEUs) that have become a dominating cause of errors in electronic equipment in flight applications.
An Acoustic Energy Approach to Modeling Combustion Oscillations
Authors: Ibrahim Z. M. , Williams F. A. , Buckley S. G. , Lee J. C. Y.
Published: September 2008

A new approach for modeling combustion instabilities using acoustic energy conservation is proposed. This approach allows the flexibility to calculate contributions from amplification and/or attenuation across all frequencies, rather than predicting eigenmodes. It is likely that such a direct acoustic energy approach could be of benefit in determining the susceptibility of all frequencies to growth or decay as operating conditions in a gas turbine change. This approach may also give designers a method for improving passive damping in the initial design phase, with the ability to scan various frequencies and investigate the susceptibility to oscillatory instability at different operating conditions. A linear model, including linear approximations to nonlinear processes, is introduced whereby the mechanisms contributing to amplification and damping of acoustic energy are assessed independently to find a net amplification coefficient, a reciprocal time (or a rate). Stability for each frequency is assessed by examining a ratio between amplification and damping. It is anticipated that this effort may provide a useful new perspective on and enhanced prediction capability for combustion oscillatory instabilities.
Taurus™ 65 Gas Turbine Product
Authors: Teraji David
Published: September 2008

This paper will review the Taurus 65 gas turbine product, the newest member of Solar Turbine’s product line. The Taurus 65 is a 6.3 MW, 32.9% efficient single shaft gas turbine specifically designed for the combined heat and power (CHP) market with low emissions and excellent exhaust heat capacity. It leverages the reliability and durability of the Centaur® and Taurus product technology. The 13-stage compressor includes the Centaur 50 compressor plus two new aft stages. The combustion system adopts Solar’s proven SoLoNOx™ technology and has a guaranteed NOx emission of 15 ppmv (15% O2). The newly designed three-stage turbine incorporates the proven Taurus 70 high efficiency design with advanced cooling and material technologies developed in the Mercury™ 50 turbine engine. Solar developed a new Taurus 65 package system design utilizing 6 Sigma methodologies. The new design incorporates features that allows for quick installation and easy operation and maintenance. A Kaizen service event successfully demonstrated the field maintenance and engine removal on the first package built. The Taurus 65 universal package design will become the standard design for the Centaur 40, Centaur 50 and Taurus 60 products, and will have the same footprint as the current Taurus 60 package. The first Taurus 65 gas turbine started development test during the fourth quarter 2004. The development test results have been excellent. A Taurus 65 gen-set unit will start endurance testing during the third quarter 2005 at Solar’s San Diego facility. The first production unit will be available for shipment in the first quarter 2006. The New Product Introduction (NPI) process, 6 Sigma process, and Kaizen processes were utilized during the product design, development and introduction phases.
Operability and Efficiency Performance of Ultra-Compact, High Gravity (g) Combustor Concepts
Authors: Zelina J. , Greenwood R. T. , Shouse D. T.
Published: September 2008

Future gas turbine engines are required to be more capable than their predecessors. This often implies severe demands on the engine that translate into increasing compressor and combustor exit temperatures, higher combustion pressures and higher fuel/air ratio combustors with greater turn-down ratios (wider operating limits between idle and maximum power conditions). Major advances in combustor technology are required to meet the conflicting challenges of improving performance, increasing durability and maintaining cost. Unconventional combustor configurations are one promising approach to address these challenges. Ultra-short combustors to minimize residence time, with special flame-holding mechanisms to cope with increased through-velocities are likely in the future. Engine cycles other than the standard Brayton cycle may also be used for special applications in order to avoid the use of excessive combustion temperatures, and to extract additional power from the system. This paper focuses on vortex-stabilized combustor technologies that can enable the design of compact, high-performance combustion systems. Compact combustors weigh less and take up less volume in space-limited turbine engine for aero applications. This paper presents a parametric design study of the Ultra-Compact Combustor (UCC), a novel design based on TVC work that uses high swirl in a circumferential cavity to enhance reaction rates via high cavity g-loading on the order of 3000 g’s. Increase in reaction rates translates to a reduced combustor volume. Three combustor geometric features were varied during experiments which included (1) high-g cavity flame-holding method, (2) high-g cavity to main airflow transport method, and (3) fuel injection method. Experimental results are presented for these combustor configurations and results have shown promise for advanced engine applications. Lean blowout fuel-air ratio limits at 25–50% the value of current systems were demonstrated. Combustion efficiency was measured over a wide range of UCC operating conditions. This data begins to build the design space required for future engine designs that may use these novel, compact, high-g combustion systems.
An Undergraduate Industrial Design Exercise at Rolls-Royce plc
Authors: Lock G. D. , Child M. , Cheng V. , Johnson R. , Mezzullo W. , Pattinson C. , Peet S. , Wright C.
Published: September 2008

The Department of Mechanical Engineering at the University of Bath has been conducting an undergraduate engine-related design exercise at Rolls-Royce, Bristol since 2000. Each year a team of six undergraduates complete an engine-related design project under supervision from the company between February and September. This work is coordinated and assessed at both the company and university, and counts overall as 20% of the student’s four-year degree. In addition to working at Rolls-Royce, the students submit reports and give seminars at the university. The design exercise is predominantly technical in nature but must include a significant business element. The students are paid as company employees, typically £7.2k for the six months. This paper describes the design exercise and how it is accommodated into the undergraduate programme of study at the University of Bath. The benefits to the university, the students and the company are discussed. In addition, the six students undertaking the 2005 exercise describe their projects. This year there were three projects, two of which were continuations from previous design exercises. The three projects are listed below. Aero-Engine Rotor-Dynamics (V Cheng and S Peet): An experimental and computation study of engine vibration using a rotor-dynamics rig, simulating the engine. The aim was to assess the accuracy and improve the modeling techniques used at Rolls-Royce. Implementing Design for Environment on Gas turbine engines using a Design Tool (W Mezzulo): A study to create a tool to enable the designer to evaluate the environmental aspects of the life of an engine component. Aero-thermodynamics of aero-engines (M Child, R Johnson and C Pattinson): Various design aspects of aero-engines, both computational and business. Note that M Child’s project is not discussed here for reasons of Rolls-Royce proprietary and confidentiality.
Physical Interpretation of Flow and Heat Transfer in Pre-Swirl Systems
Authors: Lewis Paul , Wilson Mike , Lock Gary , Owen J. Michael
Published: September 2008

This paper compares heat transfer measurements from a pre-swirl rotor-stator experiment with 3D steady state results from a commercial CFD code. The measured distribution of Nusselt number on the rotor surface was obtained from a scaled model of a gas turbine rotor-stator system, where the flow structure is representative of that found in an engine. Computations were carried out using a coupled multigrid RANS solver with a high-Reynolds-number k-ε/k-ω turbulence model. Previous work has identified three parameters governing heat transfer: rotational Reynolds number (Reφ), pre-swirl ratio (βp) and the turbulent flow parameter (λT). For this study rotational Reynolds numbers are in the range 0.8×106 < Reφ < 1.2×106. The turbulent flow parameter and pre-swirl ratios varied between 0.12 < λT < 0.38 and 0.5 < βp < 1.5, which are comparable to values that occur in industrial gas turbines. At high coolant flow rates, computations have predicted peaks in heat transfer at the radius of the pre-swirl nozzles. These were discovered during earlier experiments and are associated with the impingement of the pre-swirl flow on the rotor disc. At lower flow rates, the heat transfer is controlled by boundary-layer effects. The Nusselt number on the rotating disc increases as either Reφ or λT increases, and is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations are observed. The computed velocity field is used to explain the heat transfer distributions observed in the experiments. The regions of peak heat transfer around the receiver holes are a consequence of the route taken by the flow. Two routes have been identified: “direct”, whereby flow forms a stream-tube between the inlet and outlet; and “indirect”, whereby flow mixes with the rotating core of fluid. Two performance parameters have been calculated: the adiabatic effectiveness for the system, Θb,ab, and the discharge coefficient for the receiver holes, CD. The computations show that, although Θb,ab increases monotonically as βp increases, there is a critical value of βp at which CD is a maximum.