bluuebunny/crossref_metadata_2025 huggingface dataset:
Implement a Winning Strategy
Authors: Dobbins Richard , Pettman Barrie O.
Published: January 2008

Strategy gets you from where you are now to your ideal future. Strategy is the link between mission and profit. Establish your specialisation, your area of excellence, your core business. Establish a competitive advantage, a reason why customers should buy from you. Find the segment or niche in the market place which you can dominate. Concentrate all your resources hitting your market segment with your benefit and competitive advantage in your area of excellence. Many of the ideas in corporate strategy are similar to the goal setting and goal achieving ideas relating to individuals. This should not surprise us. Organisations do not have strategies. Only people have strategies.
People Management in Small and Medium Sized Enterprises
Authors: Vinten Gerald , Lane David A. , Hayes Nicky
Published: January 2008

There can be no doubt that the small and medium sized enterprise (SME) plays a pivotal role in most if not all economies, and that social policy makers have an interest in ensuring the viability of this sector of the economy, which plays a crucial role in the contract culture of national and international competitiveness. Quite apart from the essential symbiosis between the large multinationals and public limited companies and this sector, the sustainability of unemployment benefit payouts would be jeopardised should the sector experience a significant downturn. There are already worldwide concerns about the ability to continue to finance state pensions at anything like the present scale, and any loss of viability of the SME sector will simply exacerbate this situation. There are also useful reciprocations to be achieved by comparisons across sectors, including in significant areas such as internal control (Vinten, Lane, Hayes, 1996). The recent flurry of activity has included initiatives of the Institute of Chartered Accountants of England and Wales 1996) and the information needs of owners (Institute of Chartered Accountants of England and Wales 1996a), an Auditing Practices Board (1996) Practice Note, and a Department of Trade and Industry Consultation Document (DTI 1996).
Be Excellent at Selling
Authors: Dobbins Richard , Pettman Barrie O.
Published: January 2008

Improve your nine basic sales skills. Lead a winning sales team. Use your creativity to generate twenty ideas for improving all aspects of selling.
Developmental presence and disappearance of postsynaptically silent synapses on dendritic spines of rat layer 2/3 pyramidal neurons
Authors: Busetto Giuseppe , Higley Michael J. , Sabatini Bernardo L.
Published: January 2008

Silent synapses are synapses whose activation evokes NMDA‐type glutamate receptor (NMDAR) but not AMPA‐type glutamate receptor (AMPAR) mediated currents. Silent synapses are prominent early in postnatal development and are thought to play a role in the activity‐ and sensory‐dependent refinement of neuronal circuits. The mechanisms that account for their silent nature have been controversial, and both presynaptic and postsynaptic mechanisms have been proposed. Here, we use two‐photon laser uncaging of glutamate to directly activate glutamate receptors and measure AMPAR‐ and NMDAR‐dependent currents on individual dendritic spines of rat somatosensory cortical layer 2/3 pyramidal neurons. We find that dendritic spines lacking functional surface AMPARs are commonly found before postnatal day 12 (P12) but are absent in older animals. Furthermore, AMPAR‐lacking spines are contacted by release‐competent presynaptic terminals. After P12, the AMPAR/NMDAR current ratio at individual spines continues to increase, consistent with continued addition of AMPARs to postsynaptic terminals. Our results confirm the existence of postsynaptically silent synapses and demonstrate that the morphology of the spine is not strongly predictive of its AMPAR content.
A Novel Approach to Enhance the Hydrogen Yield of Biomass Gasification Using CO2 Sorbent
Authors: Mahishi Madhukar R. , Sadrameli M. S. , Vijayaraghavan Sanjay , Goswami D. Y.
Published: January 2008

Hydrogen yield of conventional biomass gasification is limited by chemical equilibrium constraints. A novel technique that has the potential to enhance the hydrogen yield by integrating the gasification and absorption reactions has been suggested. The method involves gasification of biomass in presence of a CO2 sorbent. Ethanol was used as the model biomass compound and CaO was the representative sorbent. Equilibrium modeling was used to determine the product gas composition and hydrogen yield. The analysis was done using ASPEN PLUS software (version 12.1) and the Gibbs energy minimization approach was followed. The effects of temperature, pressure, steam/ethanol ratio, and CaO/ethanol ratio on product yield were investigated. Three case studies were conducted to understand the effect of sorbent addition on the hydrogen yield. Thermodynamic studies showed that the use of sorbents has the potential to enhance the equilibrium hydrogen yield of conventional gasification by ∼19% and reduce the equilibrium CO2 content of product gas by 50.2%. It was also found that the thermodynamic efficiency of sorbent-enhanced gasification (72.1%) was higher than conventional gasification (62.9%). Sorbent-enhanced gasification is a promising technology with a potential to improve the yield and lower the cost of hydrogen production.
The Effect of Engine Exhaust Temperature Modulations on the Performance of Automotive Catalytic Converters
Authors: Shamim Tariq
Published: January 2008

This paper presents a computational investigation of the effect of exhaust temperature modulations on an automotive catalytic converter. The objective is to develop a better fundamental understanding of the converter’s performance under transient driving conditions. Such an understanding will be beneficial in devising improved emission control methodologies. The study employs a single-channel based, one-dimensional, nonadiabatic model. The transient conditions are imposed by varying the exhaust gas temperature sinusoidally. The results show that temperature modulations cause a significant departure in the catalyst behavior from its steady behavior, and modulations have both favorable and harmful effects on pollutant conversion. The operating conditions and the modulating gas composition and flow rates (space velocity) have substantial influence on catalyst behavior.
Design Concept for Large Output Graz Cycle Gas Turbines
Authors: Jericha H. , Sanz W. , Göttlich E.
Published: January 2008

The introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. Therefore research and development work at the Graz University of Technology since the 1990s has led to the Graz Cycle, a zero emission power cycle of highest efficiency. It burns fossil fuels with pure oxygen which enables the cost-effective separation of the combustion CO2 by condensation. The efforts for the oxygen supply in an air separation plant are partly compensated by cycle efficiencies far higher than for modern combined cycle plants. Upon the basis of the previous work, the authors present the design concept for a large power plant of 400 MW net power output making use of the latest developments in gas turbine technology. The Graz Cycle configuration is changed, insofar as condensation and separation of combustion generated CO2 takes place at the 1 bar range in order to avoid the problems of condensation of water out of a mixture of steam and incondensable gases at very low pressure. A final economic analysis shows promising CO2 mitigation costs in the range of $20–30/ton CO2 avoided. The authors believe that they present here a partial solution regarding thermal power production for the most urgent problem of saving our climate.
On Nonlinear Rotor Dynamic Effects of Aerodynamic Bearings With
Simple Flexible Rotors
Authors: Bou-Saïd B. , Grau G. , Iordanoff I.
Published: January 2008

The last decades have experienced a growing enhancement of aeronautical oil free turbomachinery. The classical linear approach of rotor dynamics commonly uses stiffness and damping coefficients to model journal bearings. In the present study, a nonlinear time dependant calculation is used for the dynamic simulation of a rotor mounted with aerodynamic (gas) bearings. A comparison between the two approaches indicates that the dynamic behavior of such bearings can be nonlinear in operating ranges where the rotor eccentricity reaches high values. In that case, the linear approach may lead to incorrect results and the nonlinear approach should be performed for better rotor dynamic prediction. A numerical procedure which analyzes the dynamic behavior of simple flexible rotors taking into account the nonlinear (transient regime) characteristics of aerodynamic bearings is presented. A simple example highlights the needs of nonlinear simulations in order to predict dynamic performance in oil-free turbomachinery.
Application of a Spark Ignition Engine Simulation Tool for Alternative Fuels
Authors: Mustafi Nirendra N. , Raine Robert R.
Published: January 2008

Investigations on alternative fuels for internal combustion engines are regarded as one of the major research areas for the age. Engine simulation tools can play an important role in such investigations without performing the experimental works. It usually saves both time and money and provides better and additional understanding where the experimental facilities are limited. A spark ignition (SI) engine simulation tool (ISIS) is used in this present study to simulate the performance and emissions of SI engines, operated on alternative fuels such as biogas and “Powergas” (a synthesis gaseous fuel mixture of mainly carbon monoxide and hydrogen). An extended investigation is done for the oxides of nitrogen emissions considering multiple burn zones. The results are verified against those obtained for engine torque/brake power, exhaust temperature, and exhaust emissions experimentally and a good agreement is found between them.
Analysis of the Pollutant Formation in the FLOX® Combustion
Authors: Schütz H. , Lückerath R. , Kretschmer T. , Noll B. , Aigner M.
Published: January 2008

FLOX®, or flameless combustion is characterized by ultralow NOx emissions. Therefore the potential for its implementation in gas turbine combustors is investigated in recent research activities. The major concern of the present paper is the numerical simulation of flow and combustion in a FLOX®-combustor [Wünning, J. A., and Wünning, J. G., 1997, “Progress in Energy and Combustion Science,” 23, pp. 81–94; Patent EP 0463218] at high pressure operating conditions with emphasis on the pollutant formation. FLOX®-combustion is a highly turbulent and high-velocity combustion process, which is strongly dominated by turbulent mixing and chemical nonequilibrium effects. By this means the thermal nitric oxide formation is reduced to a minimum, because even in the nonpremixed case the maximum combustion temperature does not or rather slightly exceeds the adiabatic flame temperature of the global mixture due to almost perfectly mixed reactants prior to combustion. In a turbulent flow, the key aspects of a combustion model are twofold: (i) chemistry and (ii) turbulence/chemistry interaction. In the FLOX®-combustion we find that both physical mechanisms are of equal importance. Throughout our simulations we use the complex finite rate chemistry scheme GRI3.0 for methane and a simple partially stirred reactor (PaSR) model to account for the turbulence effect on the combustion. The computational results agree well with experimental data obtained in DLR test facilities. For a pressure level of 20 bar, a burner load of 417 kW and an air to fuel ratio of λ=2.16 computational results are presented and compared with experimental data.
An Iterative Method for Blade Profile Loss Model Adaptation Using Streamline Curvature
Authors: Pachidis Vassilios , Pilidis Pericles , Templalexis Ioannis , Marinai Luca
Published: January 2008

The various incidence, deviation, and loss models used in through-flow analysis methods, such as streamline curvature, are nothing more than statistical curve fits. A closer look at public domain data reveals that these statistical correlations and curve fits are usually based on experimental cascade data that actually display a fairly large scatter, resulting in a relatively high degree of uncertainty. This usually leads to substantial differences between the calculated and actual performances of a given gas turbine engine component. Typically, matching calculated results from a through-flow analysis against experimental data requires the combination of various correlations available in the public domain, through a very tedious, complex, and time consuming “trial and error” process. This particular study supports the view that it might actually be much more time effective to “adopt” a given loss model against experimental data through an iterative, physics-based approach, rather than try to identify the best combination of available correlations. For example, the well-established “Swan’s model” for calculating the blade profile loss factor in subsonic and transonic axial flow compressors depends strongly on approximate correlations for calculating the blade wake momentum thickness, and therefore represents such a case. This study demonstrates this by looking into an iterative approach to blade profile loss model adaptation that can provide a relatively simple and quick, but also physics-based way of “calibrating” profile loss models against available experimental data for subsonic applications. This paper presents in detail all the analysis necessary to support the above concept and discusses Swan’s model in particular as an example. Finally, the paper discusses the performance comparison of a two-dimensional, streamline curvature compressor model against experimental data before and after the adaptation of that particular loss model. This analysis proves the potential of the simulation strategy presented in this paper to “adopt” a given loss model against experimental data through an iterative, physics-based approach.
Spiral Vibration of a Turbogenerator Set: Case History, Stability Analysis, Measurements and Operational Experience
Authors: Eckert Lothar , Schmied Joachim
Published: January 2008

A hydrogen-cooled turbogenerator operating at 3600 rpm showed the phenomenon of spiral vibration with a forward rotating unbalance vector. The relative shaft vibration measured at the non-driven end-bearing was close to the trip level. Spiral vibration is observed at various types of rotating machinery with both rotation directions of the unbalance vector, i.e., forward and backward. Spiral vibration is caused by a vibration-induced hot spot on the shaft surface generated by friction. The turbogenerator has three bearings: two main bearings and the brush gear bearing. The carbon brushes sliding on the slip rings were identified as the hot spot location. Potential modifications were studied using hot spot stability analyses with a rotor dynamic model of the generator rotor on three journal bearings. The applied method, introduced by Schmied (1987, “Spiral Vibrations of Rotors” Proc. 11th Biennial ASME Design Engineering Div. Conf., Vib. Noise, DE-Vol. 2, Rotating Machinery Dynamics, Boston, MA, ASME H0400B, pp. 449–456), allows the handling of general systems. The hot spot model is based on the theory of Kellenberger (1978, Ingenieur-Archiv, 47, pp. 223–229; 1980, Journal of Mechanical Design, 102, pp. 177–184) using a thermal equation between the shaft’s thermal deflection and the shaft displacement at the hot spot location. Three different relations between the heat input and the shaft vibration were modeled: heat input proportional to the shaft displacement, to the shaft velocity, and to the shaft acceleration. The model, in which the heat input is proportional to the velocity, is the most suitable variant for slip rings. This was confirmed by comparison with the measured vibration behavior. A modification of the shaft line was selected based on the calculation results and was successfully implemented. This generator and other generators with the same modified brush gear unit have been in operation for more than four years.
Compressor/Diffuser/Combustor Aerodynamic Interactions in Lean Module Combustors
Authors: Duncan Walker A. , Carrotte Jon F. , McGuirk James J.
Published: January 2008

The paper reports an experimental investigation into the possibility of increased interactions between combustor external aerodynamics and upstream components, e.g., prediffuser, compressor outlet guide vane (OGV), and even the compressor rotor, caused by the trend in lean module fuel injectors to larger mass flows entering the combustor cowl. To explore these component interaction effects, measurements were made on a fully annular rig comprising a single stage compressor, an advanced integrated OGV/prediffuser, followed by a dump diffuser and a generic combustor flametube with metered cowl and inner/outer annulus flows. The flow split entering the cowl was increased from 30% to 70%. The results demonstrate that, with fixed geometry, as the injector flow increases, the performance of the prediffuser and feed annuli suffer. Prediffuser losses increase and at high injector flow rates, the diffuser moves close to separation. The substantial circumferential variation in cowl flow can feed upstream and cause rotor forcing. Notable differences in performance were observed inline and between injectors at the OGV exit, suggesting that geometry changes such as an increased dump gap or nonaxisymmetric prediffuser designs may be beneficial.
Experimental Investigation of the Stability Mechanism and Emissions of a Lifted Swirl Nonpremixed Flame
Authors: Fokaides Paris A. , Kasabov Plamen , Zarzalis Nikolaos
Published: January 2008

We report on the experimental investigation of a confined lifted swirl nonpremixed flame by applying a novel Airblast nozzle (Zarzalis, N., et al., 2005, Fuel Injection Apparatus, Patent No. DE 10 2005 022 772.4, EP 06 009 563.5). 3D-laser doppler anemometry, a nonintrusive, laser-based measurement technique, is adapted for the measurement of all three mean velocity components and of the six Reynolds stress components. The determination of the temperature and mixture field occurs by employing in-flame measurement techniques. Valuable information concerning the mixing procedure, the temperature distribution, the turbulence level, and the velocity field of the flame is provided. The results demonstrate that there is sufficient residence time in the precombustion area of the lifted flame in order to achieve spatial and temporal uniformity of the mixture, leading to a quasi-premixed state. It was also found that hot reaction products, carried upstream by an annular zone of reverse flow, react with fresh unburnt mixture in a re-ignition process. The determination of the flow pattern revealed the presence of an inner weak recirculation zone in the nozzle vicinity and a dominant external recirculation zone. The examination of the probability density function of the velocity measurements was also found to be a very useful tool in terms of the analysis of the turbulence structure of the flow. The bimodal distribution in the shear layer between the downstream flow and the recirculated gases yields the existence of large scale eddies. Finally, the significant reduced NOx emissions in the lean area were also shown by means of emission measurements for elevated pressure conditions.
A Novel Free-Cooling Scheme for Combustion Turbine Inlet Air Cooling
Authors: Zamzam Montaser M. , Al-Amiri Abdalla M.
Published: January 2008

Free cooling is a well-known concept in the HVAC industry in which the cold water produced by a cooling tower is used directly to satisfy the requirement of the cooling load without assistance by the chiller; this concept, however, is not reported in the turbine inlet air-cooling applications. Free cooling works well as long as the ambient wet bulb temperature (WBT) is sufficiently low to produce cold water at the required temperature, but once WBT reaches its threshold value (hence, free-cooling mode is ceased) and the chiller kicks off working under its normal mode of operation, i.e., free cooling is either enabled or disabled. The proposed system in this paper provides, in addition to the above modes of operation, a novel mode that utilizes the cooling tower as a primary source of cooling simultaneously with the chiller that serves as a secondary source at elevated WBT. This new feature significantly reduces the yearly operating hours of the chiller and possibly its size, depending on the desired inlet air temperature, actual weather conditions, and design WBT. Chiller size can vary between 0% and 100% as compared to a similar classical chiller system with significant reduction in the operating hours. The proposed system consists basically of chiller, cooling tower, cooling coils, interconnecting piping, and controls. The arrangement of the system equipment changes with the operation modes in two configurations: dual water circulation loops and single water circulation loop. In the dual-loop configuration, the system has two separate loops such that the evaporator and the cooling coils are tied in one loop, while the cooling tower and condenser in the other loop; whereas in the single-loop configuration, all equipment is connected in series in one water circulation loop. This paper presents the major equipment and characteristics of the novel chiller scheme. In addition, the study outlines the potential reduction in the chiller load, size, and operating hours under a generalized weather envelope. The paper portrays the feasibility of using the proposed cooling scheme for turbine inlet air cooling.
The Effect of Initial Injection Conditions on the Oil Droplet Motion in a Simplified Bearing Chamber
Authors: Farrall M. , Hibberd S. , Simmons K.
Published: January 2008

Increasing demands on aeroengines to operate at higher shaft speeds and temperatures require an understanding and optimization of the integral systems. The ability to model movement of oil around bearing chambers in the form of droplets and films is a current area of interest. This paper presents a two-phase numerical modeling approach developed for predicting air, oil droplet, and oil film behavior within an aeroengine bearing chamber including the significant droplet/film interactions. In-house code is linked to the commercial CFD package CFX4.3 and a predictive algorithm for determining the outcome of droplet impact with a wall film and the associated transfer of oil mass and momentum is developed. The method is used to simulate the motion of oil droplets shed from a roller bearing in a simplified aeroengine bearing chamber geometry and through a parametric study shows that initial droplet size distribution parameters (mean diameter and spread) have a significant effect on oil deposition location. In contrast, the Sauter mean diameter of droplets within the chamber showed little sensitivity to initial injection parameters. The behavior of oil within a bearing chamber is strongly influenced by the conditions with which it leaves the bearing. There is potential for performance improvement if bearing shed can be controlled or if chamber design can be modified such that oil behavior is insensitive to initial shed conditions.
Study and Field Tests of the Novel Low Pressure Fogger System for Industrial Gas Turbine
Authors: Levy Y. , Sherbaum V. , Ovcharenko V. , Sotsenko Y. , Zlochin I.
Published: January 2008

Based on three patented innovations (air-assist atomizer, wetness sensor, and closed loop programmable logic controller (PLC)), a new low-pressure power gas turbine augmentation system was developed. Two modifications of air-assist atomizer were tested in the Jet Engine Laboratory of the Technion. The tests were performed to investigate influence of thermodynamic parameters on spray characteristics, as droplet size and velocity distribution of the spray. The system as a whole has passed field test in a gas turbine of a power station. Droplet characteristics, conceptual design aspects, and test results are described. It was found that the droplet sauter mean diameter was 20μm. The field tests demonstrated that the power augmentation system operates safely and reliably. Wetness sensors and closed loop PLC proved to be a safe method for power augmentation, which prevents droplet penetration into the compressor inlet.
Impact of Ethane, Propane, and Diluent Content in Natural Gas on the Performance of a Commercial Microturbine Generator
Authors: Hack Richard L. , McDonell Vincent G.
Published: January 2008

The impact of fuel composition on the performance of power generation devices is gaining interest as the desire to diversify fuel supplies increases. In the present study, measurements of combustion performance were conducted on a commercial natural gas-fired 60kW gas turbine as a function of fuel composition. A statistically designed experiment was carried out and exhaust emissions were obtained for significant amounts of ethane and propane. In addition, a limited study of the effect of inerts was conducted. The results show that emissions of NOx, CO, and NOx∕NO are not well correlated with common descriptions of the fuel, such as higher heating value or methane number. The results and trends indicate that the presence of higher hydrocarbons in the fuel leads to appreciably higher NOx emissions for both test devices operating under similar lean conditions, while having less impact on CO emissions.
Heavily Loaded Gas Foil Bearings: A Model Anchored to Test Data
Authors: Kim Tae Ho , San Andrés Luis
Published: January 2008

Widespread usage of gas foil bearings (FBs) into microturbomachinery to midsize gas turbine engines requires accurate performance predictions anchored to reliable test data. This paper presents a simple yet accurate model predicting the static and dynamic force characteristics of gas FBs. The analysis couples the Reynolds equation for a thin gas film to a simple elastic foundation model for the top foil and bump strip layer. An exact flow advection model is adopted to solve the partial differential equations for the zeroth- and first-order pressure fields that render the FB load capacity and frequency-dependent force coefficients. As the static load imposed on the foil bearing increases, predictions show that the journal center displaces to eccentricities exceeding the bearing nominal clearance. A nearly constant FB static stiffness, independent of journal speed, is estimated for operation with large loads, and approaching closely the bearing structural stiffness derived from contact operation without rotor spinning. Predicted minimum film thickness and journal attitude angle demonstrate good agreement with archival test data for a first-generation gas FB. The bump-foil-strip structural loss factor, exemplifying a dry-friction dissipation mechanism, aids to largely enhance the bearing direct damping force coefficients. At high loads, the bump-foil structure influences most the stiffness and damping coefficients. The predictions demonstrate that FBs have greatly different static and dynamic force characteristics when operating at journal eccentricities in excess of the bearing clearance from those obtained for operation at low loads, i.e., small journal eccentricity.
MotoGP 2007: Criteria for Engine Optimization
Authors: Mattarelli Enrico
Published: January 2008

The paper proposes some design criteria for the MotoGP engines, complying with the FIM 2007 Technical Regulations. Five configurations have been considered: engines with three cylinders in line and four cylinders in line, and three V engines with four, five, and six cylinders. All the analyzed solutions have been optimized from a fluid-dynamic point of view by means of one dimensional engine cycle simulations. Then, the engines are compared in terms of full load performance at steady conditions. Finally, the influence of engine performance, along with operation regularity and motorbike weight, is assessed by means of a lap time simulator, developed by the author on the base of real data. The best configurations turned out to be the four-cylinder engines, while three-cylinder and five-cylinder engines are quite penalizing. The key of the four-cylinder engines success is their good breathing capability and mechanical efficiency at high speed, yielding an optimum power-to-weight ratio, associated with a good engine regularity, i.e., a smooth response to throttle angle variations.
Numerical and Experimental Damping Assessment of a Thin-Walled
Friction Damper in the Rotating Setup With High Pressure Turbine
Blades
Authors: Szwedowicz J. , Gibert C. , Sommer T. P. , Kellerer R.
Published: January 2008

Underplatform friction dampers are possible solutions for minimizing vibrations of rotating turbine blades. Solid dampers, characterized by their compact dimensions, are frequently used in real applications and often appear in patents in different forms. A different type of the friction damper is a thin-walled structure, which has larger dimensions and smaller contact stresses on a wider contact area in relation to the solid damper. The damping performance of a thin-walled damper, mounted under the platforms of two rotating, freestanding high pressure turbine blades, is investigated numerically and experimentally in this paper. The tangential and normal contact stiffness that are crucial parameters in optimal design of any friction damper are determined from three-dimensional finite element computations of the contact behavior of the damper on the platform including friction and centrifugal effects. The computed contact stiffness values are applied to nonlinear dynamic simulations of the analyzed blades coupled by the friction damper of a specified mass. These numerical analyses are performed in the modal frequency domain, which is based on the harmonic balance method for the complex linearization of friction forces. The numerical dynamic results are in good agreement with the measured data of the real mistuned system. In the analyzed excitation range, the numerical performance curve of the thin-walled damper is obtained within the scatter band of the experimental results. For the known friction coefficients and available finite element and harmonic balance tools, the described numerical process confirms its usability in the design process of turbine blades with underplatform dampers.
A Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals
Authors: Childs Dara W. , Shin Yoon-Shik , Seifert Brent
Published: January 2008

Predictions are presented for hole-pattern-stator seals for which the hole depth is varied axially, showing that various depth patterns can significantly improve damping performance in terms of both increasing the seal’s effective damping and reducing its crossover frequency—the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable hole depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant hole depth (CHD) design versus predictions of 2.7. The crossover frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor-jump phenomenon, not flow path divergence. The VHD seal leaks less than a comparable CHD design.
Fuel Flexibility Influences on Premixed Combustor Blowout, Flashback, Autoignition, and Stability
Authors: Lieuwen Tim , McDonell Vince , Petersen Eric , Santavicca Domenic
Published: January 2008

This paper addresses the impact of fuel composition on the operability of lean premixed gas turbine combustors. This is an issue of current importance due to variability in the composition of natural gas fuel supplies and interest in the use of syngas fuels. This paper reviews available results and current understanding of the effects of fuel composition on combustor blowout, flashback, dynamic stability, and autoignition. It summarizes the underlying processes that must be considered when evaluating how a given combustor’s operability will be affected as fuel composition is varied.
Flame Propagation Following the Autoignition of Axisymmetric Hydrogen, Acetylene, and Normal-Heptane Plumes in Turbulent Coflows of Hot Air
Authors: Markides Christos N. , Mastorakos Epaminondas
Published: January 2008

Axisymmetric plumes of hydrogen, acetylene, or n-heptane were formed by the continuous injection of (pure or nitrogen-diluted) fuel into confined turbulent coflows of hot air. Autoignition and subsequent flame propagation was visualized with an intensified high-speed camera. The resulting phenomena that were observed include the statistically steady “random spots” regime and the “flashback” regime. It was found that with higher velocities and smaller injector diameters, the boundary between random spots and flashback shifted to higher air temperatures. In the random spots regime the autoignition regions moved closer to the injector with increasing air temperature and/or decreasing air velocity. After a localized explosive autoignition event, flames propagated into the unburnt mixture in all directions and eventually extinguished, giving rise to autoignition spots of mean radii of 2–5mm for hydrogen and 6–10mm for the hydrocarbons. The average flame propagation velocity in both the axial and radial directions varied between 0.5 and 1.2 times the laminar burning speed of the stoichiometric mixture, increasing as the autoigniting regions shifted upstream.
System-Level Performance Estimation of a Pulse Detonation Based Hybrid Engine
Authors: Goldmeer Jeffrey , Tangirala Venkat , Dean Anthony
Published: January 2008

A key application for a Pulse detonation engine concept is envisioned as a hybrid engine, which replaces the combustor in a conventional gas turbine with a pulse detonation combustor (PDC). A limit-cycle model, based on quasi-unsteady computational fluid dynamics simulations, was developed to estimate the performance of a pressure-rise PDC in a hybrid engine to power a subsonic engine core. The parametric space considered for simulations of the PDC operation includes the mechanical compression or the flight conditions that determine the inlet pressure and the inlet temperature conditions, fill fraction, and purge fraction. The PDC cycle process time scales, including the overall operating frequency, were determined via limit-cycle simulations. The methodology for the estimation of the performance of the PDC considers the unsteady effects of PDC operation. These metrics include a ratio of time-averaged exit total pressure to inlet total pressure and a ratio of mass-averaged exit total enthalpy to inlet total enthalpy. This information can be presented as a performance map for the PDC, which was then integrated into a system-level cycle analysis model, using GATECYCLE, to estimate the propulsive performance of the hybrid engine. Three different analyses were performed. The first was a validation of the model against published data for a specific impulse. The second examined the performance of a PDC versus a traditional Brayton cycle for a fixed combustor exit temperature; the results show an increased efficiency of the PDC relative to the Brayton cycle. The third analysis performed was a detailed parametric study of varying engine conditions to examine the performance of the hybrid engine. The analysis has shown that increasing the purge fraction, which can reduce the overall PDC exit temperature, can simultaneously provide small increases in the overall system efficiency.
Application of a Computational Code to Simulate Interstage Injection Effects on GE Frame 7EA Gas Turbine
Authors: Bagnoli M. , Bianchi M. , Melino F. , Peretto A. , Spina P. R. , Ingistov S. , Bhargava R. K.
Published: January 2008

This paper investigates effects of interstage water injection on the performance of a GE Frame 7EA gas turbine using aerothermodynamic modeling. To accomplish this objective, a computational code, written in FORTRAN 90 language and developed by DIEM University of Bologna, has been used. The calculation procedure considers effects of evaporation of injected water within the compressor including droplets dynamics, which are necessary in order to fully evaluate effects of wet compression on the gas turbine performance. The robustness of the computational code is demonstrated by evaluating stage-by-stage compressor performance and the overall gas turbine performance in the presence of inlet evaporative fogging, overspray fogging, and interstage water injection. The presented results show that water injection location influences compressor stage loading redistribution differently. The plausible explanations to the observed trends of various performance parameters are presented in this paper.
Neural Network Models for Usage Based Remaining Life Computation
Authors: Parthasarathy Girija , Menon Sunil , Richardson Kurt , Jameel Ahsan , McNamee Dawn , Desper Tori , Gorelik Michael , Hickenbottom Chris
Published: January 2008

In engine structural life computations, it is common practice to assign a life of certain number of start-stop cycles based on a standard flight or mission. This is done during design through detailed calculations of stresses and temperatures for a standard flight, and the use of material property and failure models. The limitation of the design phase stress and temperature calculations is that they cannot take into account actual operating temperatures and stresses. This limitation results in either very conservative life estimates and subsequent wastage of good components or in catastrophic damage because of highly aggressive operational conditions, which were not accounted for in design. In order to improve significantly the accuracy of the life prediction, the component temperatures and stresses need to be computed for actual operating conditions. However, thermal and stress models are very detailed and complex, and it could take on the order of a few hours to complete a stress and temperature simulation of critical components for a flight. The objective of this work is to develop dynamic neural network models that would enable us to compute the stresses and temperatures at critical locations, in orders of magnitude less computation time than required by more detailed thermal and stress models. The current paper describes the development of a neural network model and the temperature results achieved in comparison with the original models for Honeywell turbine and compressor components. Given certain inputs such as engine speed and gas temperatures for the flight, the models compute the component critical location temperatures for the same flight in a very small fraction of time it would take the original thermal model to compute.
Calculations of Cooled Turbine Efficiency
Authors: Horlock J. H. , Torbidoni Leonardo
Published: January 2008

The efficiency of a cooled turbine stage has been discussed in the literature. All proposed definitions compare the actual power output with an ideal output, which has to be determined; but usually, one of two definitions has been used by turbine designers. In the first, the so-called Hartsel efficiency, the mainstream gas flow, and the various coolant flows to rotor and stator are assumed to expand separately and isentropically to the backpressure. In the second, it is assumed that these flows mix at constant (mainstream) gas pressure before expanding isentropically (sometimes, the rotor coolant flow is ignored in this definition). More recently, it has been suggested that a thermodynamically sounder definition is one in which the gas and coolant flows mix reversibly and adiabatically before isentropic expansion to the backpressure. In the current paper, these three efficiencies are compared, for a typical stage—the first cooled stage of a multistage industrial gas turbine. It is shown that all the efficiencies fall more or less linearly with increase of the fractional (total) coolant flow. It is also shown that the new definition of efficiency gives values considerably lower than the other two efficiencies, which are more widely used at present. Finally, the various irreversibilities associated with the flow through a cooled turbine are calculated. Although all these irreversibilities increase with the fractional coolant flow, it is shown that the “thermal” irreversibility associated with film cooling is higher than the other irreversibilities at large fractional coolant flow.
Effects of Tailpipe Friction on the Nonlinear Dynamics of a Thermal Pulse Combustor
Authors: Mukhopadhyay Achintya , Datta Subhashis , Sanyal Dipankar
Published: January 2008

The effect of tailpipe friction on the combustion dynamics inside a thermal pulse combustor has been investigated using a nonlinear model consisting of four coupled first order ordinary differential equations. The dynamics of the system is represented through time series plots, time-delay phase plots, and Poincaré maps. The results indicate that as the tailpipe friction factor is lowered, the system undergoes a transition from steady combustion through oscillating combustion to an intermittent combustion with chaotic characteristics before extinction. The time series data are shown to be useful indicator for early detection of extinction. In one approach (thresholding), the occurrence of local peak pressures below a predefined threshold value is identified as an event and the number of events (event count) and largest number of successive cycles with such events (event duration) are recorded as the friction factor is lowered. In another approach, the statistical moments (kurtosis) of the data are used. Number of kurtosis peaks above a prescribed value and variance of the kurtosis values are recorded for decreasing values of friction factor. All these numbers sharply increase as the system approaches extinction.
Development and Validation of a Computational Code for Wet Compression Simulation of Gas Turbines
Authors: Bagnoli M. , Bianchi M. , Melino F. , Spina P. R.
Published: January 2008

In this paper, a calculation code, developed in house by the authors, able to evaluate the performance of a gas turbine with all possible fogging strategies (high pressure fogging, overspray, and interstage injection) is presented and discussed. The code has a flexible structure and can be applied to evaluate the performance of every commercial gas turbine model. The aim of the calculation code is to overcome the limits of the most widespread commercial software, especially with regard to the two phase flow compression process simulation. The calculation code was validated on results available in the literature showing a good agreement with experimental and theoretical results.
Labyrinth Seal Leakage Tests: Tooth Profile, Tooth Thickness, and Eccentricity Effects
Authors: Gamal Ahmed J. M. , Vance John M.
Published: January 2008

The effects of two seal design parameters, namely blade (tooth) thickness and blade profile, on labyrinth seal leakage, as well as the effect of operating a seal in an off-center position, were examined through a series of nonrotating tests. Two reconfigurable seal designs were used, which enabled testing of two-, four-, and six-bladed see-through labyrinth seals with different geometries using the same sets of seal blades. Leakage and cavity pressure measurements were made on each of 23 seal configurations with a in.(101.6mm) diameter journal. Tests were carried out with air as the working fluid at supply pressures of up to 100psia (6.89bar). Experimental results showed that doubling the thickness of the labyrinth blades significantly influenced leakage, reducing the flow rate through the seals by up to 20%. Tests to determine the effect of blade-tip profile produced more equivocal results, with the results of experiments using each of the two test seal designs contradicting each other. Tests on one set of hardware indicated that beveling blades on the downstream side was most effective in limiting leakage, whereas tests on newer hardware with tighter clearances indicated that seals with flat-tipped blades were superior. The test results illustrated that both blade profile and blade thickness could be manipulated so as to reduce seal leakage. However, an examination of the effects of both factors together indicated that the influence of one of these parameters can, to some extent, negate the influence of the other (especially in cases with tighter clearances). finally, for all configurations tested, results showed that leakage through a seal increases with increased eccentricity and that this phenomenon was considerably more pronounced at lower supply pressures.
Analysis of the Effect of Strip Buckling on Stability of Strip Lateral Motion With Application to Cold Rolling of Steel
Authors: Tarnopolskaya T. , Gates D. J.
Published: January 2008

A sudden loss of lateral stability (strip track-off) is a serious operational problem in cold rolling of steel that often leads to catastrophic consequences such as mill crashes and roll damage. This paper studies the causes of instability in lateral motion of a metal strip in a single span between the uncoiler and the first stand of a cold rolling mill. A mathematical model of strip lateral dynamics that includes a rolling mill model and a simplified physically based model of strip buckling is formulated. The numerical analysis of the model reveals that in the presence of strip buckling, the lateral motion becomes unstable once a critical level of asymmetry in rolling conditions is exceeded. The critical level of asymmetry increases with the increase in the tension applied to the strip. Below this critical level of asymmetry, a sudden transition to unstable motion occurs if a critical lateral deviation is reached. This paper demonstrates that the buckling of the strip can be responsible for lateral instability. The results of this paper explain the sudden onset of instability observed in metal rolling and the stabilizing effect of the tension applied to the strip, known in rolling practice.
Stability of Controlled Mechanical Systems With Ideal Coulomb Friction
Authors: Jeon Soo , Tomizuka Masayoshi
Published: January 2008

When a mechanical system with Coulomb friction is under feedback control, the closed-loop system may asymptotically converge to a point in the equilibrium set or generate nonlinear oscillations such as limit cycles depending on the control algorithm. Thus, it is important to know how to guarantee the stability in the presence of Coulomb friction. This paper presents the stability analysis of controlled mechanical systems with multiple ideal Coulomb friction sources. Common properties of controlled mechanical systems with multiple ideal Coulomb friction sources have been explored and generalized into the state space formulation leading to a class of ideal relay feedback systems. Various stability criteria are considered and a new sufficient condition for the pointwise global stability is suggested. Simulation results for a single mass system and experimental results for a single link flexible joint mechanism are presented to confirm the analysis and to illustrate various aspects of stability conditions for controlled mechanical systems with ideal Coulomb friction. The results given in this paper can be useful for the design of mechanical systems free from the limit cycle.
Conventional triode ionization gauge with carbon nanotube cold electron emitter
Authors: Xiao Lin , Qian Li , Wei Yang , Liu Liang , Fan Shoushan
Published: January 2008

The authors presented a conventional triode ionization gauge with a linear-type carbon nanotube cold electron emitter, which was made by painting technology on a nickel wire. The gauge used the ratio of the ion current to the electron current to indicate the vacuum. Although there was fluctuation in the cathode’s emission current, the ratio of the ion current to the electron current kept stable with a variation of about ±10% in each pressure decade from 10−7to10−3torr. The gauge showed good measurement linearity in the vacuum range from 10−6to10−3torr.