bluuebunny/crossref_metadata_2025 huggingface dataset:
Corrosion Resistant, Lightweight, and Inexpensive Metallic Bipolar Plates With Excellent Manufacturability for PEM Fuel Cell Power Systems
Authors: Hung Yue , El-Khatib K. M. , Tawfik Hazem
Published: November 2008

Corrosion resistant metal treated bipolar plates with higher rigidity and electrical conductivity than graphite were developed and tested for PEM fuel cell applications. Six replicas of single cells, three of which were made of graphite composites bipolar plates and the other three were made of the treated metallic plates. An Electrode Membrane Assembly (MEA) with 5.55 cm2 active electrode areas, double-sided electrodes, 0.3 mg/cm2 Pt loading and Nafion membrane 115 was fitted to each cell and operated under identical conditions. The experimental testing was conducted at room temperature 20°C. The obtained data from the three graphite cells were averaged and plotted and the other metallic cells’ data were similarly treated and plotted on the same graph for comparison. Generally, the metallic treated bipolar plate provided at least 12% saving in hydrogen consumption in comparison to graphite. This is attributed to the lower bulk and surface contact resistance of the metal used in this study in relation to graphite. The results of the lifetime testing, conducted at room temperature under variable loading showed no indication of power degradation due to metal corrosion for at least 1500 hours.
Nitride Metallic Bipolar Plates for Proton Exchange Membrane Fuel Cells
Authors: Brady Michael P. , Wang Heli , Paulauskas Irene , Yang Bing , Sachenko Pavlo , Tortorelli Peter F. , Turner John A. , Buchanan Raymond A.
Published: November 2008

Thermal nitridation of Ni- and Fe-base Cr-bearing alloys is under investigation as a means to enable use of metallic bipolar plates in proton exchange membrane fuel cells. Proof of principle for this approach was recently established by a successful single-cell fuel cell test using 50 cm2 active area anode and cathode plates made from a model nitrided Ni-50Cr alloy. Protection of the metal was accomplished by the formation of an electrically-conductive and corrosion-resistant CrN/Cr2N surface layer. This paper presents an overview of efforts to form similar Cr-nitride surfaces on Ni-Cr and Fe-Cr base alloys in commercially available composition ranges.
Durability and Performance of Press Molded Polymer Composite Monopolar Plates
Authors: Webb Vernon , Hickner Michael , Baird Donald , Case Scott , Lesko John
Published: November 2008

The electrical and mechanical properties of new lightweight graphite polymeric separator plates aged in a PEM fuel cell were investigated to assess their resistance to short-term durability. While the changes in electrical properties of great interest to the operation of the fuel cell, mechanical and dimensional stability over the life of the cell are critical. Thus, new polymeric based separator plates developed at Virginia Tech were aged under standard operating conditions in a PEM fuel cell over 300 hours at low pressure and 85°C. A comparison of conductivity, stiffness and strength of aged plates was made to as manufactured and unaged plates. Over the aging period, electrical conductivity did not decline even as the fuel cell performance showed some changes as evidenced by polarization curves. However, the mechanical strength of the monopolar plates was observed to declined less than 10% after 300 hours of fuel cell operation, due to the lack of stability of the polyester resin used to facilitate the rapid manufacturing of these new plates. These property changes were found to be independent of aging on the reduction and oxidation sides. Further work continues on plates formed through both fiber wet lay technology and those produced by compression molding of unique graphite filled epoxy systems, and to improve the electrochemical performance of cells fabricated using the resulting plates to levels comparable to those observed when using existing plate materials.
Modeling and Analysis of a Bio-Fuelled Ceramic Fuel Cell Stack
Authors: Yuan Jinliang , Zhu Bin , Shah Ramesh K. , Sunde´n Bengt
Published: November 2008

Recent development in the advanced ceramic fuel cell (CFC), working at intermediate temperature 600–700°C, brings up feasibility and new opportunity to employ renewable fuels with this innovative technology. It may offer a better solution concerning environment, natural resources and development of our civil society. Moreover, direct oxidation of hydrocarbon fuels at intermediate temperature possesses great advantage in avoiding complex and expensive external reforming process. This paper presents modeling and analysis of an intermediate temperature CFC stack. The model is a general one to evaluate the stack performance for the purpose of optimal design and/or configuration based on the specified electrical power or fuel supply rate, except that the Tafel coefficients are adjusted and/or obtained to match experimental data. The energy and gas flow data obtained from the investigation can be further used to identify the heat exchanger network configurations and optimal operating conditions using process integration techniques. The model can be applied as a stand alone one, or implemented into an overall energy system modeling for the purpose of system study.
Thermodynamic Analysis of SOFC Systems Using Different Fuel Processors
Authors: Bove Roberto , Sammes Nigel M.
Published: November 2008

Solid oxide fuel cells operate at high temperature and consequently the internal reforming of hydrocarbons, for example methane, can easily be achieved. Nevertheless, since the reforming process is strongly endothermic, internal temperature gradients can be generated, thus producing considerable limitations to the fuel cell operation. Moreover, total internal reforming can lead to carbon deposition in the anode component. In order to avoid these problems total internal reforming is generally not conducted, and part of the fuel is externally pre-reformed. In the present study, different options for the pre-conversion process are considered. The relative system performances are evaluated through a thermodynamic analysis and numerical simulations.
Manufacturability of SOFC Fuel Cell Materials Such as Ceramic Tapes and Thick-Film Pastes in an ISO/TS Environment
Authors: Webb Richard S. , Feingold Alvin H. , Topka Zachary J. , Twiname Eric R.
Published: November 2008

One challenge faced by developers of solid oxide fuel cells and cell stacks is obtaining high-quality fuel cell materials consistently, economically and in large volumes — that is, materials which are manufacturable. Two viable materials technologies are continuously-cast ceramic tapes and thick-film pastes. Paste and tape processing, whether proprietary to the fuel cell manufacturer or the materials supplier, should follow ISO 9001:2000 and, for automotive applications, QS-9000 and ISO/TS 16949 guidelines. This paper describes manufacturing of SOFC tapes and pastes using these guidelines from prototype through scale-up to high volume quantities.
The Role of Radiative Heat Transfer With Participating Gases on the Temperature Distribution in Solid Oxide Fuel Cells
Authors: VanderSteen J. D. J. , Pharoah J. G.
Published: November 2008

Solid oxide fuel cell (SOFC) technology has been shown to be viable, but its profitability has not yet been seen. To achieve a high net efficiency at a low net cost, a detailed understanding of the transport processes both inside and outside of the SOFC stack is required. Of particular significance is an accurate determination of the temperature distribution because material properties, chemical kinetics and transport properties depend heavily on the temperature. Effective utilization of the heat can lead to a substantial increase in overall system efficiency and decrease in operating cost. Despite the extreme importance in accurately predicting temperature, the majority of SOFC modeling work ignores radiative heat transfer. SOFCs operate at temperatures around or above 1200 K, where radiation effects can be significant. In order to correctly predict the radiation heat transfer, participating gases must also be included. Water vapour and carbon dioxide can absorb, emit, and scatter radiation, and are present at the anode in high concentrations. This paper presents a thermal transport model for analyzing heat transfer and improving thermal management within planar SOFCs. The model was implemented using a commercial computational fluid dynamic (CFD) code and includes conduction, convection, and radiation in a participating media. It is clear from this study that radiation must be considered when modelling solid oxide fuel cells. The effect of participating media radiation was shown to be minimal in this geometry, but it is likely to be more important in tubular geometries.
Fuel Processing for Fuel Cell Applications
Authors: Samanta I. , Shah R. K. , Wagner A.
Published: November 2008

At its essence, a fuel cell combines hydrogen and oxygen to form electricity, heat, and water. The source of this hydrogen may be from natural gas, coal, gasoline, diesel, alcohols, or natural decomposition products. Pure hydrogen is the ideal fuel, but it needs to be obtained by processing fossil fuels (natural gas, gasoline, diesel, oil, coal, etc.), biofuels (e.g., landfill gas, anaerobic digester gas, etc.), or chemical intermediates, or must be produced via renewable energy sources through electrolysis of water. Currently pure hydrogen is produced cryogenically at both a great energy and fiscal expense. In this paper, we cover all important fuel reforming processes for generating hydrogen for fuel cells and then discuss the associated reformers. The common techniques utilized for external fuel reforming processes are steam reforming, partial oxidation and autothermal reforming. For high temperature fuel cells, direct and indirect internal reforming techniques are used and will be discussed. The methods for reforming of chemical intermediates (alcohol and ammonia), reforming of bio-fuels and aviation fuels are also discussed in this paper. For low temperature fuel cells such as PEM, carbon monoxide is a poison that adversely affects fuel cell performance. The CO content must be reduced to below 100 ppm. This is accomplished by use of the water-gas shift reaction, preferential oxidation, methanation, or may be accomplished by membrane separation techniques. Special emphasis in this paper will be the challenges and opportunities in fuel processing for fuel cells.
The Design of a Catalytic Reactor/Heat Exchanger and Fuel Cell for the Covert Generation of Electricity
Authors: Hou Diana , Lesniak Ewelina , Lundquist Mark , Churchill Stuart W. , Retallick William B.
Published: November 2008

A preliminary process design is presented for a 100-kW generator of electricity for covert use by the United States Armed Forces in an arbitrary isolated site. The special features of this analysis are the novel constraints, which consist of the use of a commonly available fuel, portability (less than 450 kg) and maneuverability of the generator and accessories both by air and on the ground, minimal generation of noise, minimal release of readily identifiable gaseous emissions, and simplicity of operation with minimally trained personnel. Fixed and operational costs are not primary considerations.
Dynamic Simulation of an Autothermal Methane Reformer
Authors: Yuan Li , Brouwer Jacob , Samuelsen G. Scott
Published: November 2008

A dynamic autothermal methane reformer model has been developed and tested for the production of a hydrogen- and carbon monoxide-rich syngas. This study looks at potential advantages and disadvantages of an autothermal reformer, both operating in stand-alone mode and in conjunction with a high temperature fuel cell stack. The model uses a conservation of moles as the fundamental continuity relationship, and applies basic energy conservation equations to simulate both the gas and the catalyst bed energies. Chemical kinetic expressions using empirical constants for the Arrhenius rate terms that describe steam reformation of methane and partial oxidation of methane are simultaneously solved to provide an accurate picture of the reaction dynamics. This paper presents dynamic responses of reformer outlet temperature, hydrogen mole fraction, reaction rates and methane conversion to the perturbation of the reformer inlet variables of steam-to-carbon ratio, oxygen-to-carbon ratio and inlet gas temperature. Also explored is the concept of catalyst “light-off,” where there is found to be a lower temperature limit above which catalyst activity is substantially increased.
Seals and Sealants in PEM Fuel Cell Environments: Material, Design, and Durability Challenges
Authors: Dillard David A. , Guo Shu , Ellis Michael W. , Lesko John J. , Dillard John G. , Sayre Jay , Vijayendran Bhima
Published: November 2008

Fuel cells have significant potential to improve energy utilization efficiency, but remain quite expensive due to the cost of key components, including the membrane of PEM fuel cells, the catalyst, and the bipolar plates. Due to the cost and significance of these items, extensive research has been devoted to reducing cost and improving the quality and performance of these components. By contrast, seals, sealants, and adhesives play a more mundane role in the overall performance of fuel cells, and yet the failure of these materials can lead to reduced system efficiency, system failure, or even safety concerns. Less attention has been given to the performance and durability of these products, yet as improvements in other fuel cell components are made, these seals are becoming a more critical link in the long term performance of fuel cells. This review paper highlights the importance and background of fuel cell seals; discusses the chemical, thermal, and mechanical environments to which fuel cell seals are subjected; and suggests design and testing protocol improvements that may lead to improved fuel cell system performance.
SWNT Enhanced PEM Fuel Cells
Authors: Ruf H. J. , Landi B. J. , Raffaelle R. P.
Published: November 2008

Considerable interest exists in the application of single wall carbon nanotubes (SWNTs) to proton exchange membrane fuel cells (PEMFCs). Proposed applications include use as anode materials in both hydrogen and direct methanol fuel cells, solid polymer electrolyte additives, active cathode materials, and bipolar plate interconnects. SWNTs have extremely high electrical conductivity and catalytic surface areas which make them potentially outstanding active materials for PEMFC electrodes. Additionally the enhanced mechanical properties may play a roll in developing new fuel cell designs such as thin-film microelectronic fuel cells. In a previous study SWNTs were combined with commercially obtained E-TEK Vulcan XC-72 and Nafion® to produce composite cathode membranes. The addition of nanotubes resulted in enhanced fuel cell performance over an equivalent weight percent doping of E-TEK alone. This increased performance was achieved with a 50% reduction in the quantity of platinum present in the cathode. In the present study we investigate fuel cell performance when both the anode and cathode membranes contain graphite, platinum and SWNTs. The SWNTs were characterized by use of thermogravimetric analysis, Raman and UV/VIS/NIR spectroscopes as well as high resolution field emission scanning electron microscopy. Fuel cell performance was determined by comparison of the IV characteristics.
Electrical Contact Resistance Between Gas Diffusion Layers and Bipolar Plates for Applications to PEM Fuel Cells
Authors: Mishra V. , Yang F. , Pitchumani R.
Published: November 2008

The electrical contact resistance between gas diffusion layers and bi-polar flow channel plates is one of the important factors contributing to the operational voltage loss in fuel cells. Effective analysis and design of fuel cells therefore need to account for the contact resistance in deriving the polarization curve for the cell. Despite its significance, relatively scant work is reported in the open literature on the measurement and modeling of the contact resistance in fuel cell systems, and the present work aims to fill this void. Experimental data are reported for the first time to show the effects of different gas diffusion layer materials and contact pressure on the electrical contact resistance. A fractal asperity based model is adopted to predict the contact resistance as a function of pressure, material properties, and surface geometry. Good agreement is observed between the data and the model predictions for a wide range of contacting pressures and materials.
Combined Heat and Power Systems Based on an Externally Integrated Solid Oxide Fuel Cell – Gas Turbine Hybrid System: The Case of a Hospital Under French Legislation
Authors: Diacakis M. , Hales R. , Morin M. , Pilidis P.
Published: November 2008

High temperature Fuel Cells are an attractive technology to generate electricity at high efficiencies. Advantages over traditional heat engine systems include lower irreversibilities, stack modularity and lower maintenance requirements. Solid Oxide Fuel Cells can be coupled with Gas Turbines to further increase cycle performance. In the present study the evaluation of an Externally Integrated Solid Oxide Fuel CellGas Turbine (EISOFCGT) system is presented. The cycle has been designed to meet the requirements of a hospital with a peak thermal demand of 12 MW and electrical of 4.75 MW. Various configurations have been analyzed, with particular emphasis on the effects of operating temperature and air flow-rate in order to identify the optimum configuration. Finally a comparison has been made to a simple CHP plant in order to evaluate the system economics, taking into account the French legislation.
Partial Oxidation of Methanol Over Dispersed Silver Catalysts at Moderate Temperatures
Authors: Hung Hua-Sheng , Chen Yeong-Jey , Yeh Chuin-Tih
Published: November 2008

Supported silver catalysts displayed a moderate ignition temperature of Ti ∼ 100 °C in partial oxidation of methanol (POM). The moderate Ti was attributed to an enhanced adsorption of methanol on silver by co-adsorption of oxygen. The conversion of methanol increases with the reaction temperature and the ratio of oxygen to methanol. CO2 (instead of CO), H2 and H2O were found as the major product of POM. The selectivity of desired products, CO2 and H2, varied with the kind of support used in silver catalysts. A mechanism is proposed to account for the variation in the distribution of products.
Synthesis Gas by Partial Oxidation and the Role of Oxygen-Conducting Supports: A Review
Authors: Salazar-Villalpando Maria D. , Berry David A. , Shekhawat Dushyant , Gardner Todd H. , Celik Ismail
Published: November 2008

The objective of this review is to bring together results from experimental studies to better understand issues and the role of catalyst types and supports in the conversion of hydrocarbon fuels to synthesis gas. Fuel conversion, selectivity and carbon formation as function of type of support, metal, dispersion and temperature are presented. Reaction mechanisms for syn-gas (a mixture of CO and H2) production and formation of inactive carbon are reviewed. This review resulted in two primary conclusions: 1) Catalyst supports based on oxygen-ion conductors such as doped ceria may be used to mitigate carbon formation due to their high oxygen mobility; and 2) A more detailed and comprehensive study of these systems leading to mechanistic understanding may be of significant benefit in developing low-cost, effective, and long-duration reforming catalysts for POM and possibly higher hydrocarbon fuels.
Numerical Predication of Swept Blade Aerodynamic Effects
Authors: Xu C. , Amano R. S.
Published: November 2008

Three-dimensional blading has been used in the process of turbomachine designs. To meet the need for efficient turbine blade designs, CFD predictions of a complex 3D flow field in turbine blade passages had been used. Because the numerous advantages of 3-D CFD have been reported in the open literature, many industries already use 3D blading in their turbomachines. In addition, blade lean and sweep have been implemented to increase the blade row efficiency. Experimental studies have shown the advantages of these features. However, most of the experimental results combined other features together, making it difficult to determine the effects of individual features. The development of CFD techniques has made it possible to do three-dimensional turbulent flow analyses in a very short time. In this study, numerical studies are presented to study the sweep effects on a transonic compressor airfoil. The focus of the paper is to investigate the sweep effects without changing other compressor blade features i.e. keeping the blade out flow angle the same for all cases. The purpose of the study is to enhance the understanding of the sweep in a transonic compressor rotor blade. The results showed that the sweeps redistributes the flow reducing the secondary flow loss, depending on the baseline. It was shown that forward sweep reduces the tip loading in terms of the static pressure coefficient.
The Effect of Terminal Weight on the Prediction Horizon of a Gas Turbine Engine Using Model Predictive Control
Authors: Martucci Angelo , Fuller James , Dorobantu Elena , Rahnamai Koroush
Published: November 2008

Robust Stability Margins of a Model Predictive Control (MPC) based gas turbine engine control system can be guaranteed as long as the prediction horizon is infinite. Unfortunately, the infinite prediction horizon is impossible to implement in the real world. Even a limited prediction horizon can require computation times that make real time embedded MPC based gas turbine applications infeasible to implement. An ideal situation would be to reduce the prediction horizon so that sufficient stability robustness is realized, computation time is reduced and, most importantly, the system exhibits good dynamic response characteristics. This paper will examine if the selection of a Terminal Weight is able to reduce the prediction horizon (and thereby reduce computation time) while maintaining sufficient stability robustness and dynamic response. The selection of the terminal weight will be based upon the Linear Quadratic Regular (LQR) approach. A simplified model of a typical (generic) gas turbine engine will be used as the plant. The model is “sanitized” so that the model outputs are presented in terms of normalized (or scaled) parameters.
Design and Test of an Ultra-Low Solidity Flow-Controlled Compressor Stator
Authors: Kirtley K. R. , Graziosi P. , Wood P. , Beacher B. , Shin H.-W.
Published: November 2008

A full annulus fluidic flow-controlled compressor stator ring was designed and tested in the third stage of a four-stage low speed research compressor. The solidity of the flow-controlled stator was near unity and significantly below design practice with a commensurately high diffusion factor. The design intent was to reduce the vane count by 30% and load the stator to the point of stall at the design point then employ flow control to restore attached boundary layers and regain design-point stage-matching. The flow control applied that maintained attached flow was 1% of the compressor mass flow and was introduced via discrete steady jets on the suction side of the stator. The design method used steady CFD with the flow control jets simulated to drive stator exit angles, velocities and blockage to match the baseline machine. The experiment verified the pre-test predictions and demonstrated degraded compressor performance without flow control and restoration of the pumping characteristics of the baseline high solidity compressor when flow control was applied. An assessment of the engine cycle impact of the flow-controlled compressor shows the stage efficiency trade for the increased loading was 2.1 points. Extrapolation of the data and analysis to a high-speed compressor shows a more modest 0.5 points stage efficiency trade.
Effect of Coriolis and Centrifugal Forces on Turbulence and Heat Transfer at High Rotation and Buoyancy Numbers in a Rib-Roughened Internal Cooling Channel
Authors: Sleiti A. K. , Kapat J. S.
Published: November 2008

Prediction of three-dimensional flow field and heat transfer in a two pass rib-roughened square internal cooling channel of turbine blades with rounded staggered ribs rotating at high rotation and density ratios is the main focus of this study. Rotation, buoyancy, ribs, and geometry affect the flow within these channels. The full two-pass channel with bend and with rounded staggered ribs with fillets (e/Dh = 0.1 and P/e = 10) as tested by Wagner et. al [1992] is investigated. RSM is used in this study and enhanced wall treatment approach to resolve the near wall viscosity-affected region. RSM model was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotational numbers (0.24, 0.475, 0.74 and 1) and high-density ratios (0.13, 0.23, and 0.3). Particular attention is given to how secondary flow, Reynolds stresses, turbulence intensity, and heat transfer are affected by coriolis and buoyancy/centrifugal forces caused by high levels of rotation and density ratios. A linear correlation for 4-side-average Nusselt number as a function of rotation number is derived.
Computational Study of Parameters Affecting Turbulent Flat Plate Film Cooling
Authors: Mahjoob Shadi , Taeibi-Rahni Mohammad
Published: November 2008

Blade film cooling is one of the best methods to improve efficiency of gas turbines. In this work, two different methods of film cooling, namely, slot injection and discrete hole injection have been numerically studied on a flat plate. Incompressible, stationary, viscous, turbulent flow has been simulated using the FLUENT CFD code with the standard k-ε model. The study of injection angle and velocity ratio show that the optimum film cooling in both methods, occurs at the jet angle of 30° but with the velocity ratio of 1.5 for slot case and 0.5 for discrete hole case. The study of jet aspect ratio in discrete hole method, shows that stretching the hole in spanwise direction increases the film cooling effectiveness. Because it not only cool a larger region in both spanwise and streamwise directions, but also can sustain the cooled flow closer to the blade’s wall. The study of jet spacing shows that increasing the jet spacing decreases the effectiveness but not as much as jet aspect ration does.
Impact of Gas Turbine Outflow on Diffuser Performance: A Numerical Study
Authors: Kluß David , Wiedermann Alexander , Volgmann Werner
Published: November 2008

A systematic numerical study will be described considering a coupled arrangement of turbine and diffuser flow fields. For this purpose a multi-stage solver commonly used for industrial applications has been applied. The interaction with the turbine stage was investigated assuming two annular axis-symmetric diffuser configurations. One of these has been designed according to the performance charts by Sovran and Klomp [1] at optimum performance and the other close to stall conditions. In addition to a classical mixing plane approach, a frozen rotor solution has been considered as a first-order approach to the unsteady flow to study the effect of rotor wakes on the diffuser flow field. The predicted diffuser performance was strongly influenced by the rotor wakes, and their effect could only be obtained by an approximate frozen-rotor calculation. The results for the computed specific work and pressure recovery for both configurations showed an optimum distance of a/cR = 0.431 between rotor exit and diffuser inlet. Increase of radial rotor clearance gap has a beneficial effect on the diffuser characteristic for the built near the stall point. However, the larger tip leakage loss of the turbine rotor cannot be compensated by improved diffuser performance.
Investigation of the Conjugate Convective-Conductive Thermal Behavior of a Rib-Roughened Internal Cooling Channel
Authors: Fedrizzi Roberto , Arts Tony
Published: November 2008

The proposed contribution concerns an experimental investigation of the conjugate thermal behavior of a rib-roughened cooling channel. Previous investigations mainly were focused on the convective aspects of the heat transfer; the scaled models were made of low conductivity material and the heat conduction was not representative of the behavior inside a real metallic airfoil. To overcome this limitation, a large-scale facility with a metallic ribbed wall was designed and tested. Infrared thermography was used to measure the temperature distribution on the wetted surface. Dedicated software was developed to correct the temperature field distortions and to apply the radiation-temperature calibration. The convection coefficient was calculated as a function of the measured wall temperature and computed wall heat flux. The code FLUENT® was used to solve the energy equation into the metallic wall, providing the surface heat flux distribution. The complex contribution of the ribs, in terms of heat transfer, was highlighted.
Dust Separation in a Gas Turbine Pre-Swirl Cooling Air System: A Parameter Variation
Authors: Schneider O. , Dohmen H. J. , Benra F.-K. , Brillert D.
Published: November 2008

With the increase of cooling air passing through the internal air system of modern gas turbines, a greater amount of air borne particles is transported to the film cooling holes at the turbine blade surface. In spite of their small size, these holes are critical for blockage. A test rig has been designed to give information about the quantity of separated particles at various critical areas of the internal air system. With this test rig, the behavior of particles in the internal cooling air system could be studied at realistic flow conditions compared to a modern, heavy duty gas turbine. It is possible to simulate different particle sizes and dust concentrations in the coolant air. Numerical studies to characterize the flow behavior of the disperse phase in a continuous fluid using Lagrange Tracking were performed. The main influencing parameters, which are the mass flow through the system, the rotor speed and the nozzle angle of the pre-swirl generator, were varied. Furthermore to validate the theoretical studies, based on the presented variations a special point of operation was selected to get a comparable measurement, which is presented in the paper. Comparison between simulation and measurement shows additional influences of the particle shape, which were discussed. The resulting enhanced model and the comparison to the measurement is presented in the paper.
Active Instability Control: Feedback of Combustion Instabilities on the Injection of Gaseous Fuel
Authors: Auer M. P. , Gebauer C. , Mo¨sl K. G. , Hirsch C. , Sattelmayer T.
Published: November 2008

Modern low-emission premix combustion systems are often susceptible to combustion instabilities. Active instability control (AIC) systems are commonly used to attenuate those oscillations. For the control authority of AIC systems the effective amplitude and phase of the fuel modulation at the fuel outlet are as critical as the proper injection position. In typical cases the modulation of the fuel at the location of the actuator can be fundamentally different in amplitude and phase from the modulation of the fuel flow at the fuel outlet. In addition to the well known effects stemming from the acoustics and Mach number of the fuel system, the fuel flow in the fuel system is also modulated by the oscillation of the pressure in the combustor in case of combustion instabilities. The superposition of the upstream modulation by the actuator and the modulation downstream by the combustion instability can result in an unexpected behaviour of the fuel injection, from total compensation of the modulation to very high oscillations in the resonant case accompanied by drastic phase shifts. This paper describes the influence of the secondary fuel modulation due to the combustion instability on the control authority of AIC systems on the basis of theoretical considerations and measurements for an atmospheric test rig with a natural gas fired swirl burner.
Study of Airflow Features Through Step Seals in the Presence of Dis-Engagement Due to Axial Movement
Authors: Wang Yi , Young Colin , Snowsill Guy , Scanlon Tim
Published: November 2008

Step seals are a particular design variant of the basic labyrinth seal configuration which is widely used to limit leakage from the space between rotating and stationary components. Seals of this type are employed in aero-engines to prevent oil leakage from bearing chambers and to control the flow of secondary cooling air and it follows that the design of step seals is of great importance in the achievement of optimal aero-engine performance. In this paper, numerical modelling of the flow through stepped seals has been carried out in order to gain an insight into the behaviour of the flow in the presence of dis-engagement. In the context of this work, dis-engagement would be deemed to have occurred when to the axial movement between the rotor and stator results in a clear line of sight through the step seal. The flows through the seals were calculated using the commercial CFD package Fluent and the numerical predictions were validated by comparison with test data previously presented in the literature. The model predictions were initially obtained using a number of alternative two-equation turbulence models and the RNG k-ε turbulence model with the non-equilibrium wall function was found to be in closest agreement with the measured data. It was noted that for a given radial clearance the step seal’s flow characteristic is largely dictated by the fin tip to step distance. It was found that there are two distinct stages of step seal dis-engagement. The first stage of dis-engagement occurs when the seal fin is displaced axially from its nominal position, but the seal fin still remains within the axial extent of the corresponding seal step. In this case the flow through the seal only deviates slightly from that of the fully engaged seal. The second stage occurs when the fin is subjected to a larger axial displacement and as a result assumes a position beyond the corresponding seal step. This results in a much larger seal clearance and the flow through the seal increases significantly with the fin tip to step distance in the case.
A Novel Centrifugal Flow Gas Turbine Design
Authors: Brun Klaus , McKee Robert J. , Smalley Anthony J. , Hollingsworth Justin R. , Gernentz Ryan S.
Published: November 2008

A centrifugal gas turbine is developed based on a straight radial flow design with no axial flow turning. The geometry contains only two major elements — a rotor disk and a stator shroud. The rotor consists of a centrifugal compressor and high impulse radial outward-flow turbine connected to an electric generator. The stator shroud contains the combustor and nozzles. Fuel lines are attached to the shroud, ducted directly into the combustor. The difference between this novel design and conventional radial gas turbine is that the compressor and turbine section are installed on the same side of the rotating wheel, while the combustor and nozzle are mounted on the stationary shroud. Thus, the entire assembly consists of two components. Technical advantages are: • Single Rotating Component; • Short Axial Span; • Compact Two-Piece Construction; • Ease of Maintenance/Repair Access. Aerodynamic design, performance, and structural analysis of this design are discussed.
A Study of Impeller-Diffuser-Volute Interaction in a Centrifugal Fan
Authors: Meakhail Tarek , Park Seung O.
Published: November 2008

This paper reports velocity measurement data in the interaction region between the impeller and vaned diffuser and the results of numerical flow simulation of the whole machine (impeller, vaned diffuser and volute) of a single stage centrifugal fan. Two-Dimensional instantaneous velocity measurement is done using particle image velocimetry (PIV). Numerical simulation of impeller-diffuser-volute interaction is performed using CFX-Tascflow commercial code. A frozen rotor simulation model is used for the steady calculation and a rotor-stator simulation model is used for the unsteady calculation using the steady results as an initial guess. The simulation results show that the separated flow regime near the diffuser hub extends to the volute. Comparison between the unsteady computation and those of measurement indicates that the Rotor/Stator Model employed in the simulation predicts essential characteristics of unsteady flow in the centrifugal fan. However, quantitative agreement remains rather poor.
Adaptive Myriad Filter for Improved Gas Turbine Condition Monitoring Using Transient Data
Authors: Surender Vellore P. , Ganguli Ranjan
Published: November 2008

The removal of noise and outliers from measurement signals is a major problem in jet engine health monitoring. In this study, we look at the myriad filter as a substitute for the moving average filter which is widely used in the gas turbine industry. The three ideal test signals used in this study are the step signal which simulates a single fault in gas turbine, while ramp and quadratic signals simulate long term deterioration. Results show that the myriad filter performs better in noise reduction and outlier removal when compared to the moving average filter. Further, an adaptive weighted myriad filter algorithm that adapts to the quality of incoming data is studied. The filters are demonstrated on simulated clean and deteriorated engine data obtained from an acceleration process from idle to maximum thrust condition. This data was obtained from published literature and was simulated using a transient performance prediction code. The deteriorated engine had single component faults in the low pressure turbine and intermediate pressure compressor. The signals are obtained from T2 (IPC total outlet temperature) and T6 (LPT total outlet temperature) engine sensors with their non-repeatability values which were used as noise levels. The weighted myriad filter shows even greater noise reduction and outlier removal when compared to the sample myriad and FIR filter in the gas turbine diagnosis. Adaptive filters such as those considered in this study are also useful for online health monitoring as they can adapt to changes in quality of incoming data.
Dynamic Characteristics of the Diverging Taper Honeycomb-Stator Seal
Authors: Smalley Anthony J. , Camatti Massimo , Childs Dara W. , Hollingsworth Justin , Vannini Giuseppe , Carter Jeremy J.
Published: November 2008

This paper introduces a variant on the honeycomb-stator seal, which can extend the already strong stabilizing influence of this seal geometry for centrifugal compressors. The paper presents predicted and measured dynamic characteristics, demonstrating how a clearance, which diverges axially from inlet to outlet, increases the maximum effective damping of a honeycomb-stator seal, even though the average clearance is increased. The results also show a strong negative direct stiffness at zero and low frequency for this seal geometry (termed the “Diverging Taper Honeycomb Seal (DTHCS)”). The predictions are made with ISOTSEAL, software developed at The Texas A&M Turbomachinery Laboratory. The test data, also obtained at the Turbomachinery Laboratory, confirms the nature and magnitude of both these dynamic characteristics with close fidelity. However, measured leakage falls significantly below predicted leakage. The frequency dependence of the seal dynamic characteristics and the strong negative static stiffness require careful attention in rotor dynamics analysis.
Experimental and Numerical Investigation on the Performance of a Family of Three HP Transonic Turbine Blades
Authors: Corriveau D. , Sjolander S. A.
Published: November 2008

Experimental results concerning the performance of three high-pressure (HP) transonic turbine blades having fore-, aft- and mid-loadings have been presented previously by Corriveau and Sjolander [1]. Results from that study indicated that by shifting the loading towards the rear of the airfoil, improvements in loss performance of the order of 20% could be obtained near the design Mach number. In order to gain a better understanding of the underlying reasons for the improved loss performance of the aft-loaded blade, additional measurements were performed on the three cascades. Furthermore, 2-D numerical simulations of the cascade flow were performed in order to help in the interpretation of the experimental results. Based on the analysis of additional wake traverse data and base pressure measurements combined with the numerical results, it was found that the poorer loss performance of the baseline mid-loaded profile compared to the aft-loaded blade could be traced back to the former’s higher rear suction side curvature. The presence of higher rear suction surface curvature resulted in higher flow velocity in that region. Higher flow velocity at the trailing edge in turn contributed to reducing the base pressure. The lower base pressure at the trailing edge resulted in a stronger trailing edge shock system for the mid-loaded blade. This shock system increased the losses for the mid-loaded baseline profile when compared to the aft-loaded profile.
Whirl Frequency Dependent Alford Forces in Axial Compressors
Authors: Myllerup Claus M. , Keith Graeme
Published: November 2008

Explicit closed form expressions are derived for the whirl frequency dependence of the Alford force in an axial compressor operating in steady-state away from the onset of rotating stall. The analysis includes the compressor flow dynamics using the Moore-Greitzer approximation. By asymptotic expansion in terms of the whirl orbit amplitude, expressions for the direct and cross-coupling impedance are obtained analytically. Several components in the cross-coupling impedance are shown to change phase as the whirl frequency transits the rotating stall frequency. This implies that for a given compressor design the Alford force can be stabilizing or destabilizing depending on flow rate and whirl frequency. Further, the analysis shows that the coupling between mean flow quantities and rotor whirl is of second order. Thereby, the present asymptotic expansion results in a fluid-structure coupling model, which is consistent in accuracy with usual linearized rotordynamic analysis.
A Simple Method for Estimating Ingestion of Annulus Gas Into a Turbine Rotor Stator Cavity in the Presence of External Pressure Variations
Authors: Scanlon T. , Wilkes J. , Bohn D. , Gentilhomme O.
Published: November 2008

A simple method, for both estimating circumferential pressure variation in a turbine, and using this method to calculate the annulus flow ingested across a rim seal into the disc cavity, is presented. This method is compared with test data from 2 separate experimental programmes. The model is shown to collapse the majority of the test data well; with calibration it could form the basis of a preliminary design methodology. The model does not collapse data where unsteady pressure fluctuations were measured in the cavity, suggesting these fluctuations, when present, play an important role in determining how much annulus gas is ingested into the cavity.
Rotor-Stator Interactions in a Four-Stage Low-Speed Axial Compressor: Part II — Unsteady Aerodynamic Forces of Rotor and Stator Blades
Authors: Mailach Ronald , Mu¨ller Lutz , Vogeler Konrad
Published: November 2008

This two-part paper presents detailed experimental investigations of unsteady aerodynamic blade row interactions in the four-stage Low-Speed Research Compressor of Dresden. In part I of the paper the unsteady profile pressure distributions for the nominal setup of the compressor are discussed. Furthermore the effect of blade row clocking on the unsteady profile pressures is investigated. Part II deals with the unsteady aerodynamic blade forces, which are determined from the measured profile pressure distributions. A method to calculate the aerodynamic blade forces on the basis of the experimental data is presented. The resulting aerodynamic blade forces are discussed for the rotor and stator blade rows of the first stage and the third stage of the compressor. Different operating points between design point and stability limit of the compressor were chosen to investigate the influence of loading on the aerodynamic force excitation. The time traces and the frequency contents of the unsteady aerodynamic blade force are discussed. Strong periodic influences of the incoming wakes and of potential effects of downstream blade rows can be observed. The amplitude and shape of the unsteady aerodynamic blade force depend on the interaction of the superimposed influences of the blade rows.
Experimental Off-Design Investigation of Unsteady Secondary Flow Phenomena in a Three-Stage Axial Compressor at 68% Nominal Speed
Authors: Bohne Andreas , Niehuis Reinhard
Published: November 2008

This paper deals with unsteady measurements in a highspeed three-stage axial compressor with inlet guide vanes (IGV) and controlled diffusion airfoils (CDA) at off-design conditions. The compressor under consideration exhibits design features of real industrial compressors. The main emphasis is put on the experimental investigation of two operating points at 68% nominal speed where a significant mismatching of the stages occurs. The first operating point is the last stable one near the surge margin whereas the second one represents choke. Probe traverses with a high resolution both in space and time show the significant potential upstream influence of the rotor blades. This effect and the disturbances caused by the convected wakes do strongly influence the unsteady boundary layer behaviour of the stator blades which are detected by glue-on hot-film sensors at different spanwise positions. Dynamic pressure transducers on the casing show that the structure of the rotor tip clearance flow strongly depends on the operating conditions of the compressor. Conclusions can be drawn concerning the consideration of the discussed unsteady effects within the design process of multistage axial compressors with respect to the presented results.
A Neural Network-Based Closed Loop Identification of a Magnetic Bearings System
Authors: Medina Jose´ , Parada Mo´nica , Guzma´n Victor , Medina Luis , Di´az Sergio
Published: November 2008

This paper deals with the identification of a radial-type active magnetic bearing (AMB) system using Artificial Neural Network (ANN). Identification and validation experiments are performed on a laboratory magnetic bearing system. Since the electromechanical configuration is inherently unstable, the identification data is gathered while the AMB is operating in closed loop with a controller in the loop. From this data, the identification procedure generates an open-loop plant model. A NNARX (Neural network autoregressive external input model) structure is proposed and evaluated for emulating the system’s dynamic. The model is implemented by a Neural network, constructed using a multilayer perceptron (MLP) topology, and trained using as inputs the rotor’s displacements and excitation currents. Validation tests are performed under perturbation conditions (impact applied on the rotor). Results show that the neural network based model presented here is a powerful tool for dynamic plant’s identification, and that it could be also suitable for robust control application.