bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Vibration and Stability Analysis of Embedded Carbon Nanotubes With Internal Flow
Authors: Rasekh M. , Khadem S. E.
Published: January 2011

In this paper, for the first time, the influence of internal moving fluid on the nonlinear vibration and stability of embedded carbon nanotube is investigated. The Euler-Bernoulli beam theory is employed to model the vibrational behavior of an embedded carbon nanotube. The relationship of nonlinear amplitude and frequency for the single-wall nanotubes in the presence of internal fluid flow is expressed using the multiple scales perturbation method. The amplitude-frequency response curves of the nonlinear vibration obtained and the effects of the surrounding elastic medium, mass and the aspect ratios of nanotubes are discussed. It is shown that beyond the critical flow velocity buckling occurs and surrounding elastic medium plays a significant role in the stability of the carbon nanotube.
Influence of Hydrogen Addition on Lean Premixed Methane-Air Flame Statistics
Authors: Yilmaz Baris , O¨zdogan Sibel , Go¨kalp Iskender
Published: January 2011

Hydrogenated premixed methane/air flames under lean conditions are simulated in this study. The computational model of the high pressure chamber setup of Orleans - ICARE (France) has been developed. The k-ε turbulence model with Pope-correction is used for turbulence modeling. The laminar flame properties are computed using GRI-Mech 3.0 mechanism with Chemkin software package. The turbulent flame front statistics are investigated with three premixed combustion models, namely Zimont, Coherent Flame Model (CFM) and modified version of CFM model (MCFM) models. It has been observed that increasing the volumetric percentage of hydrogen in the mixture results in reducing the flame-end position. The flame brush thickness becomes thinner as well. Satisfactory results have been obtained compared to experiments.
Experimental Analysis of PEM Fuel Cells With Biomimetical Mixed Flows as Gas Distributors
Authors: Damian-Ascencio C. E. , Herna´ndez-Guerrero A. , Alatorre-Ordaz A. , Cuauhtemoc-Rubio A. , Elizalde-Blancas F.
Published: January 2011

A proton exchange membrane fuel cell (PEMFC) is an electrochemical device that converts the chemical energy from the gases into electrical energy. The PEMFCs consist of many parts, and the current collector plate is one of the key components among them. Channels in the bipolar plate distribute air on the cathode side and hydrogen on the anode side. Theoretically a fuel cell produces more current as more fuel is supplied. However the way in which the gases are supplied affects dramatically the performance of the cell. The present paper shows how the mixed flows improve the current density produced by fuel cells. Polarization and power density curves are presented. The results suggest that a flow with two levels of bifurcations is preferred for the anode side. This behavior is expected due to the similitude with the performance of the natural world in which geometries with this type of bifurcations transport the nutrients inside the tree leaves and plants.
Computer Assisted Simulation Model for Cryoablation of Prostate Cancer Including the Possible Injury of Rectum
Authors: Chen Chih-Wei , Kou Hong-Sen , Liu Hsueh-Erh , Chuang Cheng-Keng , Wang Li-Jen
Published: January 2011

This study is to establish a preliminary computer assisted simulation model for cryoablation of a prostate cancer. It is hoped that the results from this study can supply valuable data for the clinician to refer to before a real cryosurgery or cryotherapy. In order to reach the goal of real implementation, a radiologist and an urologist in a medical center in addition to the engineering specialist from the university participated in this interdisciplinary research program. Firstly, hundreds of the two-dimensional medical imaging photos for the patient are obtained from the magnetic resonance imaging (MRI) in the imaging department of hospital. Through the imaging reconstructive software, these photos are trimmed into building a three-dimensional solid modeling. In this step, the urethra, bladder, prostate and rectum are segmented separately into an engineering graphic solid model with high resolution. Secondly, the number of probes, the position of each probe, and the operating time duration of each probe are determined in advance according to the clinical experience from a surgeon. Meanwhile, these data are transferred into the software package of thermal calculation for numerical simulations. Thirdly, the energy equation in the commercial software is modified to behave bio-heat transfer model by the input of user subroutines. Moreover, the occurrence of phase change during some specified temperature range and the latent heat of fusion are also incorporated into bio-heat transfer model to simulate the clinical situation for cryoablation of prostate cancer. In the simulation model, the three-dimensional transient temperature distributions based on cryosurgery for prostate cancer have been demonstrated precisely. The cryoprobes with various freezing time are considered to observe the temperature distribution. In addition, the frozen rectum is displayed in a region enclosed by a critical isotherm of 0°C. The simulated results for cryosurgery of prostate cancer can be supplied for practicing physicians as reference to greatly improve the effectiveness of cryosurgery.
Does a Predictive Minimal Model of Friction-Induced Vibration Exist?
Authors: Butlin Tore , Woodhouse Jim
Published: January 2011

Highly idealised models of friction-induced vibration have been motivated by an attempt to capture what is essential to the phenomenon. This approach has resulted in a few simple mechanisms that are thought to capture common routes to instability. This paper aims to determine how well these perform as approximations to a more complex system, and whether the essential ingredients needed for a minimal model can be identified. We take a reduced-order model that exemplifies ‘mode-coupling’ and explore the extent to which it can approximate predictions based on an experimentally identified test-system. For the particular test system under study, two-mode ‘mode-coupling’ is rarely a good approximation and three modes are usually required to model a limited frequency range. We then compare predictions with results from an extensive program of sliding contact tests on a pin-on-disc rig in order to identify which ingredients are needed to explain observed squeal events. The results suggest that several minimal models would be needed to describe all observed squeal initiations, but the ‘negative-damping’ route to instability, which requires a velocity-dependent friction law, convincingly accounts for one cluster.
Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines
Authors: Hushmandi Narmin Baagherzadeh , Fridh Jens E. , Fransson Torsten H.
Published: January 2011

A Numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Because of the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disc cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital in the design process of partial admission turbine blades. Pressure plots showed that the non-uniformity in the static pressure field decrease considerably downstream the second stage stator row, while the non-uniformity in the dynamic pressure field is still large. Numerical results between the first stage stator and rotor rows showed that the leakage flow leave the blade path down to the disc cavity in the admitted channel and re-enter into the main flow in the blocked channel. This process compensate the sudden pressure drop downstream the blockage but reduce the momentum of the main flow.
The Performance of a Generic Non-Axisymmetric End Wall in a Single Stage, Rotating Turbine at On and Off-Design Conditions
Authors: Snedden Glen , Dunn Dwain , Ingram Grant , Gregory-Smith David
Published: January 2011

The application of non-axisymmetric end walls in turbine stages has gained wide spread acceptance as a means to improve the performance of turbines in both power generation and aero-derivative applications. Non-axisymmetric end walls are aimed at the control of secondary flows and to a large extent have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. Little or no literature is available describing their performance at conditions other than design. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic end wall design on the structure of secondary flows at both on and off-design flow conditions. Results indicate a 0.4% improvement in rotor efficiency at design but this was reduced at off design and at higher loading the rotor efficiency was reduced by 0.5%. Stage efficiencies were improved for all conditions but with a declining trend as load was increased. Experimental and CFD results are examined to investigate these findings further.
Compressors in High Pressure Pipeline Applications
Authors: Kurz Rainer , Ohanian Sebouh , Brun Klaus
Published: January 2011

While typical gas transmission pipelines operate at pressures up to about 100bar, a number of applications in North America and Australia use or are planning pipelines operating at significantly higher pressures. Often, these operations are referred to as ‘dense phase’. Several existing installations are described and analyzed. We will explain the underlying reasons why higher pressure pipelines are considered, as well as the trade-offs compared to traditional, lower pressure pipelines. A parametric study is presented to evaluate the impact of higher operating pressures on the net present value. The impact of a larger effort to bring the gas to the higher pressure is discussed. Since some of the pipelines are designed to transport CO2, the particulars of high pressure CO2 transport are highlighted. The impact on compressor and driver selections is also considered, in particular the impact of the higher power density of the centrifugal compressors at higher pressures.
Cogeneration Based High Efficiency LNG Liquefaction Plants
Authors: Meher-Homji Cyrus B. , Messersmith David , Tekumalla Ram , Bhatia Neeraj , Masani Karl , Weyermann Hans
Published: January 2011

High thermal efficiency of LNG liquefaction plants is of importance to minimize feed usage and to reduce CO2 emissions. The need for high efficiency becomes important in gas constrained situations where any savings in fuel auto consumption of the plant for liquefaction chilling and power generation can be converted into LNG production. The Darwin LNG Facility was the world’s first liquefaction facility to utilize high efficiency aeroderivatives and its successful operation for close to four years has increased the interest in aeroderivative based liquefaction plants. The application of aeroderivative engines allows a significantly lower CO2 footprint of about 30% compared to the use of simple cycle industrial industrial engines. Aeroderivative engines offer very attractive efficiencies where steam systems are not viable or desired by the customer. When steam systems are acceptable, a cogeneration type liquefaction facility can be attractive. Cogeneration concepts can also be used to augment the already high efficiency of aeroderivative engines. This paper will cover concepts relating to cogeneration options for LNG facilities using both aeroderivative engines and industrial engines.
Variable Regimes Operation of Cogenerative Gas-Turbine Engine With Overexpansion Turbine
Authors: Matviienko V. , Ocheretianyi V.
Published: January 2011

High energetic efficiency of cogenerative gas-turbine engine (GTE) is due to by deep utilization of exhaust gases heat and greater portion of produced electrical energy, with is achieved by complication of Brayton cycle application of overexpansion in turbine. Such method is realized in GTE with turbo-compressor utilizer (TCU) attached to exhaust of the engine. TCU consists of the overexpansion turbine, exhaust compressor and gas cooler between them. Gas cooler in TCU is used as a water boiler-utilizer. This paper presents characteristics of GTE with TCU in variable regimes of loading. It is found, that GTE with TCU at nominal and partial loadings has higher efficiency, than simple cycle GTE. Construction of GTE with TCU can be performed with free TCU and blocked TCU, which is mechanically linked to power turbine. High energy efficiency of GTE with free TCU is proved, enabling to maintain overall efficiency on high level on decrease of electrical power. It is suggested that GTE with free TCU is more efficient for energy supply of municipal objects, and its constructive scheme provides stable delivery of heat energy to consumer upon significant variation of electric loading.
Performance Test Diagnosis of a Compact Two Stage High Pressure Ratio Compressor
Authors: Rodgers C. , Brown D.
Published: January 2011

The intent of this paper was to resolve significant performance shortfalls encountered during the development of a small two stage research 15.0:1 centrifugal compressor designed fabricated and tested in the late 1990’s. The emphasis of the research project was on the aerodynamic flowpath that eliminates use of a large external diameter radial cross-over duct. This was achieved with an innovative small diameter “Sbend” crossover duct, using computational fluid dynamic (CFD) tools of the later 1990’s era to assist in the design process. Test results revealed major performance shortfalls stemming from limited efficient operating ranges of both the 1st stage mixed flow impeller and mixed flow diffuser, which precipitated stage mismatching consequently confining both 1st stage components to operate in semi-stalled modes. The performance of the conventional 2nd stage centrifugal compressor however met design expectations. Eventually program cost limitations curtailed further testing and intended supplementary CFD analyses of the performance deficiencies with more refined computational techniques. During the elapsed decade turbomachinery CFD codes have been extensively refined prompting this renewed diagnosis of the 1st stage mixed flow impeller, mixed flow diffuser and Sbend duct as described within.
Impact of Frequency Dependence of Gas Labyrinth Seal Rotordynamic Coefficients on Centrifugal Compressor Stability
Authors: Vannini Giuseppe , Thorat Manish R. , Childs Dara W. , Libraschi Mirko
Published: January 2011

A numerical model developed by Thorat & Childs [1] has indicated that the conventional frequency independent model for labyrinth seals is invalid for rotor surface velocities reaching a significant fraction of Mach 1. A theoretical one-control-volume (1CV) model based on a leakage equation that yields a reasonably good comparison with experimental results is considered in the present analysis. The numerical model yields frequency-dependent rotordynamic coefficients for the seal. Three real centrifugal compressors are analyzed to compare stability predictions with and without frequency-dependent labyrinth seal model. Three different compressor services are selected to have a comprehensive scenario in terms of pressure and molecular weight (MW). The molecular weight is very important for Mach number calculation and consequently for the frequency dependent nature of the coefficients. A hydrogen recycle application with MW around 8, a natural gas application with MW around 18, and finally a propane application with molecular weight around 44 are selected for this comparison. Useful indications on the applicability range of frequency dependent coefficients are given.
Experimental Investigation on Staggered Impingement Heat Transfer on a Rib Roughened Plate With Different Crossflow Schemes
Authors: Xing Yunfei , Weigand Bernhard
Published: January 2011

A nine-by-nine staggered jet array impinging on a flat or rib roughened plate at Reynolds numbers from 15,000 to 35,000 has been studied by the transient liquid crystal method. The jet-to-plate spacings are adjusted to be 3, 4 and 5 jet diameters. Three jet-induced crossflow schemes, referred as minimum, medium and maximum crossflow correspondingly, have been measured. The local air jet temperature is measured at several positions on the impingement plate to account for an appropriate reference temperature of the heat transfer coefficient. The heat transfer results of the rib roughened plate are compared with those of the flat plate. The best heat transfer performance is obtained with the minimum crossflow and narrow jet-to-plate spacing no matter on a flat or roughened plate. The presence of rib turbulators on the target plate produce higher heat transfer coefficients than the flat plate for narrow jet-to-plate spacing by 7.5%. Note that this value is within the measurement uncertainty of 9%.
Prediction and Analysis of Inlet Pressure and Temperature Distortion on Engine Operability From a Recent T-38 Flight Test Program
Authors: Davis Milt W. , Kidman David S.
Published: January 2011

Since the initial development of the T-38 Talon trainer, there have been upgrades to both the aircraft and to the J85-GE-5 afterburning turbojet engine to improve takeoff performance, reduce maintenance time and cost, and to decrease fuel consumption. The latest upgrades, referred to as the Propulsion Modernization Program (PMP), focused on improved performance of the T-38’s inlets, twin J85-GE-5 afterburning turbojet engines, and improved exhaust nozzle design. The T-38’s inlet includes bleed holes upstream of the engine face to provide cooling air flow from the inlet to the engine bay. However, at various locations in the flight envelope, the bay air is pressurized relative to the inlet resulting in reverse flow of hot engine bay air into the inlet. This reverse flow along with inlet heat transfer effects can cause total temperature distortion and reduce engine stability margin. During any flight maneuvers, there will be an associated level of total pressure distortion. When pressure distortion is combined with the temperature distortion due to engine bay flow reversal and inlet heat transfer, losses in stability pressure ratio (or stability margin) may further be increased. This analysis effort reported herein uses a modeling and simulation technique known as the parallel compressor theory (model) to investigate the effects of total pressure and temperature inlet distortion on system operability and makes predictions of the loss in stability pressure ratio associated with those combined pressure and temperature distortions during flight maneuvers.
3D Direct and Inverse Design Using NS Equations and the Adjoint Method for Turbine Blades
Authors: Wang D. X. , Li Y. S.
Published: January 2011

Presented in this paper are two case studies on the application of the adjoint method to turbine blading aerodynamic design optimization. One case involves the use of the adjoint method in a direct design, where the blade geometry is changed to reduce the entropy generation rate of a power turbine subject to mass flow rate and pressure ratio constraints. The other case investigates the use of the adjoint method in an inverse design, where the blade geometry is changed to approach a target static pressure loading on a blade surface, also subject to mass flow rate and pressure ratio constraints. Promising results are obtained for the two cases. Also examined in the two case studies is the application of the adjoint method to flow field with big separations, which can be detrimental to the convergence of an adjoint solution due to its linearity.
Experimental Study of Acoustic Resonances in the Side Cavities of a High-Pressure Centrifugal Compressor Excited by Rotor/Stator Interaction
Authors: Petry Nico , Benra Friedrich Karl , Koenig Sven
Published: January 2011

Under unfavorable conditions aerodynamic and aeroacoustic excitation mechanisms may lead to fatigue failures of centrifugal compressor impellers. The mechanisms for consideration are, for example, the arising pressure patterns due to rotor/stator interactions, the so-called Tyler/Sofrin modes, or acoustic resonances in the compressor housing. In a research program, a high-pressure radial compressor has been equipped with a multiplicity of sensors to investigate the excitation and interaction mechanisms in a complete centrifugal compressor stage. The current paper deals with the experimental detection of acoustic resonances in the compressor side cavities and the excitation of these acoustic eigenmodes due to Tyler/Sofrin modes. In this context the test rig and the installed instrumentation are briefly described. The methods of measuring as well as the analyzing techniques for detecting acoustic resonances and evaluating the measurements are presented. In addition, acoustic eigenmodes have been calculated by the finite-element method for the representative numerical test rig parameters. Results are presented and compared to the experimental findings. The accomplished experiments are the first available in open literature showing that the fluid core rotation in the compressor side cavities plays a crucial role for the prediction of the acoustic eigenfrequencies with respect to the rotor frame of reference. Without taking into account the effect of fluid rotation, large deviations between predicted (simulated) and measured acoustic eigenfrequencies would be the result.
Low Load Operational Flexibility for Siemens F- and G-Class Gas Turbines
Authors: Nag Pratyush , Little David , Plant Adam , Roth Douglas
Published: January 2011

The US gas turbine (GT) power generation market has seen significant volatility in recent years due to climate changes, changes in natural gas prices and the uncertain future of nuclear and coal power generation. Many gas turbine power plants originally intended to operate on a more continuous basis (base load) are operating in intermittent dispatch mode which has caused some operators to frequently shut down their units. This frequent cycling of units can increase start-up and maintenance costs. It could be beneficial to these plants to operate at lower loads when power demand is low and ramp up to higher loads as demand increases. A key issue in operating at lower loads is an increase in carbon monoxide (CO) emissions. When the engines are base loaded, the combustion system operates at high firing temperatures and most of the CO is oxidized to carbon dioxide (CO2). However, at part loads — when the firing temperature is lower — the CO to CO2 oxidation reaction is quenched by the cool regions near the walls of the combustion liner. This results in increased CO emissions at low loads. In order to provide greater operational flexibility to its F- & G-class gas turbine operators, Siemens has developed an upgrade for the engine system designed to allow the gas turbine to operate at lower loads while maintaining emissions. This low load turndown upgrade has been installed, tested and is currently in operation at 8 F and 4 G class Siemens operating gas turbines. These plants were previously operating typically between 70% and 100% of GT base load. Sometimes, when the demand for power was low, typically at night and on weekends, these plants would shut down. During these low power demand periods — with this upgrade installed — these plants continue to operate down to lower loads while maintaining CO emissions and with a capability to more quickly ramp-up to full load when the demand for power increases. This paper details the installation, testing results and continued validation of the Low Load Turndown upgrade.
Improvement of Cooled Turbine Airfoils by Special Cutback
Authors: Mamaev Boris I. , Petukhovskiy Mikhail M. , Pozdnyakov Alexander V. , Valeev Marat R.
Published: January 2011

A substantial reduction in high temperature turbine efficiency due to a thickening trailing edge on the blades can be compensated by ejection of cooling air on the airfoil pressure side near the edge, which is made thinner at the expense of a pressure-side contour bend. A blade-row midspan section of the aircraft high-pressure turbine was chosen for investigations. Flow parameters of the section: inlet and outlet angles were 36° and 65°, respectively (axial reference), outlet isentropic Mach number was 0.94. Four linear cascades were examined. They differed mainly in the airfoil trailing edge geometry. Three airfoils had the same thin trailing edges and contour bend angles ε = 10, 15 and 20°; one airfoil with a thick round edge had no bend. Widths of the slot for cooling air ejection were the same for all airfoils tested. Measurements were made for exit Mach numbers from 0.6 to 0.95 and relative cooling mass flows from 0 to 1.5%. The respective Reynolds numbers varied from 7.5·106 to 9·106. The incidence value was 2°. Pressure distributions along profiles, outlet total and static pressures, back pressures for cooling air with gas-outlet angles were measured. The experiments showed streamlining of all cascades were favorable. For the airfoils with ε = 10 and 15° the profile losses were low and normal for uncooled cascades with thin trailing edge. Hence, for such bends losses due to a step on the airfoil pressure side were negligible. As expected, the losses in the cascade with the thick rounding edge were significantly higher. The losses in the cascade with ε = 20° were the greatest. The coolant exit had no distinct influence on streamlining airfoils. The back-pressure for cooling air was approximately equal to the outlet static pressure. For cascades with ε = 10 and 15° the ejection of coolant led to a small increase of losses due to additional mixing losses. Thus, the airfoil contour bend is a powerful tool for the aerodynamic improvement of cooled turbines. It may lead to gains in stage efficiency of 1…1.5%. It should be noted that this tool has already been used successfully for several aircraft and industrial turbines of recent design.
Influence of Honeycomb Facings on the Temperature Distribution of Labyrinth Seals
Authors: Weinberger Tina , Dullenkopf Klaus , Bauer Hans-Jo¨rg
Published: January 2011

As labyrinth seals with honeycomb facings become more usual, the present paper reveals part of the honeycomb parameters which have an influence on the temperature drop across the seal and the temperature distribution along the rotor and the stator. Numerical and first experimental analyses with varying honeycomb parameters, pressure ratios and seal clearances, typical for engine operating conditions, have been carried out on a non-rotating setup in order to exclude other influencing parameters, such as windage heating. As expected, the numerical analyse shows that the honeycomb diameter, the honeycomb height and the seal clearance are of great importance for the temperature distribution of the rotor and the stator and the temperature drop across the seal.
Remaining Technical Challenges and Future Plans for Oil-Free Turbomachinery
Authors: DellaCorte Christopher , Bruckner Robert J.
Published: January 2011

The application of Oil-Free technologies (foil gas bearings, solid lubricants and advanced analysis and predictive modeling tools) to advanced turbomachinery has been underway for several decades. During that time, full commercialization has occurred in aircraft air cycle machines, turbocompressors and cryocoolers and ever-larger microturbines. Emerging products in the automotive sector (turbochargers and superchargers) indicate that high volume serial production of foil bearings is imminent. Demonstration of foil bearings in APU’s and select locations in propulsion gas turbines illustrates that such technology also has a place in these future systems. Foil bearing designs, predictive tools and advanced solid lubricants have been reported that can satisfy anticipated requirements but a major question remains regarding the scalability of foil bearings to ever larger sizes to support heavier rotors. In this paper, the technological history, primary physics, engineering practicalities and existing experimental and experiential database for scaling foil bearings are reviewed and the major remaining technical challenges are identified.
A Regenerative Flow Compressor as a Secondary Air Pump for Engine Emission Control
Authors: Engeda Abraham
Published: January 2011

The automotive engine requires a relatively rich mixture of fuel and air for smooth operation on cold start. Exhaust gases contain high levels of carbon monoxide and hydrocarbons after cold starts. The unburned hydrocarbons could be further oxidized, except there is no oxygen left after combustion. Using a Secondary Air Pump (SAP), air is fed into the exhaust manifold (secondary air), the CO and HC are oxidized through afterburning at temperatures over 600°C to form water and carbon dioxide. An activated secondary air injection system leads to an increase in oxygen content in the exhaust system. This paper discuses the performance of a Regenerative Flow Compressor (RFC) for SAP application and shows the RFC to be the best choice for satisfying the required specification of the SAP.
TGO Evolution and Coating Property Changes for EB-PVD TBC Coatings Under Cyclic Oxidation Condition
Authors: Buschinelli Mauricio , Huang Xiao , Chen Weijie
Published: January 2011

The life of a thermal barrier coating (TBC) system is governed by the microstructural evolution of the thermally grown oxide (TGO) layer between the ceramic top layer and the bond coat. While the TGO provides a barrier to the oxygen diffusion, its continuous growth imposes stresses on the TGO/bond coat and TGO/topcoat interfaces that will eventually lead to crack linkage and propagation followed by failure of the TBC system. In addition to TGO growth during thermal exposure, coating properties such as hardness, Young’s modulus and fracture toughness will also change. This study is undertaken to investigate the oxidation behaviour of an electron beam physical vapour deposition (EB-PVD) YSZ/PtAl coating system. Cyclic oxidation tests were carried out with each cycle consisting of 5 hr holding time at 1150°C followed by air cooling to room temperature. TGO evolution, coating property and maximum crack length as functions of total thermal exposure time were investigated in this study. Microstructural analyses of the coating were carried out using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Both hardness and Young’s modulus of the bond coat were measured using micro-hardness tester. The results from this study showed a parabolic TGO growth rate as a function of thermal exposure time. While no distinct mathematical relationship was found between the TGO thickness and maximum crack length, a general trend of increasing TGO thickness and maximum crack length was found with respect to exposure time. The mechanical properties of the bond coat were also found to be influenced by the thermal exposure.
Inverse Generation of Gas Turbine Component Performance Maps From Experimental Test Data
Authors: Kong Changduk , Lim Semyeong , Oh Seonghwan , Kim Jihyun
Published: January 2011

The gas turbine engine performance is greatly relied on its component performance characteristics. Generally, acquisition of component maps is not easy for engine purchasers because it is an intellectual property of gas turbine engine supplier. In the previous work, the maps were inversely generated from engine performance deck data. However this method is limited to obtain the realistic maps from the calculated performance deck data. Present work proposes a novel method to generate more realistic component maps from experimental performance test data. In order to demonstrate the proposed method, firstly the NI data acquisition device with the proposed LabVIEW on-condition monitoring program monitors and collects real-time performance data such as temperature, pressure, thrust, and fuel flow etc. from a micro turbojet engine of the test setup which is specially manufactured for this study. Real-time data obtained from the test results are used for inverse generation of the component maps after processing by some numerical schemes. Realistic component maps can then be generated from those processed data using the proposed extended scaling method at each rotational speed. Verification can be made through comparison between performance analysis results using the performance simulation program including the generated compressor map and on-condition monitoring performance data.
Sensitivity Analysis for Film Effectiveness on a Round Film Hole Embedded in a Trench Using Conjugate Heat Transfer Numerical Model
Authors: Nguyen Cuong Q. , Tran Nghia V. T. , Bernier Bryan C. , Ho Son H. , Kapat Jayanta S.
Published: January 2011

Film cooling performance is affected by many factors, for example: geometrical factors (injection angle, length-to-hole diameter ratio, surface roughness, etc.) as well as flow conditions (mass flux ratio, momentum flux ratio, turbulence intensity, etc.). In most of the film cooling literature, film effectiveness has been used as criterion to judge and/or compare between film cooling designs. Uniformity is also a critical factor, since it is determining how well the coolant spreading out downstream to protect the working surface in a gas turbine engine. Better cooling uniformity will reduce thermal stress associated with gas turbine components. A flat plate with round holes embedded in a trench is considered in this study. Although the trench may have an adverse effect on fan-shaped film hole cooling, it tremendously increases the performance of the round-hole film cooling technique in terms of film cooling effectiveness. An experimental study at CATER facility has shown that the cooling effectiveness can be retained by the addition of a trench feature while using only half a number of cooling holes. The current work is conducted based on the numerical study with a validation from in-house experimental works at CATER and the experiments from the literature. The experimental temperature distribution is captured by using Temperature Sensitive Paint and then span-wised effectiveness is calculated. The studied input parameters include flow variables (blowing ratio, BR and momentum ratio, MR) and geometrical parameters (trench-depth-to-diameter ratio, s/D and pitch-to-diameter ratio, p/D). A comparison of contributions of studied factors is investigated by using Response Surface Methodology technique. The spatially adiabatic film cooling effectiveness is selected as the primary output in the design of experimental analysis. Since the nonlinear behavior of all input factors are also of interest, three levels of each parameter will be considered. The well-know Box and Behnken design is employed to carry on this sensitivity analysis. With this method, the current study only requires 25 runs to obtain a quantified comparison of the contribution of each involved effects.
Ethanol and Distillate Blends: A Thermodynamic Approach to Miscibility Issues
Authors: Jaubert Jean-Noe¨l , Privat Romain , Molie`re Michel
Published: January 2011

In the recent years, the quest for an ever wider cluster of sustainable primary energies has prompted an increasing number of attempts to combine the emission sobriety of bio fuels with the energy density advantage of fossil fuels. A number of compositions incorporating hydrocarbons, ethanol and in some cases limited amounts of water have been proposed, especially in the forms of micro emulsions, with a variable success. Indeed due to markedly different physical and chemical properties, ethanol and gasoil are able to blend and form homogeneous solutions only in limited proportion ranges. Indeed, such mixtures often give rise to liquid-liquid equilibrium. A key parameter is thus the Minimum Miscibility Temperature (MMT), i.e. the temperature above which ethanol and gasoil become completely miscible. In fact, commercial gasoils do not constitute a monolithic product but display in the contrary a large span of compositions that influence the stability of these blends. In this context, the LRGP laboratory (Laboratoire Re´actions et Ge´nie des Proce´de´s) has undertaken an investigation program intended to understand the factors underlying the stability of ethanol/gasoil blends. The approach is based on the calculation of the liquid-liquid phase diagrams formed by anhydrous ethanol and a mixture of various hydrocarbons representative of the diesel oil pool using the group contribution concept. Indeed, for correlating thermodynamic properties, it is often convenient to regard a molecule as an aggregate of functional groups; as a result, some thermodynamic properties (heat of mixing, activity coefficients) can be calculated by summing group contributions. In this study, the universal quasichemical functional group activity coefficient (UNIFAC) method has been employed as it appears to be particularly useful for making reasonable estimates for the studied non ideal mixtures for which data are sparse or totally absent. In any group-contribution method, the basic idea is that whereas there are thousands of chemical compounds of interest in chemical technology, the number of functional groups that constitute these compounds is much smaller. Therefore, if we assume that a physical property of a fluid is the sum of contributions made by the molecule’s functional groups, we obtain a possible technique for correlating the properties of a very large number of fluids in terms of a much smaller number of parameters that characterize the contributions of individual groups. This paper shows the large influence exerted by the paraffinic, aromatic and naphthenic character of the gasoil but also the sulfur content of the fossil fraction on the shape of the liquid-liquid phase diagram and on the value of the minimum miscibility temperature.
Mistuning Identification of Bladed Disks Utilizing Neural Networks
Authors: Yu¨mer M. Ersin , Cig˘erog˘lu Ender , O¨zgu¨ven H. Nevzat
Published: January 2011

Mistuning affects forced response of bladed disks drastically; therefore, its identification plays an essential role in the forced response analysis of realistic bladed disk assemblies. Forced response analysis of mistuned bladed disk assemblies has drawn wide attention of researchers but there are a very limited number of studies dealing with identification of mistuning, especially if the component under consideration is a blisk (integrally bladed disk). This paper presents two new methods to identify mistuning of a rotor from the assembly modes via utilizing neural networks. It is assumed that a tuned mathematical model of the rotor under consideration is readily available, which is always the case for today’s realistic bladed disk assemblies. In the first method, a data set of selected mode shapes and natural frequencies is created by a number of simulations performed by mistuning the tuned mathematical model randomly. A neural network created by considering the number of modes, is then trained with this data set. Upon training the network, it is used to identify mistuning of the rotor from measured data. The second method further improves the first one by using it as starting point of an optimization routine and carries out an optimization to identify mistuning. To carry out identification analysis by means of the proposed methods, there are no limitations on the number of modes or natural frequencies to be used. Thus, they are suitable for incomplete data as well. Moreover, since system modes are used rather than blade alone counterparts, the techniques are ready to be used for analysis of blisks. Case studies are performed to demonstrate the capabilities of the new methods, using two different mathematical models to create training data sets; a lumped-parameter model and a relatively realistic reduced order model. Throughout the case studies, the effects of using incomplete mode families and random errors in assembly modes are investigated.
Heat Transfer in Turbine Hub Cavities Adjacent to the Main Gas Path
Authors: Dixon Jeffrey A. , Guijarro Antonio , Bauknecht Andreas , Coren Daniel , Atkins Nick
Published: January 2011

Reliable means of predicting heat transfer in cavities adjacent to the main gas path are increasingly being sought by engineers involved in the design of gas turbines. In this paper an interim summary of the results of a four-year research programme sponsored by the EU and several leading gas turbine manufactures and universities will be presented. Extensive use is made of CFD and FE modelling techniques to understand the thermo-mechanical behaviour of a turbine stator well cavity, including the interaction of cooling air supply with the main annulus gas (see Figure 1). The objective of the study has been to provide a means of optimising the design of such cavities for maintaining a safe environment for critical parts, such as disc rims and blade fixings, whilst maximising the turbine efficiency, and minimising the fuel burn and emissions penalties associated with the secondary airflow system. The modelling methods employed have been validated against data gathered from a dedicated two-stage turbine rig, running at engine representative conditions. Extensive measurements are available for a range of flow conditions and alternative cooling arrangements. The analysis method has been used to inform a design change which is also to be tested. Comparisons are provided between the predictions and measurements of the turbine stator well component temperature.
An Experimental System for Assessing Combustor Durability
Authors: Rudrapatna Nagaraja S. , Peterson Benjamin H. , Greving Daniel
Published: January 2011

Modern gas turbine combustors are made of high temperature alloys, employ effusion cooling and are protected by a Thermal Barrier Coating (TBC). Gas turbine combustor failure modes, such as TBC spallation, cracking and distortion resulting from oxidation, creep and thermal fatigue, are driven by hot spot peak temperature and the associated thermal gradient. Standard material characterization tests such as creep, oxidation and low cycle fatigue are indicators of a material’s potential performance but they neither fully represent the combustor geometric/material system nor fully represent the thermal fatigue conditions a combustor is subjected to during engine operation. Combustor rig tests and/or engine cyclic endurance tests to determine the suitability of new material systems for combustors are time consuming and costly. Therefore, a simple yet efficient test method for screening material systems under representative combustor conditions is needed. An experimental system has been developed to fill this gap. This paper discusses the configured specimen geometry, test methodology, observed test results and a comparison with typical failure modes observed in combustors.
Aerodynamic Research on the MCA-Type Compressor Blade Cascade
Authors: Sˇimurda David , Luxa Martin , Sˇafarˇi´k Pavel
Published: January 2011

This paper deals with an analysis of the flow through a high cambered compressor blade cascade. The profiles of the blade cascade have been designed to be of MCA-type. The geometric and aerodynamic parameters of the cascade are presented here. The aerodynamic research was performed in a transonic wind tunnel. Optical methods were applied to obtain information on the flow structures taking place in the interblade channels when operating in a range of subsonic and transonic velocities and at various angles of incidence. The internal shock waves and the flow separation in the rear part of the cascade channel were observed and studied. Their influence on the loss coefficient and exit flow angle at subsonic and low transonic region was assessed. The thickness of the sidewall boundary layer in the interblade channel was measured in order to investigate the development of the axial velocity density ratio (AVDR), which plays an important role in the interpretation of the results.
Prediction of Flow and Combustion Characteristics for a Gas Turbine Combustor Burning Low Heating Value Fuel
Authors: Shaalan M. R. , El Salmawy H. A. , Ismail M. Anwar
Published: January 2011

In this study, a numerical model has been developed to simulate the flow and combustion in a gas turbine combustor of type (Winnox-TUD-Combustor), which burns low heating value gas. The model relies on the computational code “FLUENT”. This code has been used to solve the governing equations. The characteristics of the model are; steady, turbulent, two dimensional, axisymmetric and swirling flow. The combustion process has been simulated as non-premixed combustion. The study includes the impact of several design and operational parameters on the characteristics of the flow and combustion inside the combustion chamber. These parameters include; ratio of secondary to primary air, ratio of tertiary to primary air, swirl ratio, number of inlets of the secondary air and their direction. Four performance indicators have been used to evaluate the impact of the aforementioned design and operating parameters. These indicators include; average temperature of the exhaust gases to the turbine, specific NOx emission, pattern factor and combustion efficiency of the combustor. In order to identify the optimum values of the aforementioned design and operational parameters, Artificial Neural Network (ANN) technique has been utilized to enrich the output results. This facilitates searching for the optimum values of the aforementioned parameters. Furthermore the effect of the variations in fuel composition on the combustion characteristics and accordingly on the performance indicators has been studied. It has been found that, all the studied parameters affect the performance of the combustor to a certain extent. However, fuel swirl ratio, primary to secondary air ratio and tertiary to primary air ratio as well as carbon monoxide to hydrogen ratio in the fuel are the controlling factors. Optimizing these parameters can lead to a substantial reduction in specific NOx emissions down to 4.0 gm/kg of fuel. Also an improvement in pattern factor to values below 0.3 has been achieved.
Aerodynamic Design of Transonic Tip Sections
Authors: Stein A. , Hofer D. C. , Filippenko V. , Slepski J.
Published: January 2011

This paper systematically explores the aerodynamic design space of transonic tip sections for large steam turbines. The sections studied in this work have subsonic inlet relative Mach numbers, and supersonic exit Mach numbers up to 1.75. Two-dimensional CFD evaluations using numerical solvers MISES and TACOMA are used to assess the performance impact of design parameters. Geometric features including subsonic overlap, supersonic overlap, trailing edge thickness, trailing edge wedge angle and camber distribution are evaluated for their effect on the section performance. An optimal geometry is then generated incorporating the best features from each of the individual parameter studies.