bluuebunny/crossref_metadata_2025 huggingface dataset:
A Discussion of Low-Order Numerical Integration Formulas for Rigid and Flexible Multibody Dynamics
Authors: Negrut Dan , Jay Laurent O. , Khude Naresh
Published: March 2009

The premise of this work is that the presence of high stiffness and/or frictional contact/impact phenomena limits the effective use of high order integration formulas when numerically investigating the time evolution of real-life mechanical systems. Producing a numerical solution relies most often on low-order integration formulas of which the paper investigates three alternatives: Newmark, HHT, and order 2 BDFs. Using these methods, a first set of three algorithms is obtained as the outcome of a direct index-3 discretization approach that considers the equations of motion of a multibody system along with the position kinematic constraints. The second batch of three algorithms draws on the HHT and BDF integration formulas and considers, in addition to the equations of motion, both the position and velocity kinematic constraint equations. Numerical experiments are carried out to compare the algorithms in terms of several metrics: (a) order of convergence, (b) energy preservation, (c) velocity kinematic constraint drift, and (d) efficiency. The numerical experiments draw on a set of three mechanical systems: a rigid slider-crank, a slider-crank with a flexible body, and a seven body mechanism. The algorithms investigated show good performance in relation to the asymptotic behavior of the integration error and, with one exception, result in comparable CPU simulation times with a small premium being paid for enforcing the velocity kinematic constraints.
An Efficient Multibody Divide and Conquer Algorithm and Implementation
Authors: Critchley James H. , Anderson Kurt S. , Binani Adarsh
Published: March 2009

A new and efficient form of Featherstone’s multibody divide and conquer algorithm (DCA) is presented and evaluated. The DCA was the first algorithm to achieve theoretically the optimal logarithmic time complexity with a theoretical minimum of parallel computer resources for general problems of multibody dynamics; however, the DCA is extremely inefficient in the presence of small to modest parallel computers. This alternative efficient DCA (DCAe) approach demonstrates that large DCA subsystems can be constructed using fast sequential techniques to realize a substantial increase in speed. The usefulness of the DCAe is directly demonstrated in an application to a four processor workstation and compared with the results from the original DCA and a fast sequential recursive method. Previously the DCA was a tool intended for a future generation of parallel computers; this enhanced version delivers practical and competitive performance with the parallel computers of today.
On the Formal Equivalence of Normal Form Theory and the Method of Multiple Time Scales
Authors: Wang Fengxia , Bajaj Anil K.
Published: March 2009

Multiple time scales technique has long been an important method for the analysis of weakly nonlinear systems. In this technique, a set of multiple time scales is introduced that serve as independent variables. The evolution of state variables at slower time scales is then determined so as to make the expansions for solutions in a perturbation scheme uniform in natural and slower times. Normal form theory has also recently been used to approximate the dynamics of weakly nonlinear systems. This theory provides a way of finding a coordinate system in which the dynamical system takes the “simplest” form. This is achieved by constructing a series of near-identity nonlinear transformations that make the nonlinear terms as simple as possible. The simplest differential equations obtained by the normal form theory are topologically equivalent to the original systems. Both methods can be interpreted as nonlinear perturbations of linear differential equations. In this work, the formal equivalence of these two methods for constructing periodic solutions and amplitude evolution equations is proven for autonomous as well as harmonically excited nonlinear vibratory dynamical systems. The reasons as to why some studies have found the results obtained by the two techniques to be inconsistent are also pointed out.
Thermal Radiation Involving Metallic Nanoparticles in the Near Field
Authors: Chapuis Pierre-Olivier , Volz Sebastian , Laroche Marine , Greffet Jean-Jacques
Published: March 2009

We firstly compare the electric and magnetic polarizabilities of a spherical nanoparticle. We then calculate the electromagnetic heat transfer between a metallic particle and a semi-infinite substrate. We show that the power absorbed by the particle in the near field is due to the magnetic interaction. We then calculate the energy transfer between two metallic nanoparticles and compare the heat dissipated by Joule effect and eddy currents. We find that the heat dissipated due to the magnetic fields is the leading contribution to the heat power. Both calculations show that a number of near-field effects involving metallic particles are affected by the fluctuating magnetic thermal fields.
Effect of the Excess Volume of Lattice Defects on the Enthalpy of Formation and Desorption Temperature of Metal Hydrides
Authors: Be´rube´ Vincent , Radtke Gregg , Chen Gang , Dresselhaus Mildred
Published: March 2009

Metal and complex hydrides offer very promising prospects for hydrogen storage that reach the DOE targets for 2015. However, slow sorption kinetics and high release temperature must be addressed to make automotive applications feasible. Reducing the enthalpy of formation by destabilizing the hydride reduces the heat released during the hydrogenation phase and conversely allows desorption at a lower temperature. High-energy ball milling has been shown to decrease the release temperature, increase reaction kinetics and lower the enthalpy of formation in certain cases. Increased surface and grain boundary energy could play a role in reducing the enthalpy of formation, but the predicted magnitude is too small to account for experimental observations. As the particle and grain sizes are reduced considerably under high-energy treatments, structural defects and deformations are introduced. These regions can be characterized by an excess volume due to deformations in the lattice structure, and have a significant effect on the material properties of the hydride. We propose a thermodynamic model that characterizes the excess energy present in the deformed regions to explain the change in physical properties of metal hydrides. An experimental investigation using the TEM to study the effect of lattice deformations and other nanostructures on the desorption process is underway.
An Efficiency Entitlement Study for Thermoelectric Generators
Authors: De Bock H. Peter J. , Novak Vladimir
Published: March 2009

Recent developments in thermoelectric materials and systems have led to renewed interest in thermoelectric devices for power generation. Operating conditions of the heat source and heat sink are essential in evaluating the conversion efficiency of such thermoelectric generator systems. This study provides a method for evaluating efficiency entitlement for thermoelectric power generation when thermoelectric material properties and system operating conditions are specified. The efficiency entitlement in closed form solutions for the most commonly used thermoelectric power generation configurations are presented followed by results and discussion.
Nitride Metal/Semiconductor Superlattices for High Temperature Direct Thermal-to-Electrical Energy Conversion
Authors: Rawat Vijay , Wortman Robert , Sands Tim
Published: March 2009

We have identified TiN/GaN and ZrN/ScN as two possible pure rocksalt structured metal/semiconductor combinations for fabrication of solid-state thermionic energy converters for high operational temperatures. The selection of the materials was constrained by issues that are critical to the integration of heterogeneous materials such as crystallographic compatibility and thermodynamic stability of the metal/semiconductor combinations at high operating temperatures. The first nitride superlattice system consists of TiN as the metal layer and GaN, in its metastable rocksalt phase, as the semiconductor layer, grown on rocksalt MgO substrates. The metastable rocksalt GaN (rs-GaN) phase is stabilized by pseudomorphic epitaxy on a metallic rocksalt TiN underlayer, and its existence has been verified using high-resolution x-ray diffraction and transmission electron microscopy. The critical thickness for the rocksalt-to-wurtzite phase transition has been empirically determined to be between 1 and 2 nm, although much thicker rocksalt GaN films, up to approximately 6 nm, can be maintained for several superlattice periods. The second pure rocksalt-structured superlattice system analyzed consists of alternating layers of metallic ZrN and semiconducting ScN. These epitaxial superlattices were grown on rocksalt MgO substrates using dc magnetron sputtering in a nitrogen-argon ambient.
Blade Air Cooling Feed System CFD Analysis and Validation
Authors: Ennacer Mohammed , Guevremont Grant , Djeridane Toufik , Sreekanth Sri , Lucas Terry
Published: March 2009

A cold flow static rig test and computational fluid dynamics (CFD) analyses have been performed to verify the benefits of a modified “deflector” design to the blade air cooling feed system. The area of interest is the broach passage which is a space between the bottom of the blade fixing and the blade disk. Cooling flow enters into this region from the disk cavity and then exits upward into the blade internal cooling passages. Steady Navier-Stokes analyses of the cold flow static rig geometries were performed using the in-house code NS3D and the commercial code CFX v5.6. Due to the setup of the experimental rig, the numerical domain model with appropriate boundary conditions had to be carefully selected. Unstructured grids including wall prism layers combined with mesh adaptation were employed for both CFD codes on the baseline geometry. The commercial adaptation code OPTIMESH was used for NS3D while CFX employed its internal grid adaptation tool. No grid adaptation was necessary for the modified geometry. The pressure and mass flow measurements for the baseline and modified blade broach geometries demonstrated a reduction in losses for the new design. The CFD flow visualization showed the presence of a strong vortex in the broach for the baseline case with an accompanying low pressure zone. The modified broach design deflects the flow thus avoiding the formation of the strong vortex and low pressure zone. The CFD pressure distributions predicted the trends qualitatively. Quantitative comparisons of the CFD pressure distributions along broach walls were reasonable for the new design. For the baseline geometry, the CFD pressure drop is higher than measurements indicate. Modeling issues associated with a screen in the rig set-up is thought to be the source of the difference.
Applications of Microstructural Characterization and Computational Modeling in Damage Analysis of a Turbine Blade Exposed to Service Conditions in a Power Plant
Authors: Tawancy H. M. , Al-Hadhrami Luai M.
Published: March 2009

Microstructural characterization and computational modeling were used to analyze the damage produced by overheating of a turbine blade exposed to service conditions in a power plant. Various electron-optical techniques were used to characterize the microstructure. Localized overheating was reflected by the microstructural features of the blade material particularly the extent of interdiffusion between the coating and alloy substrate, coarsening of the g′-phase, and re-precipitation of M23C6 carbide by a discontinuous mechanism at grain boundaries. Damage associated with these effects included creep cavities at grain boundaries and intergranular oxidation leading to ductile intergranular cracking at the leading edge of the blade. Most evidence pointed out that improper internal cooling of the blade resulted in excessive overheating at leading edge. Qualitatively, the temperature profile across the blade as indicated by microstructural variations was consistent with the results derived from computational modeling.
The Augmentation of Internal Blade Tip-Cap Cooling by Arrays of Shaped Pins
Authors: Bunker Ronald S.
Published: March 2009

The objective of the present study is to demonstrate a method to provide substantially increased convective heat flux on the internal cooled tip cap of a turbine blade. The new tip cap augmentation consists of several variations involving the fabrication or placement of arrays of discrete shaped pins on the internal tip cap surface. Due to the nature of flow in a 180-degree turn, the augmentation mechanism and geometry have been designed to accommodate a mixture of impingement-like flow, channel flow, and strong secondary flows. A large-scale model of a sharp 180-degree tip turn is used with the liquid crystal thermography method to obtain detailed heat transfer distributions over the internal tip cap surface. Inlet channel Reynolds numbers range from 200,000 to 450,000 in this study. The inlet and exit passages have aspect ratios of 2:1, while the tip turn divider-to-cap distance maintains nearly the same hydraulic diameter as the passages. Five tip cap surfaces were tested including a smooth surface, two different heights of aluminum pin arrays, one more closely spaced pin array, and one pin array made of insulating material. Effective heat transfer coefficients based on the original smooth surface area were increased by up to a factor of 2.5. Most of this increase is due to the added surface area of the pin array. However, factoring this surface area effect out shows that the heat transfer coefficient has also been increased by about 20 to 30%, primarily over the base region of the tip cap itself. This augmentation method resulted in negligible increase in tip turn pressure drop over that of a smooth surface.
Reynolds Analog in Combustor Modeling
Authors: Jiang Lei-Yong , Campbell Ian
Published: March 2009

Accurate temperature prediction is vital for the development of advanced combustion systems. The Reynolds analogy concept has been almost exclusively used in current turbulent reacting flow RANS simulations. In this paper, this hypothesis applied to a diffusion flame model combustor is discussed and assessed. Some of the numerical results obtained from a flamelet combustion model with the turbulence Prandtl/Schmidt number from 0.25 to 0.85 are presented, and compared with a benchmark experimental database. It is found that the turbulence Prandtl/Schmidt number has significant effect on the predicted temperature and species fields inside the combustor, as well as the temperature profile at the combustor wall. In contrast, its effect on the velocity field is insignificant in the range assessed. With the optimized turbulence Prandtl/Schmidt number, both velocity and scalar fields can be reasonably and quantitatively predicted. For the present configuration and operating conditions, the optimal Prandtl/Schmidt number is 0.5, lower than the commonly accepted values, ∼0.70. This study suggests that for accurate prediction of scalar transfers in turbulent reacting flows, the Reynolds analogy concept should be improved and new approaches should be developed.
Erosion Resistant Nano Technology Coatings for Gas Turbine Components
Authors: Swminathan V. P. , Wei Ronghua , Gandy David W.
Published: March 2009

Solid particle and liquid particle erosion in the compressor section of gas turbines and steam turbine vanes and blades lead to significant reduction in turbine efficiency over time. This results in increased downtime and operating cost of the power plants. Some of the conventional coatings and erosion protection shields used by the currently available commercial processes have limitations in their temperature and erosion protection capabilities. Under a project funded by the Electric Power Research Institute (EPRI), nano coatings with thickness within 40 microns (about 1.5 mils) have been produced on test samples using a state-of-the-art Plasma Enhanced Magnetron Sputtering (PEMS) technique. Five coatings were selected for the initial screening tests. Titanium silicon carbonitride nano-composite (TiSiCN), stellite and modified stellite, chromium carbide and Ti-TiN nano layered coatings are being studies in this project. The substrate selection is based on some of the alloys currently used in aeroderivative engine compressor blades, land based gas turbine compressor blades and steam turbine blades and vanes. They include titanium alloys and stainless steels. The PEMS coating technique differs significantly from the conventional techniques such as air plasma spray (APS), low-pressure plasma spray (LPPS), diffusion coatings, chemical or physical vapor deposition (CVD or PVD) used on blades and vanes. PEMS method involves a magnetron sputtering process using a vacuum chamber with an independently generated plasma source from which high current density can be obtained. This method used heavy ion bombardment prior to and during deposition to increase the coating adhesion and limit columnar growth in the coatings. Single-layered thick nitrides coatings up to about 80μm and thick carbonitride coatings of TiSiCN about 30μm have been obtained by this process. A novel method using trimethylsilane gas instead of solid targets was successful in producing this nanocomposite. Initial tests conducted on some of the coated titanium alloy samples produced thus far show significant improvement in the erosion resistance in laboratory sand erosion tests. It was observed that TiSiCN exhibited the best low-angle erosion resistance — nearly 25 times higher than the uncoated Ti-6Al-4V and about 5–10 times higher than all other nitrides. This paper covers a brief description of the deposition technology and the properties of the coatings. Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS), and X-Ray diffraction (XRD) analysis were used to study the microstructure and morphology of these coatings. Nanoindentation was conducted to determine the hardness and Young’s modulus, while sand erosion tests were conducted to rank the erosion resistance of the coatings produced using several processing variables.
Influence of Hot Streak Temperature Ratio on Low Pressure Stage of a Vaneless Counter-Rotating Turbine
Authors: Zhao Qingjun , Tang Fei , Wang Huishe , Du Jianyi , Zhao Xiaolu , Xu Jianzhong
Published: March 2009

In order to explore the influence of hot streak temperature ratio on low pressure stage of a Vaneless Counter-Rotating Turbine, three-dimensional multiblade row unsteady Navier-Stokes simulations have been performed. The predicted results show that hot streaks are not mixed out by the time they reach the exit of the high pressure turbine rotor. The separation of colder and hotter fluids is observed at the inlet of the low pressure turbine rotor. After making interactions with the inner-extending shock wave and outer-extending shock wave in the high pressure turbine rotor, the hotter fluid migrates towards the pressure surface of the low pressure turbine rotor, and the most of colder fluid migrates to the suction surface of the low pressure turbine rotor. The migrating characteristics of the hot streaks are predominated by the secondary flow in the low pressure turbine rotor. The effect of buoyancy on the hotter fluid is very weak in the low pressure turbine rotor. The results also indicate that the secondary flow intensifies in the low pressure turbine rotor when the hot streak temperature ratio is increased. The effects of the hot streak temperature ratio on the relative Mach number and the relative flow angle at the inlet of the low pressure turbine rotor are very remarkable. The isentropic efficiency of the Vaneless Counter-Rotating Turbine decreases as the hot streak temperature ratio is increased.
A Study on the Life Cycle Impact of Steam Injection
Authors: Jin H. , Marson E. , Pistor R. , Dempsey L.
Published: March 2009

Water or steam injection for NOX control or power augmentation can impact turbine hot section component life and maintenance interval. This relates to the effect of added water on hot-gas transport properties. Higher gas conductivity, in particular, increases heat transfer to blade and vane, and can lead to higher metal temperature and reduced part life. Part life impact from steam or water injection is also related to the way engine is controlled. Life cycle impact of steam injection on the LM6000PC HP turbine blade has been studied. The relationship between steam injection, LP turbine inlet temperature control, blade metal temperature, and corresponding life change was analyzed. The analysis result can be used for the assessment of life cycle impact with steam injection and temperature control limit.
The Reduction of CO2 Emission of Gas Turbine Power Plant by Using a Molten Carbonate Fuel Cell
Authors: Milewski Jarosław , Sałacin´ski Jacek , Miller Andrzej
Published: March 2009

The possibility of using a Molten Carbonate Fuel Cell (MCFC) to reduce the CO2 emission from Gas Turbine Power Plant (GTPP) is shown. The MCFC is placed after a gas turbine. The main advantages of this solution are: higher total electric power generated by hybrid system and reduced CO2 emission with remained system efficiency. A comparison of three systems: standard GTPP, GT-MCFC, and GT-MCFC with additional heat exchangers is shown. The application of MCFC could reduce CO2 emission of 73% (absolutely) and 77% relative to produced power.
Application of a One-Dimensional Modular Dynamic Model for Compressor Surge Avoidance
Authors: Morini M. , Pinelli M. , Venturini M.
Published: March 2009

In this paper, a one-dimensional model for the simulation of surge is used to study the dynamic behavior of a compression station. The station consists of a main line where the compressor operates and of a secondary line which allows the recirculation of the working fluid in order to prevent surge occurrence. With respect to the three maneuvers considered (from startup to normal operation, emergency shutdown and operating point variation), a sensitivity analysis is carried out to evaluate the influence of: • working fluid (methane and biogas); • surge margin value; • presence of a suitable PID controller; • presence of a cooler along the main flow line; • compressor driver (gas turbine and electric motor).
Fusion of Gas Turbines Diagnostic Inference: The Dempster-Schafer Approach
Authors: Romessis C. , Kyriazis A. , Mathioudakis K.
Published: March 2009

This paper proposes a fusion technique allowing the merge of conclusions provided by diagnostic methods that act independently for the detection of gas turbine faults. The proposed technique adopts the principles of Dempster-Schafer theory for the fusion of two diagnostic methods output; these are the method of Bayesian Belief Networks (BBN) and the method of Probabilistic Neural Networks (PNN). The proposed technique has been applied for the detection of thermodynamic as well as mechanical faults on gas turbines. First, the case of a turbofan engine of civil aviation is examined. The proposed technique allows the fusion of diagnostic inference on the presence of several faults of thermodynamic nature. Then the case of a radial and an axial compressor are examined, where several mechanical faults are deliberately implemented. In all cases, the effectiveness of the proposed fusion technique demonstrates that the merge of diagnostic information from different sources leads to better and safer diagnosis.
Inlet Air Cooling Applied to Combined Cycle Power Plants: Influence of Site Climate and Thermal Storage Systems
Authors: Palestra Nicola , Barigozzi Giovanna , Perdichizzi Antonio
Published: March 2009

The paper presents the results of an investigation on inlet air cooling systems based on cool thermal storage, applied to combined cycle power plants. Such systems provide a significant increase of electric energy production in the peak hours; the charge of the cool thermal storage is performed instead during night time. The inlet air cooling system also allows the plant to reduce power output dependence on ambient conditions. A 127 MW combined cycle power plant operating in the Italian scenario is the object of this investigation. Two different technologies for cool thermal storage have been considered: ice harvester and stratified chilled water. To evaluate the performance of the combined cycle under different operating conditions, inlet cooling systems have been simulated with an in-house developed computational code. An economical analysis has been then performed. Different plant location sites have been considered, with the purpose to weigh up the influence of climatic conditions. Finally, a parametric analysis has been carried out in order to investigate how a variation of the thermal storage size affects the combined cycle performances and the investment profitability. It was found that both considered cool thermal storage technologies perform similarly in terms of gross extra-production of energy. Despite to that, ice harvester shows higher parasitic load due to chillers consumptions. Warmer climates of plant site resulted to increase more the amount of operational hours than power output augmentation; investment profitability is different as well. Results of parametric analysis showed how important may be, for economical results, the size of inlet cooling storage.
Lifetime Reliability Prediction of Ceramics Subjected to Thermal and Mechanical Cyclic Loads
Authors: Nemeth Noel N. , Jadaan Osama M. , Baker Eric H. , Gyekenyesi John P.
Published: March 2009

A methodology is shown for predicting the time-dependent reliability (probability of survival) of ceramic components against catastrophic rupture when subjected to thermal and mechanical cyclic loads. This methodology is based on the Weibull distribution to model stochastic strength and a power law that models subcritical crack growth. Changes in material response that can occur with temperature or time (i.e. changing fatigue and Weibull parameters with temperature or time) are accommodated by segmenting a cycle into discrete time increments. Material properties are assumed to be constant within an increment, but can vary between increments. This capability has been added to the NASA CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code. The code has been modified to have the ability to interface with commercially available finite element analysis codes such as ANSYS executed for transient load histories. Examples are provided to demonstrate the features of the methodology as implemented in the CARES/Life program.
Probabilistic Engine Performance Scatter and Deterioration Modeling
Authors: Spieler Stefan , Staudacher Stephan , Fiola Roland , Sahm Peter , Weißschuh Matthias
Published: March 2009

The change of performance parameters over time due to engine deterioration and production scatter plays an important role to ensure safe and economical engine operation. A tool has been developed which is able to model production scatter and engine deterioration on the basis of elementary changes of numerous construction features. In order to consider the characteristics of an engine fleet as well as random environmental influences, a probabilistic approach using Monte Carlo Simulation (MCS) was chosen. To quantify the impact of feature deviations on performance relevant metrics, non-linear sensitivity functions are used to obtain scalars and offsets on turbomachinery maps which reflect module behavior during operation. Probability density functions (PDFs) of user-defined performance parameters of an engine fleet are then calculated by performing an MCS in a performance synthesis program. For the validation of the developed methodology pass-off test data, endurance engine test data, as well as data from engine maintenance incoming tests have been used. For this purpose, measured engine fleet performance data have been corrected by statistically eliminating the influence of measuring errors. The validation process showed the model’s ability to predict more than 90% of the measured performance variance. Furthermore, predicted performance trends correspond well to performance data from engines in operation. Two model enhancements are presented, the first of which is intended for maintenance cost prediction. It is able to generate PDFs of failure times for different features. The second enhancement correlates feature change and operating conditions and thus connects airline operation and maintenance costs. Subsequently, it is shown that the model developed is a powerful tool to assist in aircraft engine design and production processes thanks to its ability to identify and quantitatively assess main drivers for performance variance and trends.
Recovery Control for Rotors Established in Stable Periodic Contact Modes
Authors: Schlotter Michael , Keogh Patrick
Published: March 2009

Previous research has shown that flexible rotors can become established in potentially damaging stable periodic contact modes after initial impact with housings, seals, or auxiliary bearings. These modes are characterized by periodic motion and a fixed contact point in a rotating frame. A contact recovery strategy is developed, with the aim to destabilize the modes and return the rotor to a contact-free orbit. This is achieved by applying compensation forces through magnetic bearings, which reduces the effective synchronous forcing that is causing the contact to a low level. It is shown that even in presence of highly nonlinear contact dynamics, a linear FEM rotor model can be used to calculate appropriate influence coefficients. The contact recovery principle is demonstrated by simulations of a simple disk system and a simple flexible rotor. It is then applied to an experimental flexible rotor test facility. Error margins are investigated, and possible limitations of the method are discussed.
A New Bump-Type Foil Bearing Structure Analytical Model
Authors: Le Lez Se´bastien , Arghir Mihai¨ , Frene Jean
Published: March 2009

A gas bearing of bump foil type comprises an underlying structure made of one or several strips of corrugated sheet metal covered by a top foil surface. The fluid film pressure needs to be coupled with the behavior of the structure for obtaining the whole bearing characteristics. Unlike in classical elasto-aerodynamic models, a foil bearing (FB) structure has a very particular behavior due to friction interfaces, bump interactions and non-isotropic stiffness. Some authors have studied this complex behavior with the help of three-dimensional finite element simulations. These simulations evidenced a lack of reliable analytical models that can be easily implemented in a FB prediction code. The models found in literature tend to over-estimate the foil flexibility because most of them do not consider the interactions between bumps that are highly important. The present work then develops a model that describes the FB structure as a multidegree of freedom system of interacting bumps. Each bump includes three degrees of freedom linked with elementary springs. The stiffness of these springs are analytically expressed so that the model can be adjusted for any dimensions and material properties. Once the stiffness matrix of the whole FB structure is obtained, the entire static system is solved taking friction into account. Despite its relative simplicity, comparisons with finite elements simulations for various static load distributions and friction coefficients show a good correlation. This analytical model has been integrated into a foil bearing prediction code. The load capacity of a first generation foil bearing was then calculated using this structure model as well as other simplified theoretical approaches. Significant differences were observed, revealing the paramount influence of the structure on the static and dynamic characteristics of the foil bearing. Some experimental investigations of the static stiffness of the structure were also realized for complete foil bearings. The structure reaction force was calculated for a shaft displacement with zero rotation speed, using either the multidegree of freedom model or the usual stiffness formulas. The comparisons between theoretical and experimental results also tend to confirm the importance of taking into account the bump interactions in determining the response of the structure.
Interlaminar Crack Growth Resistances of Various Ceramic Matrix Composites in Mode I and Mode II Loading
Authors: Choi Sung R. , Kowalik Robert W.
Published: March 2009

Interlaminar crack growth resistances were evaluated for five different SiC fiber-reinforced ceramic matrix composites (CMCs) including three gas-turbine grade MI SiC/SiC composites. Modes I and II crack growth resistances, GI and GII, were determined at ambient temperature using double cantilever beam (DCB) and end notched flexure (ENF) methods, respectively. The CMCs exhibited GI = 200–500 J/m2 and GII = 200–900 J/m2. All the composites (except for one SiC/CAS composite) showed rising R-curve behavior either in mode I or in mode II, presumably attributed to fiber bridging (in modes I and II) and frictional constraint (mode II) in the wake region of a propagating crack. A glass fiber-reinforced epoxy polymer matrix composite, used as comparison, showed typically 2-3 and 8 times greater in GI and GII, respectively, compared to the CMCs. Experimental error analysis regarding the effect of the off-the-center of a crack plane on GI and GII was also made.
Dynamics of Multi-Stage Bladed Disks Systems
Authors: Laxalde Denis , Lombard Jean-Pierre , Thouverez Fabrice
Published: March 2009

This paper presents a new and original method for dynamical analysis of multi-stage cyclic structures such as turbomachinery compressors or turbines. Each stage is modeled cyclically by its elementary sector and the inter-stage coupling is achieved through a cyclic recombination of the interface degrees of freedom. This method is quite simple to set-up; it allows to handle the finite element models of each stage’s sector directly and, as in classical cyclic symmetry analysis, to study the nodal diameter problems separately. The method is first validated on a simple case study which shows good agreements with a complete 360° reference calculation. An industrial example involving two HP compressor stages is then presented. Then the forced response application is presented in which synchronous of engine order type excitations are considered.
Effect of Upstream Wake With Vortex on Turbine Blade Platform Film Cooling With Simulated Stator-Rotor Purge Flow
Authors: Wright Lesley M. , Blake Sarah A. , Rhee Dong-Ho , Han Je-Chin
Published: March 2009

Detailed film cooling effectiveness distributions were experimentally obtained on a turbine blade platform within a linear cascade. The film cooling effectiveness distributions were obtained on the platform with upstream disturbances used to simulate the passing vanes. Cylindrical rods, placed upstream of the blades, simulated the wake created by the trailing edge of the stator vanes. The rods were placed at 4 locations to show how the film cooling effectiveness was affected relative to the vane location. In addition, delta wings were placed upstream of the blades to model the effect of the passage vortex (generated in the vane passage) on the platform film cooling effectiveness. The delta wings create a vortex similar to the passage vortex as it exits the upstream vane passage. The film cooling effectiveness was measured with the delta wings placed at 4 locations, to investigate the effect of the passing vanes. Finally, the delta wings were coupled with the cylindrical rods to examine the combined effect of the upstream wake and passage vortex on the platform film cooling effectiveness. The detailed film cooling effectiveness distributions were obtained using pressure sensitive paint (PSP) in the five blade linear cascade. An advanced labyrinth seal was placed upstream of the blades to simulate purge flow from a statorrotor seal. The coolant flow rate varied from 0.5% to 2.0% of the mainstream flow, while the Reynolds number of the mainstream flow remained constant at 3.1*105 (based on the inlet velocity and chord length of the blade). The film cooling effectiveness was not significantly affected with the upstream rod. However, the vortex generated by the delta wings had a profound impact on the film cooling effectiveness. The vortex created more turbulent mixing within the blade passage, and the result is reduced film cooling effectiveness through the entire passage. When the vane induced secondary flow is included, the need for additional platform cooling becomes very obvious.
Transonic Turbine Stage Heat Transfer Investigation in Presence of Strong Shocks
Authors: de la Loma A. , Paniagua G. , Verrastro D. , Adami P.
Published: March 2009

This paper reports the external convective heat transfer distribution of a modern single-stage transonic turbine together with the physical interpretation of the different shock interaction mechanisms. The measurements have been performed in the compression tube test rig of the von Karman Institute using single and double-layered thin film gauges. The three pressure ratios tested are representative of those encountered in actual aero-engines, with M2, is ranging from 1.07 to 1.25 and a Reynolds number of about 106. Three different rotor blade heights (15%, 50% and 85%) and the stator blade at mid-span have been investigated. The measurements highlight the destabilizing effect of the vane left running shock on the rotor boundary layer. The stator unsteady heat transfer is dominated by the fluctuating right running vane trailing edge shock at the blade passing frequency.
Prediction of Lapse Rate in Low Pressure Turbines With and Without Modeling of the Laminar-Turbulent Transition
Authors: Mansour Mahmoud L. , Konan S. Murthy , Goswami Shraman
Published: March 2009

Although turbo-machinery main stream flows are predominantly turbulent, the low pressure turbine airfoil surface boundary layer may be either laminar or turbulent. When boundary layer flow is laminar and passes through a zone of adverse pressure gradient, bypass or separation transition can occur via the Tollmien-Schlichting or Kelvin-Helmholtz instabilities. As the gas turbine’s low pressure turbine operating condition changes from sea level take-off to the altitude cruise, Reynolds number is significantly lowered and the turbine’s performance loss increases significantly. This fall-off in performance characteristic is known as lapse rate. Ability to accurately model such phenomenon is a prerequisite for reliable loss prediction and essential for improving low pressure turbine designs. Establishing such capability requires the validation and evaluation of existing low Reynolds number turbulence models, with laminar-turbulent transition modeling capability, against test cases with measured data. This paper summarizes the results of evaluating and validating two 3D viscous “RANS” Reynolds-Averaged Navier-Stokes programs for two test cases with test data. The first test case is the ERCOFTAC’ flat plate with and without pressure gradient, and the second is a Honeywell three-and-half-stage low pressure turbine with available test data at high and low Reynolds number operations. In addition to evaluating the CFD codes against test data, the flat plate test cases were used to establish the meshing and modeling best practice for each code before performing the validation for the Honeywell multistage low pressure turbine. The RANS CFD programs are Numeca’s Fine Turbo and ANSYS/CFX. Numeca’s Fine Turbo employs a two-equation K-ε turbulence model without laminar-turbulent transition modeling capability and the one-equation Spallart-Allmaras turbulence model with laminar-turbulent transition modeling capability. The ANSYS/CFX, on the other hand, employs a two-equation K-ω turbulence model (AKA SST or shear stress transport) with ability to model laminar-turbulent transition. Predictions of the CFD codes are compared with test data and the impact of modeling the laminar-turbulent transition on the prediction accuracy is assessed and presented. Both CFD codes are commercially available and the evaluation presented here is based on users’ prospective that targets the applicability of such predictive tools in the turbine design process.
Operating Experience of High Flexibility Syngas Burner for IGCC Power Plant
Authors: Bonzani Federico , Gobbo Paolo
Published: March 2009

Ansaldo Energia Low BTU engines have been accumulating more than 150000 EOH (Equivalent Operating Hours) burning low Btu Fuels on two different projects such as Isab Priolo and Elettra Servola. More over a new unit Ferrera Erbognone 3 has started to be commissioned in March 2006 burning syngas from tar gasification. This latter will be the first real commercial power plant in Italy to be operated without taking into account the high benefits once available according to the national law (CIP6/1992) specifically dealing with recovery fuel usage (alternative to natural gas). The end of the first phase of commissioning of Ferrera Erbognone 3 will give the opportunity to present the results achieved and to validate the burner design process for this specific power plant. In the IGCC gasifier island of Ferrera 3 power plant, it will be possible to separate hydrogen in variable quantity from the syngas according to the demands of the refinery located nearby the power plant, thus giving a high composition variability as output fuel. Also, if the maximum quantity of hydrogen will be separated, an integration with natural gas will be performed in order to get the maximum power output of the power plant. As a consequence, the syngas burner has been designed taking into account all the fuel characteristics depending on the different composition carried out. According to these, the burner has been optimised in order to fit the various syngas blends to be fuelled when running the engine. The paper describes the experience achieved during the commissioning activity prior to the commercial operation started in September 2006 highlighting the main results achieved with respect to the plant requirement. Furthermore a description of the functional improvement of the engine in order to face the unexpected off design conditions will be reported.
Film Cooling Effectiveness on a Rotating Turbine Platform Using Pressure Sensitive Paint Technique
Authors: Suryanarayanan A. , Ozturk B. , Schobeiri M. T. , Han J. C.
Published: March 2009

Film cooling effectiveness is measured on a rotating turbine blade platform for coolant injection through discrete holes using pressure sensitive paint technique (PSP). Most of the existing literatures provide information only for stationary end-walls. The effects of rotation on the platform film cooling effectiveness are not well documented. Hence, the existing 3-stage turbine research facility at TPFL, Texas A&M University was re-designed and installed to enable coolant gas injection on the 1st stage rotor platform. Two distinct coolant supply loops were incorporated into the rotor to facilitate separate feeds for upstream cooling using stator-rotor gap purge flow and downstream discrete-hole film cooling. As a continuation of the previously published work involving stator-rotor gap purge cooling, this study investigates film cooling effectiveness on the 1st stage rotor platform due to coolant gas injection through nine discrete holes located downstream within the passage region. Film cooling effectiveness is measured for turbine rotor frequencies of 2400rpm, 2550rpm and 3000rpm corresponding to rotation numbers of Ro = 0.18, 0.19 and 0.23 respectively. For each of the turbine rotational frequencies, film cooling effectiveness is determined for average film-hole blowing ratios of Mholes = 0.5, 0.75, 1.0, 1.25, 1.5 and 2.0. To provide a complete picture of hub cooling under rotating conditions, simultaneous injection of coolant gas through upstream stator-rotor purge gap and downstream discrete film-hole is also studied. The combined tests are conducted for gap purge flow corresponding to coolant to mainstream mass flow ratio of MFR = 1% with three downstream film-hole blowing ratios of Mholes = 0.75, 1.0 and 1.25 for each of the three turbine speeds. The results for combined upstream stator-rotor gap purge flow and downstream discrete holes provide information about the optimum purge flow coolant mass, average coolant hole blowing ratios for each rotational speed and coolant injection location along the passage to obtain efficient platform film cooling.
Experimental Investigation of the Stability Mechanism and Emissions of a Lifted Swirl Non-Premixed Flame
Authors: Fokaides Paris A. , Kasabov Plamen , Zarzalis Nikolaos
Published: March 2009

We report on the experimental investigation of a confined lifted swirl non-premixed flame by applying a novel Airblast nozzle [1]. 3D-Laser Doppler Anemometry, a non-intrusive, laser-based measurements technique, is adapted for the measurement of all three mean velocity components and of the six Reynolds stress components. The determination of the temperature and mixture field occurs by employing in-flame measurement techniques. Valuable information concerning the mixing procedure, the temperature distribution, the turbulence level and the velocity field of the flame is provided. The results demonstrate that there is sufficient residence time in the pre-combustion area of the lifted flame in order to achieve spatial and temporal uniformity of the mixture, leading to a quasi premixed state. It was also found that hot reaction products, carried upstream by large vortices along the jet, could possibly react with fresh unburnt mixture in a reignition process. The determination of the flow pattern revealed the presence of an inner weak recirculation zone in the nozzle vicinity and a dominant external recirculation zone. The examination of the probability density function (PDF) of the velocity-measurements was also found to be a very useful tool in terms of the analysis of the turbulence structure of the flow. The bimodal distribution yield the existence of large scaled eddies in the shear layer between the downstream flow and the recirculated gases. Finally, the significant reduced NOx emissions in the lean area were also shown by means of emission measurements for elevated pressure conditions.