bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodontal disease in research beagle dogs – an epidemiological study
Authors: Kortegaard H. E. , Eriksen T. , Baelum V.
Published: September 2008

Objectives: To estimate the prevalence and describe the extent and severity of periodontal disease and associated periodontal parameters in beagle dogs.

Methods: A full‐mouth, site‐specific examination was performed in 98 beagle dogs. Focus was placed on clinical attachment loss, pocket depth and bleeding on probing.

Results: The prevalence of clinical attachment loss greater than equal to 1 mm was 20 per cent in the one‐year‐old dogs, increasing to 84 per cent of the dogs aged more than three years. The number of sites affected with clinical attachment loss greater than equal to 1 mm showed a skewed distribution. The prevalence of clinical attachment loss greater than equal to 4 mm was only seven per cent. A probing pocket depth of 4+ mm was observed in 44 to 81 per cent of the dogs, depending on age. Also, the distribution of the number of deepened pockets/dog was skewed. The teeth most prone to clinical attachment loss greater than equal to 1 mm were the P2, the P3 and the P4 of the maxilla. The teeth most prone to pocket depth greater than equal to 4 mm were the maxillary canines.

Clinical Significance: Periodontal disease in terms of clinical attachment loss greater than equal to 1 mm and pocket depth greater than equal to 4 mm is common in beagle dogs, but the major disease burden is carried by only a few dogs. The prevalence increases with increased age but is high already at the age of two years.
Long‐term results of subtotal colectomy for acquired hypertrophic megacolon in eight dogs
Authors: Nemeth T. , Solymosi N. , Balka G.
Published: September 2008

Objectives:To evaluate the long‐term results of subtotal colectomy for acquired hypertrophic megacolon in the dog.

Methods:Eight dogs with acquired hypertrophic megacolon underwent subtotal colectomy with preservation of the ileocolic junction. Long‐term follow‐up was obtained by clinical records and telephone interviews with the owners.

Results:Eight large‐breed dogs (age range: 6 to 12 years; mean age: 10·75 years) were enrolled. The use of bone meal, low levels of exercise, chronic constipation with dyschesia and tenesmus refractory to medical management were factors predisposing dogs to acquired hypertrophic megacolon. The diagnosis was confirmed in all animals by abdominal palpation, plain radiography and postoperative histopathological findings. There were no intraoperative complications. One dog died as a result of septic peritonitis. The clinical conditions (that is, resolution of obstipation and stool consistency) of the remaining seven dogs were improved at discharge; all animals returned to normal defecation in five to 10 weeks (mean: 7·3 weeks) and were alive 11 to 48 months (mean: 40·5 months) after surgery.

ClinicalSignificance:Predominantly bony diet and/or low levels of physical activity may predispose dogs to acquired hypertrophic megacolon. Our results emphasise the long‐term effectiveness of subtotal colectomy with preservation of the ileocolic junction in this condition.
Local energetic regulation of sarcoplasmic and myosin ATPase is differently impaired in rats with heart failure
Authors: Joubert Frederic , Wilding James R. , Fortin Dominique , Domergue‐Dupont Valérie , Novotova Marta , Ventura‐Clapier Renée , Veksler Vladimir
Published: September 2008

Local control of ATP/ADP ratio is essential for efficient functioning of cellular ATPases. Since creatine kinase (CK) activity and mitochondrial content are reduced in heart failure (HF), and cardiomyocyte ultrastructure is altered, we hypothesized that these changes may affect the local energetic control of two major cardiac ATPases, the sarcoplasmic reticulum (SR) Ca2+‐ATPase (SERCA) and the myosin ATPase. Heart failure was induced by aortic stenosis in rats. Electron microscopy confirmed that failing cardiomyocytes had intracellular disorganization, with fewer contacts between mitochondria and myofibrils. Despite normal SERCA protein content, spontaneous Ca2+ release measurements using Fluo‐4 on saponin‐permeabilized cardiomyocytes showed a lower SR loading in HF even when endogenous CK and mitochondria were fully activated. Similarly, in permeabilized fibres, SR Ca2+ loading supported by SR‐bound CK and mitochondria was significantly reduced in HF (by 49% and 40%, respectively, 43% when both systems were activated, P < 0.05). Alkaline phosphatase treatment had no effect, but glycolytic substrates normalized calcium loading in HF to the sham level. The control by CK and mitochondria of the local ATP/ADP ratio close to the myosin ATPase (estimated by rigor tension) was also significantly impaired in HF fibres (by 32% and 46%, respectively). However, while the contributions of mitochondria and CK to local ATP regeneration were equally depressed in HF for the control of SERCA, mitochondrial contribution was more severely impaired than CK (P < 0.05) with respect to myofilament regulation. These data show that local energetic regulation of essential ATPases is severely impaired in heart failure, and undergoes a complex remodelling as a result of a decreased activity of the ATP‐generating systems and cytoarchitecture disorganization.
Sleep fragmentation impairs ventilatory long‐term facilitation via adenosine A1 receptors
Authors: McGuire Michelle , Tartar Jaime L. , Cao Ying , McCarley Robert W. , White David P. , Strecker Robert E. , Ling Liming
Published: September 2008

Sleep fragmentation (SF), a primary feature of obstructive sleep apnoea (OSA), impairs hippocampal long‐term potentiation and causes cognitive/attention deficits. However, its influence upon respiratory control has hardly been studied. This study examined the effect of SF on ventilatory long‐term facilitation (LTF, a persistent augmentation of respiratory activity after episodic hypoxia) and the hypoxic ventilatory response (HVR), and investigated the role of adenosine A1 receptors in these SF effects in conscious adult male Sprague–Dawley rats. SF, confirmed by sleep architecture recordings, was achieved by periodic, forced locomotion in a rotating drum (30 s rotation/90 s stop for 24 h). LTF, elicited by five episodes of 5 min poikilocapnic hypoxia (10% O2) with 5 min intervals, was measured by plethysmography. Resting ventilation and metabolic rate were unchanged, HVR was reduced (150.6 ± 3.5%versus 110.4 ± 12.3%) and LTF was eliminated (22.6 ± 0.5%versus−0.1 ± 1.3%) shortly after 24 h SF. The SF‐induced impairments were SF duration dependent, and completely reversible as HVR (< 24 h) and LTF (< 48 h) returned spontaneously to their pre‐SF values. The SF‐impaired HVR was improved (130.3 ± 4.2%) and SF‐eliminated LTF was restored (19.6 ± 0.9%) by systemic injection of the adenosine A1 receptor antagonist 8‐CPT (2.5 mg kg−1) ∼30 min before LTF elicitation. Both HVR and LTF were also similarly impaired by 24 h total sleep deprivation or 24 h repeated cage tapping‐induced SF, but not by a 24 h locomotion control protocol for SF. Collectively, these data suggest that: (1) 24 h SF impairs LTF and poikilocapnic HVR; (2) these impairments require A1 receptors; and (3) SF of OSA may exacerbate OSA via impaired ventilatory control mechanisms.
Experimental Investigation of Porosity Formation During the Slow Injection Phase in High-Pressure Die-Casting Processes
Authors: Zamora R. , Hernandez-Ortega J. J. , Faura F. , Lopez J. , Hernandez J.
Published: September 2008

The air entrapment mechanisms in die-casting injection chambers that may produce porosity in manufactured parts are analyzed in this work using visualization techniques of the flow in a transparent injection chamber model, using water as working fluid. In particular, results for the free-surface profile evolution and for the volume of air remaining in the chamber at the instant at which the water begins to flow through the runner are analyzed for different maximum plunger speeds and initial filling fractions. A comparison between these visualizations and the numerical results of Zamora et al. (2007, “Experimental Verification of Numerical Predictions for the Optimum Plunger Speed in the Slow-Phase of a High-Pressure Die Casting Machine,” Int. J. Adv. Manuf. Technol., 33, pp. 266–276) which were obtained using a three-dimensional numerical model, shows a good degree of agreement. After discussing the air entrapment mechanisms that may produce porosity in manufactured parts, different experiments, which were carried out under real operating conditions using an aluminum alloy in a high-pressure die-casting machine with horizontal cold chamber, will be presented. The die-cavity geometry used in the experiments was appropriately modified to isolate the slow shot phase from the rest of the injection process, and the porosity levels in the manufactured parts were measured using a gravimetric technique. The optimum values of the maximum plunger speed that minimizes porosity in the manufactured parts have been determined. These values are very close to the previous numerical predictions of López et al. (2003, “On the Critical Plunger Speed and Three-Dimensional Effects in High-Pressure Die Casting Injection Chambers,” ASME J. Manuf. Sci. Eng., 125, pp. 529–537)
Incremental Forming of Sheet Metal by Means of Parallel Kinematics Machines
Authors: Callegari Massimo , Gabrielli Andrea , Palpacelli Matteo-Claudio , Principi Marco
Published: September 2008

The incremental forming of metal sheet parts can be an interesting alternative to the manual forging of the blanks or to the manufacturing of resin dies for the production of prototypes or small lots of parts. Indeed, the characteristics of small-volume production would call for an increase in the level of automation, possibly leading to a robotized cell able to complete the part after forming: in this case, the robot performing the deformation could automatically change its tools, cut the part, bend or flange the borders, load/unload the part, etc. Unfortunately, the conventional industrial robots do not have the required stiffness and are unable to apply the necessary forces to the blank. However, the rather new family of parallel robots has characteristics similar to machining centers, while still keeping the versatility of a robot. The present paper outlines the studies that have been performed at the Polytechnic University of Marche in Ancona to assess the feasibility of the automated processing by using a hybrid robot interlocked to the incremental forming cell. The complexity of the experimental setup required the use of several simulation tools enabling off-line design of the experiments. In the end, an effective development environment has been set up, able to interface the different software tools in order to support the process designer in making the correct choices.
Upper Bound Analysis of the ECAE Process by Considering Strain Hardening Materials and Three-Dimensional Rectangular Dies
Authors: Luri R. , Luis Pérez C. J.
Published: September 2008

Equal channel angular extrusion (ECAE) or pressing is a process used to introduce severe plastic deformations to processed materials with the aim of improving their mechanical properties by reducing the grain size. At present, there are no analytical studies that have considered strain hardening materials in order to determine the required force to carry out the process. All the existing papers have only considered nonstrain hardening materials. Furthermore, all those studies have been done by considering plane strain conditions. In this work, an upper bound analysis of the required force for performing the ECAE process is made by considering a full three-dimensional geometry with a rectangular cross section. From this analysis, the influence of the geometric and the material parameters is studied by considering both friction and strain hardening materials. By using the upper bound method, an analytical formulation was obtained and the influence of all the parameters was determined. With this work, it is possible to have a wider knowledge of the influence of the main affecting parameters in the ECAE process and to optimize them.
Application of an Extended Stress-Based Forming Limit Curve to Predict Necking in Stretch Flange Forming
Authors: Simha C. Hari Manoj , Grantab Rassin , Worswick Michael J.
Published: September 2008

An extension of the stress-based forming limit curve (FLC) advanced by Stoughton (2000, “A General Forming Limit Criterion for Sheet Metal Forming,” Int. J. Mech. Sci., 42, pp. 1–27) is presented in this work. With the as-received strain-based FLCs and stress-strain curves for 1.6-mm-thick AA5754 and 1-mm-thick AA5182 aluminum alloy, stress-based FLCs are obtained. These curves are then transformed into extended stress-based forming limit curves (XSFLCs), which consist of the invariants, effective stress, and mean stress. By way of application, stretch flange forming of these aluminum alloy sheets is considered. The AA5754 stretch flange displays a circumferential crack during failure, whereas the AA5182 stretch flange fails through a radial crack at the edge of the cutout. It is shown that the necking predictions obtained using the strain- and stress-based FLCs in conjunction with shell element computations are inconsistent when compared with the experimental results. By comparing the results of the shell element computations with those in which the mesh comprises eight-noded solid elements, it is demonstrated that the plane stress approximation is not valid. The XSFLC is then used with results from the solid-element computations to predict the punch depths at the onset of necking. Furthermore, it is shown that the predictions of failure location and failure mode obtained using the XSFLC are in accord with the differences observed between the two alloys/gauges.
Patient-Specific Compliant Vessel Manufacturing Using Dip-Spin Coating of Rapid Prototyped Molds
Authors: Arcaute Karina , Wicker Ryan B.
Published: September 2008

A procedure for manufacturing cardiovascular system models using patient-specific data, rapid prototyping, and a multistep dip-spin coating process is presented here. Improvements to a previously developed process permitted the fabrication of flexible complex vascular replicas. The primary improvement included the development of a two-axis rotation mechanism that enabled a pseudorandom rotation of the coated mold in space, providing uniform coats. Other improvements included the use of a low viscosity (1500–2000cP) silicone solution that allowed for complete coverage of the mold, and developing a procedure for fixing defects. The dip-spin coating procedure was shown to be effective for the manufacture of compliant cardiovascular membranes, such as an arterial bypass graft with an internal flow passage and an abdominal aorta with nonuniform radial geometry, tapered diameters, bifurcations, and small branches. Results from a design of experiments comparing two dipping setups demonstrated that horizontally dipping the model produced coatings with more uniform thicknesses along the length of the model when compared to vertical dipping. For a 250-mm-long model, the difference in thickness between the top and bottom of the membrane was 0.42±0.069mm and 0.09±0.077mm for vertical and horizontal dippings, respectively. Mold diameter also affected the thickness of the membrane, with membrane thickness increasing as mold diameter decreased. Thickness data comparing locations at approximately the same height of the mold but with different diameters showed thicknesses of 2.54±0.198mm and 1.95±0.140mm for 7.85mm and 15.20mm diameters, respectively. Moreover, the differences in thickness between these locations were 0.60±0.128mm and 0.58±0.231mm for vertical and horizontal dippings, respectively; thus, membrane thickness variations occurred with mold diameter irrespective of the dipping setup. Depending on the prescribed tolerance for membrane thickness, the vertical dipping setup may be recommended for use because (1) it was easier to use since only the mold was immersed in the coating solution and no special protection of the dipping mechanism was required and (2) it produced fewer defects in the coatings since the solution always dripped from downfacing surfaces of the mold. Using this dip-spin coating procedure, patient-specific cardiovascular membranes can be manufactured and used in the development of medical devices, research requiring accurate anatomical models, and education and training.
Cutter-Workpiece Engagement Calculations by Parallel Slicing for Five-Axis Flank Milling of Jet Engine Impellers
Authors: Ferry W. , Yip-Hoi D.
Published: September 2008

Cutter-workpiece engagement maps, or cutting flute entry/exit locations as a function of height, are a requirement for prediction of cutting forces on the tool and workpiece in machining operations such as milling. This paper presents a new method of calculating tool-part intersection maps for the five-axis flank milling of jet engine impellers with tapered ball-end mills. The parallel slicing method (PSM) is a semi-discrete solid modeling technique written in C++ using the ACIS boundary representation solid modeling environment. The tool swept envelope is generated and intersected with the workpiece to obtain the removal volume. It is also subtracted from the workpiece to obtain the finished part. The removal volume is sliced into a number of parallel planes along a given axis, and the intersection curves between each tool move and plane are determined analytically. The swept area between successive tool positions is generated using the common tangent lines between intersection curves, and then removed from the workpiece. This deletes the material cut between tool moves, ensuring correct engagement conditions. Finally, the intersection curves are compared to the planar slices of the updated part, resulting in a series of arcs. The end points of these arcs are joined with linear segments to form the engagement polygon that is used to calculate the engagement maps. Using this method, cutter-workpiece engagement maps are generated for a five-axis flank milling toolpath on a prototype integrally bladed rotor with a tapered ball-end mill. These maps are compared to those obtained from a benchmark cutter-workpiece engagement extraction method, which employs a fast, z-buffer technique. Overall, the PSM appears to obtain more accurate engagement zones, which should result in more accurate prediction of cutting forces. With the method’s current configuration, however, the calculation time is longer.
Computational Flow Analysis of Bipolar Plate for Fuel Cells
Authors: Boddu Rajesh , Majumdar Pradip
Published: September 2008

A trilayer fuel cell includes separate flow channels for hydrogen and oxygen. One potential alternative flow channel design is the use of a bipolar plate that connects cathode of a trilayer fuel cell to anode of the next trilayer fuel cell in order to provide an efficient flow of current through the cells with reduced voltage loss. The design of the bipolar plates provides considerable engineering challenges. It requires being thin with good contact surfaces for the purpose reduced electrical resistances as well as efficient transport processes for the reactant gasses in microchannels with reduced pressure drops. Fluid flow and heat and mass transport in gas flow channels play an important role in the effective performance of the fuel cell. A bipolar plate design with straight parallel channels is considered and flow field in gas flow channels are analyzed using computational fluid dynamic model. Results for pressure drop coefficient and heat transfer coefficients with varying flow Reynolds number are presented
A Low-Order Dynamic Model for Planar Solid Oxide Fuel Cells Using Online Iterative Computation
Authors: Xi Handa , Sun Jing
Published: September 2008

High-fidelity dynamic models of solid oxide fuel cells (SOFCs) capture the spatial distribution of key performance variables by considering the cells as distributed parameter systems. As such, they are often complex and require extensive computational resources. In this paper, driven by the need to support the control strategy development and system optimization, we develop a low-order SOFC model by approximating the mass and energy balance dynamics in the fuel and air bulk flows using quasi-static relations. However, due to the coupling between the quasi-static mass balance and current distribution, this approximation leads to a large set of coupled nonlinear algebraic equations that have to be solved online using iterative computation. In order to mitigate the computational cost involved, an efficient iterative algorithm is proposed to solve these equations. The new algorithm requires to iterate on only one variable—the cell voltage—to determine the current and flow compositions and their distributions. The low-order model with 16 states is compared to the baseline model, which has 160 states that incorporates fully the mass and energy balance dynamics. Simulations are performed to evaluate the model performance for both steady-state and transient operations, and to assess the computational cost associated with the low-order and full order models. It is shown that the low-order model closely matches the original baseline model, while the computation time is reduced by more than 50% compared to the baseline model.
Dynamic Error Characterization for Non-Contact Dimensional Inspection Systems
Authors: Srivatsan Vijay , Katz Reuven , Dutta Debasish , Powałka Bartosz
Published: September 2008

High-precision non-contact dimensional inspection systems typically utilize high-precision motion stages to manipulate the sensor. Such motion stages are susceptible to position errors, which need to be characterized. While geometric and thermal errors can be characterized and compensated, compensation of dynamic errors is a challenging task. This paper presents a method for dynamic error characterization that is significantly different from dynamic error characterization on contact-based systems. A mathematical model to translate the vibrations on the sensor to the measurement errors on the part is presented. Through experiments on a four-axis system, a relationship between sensor motion speed, sampling frequency, and measurement accuracy is derived. The results of the experiments are used to describe the selection of optimal operating parameters for best accuracy and least uncertainty.
Thermocouple Fixation Method for Grinding Temperature Measurement
Authors: Shen Bin , Xiao Guoxian , Guo Changsheng , Malkin Stephen , Shih Albert J.
Published: September 2008

A new thermocouple fixation method for grinding temperature measurement is presented. Unlike the conventional method using a welded thermocouple, this new method uses epoxy for affixing the embedded thermocouple within a blind hole in the workpiece subsurface. During grinding, the thermocouple junction is exposed and bonded to provide direct contact with the ground surface by the smearing of the workpiece material. Experiments were conducted to evaluate this simplified thermocouple fixation method including the effect of thermocouple junction size. Heat transfer models were applied to calculate the energy partition for grinding under dry, wet, and minimum quantity lubrication (MQL) conditions. For shallow-cut grinding of cast iron using a vitreous bond aluminum oxide wheel, the energy partition using a small wheel depth of cut of 10 μm was estimated as 84% for dry grinding, 84% for MQL grinding, but only 24% for wet grinding. Such a small energy partition with wet grinding can be attributed to cooling by the fluid at the grinding zone. Increasing the wheel depth of cut to 25 μm for wet grinding resulted in a much bigger energy partition of 92%, which can be attributed to fluid film boiling and loss of cooling at the grinding zone.
Gas Turbine Heat Transfer: 10 Remaining Hot Gas Path Challenges
Authors: Bunker Ronald S.
Published: September 2008

The advancement of turbine cooling has allowed engine design to exceed normal material temperature limits, but it has introduced complexities that have accentuated the thermal issues greatly. Cooled component design has consistently trended in the direction of higher heat loads, higher through-wall thermal gradients, and higher in-plane thermal gradients. The present discussion seeks to identify ten major thermal issues, or opportunities, that remain for the turbine hot gas path today. These thermal challenges are commonly known in their broadest forms, but some tend to be little discussed in a direct manner relevant to gas turbines. These include uniformity of internal cooling, ultimate film cooling, micro cooling, reduced incident heat flux, secondary flows as prime cooling, contoured gas paths, thermal stress reduction, controlled cooling, low emission combustor-turbine systems, and regenerative cooling. Evolutionary or revolutionary advancements concerning these issues will ultimately be required in realizable engineering forms for gas turbines to breakthrough to new levels of performance. Herein lies the challenge to researchers and designers. It is the intention of this summary to provide a concise review of these issues, and some of the recent solution directions, as an initial guide and stimulation to further research.
An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs
Authors: Maurer Michael , von Wolfersdorf Jens , Gritsch Michael
Published: September 2008

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.
DMTrade: A Rolls-Royce Tool to Model the Impact of Design Changes and Maintenance Strategies on Lifetime Reliability and Maintenance Cost
Authors: Burkett Michael A.
Published: September 2008

For complex repairable products, the lifetime reliability and maintenance cost attributes are a complex function of the component reliability distributions and the selected maintenance strategy. Understanding and accommodating this complexity is key when some components exhibit wearout, others fail randomly, and still others exhibit infant mortality. Further complications arise when some failure modes are more costly to repair than others, thereby having a disproportionate impact on lifetime maintenance cost. To fully consider these complexities, Rolls-Royce has developed DMTrade, a Monte Carlo simulation tool that simulates a product through its lifetime of failures, repairs, and scheduled maintenance. This paper defines the methodology used by DMTrade, and illustrates how this methodology can be used to identify the highest value improvement opportunities, both for product design and maintenance strategy.
The Development of Data Match Acceptance Criteria for the Validation of a Thermal Model
Authors: Ruedel U. W. , Turner J. R.
Published: September 2008

The validation of life predictions of gas turbine engines is usually based on an engine test where the temperature response is measured during a representative mission cycle. A thermal model of the test engine is developed which is then validated by the measured temperature data to within certain datamatch acceptance criteria (steady state and transient) which will provide acceptably accurate predictions of creep life and low-cycle fatigue (LCF). Once the thermal model has been validated, the predicted temperature data are used as boundary conditions for the mechanical (stress) model. This allows the prediction of the fatigue life due to LCF and due to creep. Since it is often almost impossible to validate the mechanical (stress) model by reliable means, it is of great importance to validate the thermal model to within the greatest accuracy possible. Therefore, the tolerances to within which the thermal model is validated has a direct effect on the quality of the predicted life and hence engine reliability. This paper describes the development and implementation of datamatch acceptance criteria (DMAC) for the validation of a thermal model against measured data. The validated thermal model then forms the basis for reliable predictions of the component’s life in terms of LCF and creep. The datamatch acceptance criteria take into account spatial variations of the life-temperature sensitivity as different areas of the rotor are exposed to different temperature gradients and levels. In the following, both life-limiting mechanisms, LCF and creep, will be considered individually. This will result in different datamatch acceptance criteria for steady state and transient conditions, the former relating to creep life and the latter to LCF. The quality of the datamatch is then assessed in terms of a colour code (green/yellow/red) where the various colours represents different levels of acceptance for the thermal model.
Transient Thermal and Flow Field in a Turbine Disk Rotor-Stator System
Authors: Okita Yoji
Published: September 2008

Thermal and flow field in a rotor-stator system around a single stage HP-turbine disk are investigated. In the previous work, the authors’ group applied a newly developed conjugate analysis method to the system at a steady-state condition, compared the thermal field with the measured data, and concluded that a satisfactory level of accuracy can be achieved with the proposed method at the steady-state condition. The present paper focuses on a heat and fluid flow in the same rotor-stator system, but at a transient condition which simulates a typical accelerating and decelerating schedule expected in actual aero-engine operations. First, detailed measurement of secondary-air and metal temperatures around the turbine disk is carried out in the transient condition. Then, the 3D fluid / solid conjugate analysis is applied to the whole accelerating and decelerating schedule. The results show that the transient thermal behavior of the rotor-stator system is well captured and reproduced with the present conjugate method.
Calibration of a Subscale F/A-22 Engine Inlet Empirical Model Using Ground and Flight Test Data
Authors: Monaco Jeffrey F. , Kidman David S. , Bickford Randall L. , Malloy Donald J.
Published: September 2008

The US Air Force’s two main aeropropulsion test centers, Arnold Engineering Development Center and the Air Force Flight Test Center, are developing a common suite of modeling and simulation tools employing advanced predictive modeling technologies. This common set of modeling and simulation tools incorporates real-time data validation, system identification, parameter estimation model calibration, and automated model updating as new test results or operational data become available. The expected benefit is improved efficiency and accuracy for online diagnostic monitoring of Air Force assets. These resultant models could also be used for flight manual development, determining compliance to specifications, or to aid in real-time equipment monitoring. This paper describes the integrated approach to system identification, parameter estimation, and model updating. Implementation of a software package to enable efficient model handoff between test groups and centers is discussed. An F/A-22 inlet model is used to demonstrate the approach. Compact polynomial function models of the distortion and recovery flow descriptors and 40-probe pressure values are derived from quasi-steady and instantaneous subscale wind tunnel data. The model parameters are then calibrated with F/A-22 flight test data. Results show that the modeling algorithm captures the relevant nonlinear physics of the application, and the calibration and updating procedure improves the model match to flight data. A companion paper provides preliminary results from integrating the calibrated total-pressure inlet distortion and recovery models into a real-time equipment health monitoring system to support test operations.
Inverse Modeling Techniques for Parameter Estimation in Engineering Simulation Models
Authors: Akkaram Srikanth , Beeson Don , Agarwal Harish , Wiggs Gene
Published: September 2008

Computational simulation models are extensively used in the development, design and analysis of an aircraft engine and its components to represent the physics of an underlying phenomenon. The use of such a model-based simulation in engineering often necessitates the need to estimate model parameters based on physical experiments or field data. This class of problems, referred to as inverse problems [1] in the literature can be classified as well-posed or ill-posed dependent on the quality (uncertainty) and quantity (amount) of data that is available to the engineer. The development of a generic inverse modeling solver in a probabilistic design system [2] requires the ability to handle diverse characteristics in various models. These characteristics include (a) varying fidelity in model accuracy with simulation times from a couple of seconds to many hours (b) models being black-box with the engineer having access to only the input and output (c) non-linearity in the model (d) time-dependent model input and output. The paper demonstrates methods that have been implemented to handle these features with emphasis on applications in heat transfer and applied mechanics. A practical issue faced in the application of inverse modeling for parameter estimation is ill-posedness that is characterized by instability and non-uniqueness in the solution. Generic methods to deal with ill-posedness include (a) model development, (b) optimal experimental design and (c) regularization methods. The purpose of this paper is to communicate the development and implementation of an inverse method that provides a solution for both well-posed as well as ill-posed problems using regularization based on the prior values of the parameters. In the case of an ill-posed problem, the method provides two solution schemes — a most probable solution closest to the prior, based on the singular value decomposition (SVD) and a maximum a-posteriori probability solution (MAP). The inverse problem is solved as a finite dimensional non-linear optimization problem using the SVD and/or MAP techniques tailored to the specifics of the application. The paper concludes with numerical examples and applications demonstrating the scope as well as validating the developed method. Engineering applications include heat transfer coefficient estimation for disk quenching in process modeling, material model parameter estimation, sparse clearance data modeling, steady state and transient engine high-pressure compressor heat transfer estimation.
Modelling of Flameless Combustion Using Large Eddy Simulation
Authors: Duwig Christophe , Szasz Robert-Zoltan , Fuchs Laszlo
Published: September 2008

The challenge of achieving a clean and stable combustion in modern power plants or aero engines leads to develop new technologies and new combustors. Pioneer work on ‘flameless’ combustion has shown the great potential of such a technology for meeting modern requirements in term of safety and low emissions. The idea behind this technique is to ensure low emissions by operating at very low fuel/air equivalence ratio but with high preheating to stabilize the combustion. In addition, a careful design of the combustor should ensure that fresh gases are diluted by hot exhaust gases. The result is a distributed but efficient oxidation region. This paper presents a new efficient model for simulating ‘flameless’ oxidation. The model is based on Large Eddy Simulation (LES) ensuring an accurate description of the mixing. In addition, a ‘low-cost’ technique for coupling the LES code with some complex chemistry is presented. This approach was used for simulating a reacting jet close to the ‘flameless’ regime. The simulation showed the capability of the present LES tool for understanding the flow dynamics and improving the design of ‘flameless’ combustors.
Numerical Investigation of Lean Blow Out of a Model Gas Turbine Combustion Chamber Using a Presumed JPDF-Reaction Model by Taking Heat Loss Processes Into Account
Authors: Wetzel Frank , Habisreuther Peter , Zarzalis Nikolaos
Published: September 2008

Due to their excellent behaviour within the scope of mixing, ignition and burnout, swirl-flames are used within quite a manifold of scientific and industrial applications. The development of a swirl-induced inner recirculation zone, which provides heat and active chemical species to the ignition domain of the flame, plays an important role for stabilisation of these highly turbulent flames. Modern concepts for reducing thermal NOx emissions require high ignition stability even if very lean fuel/air-mixtures are in use. Therefore, there is a great demand for models which are able to predict lean blow out of turbulent, aerodynamically stabilised flames. In contrast to the integral approach of many stability models which mostly are based on global quantities, numerical models offer highest possible flexibility aiming at variation of geometry, operating conditions and further parameters. For solving the convective-diffusive problem, a RANS (Reynolds Averaged Navier Stokes) method based on a finite volume approach is applied, using the standard k-ε turbulence model. A joint-probability-density model with an assumed shape of the probability-density-function (presumed shape JPDF-model) describes the interaction of turbulence and chemical reaction. The latter is based on one single variable, describing the mixing state and one single variable, describing the state of reaction progress. The demand, to apply a chemical reaction mechanism, which is based on one single reaction progress variable, is solved by using the concept of the semi-global 2-domain-1-step chemical kinetics scheme. To predict lean blow out for confined diffusive swirl-flames makes it necessary to take into account the convective and radiative heat loss processes. To consider the influence of heat loss on the chemical reaction, the 2-domain-1-step chemical kinetics scheme had to be extended. The local distribution of heat loss inside the flow field is covered by a variable named “enthalpy-index”, which describes the normalised ratio of the local enthalpy and local enthalpy under adiabatic conditions for a given mixture composition. With this combined model LBO (Lean Blow Out) limits have been deduced for a Methane/Air-flame in a model gas turbine combustor. The results confirm, that lean blow out is predicted at much lower thermal loads if taking heat loss processes into account.
Operation Characteristics of a Premixed Sub-ppm NOx Burner With Periodical Recirculation of Combustion Products
Authors: Bru¨ckner-Kalb Jochen R. , Hirsch Christoph , Sattelmayer Thomas
Published: September 2008

The concept of the periodic mixing and combustion process, which has been presented earlier [1,2], has been implemented in a nearly adiabatic combustor for investigations at atmospheric pressure. The objective of this combustion process is to achieve stable combustion at adiabatic flame temperatures being considerably lower than the lean blowout temperature of aerodynamically stabilized flames with low pressure drop in the combustor in order to reduce NOx emissions and to achieve CO emissions near the thermodynamic equilibrium. For preheat temperatures between 390 K and 790 K, the periodic mixing combustor can be operated near the lean blowout limit with adiabatic flame temperatures down to 1510 K – 1600 K. The test combustor yields over the entire operation range of 1:4 (thermal powers from 47 kW up to 175 kW) very low emissions of NOx below 1 ppm(v) (15% O2, dry) and of CO below 8 ppm(v).
Investigation of Entropy Noise in Aero-Engine Combustors
Authors: Bake Friedrich , Michel Ulf , Roehle Ingo
Published: September 2008

Strong evidence is presented that entropy noise is the major source of external noise in aero-engine combustion. Entropy noise is generated in the outlet nozzles of combustors. Low frequency entropy noise — which was predicted earlier in theory and numerical simulations — was successfully detected in a generic aero-engine combustion chamber. It is shown that entropy noise dominates even in the case of thermo-acoustic resonances. In addition to this, a different noise generating mechanism was discovered that is presumably of even higher relevance to jet engines: There is strong evidence of broad band entropy noise at higher frequencies (1 kHz to 3 kHz in the reported tests). This unexpected effect can be explained by the interaction of small scale entropy perturbations (hot spots) with the strong pressure gradient in the outlet nozzle. The direct combustion noise of the flame zone seems to be of minor importance for the noise emission to the ambiance. The combustion experiments were supplemented by experiments with electrical heating. Two different methods for generating entropy waves were used, a pulse excitation and a sinusoidal excitation. In addition, high-frequency entropy noise was generated by steady electrical heating.
Assessment of the Robustness of Gas Turbine Diagnostics Tools Based on Neural Networks
Authors: Bettocchi R. , Pinelli M. , Spina P. R. , Venturini M. , Zanetta G. A.
Published: September 2008

The paper deals with the set-up and the application of an Artificial Intelligence technique based on Neural Networks (NNs) to gas turbine diagnostics, in order to evaluate its capabilities and its robustness. The data used for both training and testing the NNs were generated by means of a Cycle Program, calibrated on a Siemens V94.3A gas turbine. Such data are representative of operating points characterized by different boundary, load and health state conditions. The analyses carried out are aimed at the selection of the most appropriate NN structure for gas turbine diagnostics, by evaluating NN robustness with respect to: • interpolation capability and accuracy in the presence of data affected by measurement errors; • extrapolation capability in the presence of data lying outside the range of variation adopted for NN training; • accuracy in the presence of input data corrupted by bias errors; • accuracy when one input is not available. This situation is simulated by replacing the value of the unavailable input with its nominal value.
Integrated Pressurized Gasification of Biomass for Small Gas Turbines
Authors: Alfaro Jose´ A. , Lecuona A. , Roa J. , Ferru´s E.
Published: September 2008

Nowadays small and micro gas turbines are increasingly used for on-site cogeneration. Although this means a dramatic increase in energy efficiency, liquid or gaseous fossil fuels are used. At the same time, there is interest in using solid biomass for electricity production in a distributed generation scheme. Unfortunately, conventional gas turbines can not burn solid biomass. This paper presents a thermodynamic simulation of a pressurized gasification system integrated into a gas turbine Brayton cycle, in order to study the feasibility of using biomass. The critical process of burning the resulting low-calorific-value gas is experimentally scrutinized for feasibility using a LOWNOX-LPP combustor and a synthetic gas. The results are promising. The thermochemical processing of biomass gasification using air produces a fuel barely suitable for gas turbines. Biomass gasification using air with no cooling provides outlet temperatures in the range from 700 K to 900 K and heat values of around 6 MJ/kg, being the tar content low and in a gaseous state, especially with down-draft moving bed gasifiers. Fuel gas cleaning is possible in a cyclone particle separator without previous cooling. This system requires a special design to bear the high temperature and to separate the ash particles down to turbine tolerance, without causing too much pressure loss and clogging. Additional hot filtering using porous media is also feasible. Two benefits arise due to high temperature cleaning. Firstly, tars do not condense but burn in the combustor increasing the biogas calorific value. Secondly, the thermal enthalpy from gasification is recovered. Therefore, the whole biomass primary energy is injected in the working gases, except heat losses. On the other hand, the gasification reactor needs to work pressurized (at a slightly higher pressure than the combustor pressure) thus requiring an additional power to overcome the head loss caused by the biomass bed and the cyclone particle separator. Thermodynamic analysis shows that under favourable conditions, a fall of around 1% of the overall efficiency appears. The heat value of gas and fuel-to-air ratio of the mixture affect flame stability inside the combustor. Nevertheless, with a swirl stabilized flame it has been demonstrated that it is possible to obtain stable flames down to 6 MJ/kg heating value with low CO and NOx emissions. For these preliminary experiments synthetic gases representing gasifiers output have been used. Using the integrated scheme here studied for feasibility, off-the-shelf gas turbines could be transformed into biomass burning micro-cogenerators, thus contributing to greenhouse gases emission reduction.
Mapping the Control Parameters of an Analog Fuel Control to Prepare for the Retrofit of a Digital Control Unit
Authors: Scheidler Stephan G. , Bindl Stefan , Mundt Christian
Published: September 2008

In the present publication, an existing twin-spool turbofan engine (Larzac 04 C5 as an example for a real engine utilized onboard an aircraft) is used for the preparation of a digital control system for an aero-engine which was originally driven by an analog controller. The application of the digital control itself is not yet covered by this paper, only the analog control baseline preparation and the combined testing are accomplished. A future publication will address the results of the digital control configuration, for which this paper is the basis. The assembly of the engine, the experimental setup, the instrumentation and the preparation work for the adaptation of the digital control system as well as the experimental results gained with the analog controller for later comparison purposes are described.