bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of compliance in medicaid versus non‐Medicaid patients
Authors: Dobbs Mary Ellen , Manasse Robert , Kusnoto Budi , Grace Costa Viana Maria , Obrez Ales
Published: August 2014

Background

Medicaid patients have been associated with lack of compliance during their orthodontic treatment in comparison with the non‐Medicaid patients. In this study, Medicaid and non‐Medicaid orthodontic patients’ compliance from a state university and private practice orthodontic clinic within close location were analyzed.

Methods

Charts of 30 Medicaid and 30 non‐Medicaid orthodontic patients at each orthodontic clinic were reviewed. From each chart, mean percentage of failed and late appointments, number of broken appliances, number of comments on compliance with auxiliary wear and number of comments on oral hygiene maintenance were recorded.

Results

Statistically significant differences between Medicaid and non‐Medicaid orthodontic patients were not found.

Conclusions

The results of this study indicated that in general there are no differences between Medicaid and non‐Medicaid orthodontic patients.

Practical Implications

These results may alleviate the doubts of the dental practitioner in treating Medicaid patients.
L‐moments skewness and kurtosis as measures of regional convergence and cohesion
Authors: Kopczewska Katarzyna
Published: August 2014

The paper deals with the statistical modeling of convergence and cohesion over time with the use of kurtosis, skewness and L‐moments. Changes in the shape of the distribution related to the spatial allocation of socio‐economic phenomena are considered as an evidence of global shift, divergence or convergence. Cross‐sectional time‐series statistical modeling of variables of interest is to overpass the minors of econometric theoretical models of convergence and cohesion determinants. L‐moments perform much more stable and interpretable than classical measures. Empirical evidence of panel data proves that one pure pattern (global shift, polarization or cohesion) rarely exists and joint analysis is required.
Semiquantitative immunohistochemical marker staining and localization in canine thyroid carcinoma and normal thyroid gland
Authors: Pessina P. , Castillo V. , Sartore I. , Borrego J. , Meikle A.
Published: August 2014

Immunoreactive proteins in follicular cells, fibroblasts and endothelial cells were assessed in canine thyroid carcinomas and healthy thyroid glands. No differences were detected in thyrotropin receptor and thyroglobulin staining between cancer and normal tissues, but expression was higher in follicular cells than in fibroblasts. Fibroblast growth factor‐2 staining was more intense in healthy follicular cells than in those of carcinomas. Follicular cells in carcinomas presented two‐ to three‐fold greater staining intensity of thyroid transcription factor‐1 and proliferating cell nuclear antigen, respectively, than healthy cells, and a similar trend was found for the latter antigen in fibroblasts. Vascular endothelial growth factor staining was more intense in the endothelial cells of tumours than in those of normal tissues. In conclusion, greater expression of factors related to proliferation and angiogenesis was demonstrated in several cell types within thyroid carcinomas compared to healthy tissues, which may represent mechanisms of tumour progression in this disease.
Feedstock Blending in a Continuously Fed Gasifier
Authors: Schaefer Greg P. , Green Alex E. S.
Published: August 2014

Imported oil, nuclear and coal now contribute about 55% of the energy the USA consumes, and those forms of energy are under environmental, social and legal scrutiny. There are limits to which non-“clouded” natural gas and renewables can replace these sources. This has motivated the CCTL to pursue R&D on blending domestically available fuels in thermal reactors to produce more useful gaseous or liquid fuels. Feedstock blending results with batch-fed indirectly heated gasifiers (IHGs) were reported at the three previous Turbo Expo meetings. This is a progress report on initial work with a continuously fed IHG scaled to potentially give a gaseous output suitable for a 5–20 kW microturbine or a reciprocating engine. An electric tube furnace is now used rather than a combustor fueled by the residual char or part of the gaseous or liquid output. Some novel features of this current effort are: a) Biomass blends are auger-fed through a reactor tube fabricated out of available components to simulate a conical shape, b) The output gas is filtered and partially cooled by the incoming biomass feedstock, c) The system has been designed to facilitate feedstock blending studies, d) A trap and external heat exchanger condenses the residual tar, water vapor, and volatile metals, e) The char-ash is collected and stored in a pressure vessel, f) Gas output volume is measured with an orifice dividing system and respirometer. The results of runs in a semi-continuously fed system with various biomass particle sizes and with various blends of biomass and coal are presented. The fate of volatile metals contained in the input feedstock is assessed. With the completion of an external hopper-feeder and the replacement of the electric tube furnace by an output gas or charcoal combustor, a later application to microturbines is within reach.
Neural Network Modeling of Turbofan Parameters
Authors: Embrechts Mark J. , Schweizerhof Aaron L. , Bushman Mark , Sabatella Mike H.
Published: August 2014

This research involves the development and validation of neural network models for several engine parameters for a turbofan engine. The investigation encompasses data collection, data translation, development of the neural network models, and testing. The data used to train and validate the neural network models was acquired from state of the art models as well as flight tests. During this study, different neural network architectures and training algorithms are exercised and evaluated for a turbofan engine operating at steady-state conditions. In addition, studies are performed to optimize the neural network architecture and resolution of data used for training.

The resulting models are thoroughly validated using data for approximately sixty thousand flight conditions. The neural network models trained and tested with data acquired from state of the art models are capable of predicting their respective parameters with a maximum of 5.3 percent error. A neural network model created with a small set of flight test data and validated with a slightly larger set of data resulted in a maximum error of 4.6 percent.
Structural Health Monitoring With Piezoelectric Active Sensors
Authors: Winston Howard A. , Sun Fanping , Annigeri Balkrishna S.
Published: August 2014

A technology for non-intrusive real-time structural health monitoring using piezoelectric active sensors is presented. The approach is based on monitoring variations of the coupled electromechanical impedance of piezoelectric patches bonded to metallic structures in high-frequency bands. In each of these applications, a single piezoelectric element is used as both an actuator and a sensor. The resulting electromechanical coupling makes the frequency-dependent electric impedance spectrum of the PZT sensor a good mapping of the underlying structure’s acoustic signature. Moreover, incipient structural damage can be indicated by deviations of this signature from its original baseline pattern.

Unique features of this technology include its high sensitivity to structural damage, non-intrusiveness to the host structure, and low cost of implementation. These features have potential for enabling on-board damage monitoring of critical or inaccessible aerospace structures and components, such as aircraft wing joints, and both internal and external jet engine components. Several exploratory applications will be discussed.
X-Ray Refraction Characterization of the Interface Structure of Ceramics
Authors: Hentschel Manfred P. , Harbich Karl-Wolfram , Schors Joerg , Lange Axel
Published: August 2014

Advanced ceramics require specific methods for their nondestructive characterization. X-ray refraction techniques determine the specific surfaces and interfaces of high performance ceramics, composites and other low density materials down to nano-meter dimensions. X-ray refraction occurs due to the interference of phase shifted X-rays in ultra small angle X-ray scattering (USAXS) at objects above 100 nm size. Applications to monolithic ceramics and ceramic composites are presented. The well localized mean pore size of ceramics and the crack growth of ceramic composites are measured non-destructively.
Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions — Damage Assessment in Life Prediction Testing
Authors: Choi Sung R. , Gyekenyesi John P.
Published: August 2014

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.
Modeling the Tensile Behaviour of a SiC/SiC Composite by Master Curves
Authors: Shi J.
Published: August 2014

Scatter in test results is common for relatively brittle materials such as ceramic matrix composites. The scatter may come from differences in material processing conditions, specimen machining/handling and from variations in test parameters for nominally the same test material. Large scatter in test results makes material modeling difficult. In the past, master curve concepts have been proposed to reduce scatter in tensile data and to interpret fatigue/creep results. In this paper, one such concept is examined in detail by applying it to the recent tensile test results of a SiC/SiC composite. It was found that the way to construct master curves did not apply to the CMC studied and thus a new master curve was developed to better represent the tensile data. In addition, the test data were analysed statistically based on the new master curve.
Prediction of Acoustic Pressure Spectra in Combustion Systems Using Swirl Stabilized Gas Turbine Burners
Authors: Schuermans Bruno B. H. , Polifke Wolfgang , Paschereit Christian Oliver , van der Linden Jan H.
Published: August 2014

A method to predict pressure spectra of gas turbine combustion chambers with premixed, turbulent, swirl-stabilized flames is presented. The combustion system is represented as a network of acoustic elements, where each element is characterized by its transfer matrix. Analytic equations can be derived for most of the elements in such a network (e.g. ducts with variable cross-sectional area, sudden area changes etc.). However, the description of the acoustic properties of the burner and flame still require experimental input because of the complex interaction between the turbulent swirling flow, fuel supply and unsteady heat release. Acoustic excitation can be applied up-, and downstream of the burner in order to determine the transfer matrix of burner and flame. Due to the turbulent flow and combustion, the flame itself may also act as an independent source of sound. Thus, the burner does not only transmit and reflect incoming signals, but generates its own signal, independent of the acoustic state upstream and downstream. This quantity, the source-term, has been determined experimentally as well. Having determined the acoustic properties of all the elements (either analytically or by experiment) the thermoacoustic network can be built up. The frequency spectrum of the acoustic oscillations can then be investigated by solving the non-homogeneous system of equations, where the inhomogeneties are due to the source term of the flame. Because of the network approach, the influence of different acoustic boundary conditions on the frequency response has been determined. Application of the method to an atmospheric combustion test-rig with a gas turbine burner showed that the predicted frequency response and stability were in good agreement with experimental data.
Modelling of the Combustion Process of a Premixed DLE Gas Turbine
Authors: Eggels R. L. G. M.
Published: August 2014

To obtain a better understanding of the internal combustion processes of gas turbines, CFD computations of a combustion chamber, based on a Rolls-Royce industrial gas turbine, were performed. Minor simplifications are made to generate a 3-D rotational symmetric geometry. Computations are performed at typical gas turbine conditions and natural gas is used as the fuel. An internal Rolls-Royce CFD code is applied to perform the computations. This paper explains the models used for the CFD computations and describes the advantages and limitations on the applied models.

The combustion process has been modelled using a two-step global reaction mechanism and Intrinsic Low Dimensional Manifold (ILDM) reduced reaction mechanisms. The global reaction mechanisms are optimised for the considered operating conditions by modification of the reaction rates so that the same burning velocity and the amplitude CO-peak are obtained as predicted by detailed reaction mechanism (GRI 2.11, Bowman 1995). This optimisation is done considering a one-dimensional laminar flame. Although the global reaction mechanism is optimised for one particular operating condition, it appears that it is suitable for use over the entire range of operating conditions. The ILDM reduced reaction mechanisms are derived from GRI 2.11. Two ILDM tables are used to model two operating conditions, as they are specific for the pressure and inlet temperature. The interaction between turbulence and chemistry is modelled using presumed Probability Density Functions (PDF).

The flow field in the combustion chamber is studied at isothermal and combusting conditions. It appeared that the flow field for burning and non-burning circumstances is quite different.

There is a lack of experimental data so that it is not possible to verify the CFD results in detail. However, there is knowledge about the mechanisms by which the flame is stabilised and emissions are measured in the exhaust. The predicted flame front position agrees with that which is experimentally observed. The predicted increase of CO at low power is at the same order of magnitude as the measured emissions.
Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model
Authors: Polifke Wolfgang , Flohr Peter , Brandt Martin
Published: August 2014

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the Turbulent Flame speed Closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e. the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.
Gas Turbine Performance Using Carbon Dioxide as Working Fluid in Closed Cycle Operation
Authors: Jackson Anthony J. B. , Codeceira Neto Alcides , Whellens Matthew W. , Audus Harry
Published: August 2014

The world’s main atmospheric “greenhouse gas” is carbon dioxide (CO2). The CO2 content of the atmosphere continues to rise due to increasing world demand for energy, and thus further means are needed to achieve its abatement.

Most gas turbine powered electricity generating plants use hydro-carbon fuels and this inevitably produces CO2 in the engine exhaust. This paper discusses a scheme for concentrating the gas turbine exhaust CO2, thus facilitating its extraction. The scheme is a gas turbine operating synchronously in closed cycle, with CO2 as the working fluid. The additional CO2 and water produced in the combustion process are removed continuously.

CO2 and air have substantially different gas properties. This significantly affects the performance of the gas turbine. It is shown that any gas turbine designed to use air, and operating synchronously, would need considerable modifications to its compressor and combustion systems to use carbon dioxide as its working fluid.
Microturbine / Fuel-Cell Coupling for High-Efficiency Electrical-Power Generation
Authors: Massardo Aristide F. , McDonald Colin F. , Korakianitis Theodosios
Published: August 2014

Microturbines and fuel cells are currently attracting a lot of attention to meet future users needs in the distributed generation market. This paper addresses a preliminary analysis of a representative state-of-the-art 50 kW microturbine coupled with a high-temperature solid-oxide fuel cell (SOFC). The technologies of the two elements of such a hybrid-power plant are in a different state of readiness. The microturbine is in an early stage of pre-production and the SOFC is still in the development phase. It is premature to propose an optimum solution. Based on today’s technology the hybrid plant, using natural gas fuel, would have a power output of about 389 kW, and an efficiency of 60 percent. If the waste heat is used the overall fuel utilization efficiency would about 80 percent. Major features, parameters and performance of the microturbine and the SOFC are discussed. The compatibility of the two systems is addressed, and the areas of technical concern, and mismatching issues are identified and discussed. Fully understanding these, and identifying solutions, is the key to the future establishing of an optimum overall system. This approach is viewed as being in concert with evolving technological changes. In the case of the microturbine changes will be fairly minor as they enter production on a large scale within the next year or so, but are likely to be significant for the SOFC in the next few years, as extensive efforts are expended to reduce unit cost. It is reasonable to project that a high performance and cost-effective hybrid plant, with high reliability, will be ready for commercial service in the middle of the first decade of the 21st century.

While several microturbines can be packaged to give an increased level of power, this can perhaps be more effectively accomplished by coupling just a single gas turbine module with a SOFC. The resultant larger power output unit opens up new market possibilities in both the industrial nations and developing countries.
Managing Fuel Oil Nozzle Coking to Improve Gas Turbine Availability
Authors: Burgett Leo R. , Mercer Tim
Published: August 2014

Fuel oil nozzle coking has been a continuing problem for operators of gas turbine power plants. Over the years, several “solutions” to eliminate the coking of the fuel oil have been implemented to improve plant reliability and availability. When the fuel oil nozzle is “coked”, the startup and operation of the gas turbine are impaired and an unscheduled outage is needed to clean the fuel oil nozzle.

In 1997, a project was initiated to investigate the coking problem as it affects the operation of the dual fuel burner of the ABB ALSTOM POWER Inc. GT11N1 single burner (SBK) gas turbine. The GT11N1 SBK fuel oil nozzle (see FIGURE 1) was failing to operate properly because of “coked” fuel oil residue on its internal components (stationary and moveable). ABB ALSTOM POWER Inc. teamed with Savannah Electric & Power Company and collected data that indicated adequate nozzle cooling air could reduce the rate of fuel oil coking.

A nozzle cooling air system modification was installed on one of the ABB ALSTOM POWER Inc. 11N1 gas turbines at the Savannah Electric & Power Company McIntosh Power Plant. The modification included an AC motor driven air blower to provide cooling air to the fuel oil nozzle after shutdown of the gas turbine. Inspection of the components inside the fuel oil nozzle showed that very little fuel oil oxidation had occurred inside the nozzle during the three-month test period. By improving the fuel oil nozzle cooling air system, the coking problem can be better managed.
Heat Transfer and Pressure Distributions on a Gas Turbine Blade Tip
Authors: Azad Gm S. , Han Je-Chin , Teng Shuye , Boyle Robert J.
Published: August 2014

Heat transfer coefficient and static pressure distributions are experimentally investigated on a gas turbine blade tip in a five-bladed stationary linear cascade. The blade is a 2-dimensional model of a first stage gas turbine rotor blade with a blade tip profile of a GE-E3 aircraft gas turbine engine rotor blade. The flow condition in the test cascade corresponds to an overall pressure ratio of 1.32 and exit Reynolds number based on axial chord of 1.1×106. The middle 3-blade has a variable tip gap clearance. All measurements are made at three different tip gap clearances of about 1%, 1.5%, and 2.5% of the blade span. Heat transfer measurements are also made at two different turbulence intensity levels of 6.1% and 9.7% at the cascade inlet. Static pressure measurements are made in the mid-span and the near-tip regions as well as on the shroud surface, opposite the blade tip surface. Detailed heat transfer coefficient distributions on the plane tip surface are measured using a transient liquid crystal technique. Results show various regions of high and low heat transfer coefficient on the tip surface. Tip clearance has a significant influence on local tip heat transfer coefficient distribution. Heat transfer coefficient also increases about 15–20% along the leakage flow path at higher turbulence intensity level of 9.7% over 6.1%.
Flow and Heat Transfer at the Hub Endwall of Inlet Vane Passages — Experiments and Simulations
Authors: Roy R. P. , Squires K. D. , Gerendas M. , Song S. , Howe W. J. , Ansari A.
Published: August 2014

The heat transfer distribution on the hub endwall of a model turbine vane passage was studied experimentally and by numerical simulation. The experiments were carried out in a low speed wind tunnel featuring a linear cascade of scaled-up inlet vanes. Measurements were made both without and with secondary air injection through slots located upstream of the vane leading edge using the transient liquid crystal technique. Results are presented for ReCax, in = 6.76 × 104 and blowing ratios of zero (no secondary air injection) and 1.3. Simulations were performed on unstructured grids using Fluent. A near-wall description of the flow field was employed. Turbulent stresses in the momentum equations were closed using the Spalart-Almaras model, and the turbulent heat flux in the thermal energy equation was closed using a constant turbulent Prandtl number. The agreement between the measurements and the simulations is generally good.
Investigation of Heat Transfer in a Film Cooled Transonic Turbine Cascade: Part II — Unsteady Heat Transfer
Authors: Popp O. , Smith D. E. , Bubb J. V. , Grabowski H. C. , Diller T. E. , Schetz J. A. , Ng W. F.
Published: August 2014

This paper reports on an investigation of the heat transfer on the suction side of a transonic film cooled turbine rotor blade in a linear cascade. A shock wave is generated in a shock tube and passes into the cascade upstream of the blade row to simulate the interaction of a shock emerging from the trailing edge of an upstream nozzle guide vane on the downstream rotating blade row. The unsteady heat transfer caused by the shock wave passing over the suction side of the rotor blade is analyzed and compared to predictive models published in the literature. The investigation includes experiments with and without film cooling and a variation of the most relevant physical parameters. From the analysis and the comparison of the unsteady heat flux it is concluded that the heat transfer coefficient is not affected strongly by the passing shock. Most of the unsteady heat transfer is induced by the variation of temperature caused by the shock wave.
Augmentation of Stagnation Region Heat Transfer due to Turbulence From a DLN Can Combustor
Authors: Van Fossen G. James , Bunker Ronald S.
Published: August 2014

Heat transfer measurements have been made in the stagnation region of a flat plate with a circular leading edge. Electrically heated aluminum strips placed symmetrically about the leading edge stagnation region were used to measure spanwise averaged heat transfer coefficients. The maximum Reynolds number obtained, based on leading edge diameter, was about 100,000. The model was immersed in the flow field downstream of an approximately half scale model of a can-type combustor from a low NOx, ground based power-generating turbine. The tests were conducted with room temperature air; no fuel was added. Room air flowed into the combustor through six vane type fuel/air swirlers. The combustor can contained no dilution holes.

The fuel/air swirlers all swirled the incoming airflow in a counter clockwise direction (facing downstream). A 5-hole probe flow field survey in the plane of the model stagnation point showed the flow was one big vortex with flow angles up to 36° at the outer edges of the rectangular test section. Hot wire measurements showed test section flow had very high levels of turbulence, around 28.5%, and had a relatively large axial-length scale-to-leading edge diameter ratio of 0.5. X-wire measurements showed the turbulence to be nearly isotropic. Stagnation heat transfer augmentation over laminar levels was around 77% and was about 14% higher than predicted by a previously developed correlation for isotropic grid generated turbulence.
Effect of Partial Coating Blockage on Film Cooling Effectiveness
Authors: Bunker Ronald S.
Published: August 2014

A simple experimental study has been undertaken to determine the effects of typical turbine airfoil protective coatings on film cooling effectiveness due to the partial blockage of film hole exits by the coatings. Two types of film holes have been tested with and without coatings, a single row of axial round holes and a single row of axial shaped diffuser holes, each at an angle of 30-degrees to the surface. Both film rows have been manufactured with electro-discharge machining in flat plates, and have nominal throat diameters of 1.778 mm and a pitch-to-diameter spacing of 3.5. A series of tests was first performed without the use of protective surface coatings to provide the baseline film effectiveness performance. Each plate was then coated first with a layer of metallic bondcoat and then a layer of air-plasma sprayed thermal barrier coating (TBC), and the film tests repeated for the same coolant flow rates. Downstream thermocouple measurements are used to show the adiabatic film effectiveness along the midspan centerline location. Micrographs of the coated hole cross-sections depict the extent and form of coating blockage. Results show that significant degradation to film performance can result from coatings which are deposited in the hole exit regions, or inside the holes themselves, during the spray application process. Results also show that shaped film holes are generally very tolerant of coatings. The results of this study demonstrate the need for a film cooling and heat transfer database which accounts for the effects of film hole blockage as experienced in actual turbine operation.
Numerical and Experimental Investigations of the Influence of Different Swirl Ratios on the Temperature Streak Development in a 4-Stage Turbine
Authors: Bohn Dieter , Funke Harald , Heuer Tom , Bütikofer Jürg
Published: August 2014

In the development of modern gas turbines the increase in the turbine inlet temperature is restricted by the need for cooling the first stages of the turbine. In addition, the flow leaving the combustor is thermally inhomogeneous. Since the blade cooling has to be designed for the actual local hot gas temperatures, it is important to know how these temperature inhomogeneities develop and attenuate inside the multistage flow passage.

In this investigation the development of a circumferential and a radial temperature inhomogeneity inside a 4-stage turbine is analyzed at three different swirl ratios. Since the experimental setup allows a circumferential temperature streak, a radial temperature streak has also been applied at different swirl ratios to the same geometrical configuration for a numerical investigation.

The first stage has a significant impact on the attenuation and change in form of a circumferential temperature streak depending on the swirl. For the radial streak the hot streak segregation effect can be eliminated by increasing the swirl. Consequently, the temperature equalization process is weakened.
Thermal Conjugate Analysis of a First Stage Blade in a Gas Turbine
Authors: Takahashi Toshihiko , Watanabe Kazunori , Takahashi Takeshi
Published: August 2014

Three-dimensional numerical analyses of heat transfer were conducted by thermal conjugation of the inside and outside fields of a first stage rotor blade in a gas turbine, which consists of convection heat transfer and thermal conduction. The target of the analysis was a blade with multiple cooling holes. In order to make an accurate estimation of the blade temperature, the heat exchange in cooling passages, the outflow of cooling air and the effect of rotation were taken into account by the numerical method. The predicted distribution of surface temperature was in good agreement with the observed surface pattern on an actual blade. In addition case studies for bucket temperature were carried out using the present numerical method. It was shown that the temperature field inside the blade was severely influenced by the assumed distribution of inlet gas temperature and cooling air flow conditions. As a result, it is clear that the present analytical method is useful for prediction of blade temperature depending on various conditions in operation.
Conjugate Heat Transfer Analysis of an Engine Internal Cavity
Authors: Montenay A. , Paté L. , Duboué J. M.
Published: August 2014

The analysis of heat transfer in engine cavities or blade internal cooling systems is one of the most challenging work for aircraft engines designers for two main reasons. Firstly, the efficiency of such systems has a direct influence on both life and performance of these engines. Secondly, the available tools to predict heat transfer in both solid parts and surrounding cooling gases, i.e. Navier Stokes and conduction codes, are often used independently. An interaction model between the fluid and solid media is generally required and remains a difficult issue in engine configurations. A coupling procedure between a Navier-Stokes code and a conduction solver is therefore the only way to achieve heat transfer predictions in all flow situations. The objective of this work is to present such a procedure, which has been developed at Snecma and based on a Finite Volume Navier-Stokes code and a commercial Finite Element solver.

The first application showed in the paper demontrates, with an uncoupled calculation that the Navier-Stokes code MSD, from ONERA, is able to predict heat transfer with an acceptable accuracy. The discretization used in the solid to predict heat conduction is briefly presented. Then the steady state coupling procedure is exposed and validated with an analytical solution. Finally, a conjugate heat transfer computation in a rotor/rotor cavity of a real engine, with rotating solid disks, is described in detail.
Optimum Management System With Environmental Monitoring
Authors: Cerri G. , Evans R. , Frangopoulos C. A. , Parrella M. , Pitt R. U. , Psychogios J. , Salvador S. , Sepielli M. , Seyedan B.
Published: August 2014

This paper describes a software package designed to optimize the economic and environmental performance of industrial cogeneration plants. The optimization is through a procedure, which optimizes the load allocation between the plant components. The computer procedure is capable of recognizing equipment status and establishes the optimum load allocation between the plant components minimizing an objective function. The objective function is related to the economic and environmental models of the plant components and to the plant boundary conditions. Two prototypes were realized based on two real cogeneration plant. The paper discusses the general modular description of the components and block diagrams of the systems. The model calibrations and load allocations are analyzed and discussed.
Remote Monitoring and Diagnostics System for GE Heavy Duty Gas Turbines
Authors: Ozgur Dincer , Lakshminarasimha Arkalgud N. , Rucigay Richard , Morjaria Mahesh , Sanborn S.
Published: August 2014

The paper describes GE’s Remote Monitoring and Diagnostic (RM&D) system, its operation, its unique features and our experiences in applying it to improve performance and availability of heavy-duty gas turbine fleet worldwide. A key success factor of the system is that it relies upon an effective combination of advanced computer automation complemented by technical experts who have an in-depth understanding of the power generation equipment to achieve its objectives.

The RM&D system enables GE experts to remotely access operational data of power plants operating world wide, and exercise sophisticated algorithms, which can detect abnormal operating conditions. The experts, with ready access to the design information, operation and maintenance information and in-depth knowledge about the turbines, identify and track operational signatures, which may indicate potential problems. The real key is to be able to distinguish false indications from the ones that are true early indicators of potential problems. In this paper we describe a design approach for developing a successful RM&D system. We illustrate our approach through various examples of performance, vibration and combustion diagnostics scenarios.
Degradation in Gas Turbine Systems
Authors: Kurz Rainer , Brun Klaus
Published: August 2014

Any prime mover exhibits the effects of wear and tear over time. The problem of predicting the effects of wear and tear on the performance of any engine is still a matter of discussion. Because the function of a gas turbine is the result of the fine tuned cooperation of many different components, the emphasis of this paper is on the gas turbine and its driven equipment (compressor or pump) as a system, rather than on isolated components. We will discuss the effect of degradation on the package as part of a complex system (e.g. a pipeline, a reinjection station, etc.).

Treating the gas turbine package as a system reveals the effects of degradation on the match of the components as well as on the match with the driven equipment. This article will contribute insights into the problem of gas turbine system degradation. Based on some detailed studies on the mechanisms that cause engine degradation, namely

- changes in blade surfaces due to erosion or fouling, and the effect on the blade aerodynamics;

- changes in seal geometries and clearances, and the effect on parasitic flows,

- changes in the combustion system (e.g. which result in different pattern factors),

the effects of degradation will be discussed.

The study includes a methodology to simulate the effects of engine and driven equipment degradation. With a relatively simple set of equations that describe the engine behavior, and a number of linear deviation factors, which can easily be obtained from engine maps or test data, the equipment behavior for various degrees of degradation will be studied. A second model, using a stage by stage model for the engine compressor, is used to model the compressor deterioration. The authors have avoided to present figures about the speed of degradation, because it is subject to a variety of operational and design factors, that typically cannot be controlled entirely.
Development of a Passive Turbine Blade Damper Using Magnetomechanical Coating
Authors: Yen H. -Y. , Shen M. -H. Herman
Published: August 2014

The feasibility of using magnetomechanical coating for enhancing high damping capacity on turbine blades is investigated. An analytical procedure is developed for modeling the dynamic behavior of beams and blades coated with a plasma sprayed iron-chromium based coating. A probabilistic distribution function proposed by Smith and Birchak (1968, 1969) is used to evaluate and qualify the stress or strain distribution on the coating material. The equations of motion and associated boundary conditions are derived for uniform coated beams and blades. The resulting equation of motion is solved for simply supported and cantilevered beams and blades with a free surface coating layer by a closed form procedure and finite element approximation. The results show that a 2–5% beam and blade thickness free surface magnetomechanical coating layer can have a significant contribution on the damping enhancement and the reduction of vibratory stresses.
Instability of an Over-Hung Rigid Centrifuge Rotor Partially Filled With Fluid
Authors: Zhu Changsheng , Ulbrich H.
Published: August 2014

The objective of this paper is to experimentally investigate the instability of an over-hung rigid centrifuge rotor partially filled with fluid. Specific attention is paid to the developing process of rotor instability, the dynamical behaviour of rotor system while the instability occurs, and the whirling frequency and direction of rotor system within the unstable region. The effects of the fluid fill ratio on the whirling frequency, the unstable region and the rotor imbalance are also studied. The results clarify some issues and show many new phenomena about the instability of the rotor partially filled with fluid for the first time. The phenomena include the sub-synchronous frequency that does not result in the instability of rotor system and which disappears in the unstable region at the large fluid fill ratios; different whirling frequencies existing in the unstable region between the slowly increasing and decreasing rotational speed operations, hysteresis phenomenon in the upper side of the unstable region and the breaking-down phenomenon of the fluid free surface.
Flexible Bearing Supports, Using Experimental Data
Authors: Vázquez José A. , Barrett Lloyd E. , Flack Ronald D.
Published: August 2014

A laboratory rotor, representing a scaled down model of a three stage compressor supported by fluid film bearings on anisotropic flexible supports was analyzed. The support characteristics were measured at the bearing locations by exciting the bearing housings with electromechanical shakers and measuring the acceleration. Direct, cross-coupled and cross talk accelerance between supports were measured. Unbalance response and stability analyses of the rotor were performed using polynomial transfer functions extracted from the measured accelarance data. The predicted critical speeds and instability threshold agree with measured data. Predictions using other support models are included to show the effectiveness of this method.
Non-Uniform Flow in a Compressor due to Asymmetric Tip Clearance
Authors: Song Seung Jin , Cho Seung Ho
Published: August 2014

This paper presents an analytical study of flow redistribution in a compressor stage due to asymmetric tip clearance distribution. The entire stage is modeled as an actuator disc, and it is assumed that upstream and downstream flow fields are determined by the local tip clearance. The flow is assumed to be inviscid and incompressible. First, an axisymmetric flow model is used to connect upstream and downstream flows. Second, a linear perturbation approximation is used for non-axisymmetric analysis in which each flow variable is assumed to consist of a mean (axisymmetric value) plus a small perturbation (asymmetric value). Thus, the perturbations in velocity and pressure induced by the tip clearance asymmetry are predicted. Furthermore, rotordynamic effects of such flow non-uniformity are examined as well.
Aerodynamic Response of Turbomachinery Blade Rows to Convecting Density Wakes
Authors: Wijesinghe H. S. , Tan C. S. , Covert E. E.
Published: August 2014

A two–dimensional computational study was conducted to characterize the density wake induced force and moment fluctuations on a compressor blade row. The flow simulations indicate unsteady blade excitation generated by: (1) density wake fluid directed to the blade suction surface, (2) axial deflection of the blade passage shock wave position and (3) formation of a separation bubble on the blade suction surface. The blade force and moment fluctuation amplitudes are found to scale with the nondimensional density wake width w/c and a non–dimensional density parameter ρ*.
Life Assessment of Turbine Components Under Random Loading
Authors: Rusin Andrzej M. , Kosman Gerard P. , Daciuk Łukasz K.
Published: August 2014

Life assessment of gas turbine components under random loading is presented in the paper. Two examples were considered. One examines changes in the probability of failure of an expansion turbine rotor after an increase of the gas temperature. The other assesses the probability of failure of a shell due to fatigue.
Thermoelastic Stress Analysis: A NDE Tool for Residual Stress Assessment of Metallic Alloys
Authors: Gyekenyesi Andrew L. , Baaklini George Y.
Published: August 2014

The primary objective of this report involves studying and developing various experimental techniques for accurate measurement of the mean stress effect in Thermoelastic Stress Analysis (TSA, also recognized as SPATE: Stress Pattern Analysis by Thermal Emission). The analysis of cyclic mean stresses at the coupon level directly relates to the measurement of residual stresses in structures. In a previous study by the authors1, it was shown that cyclic mean stresses significantly influenced the TSA results for titanium and nickel based alloys, although, difficulties were encountered concerning the quantification of the mean stress effect because of large test-to-test variations. This study continues the effort of accurate direct measurements of the mean stress effect by implementing various experimental modifications. In addition, a more in-depth analysis is included which involves analyzing the second harmonic of the temperature response. By obtaining the amplitudes of the first and second harmonics, the stress amplitude and the mean stress at a given point on a structure subjected to a cyclic load can be simultaneously obtained. The rather complex analysis of the temperature response involves obtaining the first and second harmonic amplitudes for 16384 infrared detectors (128 × 128 focal plane array). Upon establishing a protocol for mean stress measurements in the laboratory using the TSA technique, the next step is to utilize the method to assess residual stress states in complex structures during manufacturing and life.
Effect of the Decaying Overshoot of the Rankine Vortex on the Axial Flow Field Behind the Inlet Guide Vane of Centrifugal Compressors
Authors: Chen Y. N. , Hagelstein D. , Kassens I. , Haupt U. , Rautenberg M.
Published: August 2014

The present analysis of the experimental results obtained by Kassens (1997), and Kassens and Rautenberg (1998) about the variation of the axial velocity profile of the rotating flow travelling downstream the inlet guide vane revealed the controlling effect of the decaying overshoot of the Rankine vortex in this process.

The disappearance of the overshoot indicates the stop of its excessive drive on the rotating flow. It will be shown that this decay process is directly connected to the braking effect of the impeller blades on the rotating flow generated by the IGV. For the case of an IGV setting angle of 60°, the flow with a very strong swirl component generated by the IGV outlet cannot be admitted by the inlet of the impeller without shock. This shock acts as a braking force of the impeller blades on the swirl component of the approaching flow, a process that is expressed as the spin-down of the swirling flow. A secondary toroidal ring vortex in the frontal zone of the impeller will be generated by the fundamental flow. The recirculation velocity of this toroidal ring vortex has an axial component, which directs towards the impeller in the outer zone of the suction duct, but turns away from the impeller in its central zone.

At the same time, the field of the uniform tangential velocity of the IGV outlet is getting into the influence sphere of the spin-down mentioned. As a consequence, it will be converted into the flow field of a potential vortex, which is accompanied by a field of axial velocity having a normal value uniformly distributed in its outer potential zone and a strongly peaked value over its central core. This process is similar to that of the flow field in a bathtub vortex during draining its fluid out of the central pipe. The new flow field consists of a secondary toroidal ring vortex superimposed on the fundamental flow. The rotating sense of this new toroidal ring vortex is just opposite to that formed in front of the impeller.

We then have a pair of toroidal ring vortices staying one behind another between the IGV outlet and the impeller inlet. Each member of the pairs serves as the border for the other one. It can thus be concluded that the pair is induced simultaneously by the spin-down of the swirling flow of the IGV outlet brought about by the braking effect of the impeller blades.
Impeller-Diffuser Interaction in Centrifugal Compressor
Authors: Shum Y. K. P. , Tan C. S. , Cumpsty N. A.
Published: August 2014

A study has been conducted, using an unsteady three-dimensional Reynolds-averaged Navier-Stokes simulation, to define the effect of impeller-diffuser interaction on the performance of a centrifugal compressor stage. The principal finding from the study was that the most influential aspect of this unsteady interaction was the effect on impeller tip leakage flow. In particular, the unsteadiness due to the upstream potential effect of the diffuser vanes led to larger viscous losses associated with the impeller tip leakage flow. The consequent changes at the impeller exit with increasing interaction were identified as reduced slip, reduced blockage, and increased loss. The first two were beneficial to pressure rise while the third one was detrimental. The magnitudes of the effects were examined using different impeller-diffuser spacings and it was shown that there was an optimal radial gap size for maximum impeller pressure rise. The physical mechanism was also determined: when the diffuser was placed closer to the impeller than the optimum, increased loss overcame the benefits of reduced slip and blockage. The findings provide a rigorous explanation for experimental observations made on centrifugal compressors. The success of a simple flow model in capturing the pressure rise trend indicated that although the changes in loss, blockage and slip were due largely to unsteadiness, the consequent impacts on performance were mainly one-dimensional. The influence of flow unsteadiness on diffuser performance was found to be less important than the upstream effect, by a factor of seven in terms of stage pressure rise in the present geometry. It is thus concluded that the beneficial effects of impeller-diffuser interaction on overall stage performance come mainly from the reduced blockage and reduced slip associated with the unsteady tip leakage flow in the impeller.