bluuebunny/crossref_metadata_2025 huggingface dataset:
Impairment of Host Resistance to Helminthes with Age in Murine Small Intestine
Authors: Morimoto M. , Saito C. , Muto C. , Akamatsu Y. , Chiba T. , Abe T. , Azuma N. , Suto Y.
Published: December 2014

Age‐associated alterations of Th2 immune responses against nematode parasites are largely unknown. We investigated primary and memory responses against two types of gastrointestinal nematode parasites, Heligmosomoides polygyrus (Hp) and Nippostrongylus brasiliensis (Nb), in aged mice. The small intestinal gene expression of Th2 cytokines was almost unchanged after primary (Nb and Hp) and secondary infection (Hp) in aged mice in contrast to strongly increased small intestinal gene expression of Th2 cytokines in young (3‐month‐old) mice. Mucus production decreased (Nb), and worm expulsion was impaired (Nb and Hp) compared with the young mice. Immunofluorescent staining revealed that after Hp infection, the number of alternatively activated macrophages, which are induced by Th2 cytokines, was lower in the aged mice. On the other hand, the number of CD4+ T cells recruited to the worm cysts was normal compared with the young mice. These results suggest that migration of CD4+ T cells to the host–parasite interface is not affected by ageing. Alterations in Th2 immune responses in aged mice might be due to inappropriate or insufficient activation of CD4+ T cells in the submucosa.
Fractional Price Matching Policies Arising from the Ocean Freight Service Industry
Authors: Lee Chung‐Yee , Tang Christopher S. , Yin Rui , An Jaehyung
Published: December 2014

We consider a situation in which shippers (customers) can purchase ocean freight services either directly from a carrier (service provider)in advance or from the spot market just before the departure of an ocean liner. The price is known in the former case, while the spot price is uncertain ex‐ante in the latter case. Consequently, some shippers are reluctant to book directly from the carrier in advance unless the carrier is willing to “partially match” the realized spot price when it is lower than the regular price. This study is an initial attempt to examine if the carrier should bear some of the “price risk” by offering a “fractional” price matching contract that can be described as follows. The shipper pays the regular freight price in advance; however, the shipper will get a refund if the realized spot price is below the regular price, where the refund is a “fraction” of the difference between the regular price and the realized spot price. By modeling the dynamics between the carrier and the shippers as a sequential game, we show that the carrier can use the fractional price matching contract to generate a higher demand from the shippers compared to no price matching contract by increasing the “fraction” in equilibrium. However, as the carrier increases the “fraction,” the carrier should increase the regular price to compensate for bearing additional risk. By selecting the fractional price matching contract optimally, we show that the carrier can afford to offer this price matching mechanism without incurring revenue loss: the optimal fractional price matching contract is “revenue neutral.”
Concordance of Noncarcinogenic Endpoints in Rodent Chemical Bioassays
Authors: Wang Bing , Gray George
Published: December 2014

Prediction of noncancer toxicologic outcomes in rodent bioassays of 37 chemicals from the National Toxicology Program was evaluated. Using the nonneoplastic lesions noted by NTP pathologists, we evaluate both agreement in toxic lesions across experiments and the predictive value of the presence (or absence) of a lesion in one group for other groups. We compare lesions between mice and rats, male mice and male rats, and female mice and female rats in both short‐term and long‐term bioassays. We also examine whether lesions found in a specific organ in a short‐term test are also found in the long‐term test of the same chemical. We find agreement (concordance) across species for specific lesions, as evaluated by the Kappa statistic, ranging from 0.58 (for concordance of nasal lesions between female mice and rats in long‐term studies) to −0.14 (lung lesions between mice and rats in long‐term studies). Predictive values are limited by the relatively small numbers of observations of each type of lesion. Positive predictive values range from 100% to 0%. Comparing the lesions found in short‐term tests to those found in long‐term tests resulted in Kappa statistic values from 0.76 (spleen lesions in male rats) to −0.61 (lung lesions in female mice). Positive predictive values of short‐term tests for long‐term tests range from 70% to 0%. Overall, there is considerable uncertainty in predicting the site of toxic lesions in different species exposed to the same chemical and from short‐term to long‐term tests of the same chemical.
Evaluation of Inhaled Versus Deposited Dose Using the Exponential Dose‐Response Model for Inhalational Anthrax in Nonhuman Primate, Rabbit, and Guinea Pig
Authors: Gutting Bradford W. , Rukhin Andrey , Mackie Ryan S. , Marchette David , Thran Brandolyn
Published: December 2014

The application of the exponential model is extended by the inclusion of new nonhuman primate (NHP), rabbit, and guinea pig dose‐lethality data for inhalation anthrax. Because deposition is a critical step in the initiation of inhalation anthrax, inhaled doses may not provide the most accurate cross‐species comparison. For this reason, species‐specific deposition factors were derived to translate inhaled dose to deposited dose. Four NHP, three rabbit, and two guinea pig data sets were utilized. Results from species‐specific pooling analysis suggested all four NHP data sets could be pooled into a single NHP data set, which was also true for the rabbit and guinea pig data sets. The three species‐specific pooled data sets could not be combined into a single generic mammalian data set. For inhaled dose, NHPs were the most sensitive (relative lowest LD50) species and rabbits the least. Improved inhaled LD50s proposed for use in risk assessment are 50,600, 102,600, and 70,800 inhaled spores for NHP, rabbit, and guinea pig, respectively. Lung deposition factors were estimated for each species using published deposition data from Bacillus spore exposures, particle deposition studies, and computer modeling. Deposition was estimated at 22%, 9%, and 30% of the inhaled dose for NHP, rabbit, and guinea pig, respectively. When the inhaled dose was adjusted to reflect deposited dose, the rabbit animal model appears the most sensitive with the guinea pig the least sensitive species.
Civil Society and Political Participation: What Type of Political Participation is Influenced by Community Level Involvement in Civil Society?
Authors: Wallman Lundåsen Susanne
Published: December 2014

The aim of this paper is thus to further explore the relationship between involvement in voluntary associations at the community level and specific forms of political participation. We pose the following questions. Do voluntary associations contribute to specific forms of individual political participation in a consociational context? Do voluntary associations encourage forms of political participation aimed at directly interacting with the policy process, or do they promote extraparliamentary forms of protest? The study contributes with testing three different measurements of community level involvement in voluntary associations and their correlations with individual level political participation. The empirical data is based upon a mulitilevel sample of 4232 individuals located in 33 different Swedish municipalities. Results show that only direct contacts with local elites are significantly correlated with community level participation in civil society organizations. This result may be interpreted as indicating that local voluntary associations contribute to the local political culture.
Recreational potential of the regulated watercourse Ostravice river in Ostrava urban area
Authors: Lampartová I. , Schneider J.
Published: December 2014

Water coursess are segments in the country increasing its recreational potential. The current goal of revitalization measures in the landscape primarily consists of the optimization of landscape water regime, incl. flood control measures and the promotion of biodiversity, but the current philosophy speaks of multifunctional land usage. In the society there has been indicated the necessity for recreation, because a large part of the population lives in urban settlements and is employed in an artificial technical environment that has largely inadequate sanitary conditions (unfavourable microclimate, noise, dust, etc.). Recreation as a social phenomenon is therefore a permanent part of the lifestyle in economically developed countries. However, the revitalization is currently underappreciated in the Czech Republic and it is important to increase recreational potential of the landscape. The subject of this article is evaluation of regulated watercourse Ostravice river in Ostrava urban area. The model area of river Ostravice in Ostrava region is described here. In the model area is evaluated some elements of recreational potential of revitalization by the proposed methodology. The outcome of the work is to propose an ongoing systematic procedure for assessment of the relevance of revitalization actions in terms of the recreational potential of the landscape and their impact on the development opportunities of the region.
Ecological stability of alpine treeline ecotone formed by beech (Fagus sylvatica L.) in Ďumbier Low Tatras
Authors: Mičovský J.
Published: December 2014

The paper analyses the results of the ecological stability research of beech (Fagus sylvatica L.) stands at the alpine tree-line ecotone in the Ďumbier part of Law Tatras. The applied methodology by Vološčuk (2000) is based on the approximation of the current tree species composition with respect to the original ones, crown ratio, slenderness quotient, sanitary coefficient and vertical species profile of the stands. The resulting value of ecological stability of the stands, typologically classified into a group of forest types Fageto-Aceretum humile, was increased by approximation of 80.0–82.5%, slenderness quotient 0.55–0.60 m.cm−1 and sanitary coefficient. Vitality was assessed with regard to the most common damage to individual, more than 160-year-old beech trees at the alpine treeline ecotone in the form of necrosis. Vertical and horizontal structure of the stands was influenced mainly by dense tree clusters. The value of ecological stability was decreased by average crown ratio of individual trees ranging from 0.47–0.57. Based on the final index of ecological stability ES 16–24, beech forests in the alpine treeline ecotone may be considered as very stable.
Effect of differentiated liming on the development of acidity of surface forest soil
Authors: Podrázský Vilém
Published: December 2014

Results obtained during 16 years of the experiment are presented. Extreme site conditions are determined by: 8thvegetation altitudinal zone, podzolic soil and harsh climate – average annual temperature 4 °C, average annual precipitation around 1200 mm. Effects of surface experimental liming were studied on immission clear-cuts in long time period, study area is located on the Velká Deštná locality on the main Orlické hory Mts. range. Research plots were established in spring of 1988, studies of liming effects were performed in the period 1987–2004. On particular plots, 0, 1308, 2826, 3924 and 8478 kg/ha of fine limestone (grain size under 1 mm) was distributed by hands on the soil surface. Results are available for the forestry practice, research has to continue in the future – potential of negative liming impacts is topical here, consisting in humus mineralization and nutrients losses. Maximum effects on the soil reaction were observed in 8–10 years after limestone application at the soil surface (F – horizon) and in the period 10–15 years lower (H, A – horizons). Base saturation dynamics shows the time delay 2–4 years following pH values changes.
Assessment of the Norway spruce plantation growth on a mountain forest site disturbed by windrowing and ameliorated by green alder
Authors: Šach F. , Černohous V.
Published: December 2014

Mechanized windrowing in the top region of the Orlické hory Mts. has disturbed hundreds of hectares of immission clearcuts during eighties. The soil surface on the Velká Deštná Mountain was disturbed in 1987. One year later the Forest Research Station at Opočno established on this place the long-term research plot. Degree and extent of soil surface disturbance were recorded. Besides other experiments, the experimental Norway spruce plantation was established on three strips: control strip, strip treated by fertilizers or limestone (1991), and strip ameliorated byAlnus viridisplantation (1992). The effect of site degradation by mechanized windrowing has been indicated by young spruce growth for a long time period. The assessment of 17 years old spruce growth on the control strip shows significantly greater height increment on negligibly disturbed sites comparing to that on remarkably and very remarkably disturbed sites. Amelioration of spruce trees brings perspective outcomes on the strip biologically amended byAlnus viridis. High atmospheric depositions especially of nitrogen compounds, fungal disease by Ascocalyx abietina, climatic fluctuations, and high values of groundlevel ozone have brought new problems into spruce plantation performance since 1999. Nevertheless, it has been more substantially reduced by green alder.
Stress and Fracture Analyses of Solar Silicon Wafers During Suction Process and Handling
Authors: Saffar S. , Gouttebroze S. , Zhang Z. L.
Published: December 2014

Solar wafer/cell breakage depends on the combination of the stresses generated in the handling and the presence of structural defects such as cracks. Suction process is a common loading during silicon wafer handling. This paper presents a systematic static and dynamic analysis of the suction process. Optimum suction pad diameter and locations are obtained by minimizing the stress distribution under both static and dynamic loading, and the effect of the impact time on the crack driving force is also investigated in this optimum situation. The results show that the four pads configuration with diameter of 20 mm placed in a rhombus shape with 18 and 38 mm diagonal lengths yields lowest maximum principle stress among the cases analyzed. In the dynamic fracture analyses, the maximum J integral appears at 800 and 1400 μs for continued holding and unloading cases after reaching the maximum load, respectively. The J integral for the unloading cases are always smaller than the holding cases. It has been found that when the impact time is longer than 3 s and 5600 μs the dynamic fracture mechanics analysis of the suction impact process can be replaced by a static fracture mechanics analysis for the holding and unloading cases, respectively.
A Novel Model for Daily Energy Production Estimation of Grid-Connected Photovoltaic System
Authors: Fen Li , Quanquan Yan , Shanxu Duan , Jinbin Zhao , Nianjun Ma , Zhenghong Chen
Published: December 2014

The rapidly growing markets for distributed and centralized grid-connected photovoltaic (PV) systems require the reliable and available information for reflecting and predicting the electricity generation of PV systems. In this work, the relationship between PV energy production and meteorological environmental factors is discussed by correlation analysis and partial correlation analysis. Meteorological data available, including the clearness index, diurnal temperature range, the global radiation on horizontal surface, and etc., are used as inputs. Then, according to factor analysis, these various interaction factors are extracted as two independent common factors. Finally, a new method based on factor analysis and multiple regression analysis has been developed for estimating the daily PV energy production. The meteorological data are collected from Wuhan Observatory, and power data from a roof grid-connected PV system located at Huazhong University of Science and Technology in Wuhan. The data of the whole year (from March in 2010 to February in 2011) has been used for model calibration and the following data of March in 2011 is used to test the predictions. The results show that there is significant positive correlation between the estimated values and the measured values; the rMBE per day is −0.14%, MAPE per day is 13.60% and rRMSE per day is 18.04%.
Two-Phase Flow With Phase Change in Porous Channels
Authors: Tomar Gaurav
Published: December 2014

Phase change heat transfer in porous media finds applications in various geological flows and modern heat pipes. We present a study to show the effect of phase change on heat transfer in a porous channel. We show that the ratio of Jakob numbers based on wall superheat and inlet fluid subcooling governs the liquid–vapor interface location in the porous channel and below a critical value of the ratio, the liquid penetrates all the way to the extent of the channel in the flow direction. In such cases, the Nusselt number is higher due to the proximity of the liquid–vapor interface to the heat loads. For higher heat loads or lower subcooling of the liquid, the liquid–vapor interface is pushed toward the inlet, and heat transfer occurs through a wider vapor region thus resulting in a lower Nusselt number. This study is relevant in the designing of efficient two-phase heat exchangers such as capillary suction based heat pipes where a prior estimation of the interface location for the maximum heat load is required to ensure that the liquid–vapor interface is always inside the porous block for its operation.
Effects of Surface Roughness on Heat Transfer and Aerodynamic Performance of Turbine Airfoils
Authors: Abuaf N. , Bunker R. S. , Lee C. P.
Published: December 2014

Aerodynamic flow path losses and turbine airfoil gas side heat transfer are strongly affected by the gas side surface finish. For high aero efficiencies and reduced cooling requirements, airfoil designs dictate extensive surface finishing processes to produce smooth surfaces and enhance engine performance. The achievement of these requirements incurs additional manufacturing finishing costs over less strict requirements. The present work quantifies the heat transfer (and aero) performance differences of three cast airfoils with varying degrees of surface finish treatment. An airfoil which was grit blast and Codep coated produced an average roughness of 2.33 μm, one which was grit blast, tumbled, and Aluminide coated produced 1.03 μm roughness, and another which received further post coating polishing produced 0.81 μm roughness. Local heat transfer coefficients were experimentally measured with a transient technique in a linear cascade with a wide range of flow Reynolds numbers covering typical engine conditions. The measured heat transfer coefficients were used with a rough surface Reynolds Analogy to determine the local skin friction coefficients, from which the drag forces and aero efficiencies were calculated. Results show that tumbling and polishing reduce the average roughness and improve performance. The largest differences are observed from the rumbling process, with smaller improvements realized from polishing.
A Probabilistic Approach to Aircraft Turbine Rotor Material Design
Authors: Leverant Gerald R. , Littlefield David L. , McClung R. Craig , Millwater Harry R. , Wu Justin Y.
Published: December 2014

A probabilistic design code is being developed for high energy disks and rotors used in aircraft gas turbine engines. This code is intended to augment, not replace, the current safe-life approach to the design of these critical components. While the code will ultimately be applicable to a range of disk alloys, initial emphasis has been placed on titanium alloys containing hard alpha defects. The approach involves developing an enhanced defect distribution for hard alpha, obtaining crack initiation data for hard alpha and fatigue crack growth data for three titanium alloys, and integrating this information into a software code that is sufficiently efficient that it can be routinely used for design and life prediction.
The Influence of Coolant Supply Geometry on Film Coolant Exit Flow and Surface Adiabatic Effectiveness
Authors: Burd Steven W. , Simon Terrence W.
Published: December 2014

Experimental hot-wire anemometry and thermocouple measurements are taken to document the sensitivity which film cooling performance has to the hole length and the geometry of the plenum which supplies cooling flow to the holes. This sensitivity is described in terms of the effects these geometric features have on hole-exit velocity and turbulence intensity distributions and on adiabatic effectiveness values on the surface downstream. These measurements were taken under high freestream turbulence intensity (12%) conditions, representative of operating gas turbine engines. Coolant is supplied to the film cooling holes by means of (1) an unrestricted plenum, (2) a plenum which restricts the flow approaching the holes, forcing it to flow co-current with the freestream, and (3) a plenum which forces the flow to approach the holes counter-current with the freestream. Short-hole (L/D = 2.3) and long-hole (L/D = 7.0) comparisons are made. The geometry has a single row of film cooling holes with 35°-inclined streamwise injection. The film cooling flow is supplied at the same temperature as that of the freestream for hole-exit measurements and 10°C above the freestream temperature for adiabatic effectiveness measurements, yielding density ratios in the range 0.96–1.0. Two coolant-to-freestream velocity ratios, 0.5 and 1.0, are investigated. The results document the effects of (1) supply plenum geometry, (2) velocity ratio, and (3) hole L/D.
ARX Linear Model Set-Up for Fault Diagnosis of Gas Turbine Sensors
Authors: Bettocchi R. , Spina P. R.
Published: December 2014

The diagnosis of gas turbine sensor faults requires models of the system to calculate estimates of the measured output system variables.

The model set-up phase is of great importance since the reliability of the diagnostic tool depends on the model accuracy.

In the paper two different methodologies of I/O linear model set-up are analyzed and compared to find the more simple and general one.

The first methodology consists in obtaining the I/O linear models by directly linearizing the physical laws (system modeling).

The second one uses statistical methods (system identification) to calculate model parameters from time series data measured on the machine. The models used are of the ARX (Auto Regressive with eXternal input) type. The number of models and the measured variables correlated by each of them have been determined in order to obtain unambiguous fault signatures for each sensor.

The system identification method proves to be more suitable to the system modeling because of its greater simplicity in the fault diagnosis application.
A Direct Coal-Fired Combustion Turbine Power System Based on Slagging Gasification With In-Situ Gas Cleaning
Authors: Newby Richard A. , Bannister Ronald L.
Published: December 2014

Westinghouse began the development of a compact, entrained, slagging gasifier technology utilizing in-situ fuel gas cleaning for combustion turbine power cycles in 1986. The slagging gasifier is air-blown, and produces a hot, low-heating value fuel gas that can be combusted and quenched to combustion turbine inlet temperatures while maintaining low levels of NOx emissions. The U.S. Department of Energy sponsored engineering studies and pilot testing during the period 1986 to 1992. This work has shown that the technology has promise, although performance improvements are required in some key areas. A major challenge has been the development of in-situ removal of sulfur, alkali vapor, and particulate to low enough levels to permit its use in combustion turbine power systems without additional, external gas cleaning. This paper reviews the Westinghouse slagging gasifier, direct coal-fired turbine power generation concept; the pilot test results; and the current development activities that Westinghouse is engaged in.
Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors
Authors: Furukawa Masato , Saiki Kazuhisa , Nagayoshi Kenya , Kuroumaru Motoo , Inoue Masahiro
Published: December 2014

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 degrees and 45 degrees, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in the behavior of the tip leakage flow substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.
The Flowfield Calculations of a Centrifugal Pump With Volute
Authors: Chen Shih H. , Liaw Lu-Fu
Published: December 2014

The volute very frequently has profound effect on impeller performance. It can cause the impeller to work very inefficiently and cause large vibrations if it is designed improperly. Although advanced computational fluid dynamic methods have been used extensively in impeller design, the volute has been neglected or considered independently. In the present study, a finite volume computational method is used to solve the three-dimensional Reynolds-averaged flow field of an impeller with a volute. The study is aimed at the understanding of the effect of volute on the performance of impeller and its associated unsteady effect. As its configuration and solution procedure of the physical problem is more complicated than a traditional single blade passage analysis, the grid generation and solution procedure will be described in more detail. A traditional single blade passage without volute and at steady state condition is calculated first. Later a volute is added and the calculated results are compared with single-passage calculation. It is found that the predicted mean performance of the impeller and volute agrees better with the test data, while the fluctuation of the flow is significant, especially while the trailing edges of impeller is passing the volute tongue.
The Effect of Tip Clearance on the Development of Loss Behind a Rotor and a Subsequent Nozzle
Authors: Kaiser I. , Bindon J. P.
Published: December 2014

In a previous work of a similar nature, the performance of a low speed axial turbine with a second stage nozzle was examined. Present findings suggest some interesting phenomena, including the effect of tip clearance on the flow within the rotor and show that poor resolution of a transducer and insufficient data points near the endwall were responsible for a number of incorrect conclusions in the original study.

In terms of blade tip geometry, a standard flat tip shape was found to deliver only a marginally better performance when compared to two streamlined shapes previously investigated and a double squealer tip. Although contemporary opinion suggests that a streamlined tip should increase the leakage flow and hence cause greater mixing losses, the machine efficiency was not significantly reduced. This is an exciting result since it suggests that a streamlined tip shape can be used to alleviate the problem of blade tip burnout without significantly reducing machine efficiency.

The flow behind the rotor (ie time averaged) was found to be in reasonable agreement with linear cascade data when time averaged even though the latter did not include any effects of relative motion. An increase in clearance was seen to reduce the Euler work and also to cause a deficit of mass flow across the remainder of the blade right down to the hub.

As in the previous study, the second stage nozzle efficiency was seen to be independent of tip clearance or tip shape. However, the improvement in comparison with the first nozzle was not found to be as large, due to a previously undetected very thin ring of high energy leakage fluid. When this is taken into account, the efficiency of the second stage nozzle is comparable to the first.

The second nozzle was seen to have a flow straightening effect on the undetected high energy leakage flow, causing a rapid mixing process within these downstream blade passages. The growth of secondary flow was reduced at both the hub and the tip and this is believed to result in a slight reduction in loss. The outlet flow was closer to design conditions than that of the first stage nozzle.
Development and Optimization of Advanced Atomizers for Application in Premix Ducts
Authors: Maier Georg , Willmann Michael , Wittig Sigmar
Published: December 2014

Lean premixed prevaporized combustion (LPP) is a promising approach for the reduction of emissions in gas turbine combustion. Typically, modern gas turbines operate at high pressure and high temperature flow conditions, giving rise to very short self ignition times. Consequently, the residence time of the mixture in the premix duct has to be minimized. Complete fuel vaporization and mixing can only be achieved by an improvement of the atomization process towards a fine droplet size spectrum over the whole range of operating conditions. In this paper an air assisted pressure swirl atomizer is introduced and analyzed. The special design of the nozzle under investigation enhances the interaction between the liquid sheet of the atomizer and the co-flowing air around the nozzle. The visualization of the atomization process gives detailed insight into the fundamental atomization phenomena of the atomizer. In addition, extensive measurements of droplet size distributions describe the dependence of the atomization process on liquid flow rate and air velocity, respectively. All phenomena occurring are explained in detail by means of a theoretical analysis of the flow pattern. With the help of this kinematic model, it can be shown why co-rotating swirls of atomization air and liquid cone lead to better atomization than counter rotating swirls.
The Development of a Dry Low NOx Combustion System for the EGT Typhoon
Authors: Kowkabi Mahmoud , Noden Richard , De Pietro Simon
Published: December 2014

This paper describes the development of an ultra low NOx (i.e. sub 10 ppmvd) combustion system from the successful completion of a high pressure rig programme, to the installation of the system on a gas turbine in commercial operation. It includes a detailed description of early screening tests for DLN concepts and an explanation of how these were developed on both rig and engine test bed.

Specific discussions include the concepts and technology for:

1) NOx reduction

2) Optimisation of premix turndown for carbon monoxide control at part load conditions

3) Control of combustion driven pressure oscillation (combustor dynamics) and the failures resulting from the lack of control.

In addition to the DLN aerothermal development, an outline description of the combustor mechanical design and the control and systems modification from the conventional combustion system is given.
Aero-Thermal Design and Testing of Advanced Turbine Blades
Authors: Haendler M. , Raake D. , Scheurlen M.
Published: December 2014

Based on the experience gained with more than 80 machines operating worldwide in 50 and 60 Hz electrical systems respectively, Siemens has developed a new generation of advanced gas turbines which yield substantially improved performance at a higher output level. This “3A-Series” comprises three gas turbine models ranging from 70 MW to 240 MW for 50 Hz and 60 Hz power generation applications.

The first of the new advanced gas turbines with 170 MW and 3600 rpm was tested in the Berlin factory test facility under the full range of operation conditions. It was equipped with various measurement systems to monitor pressures, gas and metal temperatures, clearances, strains, vibrations and exhaust emissions.

This paper presents the aero-thermal design procedure of the highly thermal loaded film cooled first stage blading. The predictions are compared with the extensive optical pyrometer measurements taken at the Siemens test facility on the V84.3A machine under full load conditions. The pyrometer was inserted at several locations in the turbine and radially moved giving a complete surface temperature information of the first stage vanes and blades.
Evaluation of a 3D Viscous Code for Turbomachinery Flows
Authors: Calvert W. John , Stapleton Andrew W. , Emmerson Paul R. , Buchanan Cecil R. , Nott Christopher M.
Published: December 2014

Computational Fluid Dynamics (CFD) codes play an increasingly important role in the design and development of turbomachinery for modern gas turbine engines. As a result additional emphasis is being placed on the evaluation of the codes to ensure that they are working correctly and to indicate the accuracy which is likely to be achieved in practice. At DERA a programme of work has been carried out to evaluate the TRANSCode 3D viscous flow code, which was developed from the BTOB3D solver written by Dawes in 1986. A three part strategy for the validation and calibration of the code was adopted, covering comparisons with boundary layer test cases, Q3D compressor cascades and full 3D cases. The results indicated that the grids currently employed for turbomachinery flows limit the accuracy achieved for cases where there is significant laminar flow. For turbulent flows the Baldwin-Lomax turbulence model gives reasonably accurate results for 2D flows in near equilibrium, but it is less satisfactory for more complex flows, when the concept of a simple 2D boundary layer does not apply, and for strong shock wave/boundary layer interactions. Overall it is considered that the code is a valuable tool for turbomachinery analysis and design, but solutions must be assessed with care. Alternative turbulence models and other developments are being pursued for future versions of the code.
3D Reynolds Stress Modelling of Turbulent Flow in Linear Turbine Cascade
Authors: Kanniche M. , Boudjemadi R. , Déjean F. , Archambeau F.
Published: December 2014

The flow in a linear turbine cascade (Gregory-Smith et al. (1990)) is numerically investigated using a Reynolds Stress Turbulence closure. A particular attention is given to secondary flows where the normal Reynolds stresses are expected to play an important role. The most classical turbulence closure, the k-epsilon model uses the Boussinesq Eddy Viscosity concept which assumes an isotropic turbulent viscosity. The Reynolds stresses are then related to local velocity gradients by this isotropic eddy viscosity. Corollary, the principal axes of the Reynolds stress tensor are colinear with those of the mean strain tensor. The advantage of Reynolds Stress Turbulence closure is the calculation of Reynolds stresses by their own individual transport equations. This leads to a more realistic description of the turbulence and of its dependance on the mean flow.

The most classical Second Order turbulence model (Launder et al. (1975)) is applied to a linear turbine cascade, and the results are compared to secondary velocity and turbulence measurements at cross-passage planes.
Experimental Study of the Unsteady Aerodynamics in a Linear Cascade With Low Reynolds Number Low Pressure Turbine Blades
Authors: Murawski Christopher G. , Sondergaard Rolf , Rivir Richard B. , Vafai Kambiz , Simon Terrence W. , Volino Ralph J.
Published: December 2014

Low pressure turbines in aircraft experience large changes in flow Reynolds number as the gas turbine engine operates from takeoff to high altitude cruise. Low pressure turbine blades are also subject to regions of strong acceleration and diffusion. These changes in Reynolds number, strong acceleration, as well as elevated levels of turbulence can result in unsteady separation and transition zones on the surface of the blade.

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. The intent was to assess the effects of changes in Reynolds number, and freestream turbulence intensity. Flow Reynolds numbers, based on exit velocity and suction surface length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent.

Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a slightly rearward movement of the onset of separation and shrinkage of the separation zone.

Increasing the freestream turbulence intensity, without changing Reynolds number resulted in a shrinkage of the separation region on the suction surface.

Increasing both flow Reynolds numbers and freestream turbulence intensity compounded these effects such that at a Reynolds number of 300,000 and a freestream turbulence intensity of 8.1%, the separation zone was almost nonexistent.

The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. The width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number.

Numerical simulations were performed in support of experimental results. The numerical results compare well qualitatively with the low freestream turbulence experimental cases.
New Twists on the Deverson Axial-Flow Compressor Rotor
Authors: Moore Joan G. , Liu Bo , Moore John
Published: December 2014

Goto has presented data in the literature for the Deverson axial flow compressor rotor in a single stage environment. The flow features tip leakage and hub corner stall. In this paper, 3-d turbulent steady flow calculations for the rotor are used to determine if, and how, this rotor can be a useful CFD test case. The sensitivity of the CFD results to unknowns about the test case environment is computed. In particular the influences of blade twist, hub gap leakage flow between rotating and stationary components, and a departure from a radial equilibrium pressure distribution at the rotor exit are investigated. Evidence in support of these phenomena is presented and discussed, their likely magnitudes are suggested, and their influence on the rotor performance is quantified.
A Numerical Approach to Unstalled and Stalled Flutter Phenomena in Turbomachinery Cascades
Authors: Weber Stefan , Benetschik Hannes , Peitsch Dieter , Gallus Heinz E.
Published: December 2014

During the design process of compressor and turbine blades the investigation of flutter phenomena becomes increasingly important since higher load and better efficiency are desired. As an improvement on the numerical analysis and prediction of unsteady flow through turbomachine cascades with vibrating blades a time accurate Navier Stokes code for S1-stream surfaces SAFES1 is presented within the scope of this paper. To validate the code, numerical results for sub- and transonic test cases of a turbine and a compressor cascade are compared with experimental data. Their good agreement and comparison with Euler calculations show the necessity to take into account viscous effects. To cope with shock waves and areas of separation in laminar or turbulent flow, the fully non linearized Navier Stokes equations are solved using an algebraic turbulence model by Baldwin and Lomax. An approximative upwind flux difference splitting scheme suggested by Roe is implemented. Third order spatial accuracy can be achieved by the MUSCL technique in conjunction with a TVD scheme and a flux limiter by van Albada. By applying either an explicit or an implicit scheme the algorithm can give second order temporal accuracy. The implicit scheme exactly describes the time dependent solution by following a Newton subiteration for every time step.

The blades are discretized in a single passage by a C- or O-type grid. The harmonic motion of the blades is bending or torsion or both simultaneously in a non-rotating or rotating frame of reference. For the chosen mode of oscillation the time dependent axial and circumferential blade forces are determined as well as the resulting moment and damping coefficient. To handle a phaseshift between the motion of the blades a direct store method is used. For the unsteady grid movement a fast grid generation is performed in the core region.
A Probabilistic Approach to Life Management for Auxiliary Power Units
Authors: Eastman Don , Elgin Rick , Hao Beilene
Published: December 2014

Component fatigue life is a major concern in the design of gas turbine Auxiliary Power Units as it directly influences the reliability and life cycle cost of the end product. Accordingly, there is heavy emphasis placed upon designing components which safely maximize their fatigue life. Typical industry practice for managing fatigue has relied on what is commonly referred to as the “safe life approach” in which retirement lives are analytically determined for components and hardware is removed from service before fatigue related failures can occur.

The safe life approach is deterministic in nature since stress analysis results based on minimum geometry, material properties and maximum load are used to set a single life for the component. However, service experience shows that fatigue failures can occur before service life and that actual service lives are distributed over a large range of values as a result of variables not accounted for by deterministic methods.

In order to better achieve the goal of minimizing product life cycle costs while recognizing the variable nature of fatigue lives, Sundstrand Aerospace (SA) has developed a Life Management Plan (LMP) which includes probabilistic methods to augment the company’s standard safe life methodology.

Sundstrand’s LMP builds on the safe life methodology by using statistical distributions along with Monte Carlo simulations to predict initial component cracking rates. These initial predictions are used to guide an inspection program which provides actual cracking data. As this inspection data base grows, the initial simulation is modified to include the inspection data and the predicted failure rates are updated. This provides Sundstrand with a tool to manage failure risk in the field as well as to provide early warning of negative trends.

This paper will discuss how Sundstrand’s LMP was devised and implemented as well as what lessons have been learned and what changes are planned for future incorporation. A case history will be cited to illustrate how the LMP has worked, comparing predictions to actual experience.
Friction Damper Effects on Airfoil Aeromechanics
Authors: Markham Patrick D. , Fleeter Sanford
Published: December 2014

Turbomachine design is directed at performance, accomplished with blading operating near to aeromechanics stability limits. Currently, linearized friction damper models are used to predict these stability limits. However, during engine development, these linearized solutions are often found to be inadequate. Thus, for accurate blade row stability predictions, the nonlinear effects of friction dampers must be considered. This paper is directed at investigating the effects of friction damper nonlinearities on the response of a linear system and also the applicability of linear and nonlinear aeromechanics analyses. This is accomplished utilizing both linear and nonlinear aeromechanics models to analyze a nonlinear aeromechanics system with only one nonlinearity — friction damping. The linearized friction damper results are shown to be sufficient for preliminary design and for operating conditions away from stability limits. However, nonlinear friction dampers must be considered for final design or optimization near stability limits.
Zero Clearance Auxiliary Bearings for Magnetic Bearing Systems
Authors: Chen H. Ming , Walton James , Heshmat Hooshang
Published: December 2014

Active magnetic bearings (AMBs) while offering many unique design and operational opportunities for advanced rotor systems, require some form of backup or auxiliary bearing in the event of a component failure or the onset of high transient loads. A zero clearance auxiliary bearing (ZCAB) has recently been conceived and a prototype system tested. The ZCAB presented in this paper uses a series of interconnected rollers to surround a shaft. In the open position, a clearance exists between the ZCAB rollers and the shaft. When the shaft drops on the ZCAB due to either an AMB failure or transient shock, the rollers move circumferentially and radially inward to eliminate the clearance and re-center the shaft. Besides centering the shaft, the law shaft-to-ZCAB traction coefficient and composite support dynamic characteristics eliminate the possibility of backward whirl. This paper presents the design methodology used, results of an analytical design study, including time transient analysis, as well as preliminary feasibility prototype testing under simulated AMB failure and transient shock conditions. The test rotor was supported by a rolling element bearing at one end and an integrated magnetic bearing/ZCAB support system at the other end. Both rotor drop and shock tests were performed with this configuration. Experimental results under simulated AMB failure and transient shock conditions demonstrated successful operation of the ZCAB.