bluuebunny/crossref_metadata_2025 huggingface dataset:
Effectiveness of a 2% chlorhexidine solution mixed with calcium hydroxide against Candida albicans
Authors: Al‐Nazhan Saad , Al‐Obaida Mohammed
Published: November 2008

The purpose of this investigation was to examine the in vitro susceptibility of Candida albicans to a mixture of chlorhexidine and calcium hydroxide using a tube dilution test. A suspension containing C. albicans was exposed to 2% chlorhexidine solution, calcium hydroxide paste and 2% chlorhexidine mixed with calcium hydroxide in plastic tissue culture wells. The tested agents were incubated with C. albicans for 1, 24, or 72 h. All agents were effective anti‐fungals at all experimental time periods tested, with the exception of exposure to calcium hydroxide for 1 h. A mixture of 2% chlorhexidine and calcium hydroxide therefore is a very effective anti‐fungal agent against C. albicans.
An Inferentialist Approach to Semantics: Time for a New Kind of Structuralism?
Authors: Peregrin Jaroslav
Published: November 2008

The perennial question –What is meaning?– receives many answers. In this paper I present and discuss inferentialism– a recent approach to semantics based on the thesis that to have (such and such) a meaning is to be governed by (such and such) a cluster of inferential rules. I point out that this thesis presupposes that looking for meaning requires seeing language as a social institution (rather than, say, a psychological reality). I also indicate that this approach may be seen as a new embodiment of the old ideas of structuralism.
Preempting Principles: Recent Debates in Moral Particularism
Authors: McKeever Sean , Ridge Michael
Published: November 2008

Moral particularism, as recently defended, charges that traditional moral theorizing unduly privileges moral principles. Moral generalism defends a prominent place for moral principles. Because moral principles are often asked to play multiple roles, moral particularism aims at multiple targets. We distinguish two leading roles for moral principles, the role of standard and the role of guide. We critically survey some of the leading arguments both for and against principles so conceived.
Can Physicalism Be Non‐Reductive?
Authors: Melnyk Andrew
Published: November 2008

Can physicalism (or materialism) be non‐reductive? I provide an opinionated survey of the debate on this question. I suggest that attempts to formulate non‐reductive physicalism by appeal to claims of event identity, supervenience, or realization have produced doctrines that fail either to be physicalist or to be non‐reductive. Then I treat in more detail a recent attempt to formulate non‐reductive physicalism by Derk Pereboom, but argue that it fares no better.
Persistence and Location in Relativistic Spacetime
Authors: Gilmore Cody
Published: November 2008

How is the debate between endurantism and perdurantism affected by the transition from pre‐relativistic spacetimes to relativistic ones? After suggesting that the endurance vs. perdurance distinction may run together a pair of cross‐cutting distinctions (mereological endurance vs. mereological perdurance and locational endurance vs. locational perdurance), I discuss two recent attempts to show that the transition in question does serious damage to endurantism (at least of the locational variety).
Regulation of alveolar gas conductance by NO in man, as based on studies with NO donors and inhibitors of NO production
Authors: Guazzi M. , Arena R. , Vicenzi M. , Guazzi M. D.
Published: November 2008

Aim:  Nitric oxide (NO) is a mediator of the pulmonary vessel tone and permeability. We hypothesized that it may also regulate the alveolar‐capillary membrane gas conductance and lung diffusion capacity.

Methods:  In 20 healthy subjects (age = 23 ± 3 years) we measured lung diffusion capacity for carbon monoxide (DLco), its determinants (membrane conductance, Dm, and pulmonary capillary blood volume, Vc), systolic pulmonary artery pressure (PAPs) and pulmonary vascular resistance (PVR). Measurements were performed before and after administration of Ng‐monomethyl‐l‐arginine (l‐NMMA, 0.5 mg kg−1 min−1), as a NO production inhibitor, and l‐arginine (l‐Arg, 0.5 mg kg−1 min1) as a NO pathway activator. The effects of l‐NMMA were also tested in combination with active l‐Arg and inactive stereoisomer d‐Arg vehicled by 150 mL of 5%d‐glucose solution. For l‐Arg and l‐NMMA, saline (150 mL) was also tested as a vehicle.

Results:  l‐NMMA reduced Dm (−41%P < 0.01), DLco (−20%, P < 0.01) and cardiac output (CO), and increased PAPs and PVR. In 10 additional subjects, a dose of l‐NMMA of 0.03 mg kg−1 min1 infused in the main stem of the pulmonary artery was able to lower Dm (−32%, P < 0.01) despite no effect on PVR and CO. Dm depression was significantly greater when l‐NMMA was vehicled by saline than by glucose. l‐Arg but not d‐Arg abolished the effects of l‐NMMA. l‐Arg alone increased Dm (+14%, P < 0.01).

Conclusion:  The findings indicate that NO mediates the respiratory effects of l‐NMMA and l‐Arg, and is involved in the physiology of the alveolar‐capillary membrane gas conductance in humans. NO deficiency may cause an excessive endothelial sodium exchange/water conduction and fluid leakage in alveolar interstitial space, lengthening the air–blood path and depressing diffusion capacity.
Vastus lateralis surface and single motor unit electromyography during shortening, lengthening and isometric contractions corrected for mode‐dependent differences in force‐generating capacity
Authors: Altenburg T. M. , De Ruiter C. J. , Verdijk P. W. L. , Van Mechelen W. , De Haan A.
Published: November 2008

Aim:  Knee extensor neuromuscular activity, rectified surface electromyography (rsEMG) and single motor unit EMG was investigated during isometric (60° knee angle), shortening and lengthening contractions (50–70°, 10° s−1) corrected for force–velocity‐related differences in force‐generating capacity. However, during dynamic contractions additional factors such as shortening‐induced force losses and lengthening‐induced force gains may also affect force capacity and thereby neuromuscular activity. Therefore, even after correction for force–velocity‐related differences in force capacity we expected neuromuscular activity to be higher and lower during shortening and lengthening, respectively, compared to isometric contractions.

Methods:  rsEMG of the three superficial muscle heads was obtained in a first session [10 and 50% maximal voluntary contraction (MVC)] and additionally EMG of (46) vastus lateralis motor units was recorded during a second session (4–76% MVC). Using superimposed electrical stimulation, force‐generating capacity for shortening and lengthening contractions was found to be 0.96 and 1.16 times isometric (Iso) force capacity respectively. Therefore, neuromuscular activity during submaximal shortening and lengthening was compared with isometric contractions of respectively 1.04Iso (=1/0.96) and 0.86Iso (=1/1.16). rsEMG and discharge rates were normalized to isometric values.

Results:  rsEMG behaviour was similar (P > 0.05) during both sessions. Shortening rsEMG (1.30 ± 0.11) and discharge rate (1.22 ± 0.13) were higher (P < 0.05) than 1.04Iso values (1.05 ± 0.05 and 1.03 ± 0.04 respectively), but lengthening rsEMG (1.05 ± 0.12) and discharge rate (0.90 ± 0.08) were not lower (P > 0.05) than 0.86Iso values (0.76 ± 0.04 and 0.91 ± 0.07 respectively).

Conclusion:  When force–velocity‐related differences in force capacity were taken into account, neuromuscular activity was not lower during lengthening but was still higher during shortening compared with isometric contractions.
Perspectives of multi‐modal contribution of honeybee resources to our life
Authors: HOSHIBA Hidehiro , SASAKI Masami
Published: November 2008

The European honeybee, Apis mellifera, has been introduced to all continents and their products like honey, propolis, royal jelly and beeswax are well known. However, its contribution is not restricted to such direct products but extends into a much wider area. For example, the economic value of seed production by pollination exceeds the above‐mentioned bee products. The application of F1 hybrid is increased to as much as 70% of commercial crops and flowers in Japan and honeybees are important pollinators in the F1 seed production. Incorporation into the large‐scale biodiesel fuel production system by culturing rape and sunflower seeds etc. is relied on because it is good to construct possible zero‐emission systems that reduce carbon dioxide and increase the rich by‐products like honey and royal jelly.

Bees’ higher brain function and sophisticated social system of the colony opens new perspectives as a model system. Their individual ability to recognize even abstract concepts is comparable to that of higher primates. Rats or mice have no such ability. High performance learning ability of bees associated with proboscis extension reflex can be used to detect drugs at the airport. Function of the colony, on the other hand, is an excellent model for social physiology or a self‐organization system.

After the whole genome of A. mellifera was read in 2006 by the world consortium, consisting of more than 90 institutions from all over the world, many molecular biologists are coming into bee world. Nobody has yet succeeded in the challenge to make transgenic honeybee, so far, because of the difficulty in controlling the reproductive system headed by the queen. However, if someone succeeded in a breakthrough we will have stingless honeybees and a disease‐resistant strain in the future.
Mass rearing an earth mite to screen plants for resistance: A review
Authors: RIDSDILL‐SMITH T. James
Published: November 2008

A mite which is polyphagous, widespread and abundant should be relatively easy to rear. However, mass rearing redlegged earth mite, Halotydeus destructor, for use in screening plants for resistance, has been very difficult. They are found in regions of Australia with winter growing annual crops and pastures, where they are active in winter and have a summer diapause. Mites are field collected in winter for screening, but cold storage only improves availability by 2 weeks. If mites are held in controlled climate cabinets under winter conditions with short daylength, the onset of diapause is not triggered and egg laying continues. Host plant suitability is a key factor affecting the rate of multiplication of mites, and common vetch, Vicia sativa cv Blanchefleur is an optimum host for rearing. The mites spend 90% of the time on the soil surface and only climb to the upper plant canopy in pastures to feed for 10% of the time. They are thus earth mites. High humidity at the soil surface is very important for their survival and optimal multiplication. If it is too wet dead mites on the surface are attacked by verticillium fungus, and active mites are adversely affected by hyphae. Mite multiplication is greater on well‐drained sandy loam soil than a loamy soil, sand or pure loam as a substrate. Mass rearing has now been achieved after overcoming these problems.
Insects and their uses in a cold country: Finland
Authors: MEYER‐ROCHOW Victor Benno
Published: November 2008

Northern European countries, despite their geographic location and climatic conditions, have a considerable number of insect species. To date 20 532 species of insects are known from Finland. Honeybees were introduced to Finland in the 18th century. The total number of hives in the country today is 50 000, with each producing an annual 30–40 kg of honey. A considerable amount of research is carried out on bees in Finland by beekeepers and scientists and the Finnish Beekeeper Association publishes its own journal by the name of Mehiläinen for approximately 3300 subscribers. Insects also play important roles in the education and school curricula of Finnish children with insect boxes containing preserved specimens, identification keys and information on general biology available for classes. Some butterflies get framed and hung on walls, serving as room decorations. Insects also feature as motifs on Finnish t‐shirts. Forensic entomology was pioneered in Finland and numerous university departments (zoology, entomology, ecology, physiology, biophysics, pharmacology and genetics) as well as museums are engaged in research on insects. Monitoring climate change, insects in Finland (especially Lepidoptera) are highly suitable because of the many years of recorded distributions and abundances of species. Finally, the large amount of idioms in the Finnish language, making reference to insects, testifies to the intimate connection between the Finnish people and the insects of their country.
Identification and phylogeny of five male‐specific lethal genes in the silkworm Bombyx mori
Authors: LIU Wenbin , ZHANG Yong , MIAO Xuexia , HUANG Yongping
Published: November 2008

In the fruit fly (Drosophila melanogaster) dosage compensation equalization of X‐linked genes between the sexes is achieved via a complex that is termed the compensasome, which is composed of at least five male‐specific lethal (msl) genes and two non‐coding RNAs. In the present study, we cloned all five homologs (termed the msls) from the silkworm, Bombyx mori, in which the issue of dosage compensation remains controversial. Data mining and robust phylogenetic analysis revealed that msls are ubiquitously present in genomes, from insects to mammals, with unknown biological functions. However, the five genes seem to have evolved at different times due to gene duplication. Real‐time reverse transcriptase‐polymerase chain reaction experiments demonstrated that in the silkworm, some Z‐linked genes are expressed at higher levels in females than in males while others are expressed at lower levels in females than in males, which suggests that the msl genes in the silkworm and fruit fly may have different roles. We discussed the relationship of phylogeny between msl and sex‐lethal.
Insects in expanding education and entertainment in Taiwan
Authors: YANG Man‐Miao
Published: November 2008

Taiwan, an island of approximately 36000 km2 area, includes stunning diversity in both habitat and biota because of its transitional position. Where the Tropic of Cancer cuts across the middle of the island and the east Philippine plate subducts into the Eurasia plate, the landscape and weather are extremely congenial for a highly diverse biota to develop over the years in Taiwan. Such a natural endowment has enabled diverse habitats for wildlife to evolve. Insects are especially abundant in Taiwan. For example, about 400 species of butterflies occur in Taiwan. Export of aesthetically attractive insects, such as butterflies and beetles, is an ongoing key industry in Taiwan right from the early to middle 20th century. As the economic preferences moved towards high technology with a concurrent understanding of biological diversity and the concept of conservation grew strong, use of insect materials have currently moved towards education and entertainment. Besides the exhibition of traditional methods of insect collection, several newly developed insectaria are presently integrated into Taiwanese museums, zoos, and university departments using modern technology for displaying activities of live insects. Summer camps offer plentiful opportunities for children to learn about insects. Volunteers, with appropriate research skills and extensive scientific knowledge are involved in these exhibitions. Rearing of “pet” insects is popular and, consequently, enabled the growth of some specific supply companies. Traditionally, insect resources are used in many aspects, such as in medicine and food and extraction of insect products such as silk and honey; occasionally some of the insects are useful as even game animals. Fighting crickets provide entertainment, and occasionally used in gambling as well. Insects provide diverse and abundant resources and are an excellent material deserved for better exploration in many aspects.
Status of weed biological control utilizing insects in Korea
Authors: KWON Ohseok
Published: November 2008

It has been only recently that the biological control of weeds by insects was practiced in Korea. Since the diverse crop farming practices in relatively small farms, it has been underestimated by the chemical control practice. The need to find alternative methods from the presence of herbicide‐resistant weeds and growing ecological concern requires immediate action to be followed. The Integrated Weed Management Laboratory at the National Institute of Agricultural Science and Technology at the Rural Development Administration was set up to initiate weed biological control research. Since then, four research projects on weed biological control by insects were carried out. The target weed species were as follows: Rumex obtusifolius, Ambrosia trifida, Acalypha australis, and Monochoria vaginalis. In this review, some of the findings both published and unpublished were presented to show the status of the weed biological control by insects in Korea.
Reduction of Multistage Disk Models: Application to an Industrial Rotor
Authors: Sternchüss Arnaud , Balmès Etienne , Jean Pierrick , Lombard Jean-Pierre
Published: November 2008

The present study deals with the reduction of models of multistage bladed disk assemblies. The proposed method relies on the substructuring of the rotor into sectors. The bladed disks are coupled by intermediate rings, which remove the problem of incompatible meshes. The sectors are represented by superelements whose kinematic subspaces are spanned by a set of cyclic modeshapes and a set of normal modes when their left and right interfaces are fixed. The first step is to compute the cyclic modeshapes that are defined on the full rotor by enforcing the uncoupling of the spatial Fourier harmonics. This leads to a family of subproblems parametrized by the harmonic coefficient, similar to the classical approach used to deal with tuned bladed disks. The subsequent reduction process leads to compact reduced models whose accuracy has been extensively tested on simple but realistic academic models. The proposed methodology was then applied to an industrial rotor to conduct an analysis at a wider scale. This case was also the occasion to point out the fact that the assembly of individual disk models into a rotor model is really straightforward and provides an efficient tool to observe and predict coupled phenomena.
Ten Years of Experience With a Small Jet Engine as a Support for Education
Authors: Léonard O. , Thomas J. P. , Borguet S.
Published: November 2008

In 1997 the Turbomachinery Group of the University of Liège decided to acquire a small jet engine to illustrate the courses in propulsion and to provide the students with the opportunity to get some experience on data measurement, acquisition, and interpretation. Among others, the SR-30 engine from Turbine Technology Ltd. Chetek, WI was chosen. It consists of a single spool, single flow engine with a centrifugal compressor, a reversed combustion chamber, an axial turbine, and a fixed convergent nozzle. This engine was installed on a test bench allowing for manual control and providing fuel and oil to the engine. The original setup included measurements of intercomponent pressure and temperatures, exhaust gas temperature, and rotational speed. Since then both the engine and the test bench have been deeply modified. These modifications were led by a triple objective: the improvement and the enrichment of the measurement chain, the widening of the engine’s operational domain, and, last but not the least, the wish to offer appealing hands-on projects to the students. All these modifications were performed at the University of Liège and were conducted by the students as part of their Master theses. Several performance models of the engine were developed to support data validation and engine condition diagnostic. This paper summarizes the developments conducted with and by the students, and presents the experience that was gained by using this engine as a support for education.
Measurements of Leakage and Power Loss in a Hybrid Brush Seal
Authors: San Andrés Luis , Baker José , Delgado Adolfo
Published: November 2008

Simplicity, low cost, and easy replacement make labyrinth seals the primary seal type in gas turbines. However, excessive leakage and potential for rotordynamic instability are well known issues. Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low pressure differentials. Hybrid brush seals (HBSs) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, which under rotor spinning lifts off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, thus lowering the operating temperature and thermal distortions and even eliminating bristle wear. The hybrid brush seal improves sealing, is more durable and reliable than conventional brush seals, and allows reverse shaft rotation without seal damage. This paper presents measurements of power loss and leakage in a HBS for increasing pressure differentials over a range of rotor speeds. The test HBS, Haynes-25 bristle pack (∼850 bristles∕cm) and 45 deg lay angle, is 166.4 mm in diameter and integrates 20-arcuate pads connected with thin electrical-discharge machined webs (EDM-webs) to the seal casing. The webs are designed with low radial stiffness to allow for rotor excursions and high axial stiffness to avoid pad pitching motions resulting from high pressure differentials across the seal. Measured drag power at low rotor speeds (<11 m∕s at 1300 rpm) decreases as the pressure differential across the seal increases. At a fixed rotor speed, a significant drop in drag torque (and drag power) ensues as the supply pressure increases, thus demonstrating that a gas film separates the rotor from the seal pads. Additionally, the operating temperature measured at the rotor/seal interface remains approximately constant (∼24°C) during tests with shaft rotation (power loss and drag torque measurements) under pressurized conditions, indicating that the rotor and seal pads are not in contact. Flow rate measurements at room temperature (25°C) show an improved sealing ability with a leakage reduction of about 36% when compared with a first generation shoed-brush seal. The HBS calculated effective clearance (∼50 μm) is approximately 70% smaller than the radial clearance (∼180 μm) of an ideal noncontacting seal with similar rotor diameter. Improved brush seal technology will increase the efficiency of gas turbines while also aiding to improve the engine stability and to reduce vibrations.
Measurements Versus Predictions for the Rotordynamic Characteristics of a Five-Pad Rocker-Pivot Tilting-Pad Bearing in Load-Between-Pad Configuration
Authors: Carter Clint R , Childs Dara W.
Published: November 2008

Rotordynamic data are presented for a rocker-pivot tilting-pad bearing in the load-between-pad configuration for unit loads over the range 345–3101kPa and speeds over the range 4000–13,000rpm. The bearing was directly lubricated through a leading-edge groove with the following specifications: Five pads, 0.282 preload, 60% offset, 57.87deg pad arc angle, 101.587mm(3.9995in.) rotor diameter, 0.1575mm(0.0062in.) diametral clearance, and 60.325mm(2.375in.) pad length. Dynamic tests were performed over a range of frequencies to investigate frequency effects on the dynamic stiffness coefficients. Under most test conditions, the direct real parts of the dynamic stiffnesses could be approximated as quadratic functions of the excitation frequency and accounted for with the addition of an added-mass matrix to the conventional [K][C] matrix model to produce a frequency-independent [K][C][M] model. Measured added-mass terms in the loaded direction approached 60kg. At low speeds, “hardening” direct dynamic stiffness coefficients that increased with increasing frequency were obtained, which produced negative added-mass terms. No frequency dependency was obtained for the direct damping coefficients. The dynamic experimental results were compared to predictions from a bulk-flow computational fluid dynamics analysis. The static load direction in the tests was y. The direct stiffness coefficients Kxx and Kyy were slightly overpredicted. Measured direct damping coefficients Cxx and Cyy were insensitive to changes in either the load or speed in contrast to predictions of marked Cyy sensitivity for changes in the load. Only at the highest test speed of 13,000rpm were the direct damping coefficients adequately predicted. Measurable cross-coupled stiffness coefficients were obtained for the bearings with Kxy and Kyx being approximately equal in magnitude but opposite in sign—clearly destabilizing. However, the whirl frequency ratio was found to be zero at all test conditions indicating infinite stability for the bearing.
Optimal Mission Analysis Accounting for Engine Aging and Emissions
Authors: Kelaidis M. , Aretakis N. , Tsalavoutas A. , Mathioudakis K.
Published: November 2008

An aircraft mission analysis procedure, accounting for engine aging deterioration and incorporating emission estimation capability, is presented. It consists of three main modules: a flight simulation module, an engine performance simulation module, and an optimizer. A key feature of the approach is the incorporation of engine deterioration modeling. This extends the procedure’s ability to estimate onboard performance of an engine as it ages through time and usage. Additionally, the possibility to investigate environmental impact is offered through pollutant emission semi-empirical correlations, which are coupled to the engine performance calculations. The adaptive character of the models employed allows for accurate performance and emission estimations once an initial set of data is available for the engine. The proposed procedure allows the optimization of a flight scenario for a variety of aircrafts, missions, and engine condition combinations in order to meet predefined criteria. Mission profile characteristics (e.g., cruise, altitude, and speed) providing optimum overall performance in terms of fuel conservation, time related costs, or pollutant production are studied.
Three–Dimensional Transient Elastic Thermal Stress Field During Diesel Particulate Filter Regeneration
Authors: Guo Zhenhua , Zhang Zhaoyan , Sheng Biqing , Peng Wen
Published: November 2008

A displacement based 3D finite element model is developed to simulate thermal stress induced by high temperature and temperature gradient during diesel particulate filter (DPF) regeneration. The temperature field predicted by 3D regeneration model from previous work is used as input. This finite element model agrees well with commercial software. It is a self-contained package capable of implementing meshing body, assembling global stiffness matrix and solving final equilibrium equations. Numerical simulation indicates that it is peak temperature rather than temperature gradient that leads to higher compressive thermal stress during regeneration. The maximum stress always appears at the channel corner located at the end of DPF. Parametric studies are performed to investigate the effects of DPF design on pressure drop, regeneration temperature, and thermal stress. This model provides insights into the complicated DPF working mechanism, and it can be used as design tools to reduce filter pressure drop while enhance its short term and long term durability.
Effects of Key Factors on the Engine Combustion Mode Switching Between HCCI and SI
Authors: Guohong Tian , Zhi Wang , Jianxin Wang , Xu Hongming , Shijin Shuai
Published: November 2008

A technical strategy for a rapid and smooth switching between spark ignition (SI) mode and homogeneous charge compression ignition (HCCI) mode on a gasoline direct injection engine has been proposed and investigated, which involves an electrohydraulic two-stage cam profile mechanism and special injection strategies. The key factors that affect the HCCI/SI mode switching processes were analyzed on the basis of transient engine tests in terms of combustion parameters and exhaust emissions. It is shown that special care should be taken on the engine functionalities during the mode switching from SI to HCCI, which appears to be more difficult, and simultaneous control of the key parameters such as injection mass, injection timing, and spark timing is required. Various strategies and their general criteria for the mode switching were discussed. An optimized combination of selected control strategies has been demonstrated with a satisfactory switching process completed in ten engine cycles, without any abnormal combustion cycles in between.
Effect of Hydrated Salt Additives on Film Boiling Behavior at Vapor Film Collapse
Authors: Arai Takahiro , Furuya Masahiro
Published: November 2008

A high-temperature stainless steel sphere was immersed into various salt solutions to investigate film boiling behavior at vapor film collapse. The film boiling behavior around the sphere was observed with a high-speed digital-video camera. Because the salt additives enhance the condensation heat transfer, the observed vapor film was thinner. The surface temperature of the sphere was measured. Salt additives increased the quenching (vapor film collapse) temperature because the frequency of direct contact between the sphere surface and the coolant increased. Quenching temperature increases with increased salt concentration. The quenching temperature, however, approaches a constant value when the salt concentration is close to its saturation concentration. The quenching temperature is well correlated with ion molar concentration, which is a number density of ions, regardless of the type of hydrated salts.
Experimental and Numerical Modeling of Transition Matrix From Momentum to Buoyancy-Driven Flow in a Pressurized Water Reactor
Authors: Höhne Thomas , Kliem Sören , Vaibar Roman
Published: November 2008

The influence of density differences on the mixing of the primary loop inventory and the emergency core cooling (ECC) water in the cold leg and downcomer of a pressurized water reactor (PWR) was analyzed at the Rossendorf coolant mixing (ROCOM) test facility. This paper presents a matrix of ROCOM experiments in which water with the same or higher density was injected into a cold leg of the reactor model with already established natural circulation conditions at different low mass flow rates. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the cold leg, upper and lower part of the downcomer. A transition matrix from momentum to buoyancy-driven flow experiments was selected for validation of the computational fluid dynamics software ANSYS CFX. A hybrid mesh with 4×106 elements was used for the calculations. The turbulence models usually applied in such cases assume that turbulence is isotropic, whilst buoyancy actually induces anisotropy. Thus, in this paper, higher order turbulence models have been developed and implemented, which take into account that anisotropy. Buoyancy generated source and dissipation terms were proposed and introduced into the balance equations for the turbulent kinetic energy. The results of the experiments and of the numerical calculations show that mixing strongly depends on buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation with lower mass flow rates and/or higher density differences. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with the ECC injection in PWR and should be also considered in pressurized thermal shock scenarios. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.
Effects of Reynolds Number and Free-Stream Turbulence on Turbine Tip Clearance Flow
Authors: Matsunuma Takayuki
Published: November 2008

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4 × 104 to 26.6 × 104 by changing the velocity of fluid flow. The free-stream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and free-stream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.
Application of Steady State and Transient IR-Thermography Measurements to Film Cooling Experiments for a Row of Shaped Holes
Authors: Brauckmann Dennis , von Wolfersdorf Jens
Published: November 2008

This paper presents experimental investigations for the measurement of the adiabatic film cooling effectiveness as well as the heat transfer coefficient distribution in film cooling experiments with a row of fanshaped holes on a flat plate. The temperature distribution on the flat plate is measured using infrared-thermography (IR). Adiabatic wall effectiveness data are obtained using a high-temperature plastic material. Although a low thermal conductivity material is used, the measured temperature distribution is not identical with the adiabatic temperature distribution. The measured temperature field shows influences of 3D heat conduction inside the test plate. The effects of the heat conduction inside the test plate are modeled using the FE-method to re-evaluate the adiabatic wall temperature and to calculate the coolant gas exit temperature, which is used for the adiabatic film cooling effectiveness. For the measurement of the heat transfer coefficient ratio with and without film cooling (hf/h0) a transient method is used. Temperature transients on the test surface are initiated by switching the coolant flow and are recorded using IR-thermography. The measured wall temperature histories are converted into heat flux values assuming a semi-infinite wall model during the experiment.
Flow Characteristics Within and Downstream of a Single Shallow Cylindrical and Spherical Dimple: Effect of Pre-Dimple Boundary Layer Thickness
Authors: Khalatov Artem , Byerley Aaron , Vincent Robert
Published: November 2008

The objective of this study is to investigate the details of the average and unsteady flow structures in front, inside and after shallow (h/D = 0.1) spherical and cylindrical dimples placed on a flat plate at the different distances with different pre-dimple boundary layer thicknesses. The dimple projected (surface) diameter was 50.8 mm with the dimple centers located at 88 mm and 264 mm downstream of the elliptical leading edge of the flat plate. Experimental program was established in the U.S. Air Force Academy water tunnel, both dimple configurations were tested across the range of freestream water velocities from 0.07 to 0.52 m/s corresponding with diameter based Reynolds numbers ReD ranging from 3,200 to 23,500. The length based Reynolds number Rex ranged from 3,940 to 110,450 while the non-dimensional boundary layer thickness δ0/h ranged from 0.28 to 1.18. The inlet flow turbulence was below 1% at all flow speeds. Laminar flow existed upstream of the dimple for all of the flow conditions studied. Flow visualizations were performed inside and downstream of each dimple at 10 to 13 different flow speeds. All recordings were made with a SONY-DCR VX2000 video camera. Five different colors of dye were injected through five cylindrical ports, 1.0 mm in diameter, positioned at locations upstream and inside the dimples. Adobe Premiere 6.5 software was used to analyze the flow characteristics using the slow motion feature. LDV measurements were made both in front of and downstream of the dimple. The results presented include the vortex patterns, in-dimple separation zone extent, unsteady flow phenomena (bulk flow oscillations), velocity profiles after the dimple, and some features of the laminar-turbulent flow transition downstream of a single cylindrical dimple. The data obtained revealed three-dimensional and unsteady flow structures inside and downstream of the dimples, the important role of the pre-dimple boundary layer thickness. Increasing the δ0/h ratio reduces the downstream bulk flow oscillations at very low Reynolds numbers. However, at ReD>16,500 for the cylindrical dimple and at ReD>24,000 for the spherical dimple the boundary layer thickness had little effect on the bulk flow oscillations. A comparison of both spherical and cylindrical dimple geometric configurations was made to assess their relative benefits.
Turbine Airfoil Heat Transfer Predictions Using CFD
Authors: Tolpadi Anil K. , Tallman James A. , El-Gabry Lamyaa
Published: November 2008

Conventional heat transfer design methods for turbine airfoils use 2-D boundary layer codes (BLC) combined with empiricism. While such methods may be applicable in the mid span of an airfoil, they would not be very accurate near the end-walls and airfoil tip where the flow is very three-dimensional (3-D) and complex. In order to obtain accurate heat transfer predictions along the entire span of a turbine airfoil, 3-D computational fluid dynamics (CFD) must be used. This paper describes the development of a CFD based design system to make heat transfer predictions. A 3-D, compressible, Reynolds-averaged Navier-Stokes CFD solver with k-ω turbulence modeling was used. A wall integration approach was used for boundary layer prediction. First, the numerical approach was validated against a series of fundamental airfoil cases with available data. The comparisons were very favorable. Subsequently, it was applied to a real engine airfoil at typical design conditions. A discussion of the features of the airfoil heat transfer distribution is included.
Film Cooling Effectiveness and Heat Transfer on the Trailing Edge Cut-Back of Gas Turbine Airfoils With Various Internal Cooling Designs
Authors: Martini P. , Schulz A. , Bauer H.-J.
Published: November 2008

The present study deals with trailing edge film cooling on the pressure side cut-back of gas turbine airfoils. Before being ejected tangentially onto the inclined cut-back surface the coolant air passes a partly converging passage that is equipped with turbulators such as pin fins and ribs. The experiments are conducted in a generic set-up and cover a broad variety of internal cooling designs. A subsonic atmospheric open-loop wind tunnel is utilized for the tests. The test conditions are characterized by a constant Reynolds number of Rehg = 250,000, a turbulence intensity of Tuhg = 7%, and a hot gas temperature of Thg = 500K. Due to the ambient temperature of the coolant, engine realistic density ratios between coolant and gas can be realized. Blowing ratios cover a range of 0.20<M<1.25. The experimental data to be presented include discharge coefficients, adiabatic film cooling effectiveness and heat transfer coefficients in the near slot region (x/H<15). The results clearly demonstrate the strong influence of the internal cooling design and the relatively thick pressure side lip (t/H = 1) on film cooling performance downstream of the ejection slot.
Large Eddy Simulation of Flow and Heat Transfer in an Internal Cooling Duct With High Blockage Ratio 45° Staggered Ribs
Authors: Viswanathan Aroon K. , Tafti Danesh K. , Abdel-Wahab Samer
Published: November 2008

Numerical predictions of a hydrodynamic and thermally developed turbulent flow are presented for a unit period of a stationary duct with square ribs aligned at 45° to the main flow direction. The rib height to channel hydraulic diameter (e/Dh) is 0.375 and the rib pitch to rib height (P/e) is 10. The domain under consideration is a rectangular passage of aspect ratio 1:2.5 with 45° ribs on the top and bottom walls arranged in a staggered fashion. The computations are carried out for a bulk Re of 27,000. The rib geometry introduces a strong secondary flow along the rib. A large helical vortex develops behind the rib which breaks down before it reaches the outer wall. This results in higher heat transfer at the inner wall as compared to the outer wall, which is in contrast to the trend observed in a square channel with low blockage ribs. In a square duct with low blockage ribs the secondary flow has two counter-rotating cells which do not change direction through the channel. However in this case only one rotating cell is observed in this case, which changes direction as it passes over successive ribs. The average friction and the heat transfer augmentation ratios are consistent with the experimental results [1], predicting values within 15% of the measured quantities.
A Study on Local Heat Transfer Enhancement in a Rectangular Dimpled Channel With a Large Aspect Ratio
Authors: Lauffer Diane , Weigand Bernhard , Liebe Roland
Published: November 2008

In this paper the convective heat transfer in a rectangular dimpled channel with an aspect ratio of six is studied. Applications could be for gas turbine vanes, vane shrouds, ring segments and hot components in the combustor. Basic heat transfer experiments have been performed using heater foils and a steady-state method with liquid crystals. The cooling effect is achieved by a dimple configuration combined with rib turbulators. The specific subject of this study is to focus on the heat transfer enhancement in the corner regions of the dimpled large aspect ratio channel. Different configurations of rib turbulators are investigated at different Reynolds numbers. Detailed heat transfer distributions are presented for the different configurations, showing the local effect of turbulator placement and angle with respect to the main flow direction. They are complemented by pressure drop measurements and compared with numerical simulations. It is shown that locally implemented rib configurations can enhance the heat transfer in these critical regions without large pressure loss penalties.
Impact of Non-Uniform Leading Edge Coatings on the Aerodynamic Performance of Compressor Airfoils
Authors: Elmstrom Michael E. , Millsaps Knox T. , Hobson Garth V. , Patterson Jeffrey S.
Published: November 2008

A computational fluid dynamic (CFD) investigation is presented that provides predictions of the aerodynamic impact of uniform and non-uniform coatings applied to the leading edge of a compressor airfoil in a cascade. Using a NACA 65(12)10 airfoil, coating profiles of varying leading edge non-uniformity were added. A non-uniform coating is obtained when a liquid coating is applied to a surface with high curvature, such as an airfoil leading edge. The CFD code used, RVCQ3D, is a Reynolds Averaged, Navier-Stokes (RANS) solver, with a k-omega turbulence model. The code predicted that these changes in leading edge shape can lead to alternating pressure gradients in the first few percent of chord that create small separation bubbles and possibly early transition to turbulence. The change in total pressure loss and trailing edge deviation are presented as a function of a coating non-uniformity parameter. Results are presented over a range of negative and positive incidences and inlet Mach numbers from 0.6 to 0.8. A map is provided that shows the allowable degree of coating non-uniformity as a function of incidence and inlet Mach number.
Analysis of Airfoil Trailing Edge Heat Transfer and Its Significance in Thermal-Mechanical Design and Durability
Authors: Cunha F. J. , Dahmer M. T. , Chyu M. K.
Published: November 2008

The trailing edge section of modern high-pressure turbine airfoils is an area that requires a high degree of attention from turbine performance and durability standpoints. Aerodynamic loss near the trailing edge includes expansion waves, normal shocks and wake shedding. Thermal issues associated with trailing edge are also very complex and challenging. To maintain effective cooling ensuring metal temperature below design limit is particularly difficult, as it needs to be implemented in a relatively small area of the airfoil. To date little effort has been devoted to advancing the fundamental understanding of the thermal characteristics in airfoil trailing edge regions. Described in this paper are the procedures leading to closed-form, analytical solutions for temperature profile for four most representative trailing edge configurations. The configurations studied are: (1) solid wedge shape without discharge, (2) wedge with slot discharge, (3) wedge with discrete-hole discharge, and (4) wedge with pressure-side cutback slot discharge. Comparison among these four cases is made primarily in the context of airfoil metal temperature and resulting cooling effectiveness. Further discussed in the paper are the overall and detail design parameters for preferred trailing edge cooling configurations as they affect turbine airfoil performance and durability.
Turbine Cascade Flow Control Using a “Wake Filling” Pulsed Plasma Actuator
Authors: Perez-Blanco H. , Van Dyken Robert , Byerley Aaron , McLaughlin Tom
Published: November 2008

Separation bubbles in high-camber blades under part-load conditions have been addressed via continuous and pulsed jets, and also via plasma actuators. Numerous passive techniques have been employed as well. In this type of blades, the laminar boundary layer cannot overcome the adverse pressure gradient arising along the suction side, resulting on a separation bubble. When separation is abated, a common explanation is that kinetic energy added to the laminar boundary layer speeds up its transition to turbulent. In the present study, a plasma actuator installed in the trailing edge (i.e. “wake filling configuration”) of a cascade blade is used to excite the flow in pulsed and continuous ways. The pulsed excitation can be directed to the frequencies of the large coherent structures (LCS) of the flow, as obtained via a hot-film anemometer, or to much higher frequencies present in the suction-side boundary layer, as given in the literature. It is found that pulsed frequencies much higher than that of LCS reduce losses and improve turning angles further than frequencies close to those of LCS. With the plasma actuator 50% on time, good loss abatement is obtained. Larger “on time” values yield improvements, but with decreasing returns. Continuous high-frequency activation results in the largest loss reduction, at increased power cost. The effectiveness of high frequencies may be due to separation abatement via boundary layer excitation into transition, or may simply be due to the creation of a favorable pressure gradient that averts separation as the actuator ejects fluid downstream. Both possibilities are discussed in light of the experimental evidence.
Detached Eddy Simulation of Flow and Heat Transfer in a Stationary Internal Cooling Duct With Skewed Ribs
Authors: Viswanathan Aroon K. , Tafti Danesh K.
Published: November 2008

Numerical predictions of a hydrodynamic and thermally developed turbulent flow for a unit period of a stationary duct using Detached Eddy Simulation (DES) and Unsteady Reynolds Averaged Navier-Stokes (URANS) are presented. The domain under consideration is a square duct with 45° ribs on the top and bottom walls arranged in a staggered fashion. Computations are carried out for a bulk Re of 47,000. The rib height to channel hydraulic diameter (e/Dh) is 0.1 and the rib pitch to rib height (P/e) is 10. DES is applied on two grids 80 × 80 × 80 and 128 × 80 × 80 and the initial results are compared with the experimental results and LES computations. Based on this the 128 × 80 × 80 grid is chosen for the comprehensive study. DES and URANS computations are carried out on the grid. The rib geometry introduces a strong secondary flow along the rib. The presence of the secondary flow introduces a spanwise variation in the heat transfer. DES predicts flow features and heat transfer distribution which is consistent with the experimental observations and LES computations. The average friction and the augmentation ratios predicted by DES also concur with the earlier observations.