bluuebunny/crossref_metadata_2025 huggingface dataset:
Tree regeneration before and after restoration treatments in managed boreal Picea abies stands
Authors: De Chantal M. , Lilja‐Rothsten S. , Peterson C. , Kuuluvainen T. , Vanha‐Majamaa I. , Puttonen P.
Published: March 2009

Questions: What are the short‐term effects of restoration treatments, including fire and/or partial cutting with dead wood creation, on seedling density and distribution among microsites, and do they differ between upland and paludified biotopes?

Location: Mature managed Picea abies‐dominated stands in southern Finland.

Methods: The restoration treatments consisted of four levels of cutting, with and without fire: uncut, low‐CWD (partial cutting leaving 50 m3 ha−1 of standing retention trees and 5 m3 ha−1 of down retention trees, DRT), intermediate‐CWD (as previous but with 30 m3 ha−1 of DRT), and high‐CWD (as previous but with 60 m3 ha−1 of DRT).

Results: The cutting treatment alone did not affect seedling density. Fire had an immediate effect, both by itself in upland biotopes (decreasing effect on P. abies density) and in combination with cutting in paludified biotopes (increasing effect on Betula spp. density). The density of other deciduous species (Sorbus aucuparia, Populus tremula, and Salix spp.) was not affected. Before treatments, seedlings grew predominantly on level ground and mounds. After treatments, more Betula, but fewer P. abies and other deciduous species, grew on these microsites. More Betula and other deciduous species grew next to CWD and under a fallen crown; more P. abies grew under a fallen crown in unburned stands.

Conclusion: The post‐treatment tree seedling density and distribution among microsites can be affected by restoration treatments. However, knowledge of local site characteristics and their interaction with different restoration treatments is needed to achieve the goals set for restoration at the stand and landscape levels.
Changes in vegetation types and Ellenberg indicator values after 65 years of fertilizer application in the Rengen Grassland Experiment, Germany
Authors: Chytrý Milan , Hejcman Michal , Hennekens Stephan M. , Schellberg Jürgen
Published: March 2009

Question: How does semi‐natural grassland diversify after 65 years of differential application of Ca, N, P, and K fertilizers? Is fertilizer application adequately reflected by the Ellenberg indicator values (EIVs)?

Location: Eifel Mountains, West Germany.

Methods: The Rengen Grassland Experiment (RGE) was established in an oligotrophic grassland in 1941. Six fertilizer treatments (Ca, CaN, CaNP, CaNP‐KCl, CaNP‐K2SO4, and unfertilized control) were applied annually in five complete randomized blocks. Species composition of experimental plots was sampled in 2006 and compared with constancy tables representing grassland types in a phytosociological monograph of a wider area. Each plot was matched to the most similar community type using the Associa method. Mean EIVs were calculated for each treatment.

Results: The control plots supported oligotrophic Nardus grassland of the Polygalo‐Nardetum association (Violion caninae alliance). Vegetation in the Ca and CaN treatments mostly resembled montane meadow of Geranio‐Trisetetum (Polygono‐Trisetion). Transitional types between Poo‐Trisetetum and Arrhenatheretum (both from the Arrhenatherion alliance) developed in the CaNP treatment. In the CaNP‐KCl and CaNP‐K2SO4 treatments, vegetation corresponded to the mesotrophic Arrhenatheretum meadow. Major discontinuity in species composition was found between control, Ca, and CaN treatments, and all treatments with P application. EIVs for both nutrients and soil reaction were considerably higher in P treatments than in Ca and CaN treatments. Surprisingly, the control plots had the lowest EIVs for continentality and moisture, although these factors had not been manipulated in the experiment.

Conclusions: Long‐term fertilizer application can create different plant communities belonging to different phytosociological alliances and classes, even within a distance of a few meters. Due to their correlated nature, EIVs can erroneously indicate changes in factors that actually did not change, but co‐varied with factors that did change. In P‐limited ecosystems, EIVs for nutrients may indicate availability of P rather than N.
Breastfeeding protects against infectious diseases during infancy in industrialized countries. A systematic review
Authors: Duijts Liesbeth , Ramadhani Made K. , Moll Henriëtte A.
Published: March 2009

Firstly, this review was performed to assess the effect of breastfeeding on infections during infancy in industrialized countries. Secondly, the effect of duration and exclusiveness of breastfeeding were explored. Studies were identified using Medline, Cochrane Library, Science Citation Index and by a manual search from bibliographies of articles from August 1986 to January 2008. Follow‐up, case–control and randomized controlled trial (RCT) studies performed in an industrialized country, published in English, with breastfeeding as a determinant, with overall infections, gastrointestinal or respiratory tract infections as a major outcome, and at least 40 participants in the study were included. Using Bauchner's criteria published in a review in 1986, two reviewers and a peer reviewer assessed the internal validity of those studies. Twenty‐one studies that met the inclusion and internal validity criteria were included. These included 16 follow‐up and four case–control studies and one RCT. Four out of five studies observed decreased effects on overall infections in breastfed infants. With regard to gastrointestinal infections, six out of eight studies suggested that breastfeeding had a protective effect. Thirteen out of 16 studies concluded that breastfeeding protects infants against respiratory tract infections. Five studies combined duration and exclusiveness of breastfeeding. All studies observed a protective dose/duration‐response effect on gastrointestinal or respiratory tract infections. These studies strongly suggest that breastfeeding protects infants against overall infections, gastrointestinal and respiratory tract infections in industrialized countries. The optimal duration of exclusive breastfeeding for protection against infectious diseases needs to be studied in more detail.
Are We Born and do We Die?
Authors: Lash Nicholas
Published: March 2009

The stranglehold on our imagination by the mind-body dualisms that permeate the culture is such that most people seem to suppose that “body” and “soul” name distinct and separable entities. Resisting such dualisms in favour of an old-fashioned Aristotelean view of the soul as the form of the body, this essay considers two questions: do human parents produce human beings, and do human beings die? The doctrine of the special creation of the individual soul seems to require us to answer the first question in the negative because, according to this doctrine, parents only produce matter for the God-given soul to form. As to the second, many people seem to suppose that human beings do not die, only their bodies do. Arguing against the view that immortality is a natural property of human minds, the essay suggests (with the help of Joseph Ratzinger) that, whether we speak of “immortality” or of “resurrection”, life from death is neither nature, nor achievement, but gift.
‘Not One Thing Exactly’: Gender, Performance and Critical Debates over the Early Modern Boy‐Actress
Authors: Barker Roberta
Published: March 2009

Coined by Harley Granville Barker, the term ‘boy‐actress’ describes young male actors, probably aged between 10 and 22 years, who appeared in women's roles on the early modern stage of Shakespeare and his contemporaries. These boys, their techniques, and their cultural meanings have recently become the subjects of heated critical debate. In our time as in their own, the impact of their onstage cross‐dressing on their gender identities and on the sexual desires of their spectators has proved particularly controversial. This essay outlines key early modern sources for our knowledge of the boy‐actress before considering the conflicting ways in which scholars have interpreted this evidence. Critical debates about the early modern boy‐actress may have as much to teach us about our own era's constructions of gender, sexuality and performance as about the realities of the Shakespearean stage.
The association of CTLA‐4 and CD28 gene polymorphisms with idiopathic ischemic stroke in the paediatric population
Authors: Wang J.‐J. , Jiang L.‐Q. , He B. , Shi K.‐L. , Li J.‐W. , Zou L.‐P.
Published: March 2009

Autoimmune vasculitis is believed to be a critical factor in the development of idiopathic childhood ischemic stroke. The association of polymorphisms in CTLA‐4 and CD28 with some immune vasculitides, such as systemic lupus erythematosus (SLE) and Behçet's disease has been reported. The aim of the present study is to investigate the association of the genetic variants in the CTLA‐4 and CD28 genes of children who suffered idiopathic ischemic stroke using a case–control design. Two single nucleotide polymorphisms (SNPs) in the CTLA‐4 gene and an SNP in the CD28 gene were genotyped in 51 patients who suffered idiopathic ischemic stroke, and in 74 healthy controls from mainland China. An SNP, CTLA‐4+49A/G located in exon 1 of the CTLA‐4 gene, showed nominal association with the disease (P = 0.012, odds ratio (OR) = 2.09, 95% confidence interval (CI) = 1.17–3.73) using allele‐based analysis. Homozygous carriers of the G allele of this SNP were more common in the patients than in the controls (P = 0.008). The CD28IVS3 +17TT genotype was found to be more common in the patients than in the controls (P = 0.039, OR = 2.96, 95% CI = 1.02–8.58). No correlations of at‐risk genotype (G/G) of CTLA‐4+49A/G and genotype (T/T) of CD28+17T/C with the main clinical features of idiopathic childhood ischemic stroke were observed. The results suggest that polymorphisms in the CTLA‐4 and CD28 genes may contribute to the increased risk of idiopathic ischemic stroke.
Effects of time of seed maturation on dormancy and germination requirements of Sporobolus spicatus (Vahl) Kunth, a native desert grass of the United Arab Emirates
Authors: El‐Keblawy Ali , Al‐Sodany Yassen M. , Al‐Hadad Fedea A.
Published: March 2009

The effect of time of seed maturation on dormancy and germination requirements was determined for seeds of Sporobolus spicatus (Vahl) Kunth, a species that could be used in rehabilitation of the degraded salt‐affected habitats. Seeds of S. spicatus were collected in May, August and December 2005 and March 2006 from a population around Al‐Ain City, United Arab Emirates (UAE). Seeds were germinated in incubators adjusted at 20°C, 25°C, 30°C and 35°C in continuous light and in darkness. Seeds incubated at the highest temperature (35°C) germinated significantly greater and faster, compared to those at the lower temperatures. The highest germination percentage in S. spicatus was observed for seeds matured during August, followed by those matured in December and May, but the lowest germination was recorded for seeds of March. Seeds of August germinated significantly greater in dark than in light, but the reverse was true for seeds of May. Germination rate was significantly faster for seeds of December than that of other seed lots, even at the lower temperature. The results are discussed in the light of the adaptive significance of the production of tiny seeds at different times of the year in S. spicatus.
Preliminary evaluation of native grasses collected from alpine rangelands in Qinghai Province, China, as materials for breeding grazing‐tolerant fine herbage
Authors: Zhou Qingping , Ji Yajun , De Bruijn Koos , Liang Guoling , Yan Hongbo
Published: March 2009

Development and introduction of productive, high‐quality herbage grasses tolerant of heavy grazing is an urgent necessity for sustainable use of rangelands in Qinghai Province, north‐west China, where degradation of rangelands caused mainly by overstocking has become a serious problem. Four hundred and sixty‐six native grass materials (species and types) were collected in the summer of 2002 from grazed alpine rangelands (2500–4000 m a.s.l.) in Qinghai Province, as original materials for breeding the target grasses. The plants were initially grown in the nurseries in Xining and Gancha until 2003, when 177 materials were preliminarily selected. Then, 147 materials that formed the most part of the 177 materials were grown in the new nursery in Xining and evaluated in 2005 for their productivity, palatability, persistency and seed yield. Two promising materials of Agrostis gigantea, three of Elymus cylindricus, eight of Elymus dahuricus, 10 of Elymus nutans, 14 of Elymus sibiricus, one of Puccinellia diffusa, five of Puccinellia distans, one of Puccinellia glauca, four of Puccinellia hauptiana, two of Puccinellia roborovski and four of Puccinellia tenuiflora were selected for future evaluation under grazing.
Polyamine Accumulation in Transgenic Tomato Enhances the Tolerance to High Temperature Stress
Authors: Cheng Lin , Zou Yijing , Ding Shuli , Zhang Jiajing , Yu Xiaolin , Cao Jiashu , Lu Gang
Published: March 2009

Polyamines play an important role in plant response to abiotic stress. S‐adenosyl‐l‐methionine decarboxylase (SAMDC) is one of the key regulatory enzymes in the biosynthesis of polyamines. In order to better understand the effect of regulation of polyamine biosynthesis on the tolerance of high‐temperature stress in tomato, SAMDC cDNA isolated from Saccharomyces cerevisiae was introduced into tomato genome by means of Agrobacterium tumefaciens through leaf disc transformation. Transgene and expression was confirmed by Southern and Northern blot analyses, respectively. Transgenic plants expressing yeast SAMDC produced 1.7‐ to 2.4‐fold higher levels of spermidine and spermine than wild‐type plants under high temperature stress, and enhanced antioxidant enzyme activity and the protection of membrane lipid peroxidation was also observed. This subsequently improved the efficiency of CO2 assimilation and protected the plants from high temperature stress, which indicated that the transgenic tomato presented an enhanced tolerance to high temperature stress (38 °C) compared with wild‐type plants. Our results demonstrated clearly that increasing polyamine biosynthesis in plants may be a means of creating high temperature‐tolerant germplasm.
SIMPLIFIED CAPACITANCE MONITORING FOR THE DETERMINATION OF CAMPYLOBACTER SPP. GROWTH RATES
Authors: AKINS E. DEANN , RULE PATRICIA L. , KEENER MICHELLE R. , SELLERS HOLLY S. , LINE J. ERIC , SIMMONS MUSTAFA , HARRISON MARK A. , HIETT KELLI L.
Published: March 2009

Capacitance monitoring is commonly used as an efficient means to generate growth curves of bacterial pathogens. However, the use of capacitance monitoring with Campylobacter spp. was previously determined to be difficult due to the complexity of the required media. We investigated capacitance monitoring using a simplified medium for the efficient and reproducible construction of growth curves for Campylobacter spp. It was determined that Campylobacter spp. should initially be propagated on Mueller Hinton plates in a microaerobic atmosphere (5% O2, 10% CO2, 85% N2) at 37C for 24 h, followed by transfer to Mueller Hinton biphasic cultures for 6 h at 37C in a microaerobic atmosphere. Serial dilutions of the Campylobacter spp. cultures should be used for inoculation of Bactometer wells that contain 1 mL Mueller Hinton broth supplemented with 0.1 M sodium pyruvate for the completion of Campylobacter spp. growth curves with the Bactometer.

PRACTICAL APPLICATIONS

Growth rates can vary greatly among Campylobacter isolates; therefore, the rapid and reproducible methods described will prove useful in studies where the generation of growth curves is critical for subsequent experimental analyses.
RACIAL ANIMOSITY AND INTERRACIAL CRIME*
Authors: D'ALESSIO STEWART J. , STOLZENBERG LISA
Published: March 2009

The primary objective of this study is to determine the effect of a victim's race on the likelihood of him or her being seriously injured during the commission of an interracial crime. We also assess the probability of a homicide occurring during an interracial crime. A multilevel city analysis shows that black offenders are no more apt than white offenders to injure their victims seriously during an interracial robbery or rape. A black offender also does not have a greater proclivity to kill his or her victim during the commission of an interracial crime. Some evidence suggests that white victims are more likely than black victims to suffer serious physical harm during an aggravated assault. Results also reveal that contextual factors related to racial animosity, such as residential segregation, white‐to‐black economic inequality, and black‐to‐white unemployment, fail to have any moderating effect on either the severity of victim injury or the likelihood of a homicide occurring during an interracial crime. Overall, the results generated in this study tend to cast doubt on the validity of racial animosity theory. Our findings also lead us to question the veracity of the oftenmade claim that black‐on‐white crimes are punished more severely because these types of offenses are somehow more heinous in circumstance. At least in regard to serious victim injury and victim death, black‐on‐white crime is no more violent than white‐on‐black crime.
Internet and World Wide Web‐Based Tools for Neuropathology Practice and Education
Authors: Fung Kar‐Ming , Tihan Tarik
Published: March 2009

The Internet and the World Wide Web (www) serve as a source of information and a communication network. Together they form a so‐called web or network that allows for transmission and dissemination of information in unprecedented speed, volume and detail. This article presents an overview of the current status of neuropathology content on the www. As well as considering the Internet as a resource for neuropathology practice, education and research, we also address the issue of quality assurance when evaluating Internet and www content. Four major categories of websites (archival, broker, news and blog) are discussed and resources relevant to neuropathology of each type are highlighted. We believe that our report and similar attempts can provide an opportunity to discuss appropriate and effective use of the Internet by the neuropathology community.
Digital Pathology: A Tool for 21st Century Neuropathology
Authors: Guzman Miguel , Judkins Alexander R.
Published: March 2009

Digital pathology represents an electronic environment for performing pathologic analysis and managing the information associated with this activity. The technology to create and support digital pathology has largely developed over the last decade. The use of digital pathology tools is essential to adapt and lead in the rapidly changing environment of 21st century neuropathology. The utility of digital pathology has already been demonstrated by pathologists in several areas including consensus reviews, quality assurance (Q/A), tissue microarrays (TMAs), education and proficiency testing. These utilities notwithstanding, interface issues, storage and image formatting all present challenges to the integration of digital pathology into the neuropathology work environment. With continued technologic improvements, as well as the introduction of fluorescent side scanning and multispectral detection, future developments in digital pathology offer the promise of adding powerful analytic tools to the pathology work environment. The integration of digital pathology with biorepositories offers particular promise for neuropathologists engaged in tissue banking. The utilization of these tools will be essential for neuropathologists to continue as leaders in diagnostics, translational research and basic science in the 21st century.
Thermal Conductivity Measurements on Polycrystalline Silicon Microbridges Using the 3ω Technique
Authors: Hopkins Patrick E. , Phinney Leslie M.
Published: March 2009

The thermal performance of microelectromechanical systems devices is governed by the structure and composition of the constituent materials as well as the geometrical design. With the continued reduction in the characteristic sizes of these devices, experimental determination of the thermal properties becomes more difficult. In this study, the thermal conductivity of polycrystalline silicon (polysilicon) microbridges are measured with the transient 3ω technique and compared with measurements on the same structures using a steady state Joule heating technique. The microbridges with lengths from 200 μm to 500 μm were designed and fabricated using the Sandia National Laboratories SUMMiT V™ surface micromachining process. The advantages and disadvantages of the two experimental methods are examined for suspended microbridge geometries. The differences between the two measurements, which arise from the geometry of the test structures and electrical contacts, are explained by bond pad heating and thermal resistance effects.
Evaluations of Cavitation Models for Navier-Stokes Computations
Authors: Senocak Inanc , Shyy Wei
Published: March 2009

The predictive capability of three transport equation-based cavitation models is evaluated for attached turbulent, cavitating flows. To help shed light on the theoretical justification of these models, an analysis of the mass and normal-momentum conservation at a liquid-vapor interface is presented. The test problems include flows over an axisymmetric cylindrical body and a planar hydrofoil at different cavitation and Reynolds numbers. Proper grid distribution for high Reynolds number cavitating flows is emphasized. Although all three models give satisfactory predictions in overall pressure distributions, differences are observed in the closure region of the cavity, resulting from the differences in compressibility characteristics handled by each model.
Drag Reduction and Transition Delay of Bluff Body Flows by Passive Boundary Layer Control
Authors: Bruneau Charles-Henri , Mortazavi Iraj
Published: March 2009

The aim of this work is to control the flow around obstacles by a passive strategy. The idea is to modify the boundary flow in order to delay the instabilities and reduce the drag forces and the vorticity production. The target is achieved using a porous interface between the solid body and the fluid. This is easily handled by means of a penalization method that allows to modelize different media by changing the penalization parameter. The results for low and high transitional flows around a 2D square show that the porous interface is an efficient tool to control the flow dynamics. In addition, a drag reduction up to 28% is observed.
Active Control of Separation Bubbles Exploiting Laminar Baseflow Instabilities
Authors: Augustin Kai , Rist Ulrich , Wagner Siegfried
Published: March 2009

In the present paper laminar separation bubbles are investigated by means of direct numerical simulations with respect to steady and unsteady 2D and 3D Tollmien-Schlichting (TS) like boundary layer disturbances. The specific influence of several disturbance modes on the size and shape of the laminar separation bubble are considered to allow for an effective reduction of the region of separated flow. Based on these results a criterion to detect the extension of the bubble is derived which is a suitable input for a controller.
Experimental Study of Heat and Mass Transfers at the Interface of Solidification of a Binary Solution
Authors: Geoffroy Sandrien , Mergui Sophie , Benard Christine
Published: March 2009

This paper deals with the experimental analysis of the influence of thermohaline natural convection on phase change liquid-solid of multicomponent mixtures. We present solidification experiments (dendritic front) from a horizontal plane heat exchanger placed in a cavity filled with a binary NH4Cl-H2O mixture. The solid grows simultaneously on the upper and lower faces of the exchanger and permits the study of two simultaneous configurations. We qualitatively study phenomena met in the presence of thermohaline convection in the liquid phase (cooling from the top) and we analyze in detail the case of the growth without convective movement in the liquid phase (cooling from the bottom). Thus, coupled effects of salt rejection and solid fraction on the front kinetics are examined by measurements of the front temperature and solid fraction. A simple model confirms the weak role played by these two phenomena for the range of characteristic parameters studied. Two conflicting effects of the solid fraction are nevertheless put in evidence.
Super-Fine Structure in the Critical Flow-Rate of Critical Flow Venturi Nozzles
Authors: Ishibashi Masahiro
Published: March 2009

It is shown that critical flow Venturi nozzles need time intervals, i.e., more than five hours, to achieve steady state conditions. During these intervals, the discharge coefficient varies gradually to reach a value inherent to the pressure ratio applied. When a nozzle is suddenly put in the critical condition, its discharge coefficient is trapped at a certain value then afterwards approaches gradually to the inherent value. Primary calibrations are considered to have measured the trapped discharge coefficient, whereas nozzles in applications, where a constant pressure ratio is applied for a long time, have a discharge coefficient inherent to the pressure ratio; inherent and trapped coefficients can differ by 0.03–0.04%.
Parametric Study of the Discharge Coefficient on Critical Sonic Nozzles ISO-9300 With Turbulent Boundary Layer
Authors: Sa´nchez Silva F. , Cruz Maya J. A. , Go´mez Mercado A. , Tolentino Eslava G.
Published: March 2009

A parametric study on determining discharge coefficient in ISO 9300 [1] toroidal sonic nozzles have been developed. The focus of this paper is to obtain the an analytical model for the calculus of this discharge coefficient on turbulent boundary layer conditions for gases at Pr = 0.7. The problem is divided in two sections: one in which the viscous stresses are taking in to account at boundary layer zone, based on turbulent boundary layer theory and taking as starting point the work carried out by Stratford [2]. Then, curvature of flow field is studied at the nucleus of the nozzle, obtaining discharge coefficient values using numerical simulation for a two-dimensional flow. The results have a good agreement with correlations of ISO-9300 [1], experimental and numerical data of Wu-Yan [3] and the analytical model from Stratford [2].
Homogeneous Engine Cooling: An Efficient Cross-Cooling Strategy — CFD Analysis and Measurements
Authors: Etemad S.
Published: March 2009

A new precision cross-cooling strategy is developed for IC-engines to contribute to lower exhaust emissions, better fuel-economy, better engine durability and compact packaging. The heat transfer is increased by 40% in the inter-bore regions and by 160% on the exhaust valve-bridges. The cylinders are also cooled more equally. The pressure drop decreased by 26% and the flow increased by 60%. The pumping power for the whole system decreased by 9% and in addition due to some 4% reduction of thermal waste, up to 2% improvement in engine efficiency can be assumed. Increased flow also facilities enhanced performance for the radiator and cab-heater. The investigation was done by CFD and verified by measurements in engine test-bed. By displaying up to 28°C decrease in the inter-bore region and up to 15°C decrease in the valve-bridge region, the tests confirmed the CFD-predicted improvements.
An Interface Tracking Method Based on Volume Tracking in Embedded Micro Cells
Authors: Tomiyama Akio , Nakahara Yusuke , Abe Satoru
Published: March 2009

An interface tracking method based on volume tracking in micro cells embedded in regular cells is proposed. The volume tracking is based on a CIP scheme, which yields extremely sharp and jaggy interface in micro cells. However, in regular cells, the jagged interface is smoothed and the interface thickness becomes comparable to a regular cell size Δx. Single air bubbles in stagnant water and single large air bubbles in stagnant water filled in a vertical pipe are simulated with the proposed method. As a result, it is confirmed that (1) the proposed method conserves bubble volumes, (2) the interface thickness around a bubble is kept within 2Δx, and thereby the surface tension force is well evaluated by the CSF model, and (3) the method can give good predictions for bubbles in a high density-ratio system.
Unsteady Flow Structure on a Centrifugal Pump: Experimental and Numerical Approaches
Authors: Gonza´lez Jose´ , Santolaria Carlos , Blanco Eduardo , Ferna´ndez Joaqui´n
Published: March 2009

Both experimental and numerical studies of the unsteady pressure field inside a centrifugal pump have been carried out. The unsteady patterns found for the pressure fluctuations are compared and a further and more detailed flow study from the numerical model developed will be presented in this paper. Measurements were carried out with pressure transducers installed on the volute shroud. At the same time, the unsteady pressure field inside the volute of a centrifugal pump has been numerically modelled using a finite volume commercial code and the dynamic variables obtained have been compared with the experimental data available. In particular, the amplitude of the fluctuating pressure field in the shroud side wall of the volute at the blade passing frequency is successfully captured by the model for a wide range of operating flow rates. Once the developed numerical model has shown its capability in describing the unsteady patterns experimentally measured, an explanation for such patterns is searched. Moreover, the possibilities of the numerical model can be extended to other sections (besides the shroud wall of the volute), which can provide plausible explanations for the dynamic interaction effects between the flow at the impeller exit and the volute tongue at different axial positions. The results of the numerical simulation are focused in the blade passing frequency in order to study the relative effect of the two main phenomena occurring at that frequency for a given position: the blade passing in front of the tongue and the wakes of the blades.
Computational Studies for Turbomachinery Simulation (Kenote Paper)
Authors: Durbin P. A.
Published: March 2009

Three-dimensional numerical simulation of turbulent flow and of convective heat transfer are becoming integral to the complex procedure of gas turbine blade design. The application to heat transfer presents new problems in flow prediction by Reynolds averaged methods. Many fundamental and practical developments are needed before full three-dimensional computational analysis becomes reliable. This article reviews some of our work in this area. Fundamental studies of turbine flow by Direct Numerical Simulation are also surveyed. Reynolds numbers encountered in parts of the turbine are such that DNS is practicable. Our initial simulations were of a flat plate geometry, addressing the topic of wake-induced transition. More recently flow flow in a linear, low pressure turbine cascade has been simulated, examining wake-induced transition, wake distortion, vortex formation and turbulence distortions.
Meshing Method for Transient Computation With Complex Geometry in CFD
Authors: Kueny J. L. , Dore´ B. , Coppens G.
Published: March 2009

The description of mesh evolution during a transient computation with moving walls and mesh adaptation has to respect many rules. Using a good mesh for each computational time step is important for accuracy of results. The complexity of geometry can make this objective more complex. A method has been developed to obtain a good moving mesh description with complex boundary geometry. It is based on a local observation of boundary movement and can be resumed by two main ideas: • Add cells where the volume of solution domain increases. • Slide the mesh where the boundary has a tangential displacement.
Monte Carlo Simulation of Colliding Particles in Gas-Solid Turbulent Flows From a Joint Fluid-Particle PDF Equation
Authors: Fede Pascal , Simonin Olivier , Villedieu Philippe
Published: March 2009

This paper is dedicated to Lagrangian approach for modelling particle-particle interactions in gas-solid turbulent flows. This approach is based on a joint fluid-particle pdf equation solved using Monte Carlo method which has been developed to take into account the correlation between colliding particles induced by the fluid. The modification of the turbulence by the particles is not included in the simulations. The Lagrangian results are presented in comparison with LES simulations (Lavie´ville et al., 1995) and continuum model.
A Continuous Interface Model for the Direct Numerical Simulation of Phase-Change in Two-Component Liquid-Vapor Flows
Authors: Fouillet Ce´lia , Jamet Didier , Lhuillier Daniel
Published: March 2009

This paper presents a model dedicated to the numerical simulation of two-component liquid-vapor flows with phase-change. This model is an extension to binary mixtures of the second gradient method, initially dedicated to pure fluids. It is a diffuse interface method: by assuming that the free energy of the mixture depends on its density gradient, liquid-vapor interfaces are described as volumetric transition regions across which physical properties vary continuously. The corresponding governing equations of the mixture are derived and the thermodynamic closure relation is established in order to recover the equilibrium properties of a mixture. As a first validation of this model, it is applied to study a one-dimensional isothermal phase-change problem. When the system reaches a stationary state, an asymptotic analysis shows that this model is in good agreement with sharp interface models, as well as numerical calculations.
Kinetic Simulations for Analysing the Wall Collision Process of Non-Spherical Particles
Authors: Sommerfeld M.
Published: March 2009

In wall-bounded gas-solid flows the wall collision process plays an important role and may be strongly affected by wall roughness and particle shape. The modelling of the particle-wall collision mostly relies on the assumption of spherical particles. To extend such models appropriately for non-spherical particles, two-dimensional kinetic simulations were performed for different particle shapes. This implies, that the particle translational and angular motion is calculated by considering the particle shape, however neglecting fluid dynamic effects. The change of the particle velocities during the impact and rebound process was calculated by solving the impulse equations together with Coulombs law of friction. The simulations were performed for a given initial particle velocity by varying impact angle and initial angular velocity. The results for 2000 particle wall collisions allowed us to derive the distribution functions of the impact parameters required to describe the wall collision process for non-spherical particles correctly. Moreover, other wall collision properties, such as rebound angle and velocity ratios could be determined. Finally also a comparison with measurements was possible.
Resolving Turbulent Wakes
Authors: Jordan Stephen A.
Published: March 2009

Accurate resolution of turbulent wakes is a formidable task. Herein, we challenge this task by testing several compact schemes for approximating the convective derivative of the direct numerical and large-eddy simulation (DNS and LES) methodologies. The stencils house the needed resolution efficiency and numerical stability characteristics to properly resolve turbulent wakes while concurrently maintaining convergent solutions. Turbulent wakes of the circular cylinder are computed for Re = 1260 and 3900 with the results verified by the experimental evidence.
Designing a Scaled Erosion Test With Computational Fluid Dynamics Methods
Authors: Lee S. Y. , Dimenna R. A. , Duignan M. R.
Published: March 2009

The Department of Energy is sponsoring the River Protection Project, which includes the design of a facility to stabilize liquid radioactive waste that is stored at the Hanford Site. Because of its experience with radioactive waste stabilization, the Savannah River Technology Center of the Westinghouse Savannah River Company is assisting in the development and testing of parts of the waste treatment process. One part of the process is the separation of highly radioactive solids from the liquid wastes by cross-flow ultrafiltration. For the projected forty-year life of the filtration facility, wear will occur from a combination of erosion and corrosion due to the flow of slurries. A scaled cross-flow filter facility will be tested with simulated waste to quantify the wear rate so that an effective maintenance schedule can be developed. This paper discusses the application of computational fluid dynamics (CFD) methods to ensure that the test facility design would capture the erosion phenomena expected in the full-scale cross-flow ultrafiltration facility. An initial literature survey helped identify the principal drivers of erosion for a solids laden fluid. These were the solids content of the working fluid, the regions of recirculation and particle impact with the walls, and the regions of high wall shear. A series of CFD analyses was then designed to characterize slurry-flow profiles, wall shear, and particle impingement distributions in key pipe bends and fittings representative of the plant. Pipe diameters, lengths, the locations of pipefittings, and slurry velocities were scaled with the CFD calculations to ensure that the erosion drivers were appropriately represented in the test facility. This resulted in a validation of the theoretical determination of those drivers, and allowed the test results to be applied to a prediction of wear in the full-scale filtration facility.
Experimental and Numerical Study of Gas-Liquid Displacements in Flow Cells, With Application to Carbon Dioxide Sequestration in Brine Fields
Authors: Smith Duane , Ahmadi Goodarz , Ji Chuang , Bromhal Grant , Ferer Martin V.
Published: March 2009

In this paper experimental and computational modeling methods for studying viscous fingering phenomena occurring during underground CO2 sequestration were developed. In the experiment, the displacement of two immiscible fluids in a lattice-like flow cell was studied. The flow pattern during the displacement was analyzed, and the residual saturation of the displaced fluid was measured. Numerical simulations of the experimental flow cell were performed. The numerical simulation results are compared with the experimental data good agreement was observed.
Computation of Turbulent Flows and Aero-Acoustics From an Axial Fan
Authors: Bae Il-Sung , Kim Hooi-Joong , Lee Seungbae
Published: March 2009

LES formulation was applied to simulate the flow fields around rotating fan blades tested by DLR. The turbulent flows around fan blade rotating with 500 RPM were simulated and the far-field noise was exactly computed by using the Ffowcs Williams and Hawkings equation with an inclusion of quadrupole source formulation. Variations of lift forces and deviation angles in the spanwise direction were analyzed to correlate flow parameters with acoustics parameters and identify noise sources. The dipole noise computed at the far-field by computed drag and lift forces was in good agreement with experimental data and the dipole source was also found to be the major contributor to overall far-field noise from unsteady calculation.
Discretization Error Estimation Using Error Transport Equation
Authors: Celik Ismail , Hu Gusheng
Published: March 2009

The goal of this paper is to develop a dynamic algorithm that can be used in conjunction with computational fluid dynamics (CFD) simulation codes to quantify the discretization error in a selected process variable. The focus is on fluid dynamics applications where conservation equations are solved for primitive variables using finite difference and/or control volume approach. A transport equation for the error is formulated and solved along with a localized residual estimation based on modified equation concept. Spatiotemporal evolution of the error distribution is mapped and compared to exact error for various cases. A new method is suggested for deriving the modified equation specifically aimed at using it with commercial CFD codes which use finite volume approach.
Measuring Material Distributions of Multiphase Flows in Electrically Conducting Vessels Using Electrical-Impedance Tomography
Authors: Liter S. G. , Shollenberger K. A. , Torczynski J. R. , Ceccio S. L.
Published: March 2009

An implementation of resistive electrical-impedance tomography (EIT) for measuring material distributions of multiphase flows in vessels with electrically conducting walls is presented. Seven ring electrodes are equally spaced on a thin nonconducting rod that is inserted into the vessel. The vessel wall is grounded and serves as the ground electrode. Voltage distribution measurements are used to numerically reconstruct the time-averaged impedance distribution within the vessel, from which the material distributions are inferred. Experimental results for the case in which the rod is inserted coaxially into a liquid-filled vertical standpipe containing beds of different heights of nonconducting solid particles are presented. Agreement between the direct measurement and the numerical reconstruction of the particle-bed height is good. Application of this technique to a pilot-scale slurry bubble-column reactor is discussed.
Closure Laws for the Transport Equation of Interfacial Area in Dispersed Flow
Authors: Rioua X. , Fabrea J. , Colin C.
Published: March 2009

Derivation of a transport equation for the interfacial area concentration. In two-phase flows, the interfacial area is a key parameter since it mainly controls the momentum heat and mass transfers between the phases. An equation of transport of interfacial area may be very useful, especially for the two-fluid models. Such an equation should be able to predict the transition between the flow regimes. With this aim in view, we shall focus our attention on pipe flow. Besides in a first step, our study will be limited to dispersed flows. Different models are used to predict the evolution of bubble sizes. Some models use a population balance that provides a detailed description of the bubble size distributions, but they require as many equations as diameter ranges (Coulaloglou & Tavlarides1). Some others use only one equation for the transport of the mean interfacial area (Hibiki & Ishii2). In that case the bubble size distribution is treated as it would be monodispersed, its mean diameter being equal to the Sauter diameter. An intermediate approach was proposed by Kamp et al.3, in which polydispersed size distributions can be taken into account. It is the starting point of the present study in which: • The choice of an interfacial velocity is discussed. • The sink and source terms due to bubble coalescence, break-up or phase change are established. The model of Kamp et al. consists of transport equations of the various moments of the density probability function P(d) of the bubble diameter. In many experimental situations, P(d) is well predicted by a log-normal law (with two characteristic parameters d00 the central diameter of the distribution and a width parameter): The different moments of order ? of P(d) may be calculated: Sγ=n∫P(d)dγd(d)(1) where n is the bubble number density, S1/n, the mean diameter and S2/?, the interfacial area. A transport equation can be written for each moment: ∂Sγ∂t+∇·(uGSγ)=φγ(2) The lhs of (2) is an advection term by the gas velocity uG and the rhs is a source or sink term due to bubble coalescence, break-up or mass transfer. Since the bubble size distribution is characterised by the two parameters d00 and σˆ, only two transport equations (for S1 and S2) have to be solved to calculate the space-time evolution of the bubble size distribution. These two equations are still too cumbersome for a two-fluid model. Under some hypotheses (σˆ ∼ constant), they are lead to a single equation for the interfacial area. In its dimensionless form the interfacial area ai+ (ai+ = π S2 D, where D is the pipe diameter) reads: d/dt+(ai+)=f(RG,Re,We,ai+)(3) where RG is the gas fraction, Re is the Reynolds number of the mixture, We the Weber number of the mixture and t+ a dimensionless time.
Approximate Solution of the Population Balance Equation for Three Dimensional Flow Field in Bubble Columns With and Without Mass Transfer
Authors: Mewes Dieter , Wiemann Dierk
Published: March 2009

In this paper bubble size distributions and flow fields in bubble columns are calculated numerically. The population balance is simplified and reduced to a balance equation for the average bubble volume. Models are developed in order to predict the rate of bubble break-up and coalescence based on physical principals. The flow fields are numerically calculated for bubble columns with cylindrical cross section using the Euler-Euler method. The newly derived balance equations for the average bubble volumes are implemented into a commercial CFD-code. The solutions of the balance equation result for high superficial gas velocities mainly in two fractions, one for the fraction with small and one for the fraction with large bubble diameters. Both are considered as pseudo continuous phases in addition to the liquid phase. The calculated flow fields are characterized by several large scale vortices. The local volume fractions of gas and liquid are locally inhomogeneous and highly time dependent. The time averaged flow field is axisymmetric and stationary. The calculated volume fractions, velocities and bubble size distributions agree well with experimental results for bubble columns up to 0.3m in diameter.
CFD Prediction of Smoke Spread During Hot-Smoke Tests in a Warehouse
Authors: Ayranci Seyit A. , Turan O¨zden F. , Taylor Peter
Published: March 2009

A series of hot smoke tests is underway in a warehouse for comparison with more realistic fire experiments. Hot smoke tests are used commonly in the fire safety assessment of large enclosures. COMPACT is used in the numerical prediction of the spread of smoke and hot gasses in the warehouse during hot smoke tests. The comparison of numerical results with the measurements indicate satisfactory agreement. COMPACT will be utilized next in the prediction of fire experiments, as a contribution to the use of CFD tools in the development of performance based fire codes.
CFD Modeling of Non-Premixed Combustion in a Gas Turbine Combustor
Authors: Majidi Kitano
Published: March 2009

In the present study numerical calculations are used to solve reacting flow in a gas turbine combustor. A 3-D Favre-Averaged Navier-Stokes solver for a mixture of chemically reacting gases is applied to predict the flow pattern, gas temperature and fuel and species concentrations in the entire combustor. The complete combustor geometry with all important details such as air swirler vane passages and secondary holes are modeled. The calculations are carried out using three different turbulence models. Comparisons are made between the standard k-ε model, RNG k-ε model and a Reynolds stress transport model. To provide a closure for the chemical source term the Eddy Dissipation model is used. A lean direct injection of a liquid fuel is employed. Furthermore the influence of radiation will be investigated.