bluuebunny/crossref_metadata_2025 huggingface dataset:
Inconsistent Evidence: Analysis of Six National Guidelines for Vaginal Birth After Cesarean Section
Authors: Foureur Maralyn , Ryan Clare L. , Nicholl Michael , Homer Caroline
Published: February 2010

Abstract:  Background:  Guidelines are increasingly used to direct clinical practice, with the expectation that they improve clinical outcomes and minimize health care expenditure. Several national guidelines for vaginal birth after cesarean section (VBAC) have been released or updated recently, and their range has created dilemmas for clinicians and women. The purpose of this study was to summarize the recommendations of existing guidelines and assess their quality using a standardized and validated instrument to determine which guidelines, if any, are best able to guide clinical practice.

Methods:  English language guidelines on VBAC were purposively selected from national and professional organizations in the United Kingdom, United States, Canada, New Zealand, and Australia. The Appraisal of Guidelines for Research and Evaluation (AGREE) instrument was applied to each guideline, and each was analyzed to determine the range and level of evidence on which it was based and the recommendations made.

Results:  Six guidelines published or updated between 2004 and 2007 were examined. Only two of the six guidelines scored well overall using the AGREE instrument, and the evidence used demonstrated great variety. Most guidelines cited expert opinion and consensus as evidence for some recommendations. Reported success rates for VBAC ranged from 30 to 85 percent, and reported rates of uterine rupture ranged from 0 to 2.8 percent.

Conclusions:  VBAC guidelines are characterized by quasi‐experimental evidence and consensus‐based recommendations, which lead to wide variability in recommendations and undermine their usefulness in clinical practice. (BIRTH 37:1 March 2010)
Time of Pregnancy Recognition and Prenatal Care Use: A Population‐based Study in the United States
Authors: Ayoola Adejoke B. , Nettleman Mary D. , Stommel Manfred , Canady Renee B.
Published: February 2010

Background:  A woman who does not recognize her pregnancy early may not initiate prenatal care early. This study examined the relationship between the time of pregnancy recognition and the time of initiation of prenatal care, and the number of prenatal visits among women of childbearing age.

Methods:  This study analyzed the Pregnancy Risk Assessment and Monitoring System (PRAMS) data for the United States. The analysis sample was representative of resident women of childbearing age in 29 U.S. states who had live births within 2 to 6 months before being contacted. The data were weighed to reflect the complex survey design of the PRAMS, and binary and multinomial logistic regressions were used for the analyses.

Results:  Most (92.5%) of the 136,373 women in the study had recognized their pregnancy by  12 weeks of gestation, and 80 percent initiated prenatal care within the first trimester. Early pregnancy recognition was associated with significantly increased odds of initiating prenatal care early (OR = 6.05, p < 0.01), after controlling for sociodemographic and prior birth outcome data, and was also associated with lower odds of having fewer than the recommended number of prenatal visits and higher odds of having more than the recommended prenatal visits (OR: <11 visits = 0.71 and >15 visits = 1.17, p < 0.01).

Conclusions:  Early pregnancy recognition was associated with improved timing and number of prenatal care visits. Promotion of early pregnancy recognition could be a means of improving birth outcomes by encouraging and empowering women to access prenatal care at a critical point in fetal development. (BIRTH 37:1 March 2010)
The Fetal Occiput Posterior Position: State of the Science and a New Perspective
Authors: Simkin Penny
Published: February 2010

Abstract:  Background:  The fetal occiput posterior position poses challenges in every aspect of intrapartum care—prevention, diagnosis, correction, supportive care, labor management, and delivery. Maternal and newborn outcomes are often worse and both physical and psychological traumas are more common than with fetal occiput anterior positions. The purpose of this paper is to describe nine prevailing concepts that guide labor and birth management with an occiput posterior fetus, and summarize evidence to clarify the state of the science.

Methods:  A search was conducted of the databases of PubMed and the Cochrane Library. Additional valuable information was obtained from obstetric and midwifery textbooks, books and websites for the public, conversations with maternity care professionals, and years of experience as a doula.

Results:  Nine prevailing concepts are as follows: (1) prenatal maneuvers rotate the occiput posterior fetus to occiput anterior; (2) it is possible to detect the occiput posterior fetus prenatally; (3) a fetus who is occiput anterior at the onset of labor will remain in that position throughout labor; (4) back pain in labor is a reliable sign of an occiput posterior fetus; (5) the occiput posterior fetus can be identified during labor by digital vaginal examination; (6) an ultrasound scan is a reliable way to detect fetal position; (7) maternal positions facilitate rotation of the occiput posterior fetus; (8) epidural analgesia facilitates rotation; (9) manual rotation of the fetal head to occiput anterior improves the rate of occiput anterior deliveries. Concepts 1, 2, 3, 4, 5, and 8 have little scientific support whereas concepts 6, 7, and 9 are supported by promising evidence.

Conclusions:  Many current obstetric practices with respect to the occiput posterior position are unsatisfactory, resulting in failure to identify and correct the problem and thus contributing to high surgical delivery rates and traumatic births. The use of ultrasound examination to identify fetal position is a method that is far superior to other methods, and has the potential to improve outcomes. Research studies are needed to examine the efficacy of midwifery methods of identification, and the effect of promising methods to rotate the fetus (simple positional methods and digital or manual rotation). Based on the findings of this review, a practical approach to care is suggested. (BIRTH 37:1 March 2010)
Use of Incinerator Bottom Ash for Frit Production
Authors: Barberio Grazia , Buttol Patrizia , Masoni Paolo , Scalbi Simona , Andreola Fernanda , Barbieri Luisa , Lancellotti Isabella
Published: February 2010

This article presents the results of an experimental activity aimed at investigating the technical feasibility and the environmental performance of using municipal solid waste incineration bottom ash to produce glass frit for ceramic glaze (glaze frit). The process includes an industrial pretreatment of bottom ash that renders the material suitable for use in glaze frit production and allows recovery of aluminum and iron. The environmental performance of this treatment option is assessed with the life cycle assessment (LCA) methodology. The goal of the LCA study is to assess and compare the environmental impacts of two scenarios of end of life of bottom ash from municipal solid waste incineration (MSWI): landfill disposal (conventional scenario) and bottom ash recovery for glaze frit production (innovative scenario). The main results of the laboratory tests, industrial simulations, and LCA study are presented and discussed, and the environmental advantages of recycling versus landfill disposal are highlighted.
Influence of Alkaline and Niobium Excess on Sintering and Microstructure of Sodium‐Potassium Niobate (K0.5 Na0.5)NbO3
Authors: Acker Jérôme , Kungl Hans , Hoffmann Michael J.
Published: February 2010

One of the major factors limiting the application of lead‐free sodium potassium niobate‐based materials are difficulties in establishing stable processing procedures. The effects of alkaline and niobium excess on the preparation and properties of (K0.5 Na0.5)NbO3 (KNN) ceramics have been investigated. KNN ceramics with varying A/B site ratios were prepared from alkaline carbonates and niobium oxide. The properties of the powders after calcination and milling were monitored, sintering behavior was analyzed, and microstructures of the ceramics were investigated using scanning electron microscopy during several stages of the sintering process. Compared with the stoichiometric KNN, sintering shrinkage is shifted to lower temperatures by A‐site excess and toward higher temperatures by B‐site excess. When sintering close to the solidus, the stoichiometric KNN shows large 10–40‐μm‐sized, nonpolyhedral‐shaped grains with intragranular porosity. The grains of A‐site excess KNN are similar in size, but growing in cuboid forms without the presence of intragranular pores. In B‐site excess KNN, the grains remain almost one order of magnitude smaller. Attempts are made to specify the mechanisms that influence the marked differences in sintering behavior between the compositions and to relate them to the microstructural development. The results indicate the importance of the A/B stoichiometry for the microstructure of the ceramics and the development of appropriate processing procedures.
Functions of ICC‐like cells in the urinary tract and male genital organs
Authors: Hashitani Hikaru , Lang Richard J.
Published: February 2010

Overview

Individual organs

Future of ICC‐LCs research in urogenital organs

Interstitial cells of Cajal (ICC)‐like cells (ICC‐LCs) have been identified in many regions of the urinary tract and male genital organs by immunohistochemical studies and electron microscopy. ICC‐LCs are characterized by their spontaneous electrical and Ca2+ signalling and the cellular mechanisms of their generation have been extensively investigated. Spontaneous activity in ICC‐LCs rises from the release of internally stored Ca2+ and the opening of Ca2+‐activated Cl− channels to generate spontaneous transient depolarizations (STDs) in a manner not fundamentally dependent on Ca2+ influx through L‐type voltage‐dependent Ca2+ channels. Since urogenital ICC‐LCs have been identified by their immunoreactivity to Kit (CD117) antibodies, the often‐used specific marker for ICC in the gastrointestinal tract, their functions have been thought likely to be similar. Thus ICC‐LCs in the urogenital tract might be expected to act as either electrical pacemaker cells to drive the smooth muscle wall or as intermediaries in neuromuscular transmission. However, present knowledge of the functions of ICC‐LCs suggests that their functions are not so predetermined, that their functions may be very region specific, particularly under pathological conditions. In this review, we summarize recent advances in our understanding of the location and function of ICC‐LCs in various organs of the urogenital system. We also discuss several unsolved issues regarding the identification, properties and functions of ICC‐LCs in various urogenital regions in health and disease.
Measurement of a possible patch‐testing outcome indicator
Authors: Gallo Rosella , Baldari Manuela , Fausti Valentina , Montinari Martina , Santoro Francesca , Christana Konstantina , Rosso Rita , Cozzani Emanuele , Parodi Aurora
Published: February 2010

Background: Clinical performance measurements often employ outcome indicators to express the extent to which health services achieve a given clinical result.

Objective: The objective of our study was to develop an outcome indicator of patch testing. We identified and measured as a possible indicator the ratio of patients with allergic and/or photo‐allergic contact dermatitis clinically cured/improved as a result of identification of relevant allergens.

Patients/Methods: Patients with positive reactions considered relevant to their current dermatitis were interviewed by telephone 2 months after patch/photo‐patch testing in order to assess their clinical outcome in relation to the recommended elimination of supposedly relevant allergens.

Results: Over a 4‐year period positive reactions were seen in 1397 out of 2857 tested patients. Relevance was considered current in 578 subjects, and 506 of them were interviewed.

Remission/significant improvement following allergen(s) contact avoidance was reported by 431 patients, the outcome indicator (431/506) thus scoring 85.2%. Among the 75 patients who reported no improvement, 41 had not avoided contact with the offending substance(s), 17 had other persistent concomitant skin conditions, and 17 were unchanged despite elimination of the alleged relevant allergens.

Conclusions: The ratio of relevantly patch‐test‐positive patients resolved/improved after allergen avoidance is a useful patch‐testing outcome indicator.
Interlaboratory studies with a proposed patch test design to evaluate the irritation potential of surfactants
Authors: Mehling Annette , Chkarnat Catherine , Degwert Joachim , Ennen Joachim , Fink Ernst , Matthies Wolfgang , Roethlisberger Rudolf , Rossow Uwe , Schnitker Jörg , Tronnier Hagen , Wigger‐Alberti Walter , Wilhelm Klaus‐Peter
Published: February 2010

Background: Development of cosmetic products and household detergents necessitates comparative study designs to assess the skin tolerance of products. In initial tests, the epicutaneous patch test for irritation is widely used.

Objectives: This study was conducted to develop a protocol that would facilitate a comparison of results obtained when tests are conducted by different laboratories.

Methods:‘In‐house’ and standardized patch test protocols were used to assess irritation potentials of surfactant‐based products in intra‐ and interlaboratory studies using defined surfactant samples.

Results: The various in‐house protocols tested did not consistently produce equivalent results. In order to develop a study design that yields comparable results, various factors were identified and adjusted. The standardized study protocol includes occlusive application of 70 µl of the test substance to the back of 30 subjects, defined reading times and schemes, assessments based mainly on erythema, and inclusion of sodium laureth sulfate and sodium dodecyl sulfate as positive controls as well as water as a negative control.

Conclusions: Use of the standardized protocol and training of assessors improved the reliability and consistency of results whereby the irritation potentials of the references and test samples were ranked similarly by the laboratories.
Sensitive skin: closing in on a physiological cause
Authors: Farage Miranda A. , Maibach Howard I.
Published: February 2010

The phenomenon of ‘sensitive skin’ is a relatively recent complaint in which certain individuals report more intense and frequent adverse sensory effects than the normal population upon use of cosmetic (personal‐care) products. Originally defined as a minority complaint, sensitive skin is now claimed by a majority of women in industrialized countries and nearly half of men. Sensitive skin is self‐diagnosed and typically unaccompanied by any obvious physical signs of irritation, and the number of individuals who claim sensitivity has risen steadily with the number of consumer products targeted towards this supposedly uncommon group. Believed by many dermatologists, therefore, to be a ‘princess and the pea’ phenomenon, the problem of sensitive skin has largely avoided focussed research. Over the last few years, however, the evidence of documentable biophysical changes associated with the largely sensory symptoms of this disorder has accumulated, including some gained by improved methods of identifying subclinical signs of skin irritation. Although the understanding of the aetiology of this phenomenon is as yet incomplete, existing research now supports a biophysical origin for this disorder. Effective methods of diagnosis, intrinsic and extrinsic contributors to exaggerated neural sensitivity, and the specific mechanisms of the discomfort associated with the compliant are required, as are appropriate means of prevention and treatment.
Quantitative analysis of argyrophilic nuclear organizer regions in giant cell lesions of jaws
Authors: Sadri Donia , Hejazi Massoud , Jahanbani Jahanfar , Forouzandeh Aghdas
Published: February 2010

J Oral Pathol Med (2010) 39: 431–434

Background:  Giant cell lesions of the jaws are considerably similar according to histopathologic characteristics yet show different clinical behaviors. These lesions include central giant cell granuloma (CGCG), aneurysmal bone cyst, Cherubism, and Brown tumor associated with hyperparathyroidism. The present study aimed to investigate AgNORs count in these lesions as a proliferative marker and to determine whether it can be used to discriminate between them or not.

Methods:  Forty‐one cases of giant cell lesions of jaws were retrived from Oral Pathology Department (1987–2007). They included 21 cases of CGCG, eight cases of aneurysmal bone cyst (ABC), six cases of Cherubism, six cases of Brown tumor. The mean AgNORs count was calculated for all cases. To compare mean AgNORs in groups of lesions, ANOVA test was performed.

Results:  Mean AgNOR counts were: (0/85 ± 0/29) in CGCG, (0/76 ± 0/32) in ABC (0/87 ± 0/10) in Cherubism and (0/82 ± 0/16) in Brown tumor. A significant difference was not observed in AgNOR counts among these groups of lesions.

Conclusions:  Jaws giant cell containing lesions have no acceptable differences in mean AgNORs.
Implementation of best practice in the prevention of heel pressure ulcers in the acute orthopedic population
Authors: Campbell Karen E , Woodbury M Gail , Houghton Pamela E
Published: February 2010

To implement and evaluate a heel pressure ulcer prevention program (HPUPP) for orthopaedic patients. Program development of HPUPP involved input from administrators, staff and adult patients on an orthopaedic service in an academic tertiary care facility, located in a small urban centre in Canada. Prospective evaluation was conducted. Consensus exercises with clinical staff and administrators (Delphi and Nominal group) were used to, evaluate current practices, select a heel protective device, and develop key aspects of the HPUPP. HPUPP involved an individualised, bedside, staff education program, a team approach to improve patient mobility and use of a heel protective device. A 2‐inch foam wedge covered in washable vinyl was placed at the foot of all beds on the orthopedic service. After the program was implemented, the incidence of heel pressure ulcers was 0%, which was a significant reduction compared with pre‐implementation levels [13·8% (95% confidence interval 8–18%)]. Key components of the program success were initial and ongoing support from administration and surgeons, incorporation of feedback from clinical staff and patients, and keeping the program simple. Heel PU can be prevented in most orthopaedic patients using a universal heel PU prevention program.
Effects of crop debris and cultivations on the development of eyespot of wheat caused by Oculimacula spp.
Authors: Jenkyn J.F. , Gutteridge R.J. , Bateman G.L. , Jalaluddin M.
Published: February 2010

Results from a series of crop sequence and single‐year experiments that tested different straw and cultivation treatments in a total of 11 site–season combinations confirmed previous evidence that the development of eyespot disease in cereals can be decreased by debris in the seed bed even if that debris includes eyespot‐infected stem bases, which are the principal sources of primary inoculum. Two of the experiments, which followed non‐cereal break crops and tested the effects of crop debris applied after ploughing or tining on eyespot in winter wheat that was artificially inoculated with Oculimacula spp., provided convincing evidence that the effects can be attributed to the debris per se, and not to any associated husbandry practices. There were often larger effects on disease in summer than in spring or on severity than on incidence suggesting that the effects of debris cannot be explained solely by effects on inoculum or initial infection, and that debris has a disease‐suppressive effect.
RHEOLOGICAL PROPERTIES OF RICE–SOYBEAN PROTEIN COMPOSITE FLOURS ASSESSED BY MIXOLAB AND ULTRASOUND
Authors: ROSELL C.M. , MARCO C. , GARCÍA‐ALVÁREZ J. , SALAZAR J.
Published: February 2010

The rheological behavior of gluten‐free composite flours formulated with rice flour and increasing amounts of soybean protein (SP) isolate (0–2%, w/w, flour blend basis) in the presence and absence of transglutaminase (1%, w/w) was assessed using two complementary approaches, the Mixolab device and ultrasonic measurements. Dough was subjected to dual mechanical and thermal constraints, namely mechanical changes due to mixing and heating in the Mixolab and in parallel measurements of ultrasonic attenuation and velocity were performed at two different temperatures (25 and 65C). Main differences were observed during the mixing process, where SPs and transglutaminase induced an important increase of the dough consistency. Results from ultrasonic measurements were in accordance with those obtained with the Mixolab device, both approaches being able to assess the empirical rheological behavior of gluten‐free matrixes and even to detect the effects induced by protein ingredients and processing aid.

PRACTICAL APPLICATIONS

Two complementary approaches, the Mixolab device and ultrasonic measurements, are proposed for assessing rheological behavior of gluten‐free doughs. Mixolab provides information of gluten‐free dough empirical rheology following the dough physicochemical changes associated with dual mechanical shear stress and temperature constraint. Ultrasound also may be used to determine consistency changes in gluten‐free dough, resulting in an interesting potential for future development of a quality control system intended for the industrial production process of dough. Consequently, Mixolab and ultrasounds could be regarded as promising tools in order to investigate rice flour dough properties and the changes induced by other ingredients and processing aids.
Dynamic Changes in Lymphocyte GRK2 Levels in Cardiac Transplant Patients: A Biomarker for Left Ventricular Function
Authors: Bonita Raphael E. , Raake Philip W. , Otis Nicholas J. , Chuprun J. Kurt , Spivack Talya , Dasgupta Abhijit , Whellan David J. , Mather Paul J. , Koch Walter J.
Published: February 2010

G protein‐coupled receptor kinase 2 (GRK2), which is upregulated in the failing human myocardium, appears to have a role in heart failure (HF) pathogenesis. In peripheral lymphocytes, GRK2 expression has been shown to reflect myocardial levels. This study represents an attempt to define the role for GRK2 as a potential biomarker of left ventricular function in HF patients. We obtained blood from 24 HF patients before and after heart transplantation and followed them for up to 1 year, also recording hemodynamic data and histological results from endomyocardial biopsies. We determined blood GRK2 protein by Western blotting and enzyme‐linked immunosorbent assay. GRK2 levels were obtained before transplant and at first posttransplant biopsy. GRK2 levels significantly declined after transplant and remained low over the course of the study period. After transplantation, we found that blood GRK2 signifi cantly dropped and remained low consistent with improved cardiac function in the transplanted heart. Blood GRK2 has potential as a biomarker for myocardial function in end‐stage HF. Clin Trans Sci 2010; Volume #: 1–5
Mode Evolution of Asymmetric Rotors Assembled to Flexible Bearings and Housing
Authors: Kim Hyunchul , Shen I. Y.
Published: February 2010

This paper is to study how vibration modes of a stationary asymmetric rotor evolve when it is assembled to a flexible housing via multiple bearing supports. Prior to the assembly, vibration modes of the rotor are classified as “balanced modes” and “unbalanced modes.” Balanced modes are those modes whose natural frequencies and mode shapes remain unchanged after the rotor is assembled to the housing via bearings. Otherwise, the vibration modes are classified as “unbalanced modes.” In this paper, we first develop two mathematical criteria to identify balanced modes. For the first criteria, the rotor is subjected to fixed boundary conditions at the bearings prior to assembly. In this case, a vibration mode will be a balanced mode if the reactions at the fixed boundary vanish. For the second criterion, the rotor is subjected to free boundary conditions (including the bearing points) prior to assembly. In this case, a vibration mode will be a balanced mode if the bearing locations are nodal points of the vibration mode. These mathematical criteria are then applied to a rotor consisting of a rigid hub supporting a flexible structure, which appears in many practical applications. For balanced modes, the criteria lead to a conclusion that surface integrals of modal forces and moments at the flexible-rigid rotor interface will vanish. Moreover, these surface integrals can be conveniently calculated using finite element methods. To validate the mathematical criteria, modal testing was conducted on a disk with 4 pairs of brackets mounted on a rigid spindle, a ball-bearing spindle and a fluid-dynamic bearing spindle.
Stall Detection Within the Low Pressure Compressor of a Twin-Spool Turbofan Engine by Tip Flow Analysis
Authors: Bindl Stefan , Sto¨ßel Marcel , Niehuis Reinhard
Published: February 2010

In order to preserve fossil resources aviation industry faces major challenges to reduce engine fuel consumption. Therefore efforts are concentrated to increase efficiency of any engine component. Investigations at the Institute of Jet Propulsion at the University of Federal Armed Forces in Munich focus on the compressor module. The compression system is designed to work at very high loads and due to this it is one of the most critical components during transient engine operation. Occurring instabilities are mostly limited to the tip region of the compressor blades because of the tip clearance and low momentum fluid from the casing boundary layer. Prior to instability onset such as rotating stall and even surge, some so-called stall precursors commonly occur in this area. In order to predict and avoid those critical engine operations a stall detection algorithm was developed and combined with an active compressor stabilization system. As a research vehicle the Larzac 04 twin-spool turbofan engine is used at the test facility of the Institute of Jet Propulsion. The test vehicle is equipped with additional instrumentation and control systems exceeding those of conventional engine monitoring systems by far. Providing input data to the stall detection algorithm flush mounted Kulite sensors are installed within the casing of the first stage of the low pressure compressor, where stall usually arises in the Larzac 04. The described algorithm is based on the spike theory being the dominant stall precursor in nearly all operating ranges of the test engine. After the detection of an upcoming stall event active countermeasures are triggered to avoid critical engine operation. For this reason an air injection system was attached in front of the fan stage to affect the blade tip region by injecting additional air at a high velocity to re-establish the blade flow. The main emphasis of this paper is to illustrate the signal conditioning used for stall detection and to prove the reliable function of the algorithm in combination with an active countermeasure at an aircraft engine.
Steam Turbine Low Pressure Blades Fatigue Failures Caused by Operational and External Conditions
Authors: Mazur Zdzislaw , Garci´a-Illescas Rafael , Herna´ndez-Rossette Alejandro
Published: February 2010

This paper provides an overview of a steam turbine low pressure blades failures induced by flow excitation and blades torsional vibrations due to sudden changes on the grid. The analysis include L-0 and L-1 blades failures of the 110 MW [1], 28 MW [2] and 35 MW [3] geothermal units induced by unstable flow due to operation at low load low vacuum, and L-0 blades failure of the 660 MW [4] nuclear unit due combined effect of a transient phenomenon provoked by sudden load changes on the grid and some low vacuum operation period. The failure initiation was registered at different zones of the blades depending on the case, and were localized at the blades cover segments, blade root and blade airfoil close to the platform. Laboratory evaluation of the blades fracture surface indicates the failure mechanism to be high cycle fatigue (HCF).
Unsteady Flow in a Turbocharger Centrifugal Compressor: 3D-CFD Simulation, Impeller Blade Vibration and Vaned Diffuser-Volute Interaction
Authors: Dickmann Hans-Peter , Secall Wimmel Thomas , Szwedowicz Jaroslaw , Ku¨hnel Janpeter , Essig Uwe
Published: February 2010

Experimental investigations on a single stage centrifugal compressor with radial inlet duct showed that measured alternating strains of the rotating blades depend considerably on the circumferential position of the diffuser ring to the volute tongue. By modeling of the entire turbocharger compressor stage with volute and inducer casing bleed system included, 3D unsteady flow simulations provided comprehensive insight into the excitation mechanism. A part load operating point was investigated experimentally and numerically. For operating conditions due to resonance transient CFD was employed, since only then a meaningful prediction of the blade excitation, induced by the unsteady air flow, is expected. The CFD results show primarily the interaction between the volute tongue and the two different vaned diffuser ring positions. It is shown that pressure and flow angle vary significantly due to the circumferential position of the flow entering the volute and the turning impeller blades. The geometrical arrangement of the volute and suction elbow imposes a non-axisymmetric flow field, which excites rotating blades periodically. These vibrations depend on the circumferential assembly position of the vaned diffuser. Outflow and reverse flow at the tongue region also differ with respect to the vaned diffuser ring position. The time dependent pressure distribution on the impeller blades resulting from the CFD calculation was transformed into the frequency domain by Fourier decomposition. The complex modal pressure data were imposed as exciting load on the structure which was simulated by the FEM. By applying a fine FE mesh the measured resonant frequencies for the lower modes were reproduced very well by FEM. After determining the 3D mode shapes of the impeller by means of a free vibration calculation, forced response simulations without considering transient vibration effects were carried out for predicting the resonance strain amplitudes which were computed for both minimum and maximum experimental modal damping ratios. Comparisons with the experimental results at the strain gauges demonstrate that this employed methodology is capable of predicting the 3D impeller’s vibration behavior under real engine conditions up to 8 kHz. Considering strong influence of mistuning on real impeller vibrations, a new method for the comparison of experimental and numerical data has been successfully introduced. In general, this approach is based on the resonance sensitivity assessment, which takes into account the excitation, damping and mistuning parameters. Then, the measured resonance strain amplitudes of all experimental tests match very well the predicted scatter range of numerical results.
Rotordynamic Force Coefficients of a Hybrid Brush Seal: Measurements and Predictions
Authors: San Andre´s Luis , Delgado Adolfo , Baker Jose´
Published: February 2010

Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low-pressure differentials. Hybrid brush seals (HBS) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse shaft rotation operation. A HBS incorporates pads contacting the shaft on assembly; and which under rotor spinning, lift off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, reducing wear and thermal distortions. The paper presents rotordynamic measurements conducted on a test rig for evaluation of HBS technology. Single frequency shaker loads are exerted on a test rotor holding a hybrid brush seal and measurements of rotor displacements follow for operating conditions with increasing gas supply pressures and two rotor speeds. A frequency domain identification method delivers the test system stiffness and damping coefficients. The HBS stiffness coefficients are not affected by rotor speed though the seal viscous damping shows a strong frequency dependency. The identified HBS direct stiffness decreases ∼15% as the supply/discharge pressure increases Pr = 1.7 to 2.4. The HBS cross-coupled stiffnesses are insignificant, at least one order of magnitude smaller than the direct stiffnesses. A structural loss factor (γ) and dry friction coefficient (μ) represent the energy dissipated in a HBS by the bristle-to-bristle and bristle-to-pads interactions. Predictions of HBS stiffness and damping coefficients correlate well with the test derived parameters. Both model predictions and test results show the dramatic reduction of the seal equivalent viscous damping coefficients as the excitation whirl frequency increases.
A Comprehensive Set of Procedures to Estimate the Probability of Extreme Vibration Levels Due to Mistuning
Authors: Chan Y.-J. , Ewins D. J.
Published: February 2010

A set of new procedures is developed to find the probabilities of extremely high amplification factors in mistuned bladed disk vibration levels, which rarely occur. While a rough estimate can be made by curve-fitting the distribution function, the method presented here can determine an accurate upper bound and the probabilities of amplification factors near to that bound. Two examples are provided to illustrate the efficiency of the method, which can be 2 or 3 orders of magnitudes more efficient than Monte Carlo simulations.
Turbocharger Nonlinear Response With Engine-Induced Excitations: Predictions and Test Data
Authors: San Andre´s Luis , Maruyama Ash , Gjika Kostandin , Xia Sherry
Published: February 2010

Turbochargers (TCs) aid to produce smaller and more fuel-efficient passenger vehicle engines with power outputs comparable to those of large displacement engines. This paper presents further progress on the nonlinear dynamic behavior modeling of rotor-radial bearing system (RBS) by including engine-induced (TC casing) excitations. The application concerns to a semi-floating bearing design commonly used in high speed turbochargers. Predictions from the model are validated against test data collected in an engine-mounted TC unit operating to a top speed of 160 krpm (engine speed = 3600 rpm). The bearing model includes non-cylindrical lubricant films as in a semi-floating ring bearing with an anti-rotation button. The nonlinear rotor transient response model presently includes input base motions for the measured TC casing accelerations for increasing engine load conditions. Engines induce TC casing accelerations rich in multiple harmonic frequencies; amplitudes being significant at 2 and 4 times the main engine speed. FFT post-processing of predicted nonlinear TC shaft motions reveals a subsynchronous whirl frequency content in good agreement with test data, in particular for operation at the highest engine speeds. Predicted total shaft motion is also in good agreement with test data for all engine loads and over the operating TC shaft speed range. The comparisons validate the rotor-bearing model and will aid in reducing product development time and expenditures.
Determination of Blade-Alone Frequencies of a Blisk for Mistuning Analysis Based on Optical Measurements
Authors: Schoenenborn Harald , Grossmann David , Satzger Wilhelm , Zisik Herbert
Published: February 2010

Meanwhile the importance of mistuning especially for blisks is well known. Most of the mistuning studies so far done are based on assumed statistical distributions of the eigenfrequencies. But it is important to know the real eigenfrequency distribution of the blades of blisks as they come out of the manufacturing process or after they are in service for some time and have experienced erosion, wear and FOD. Some of the current analytical procedures for mistuning calculations need the blade-alone frequencies, such as the reduced-order code Turbo-Reduce which is used in the subsequent analysis. One way to determine the eigenfrequency distribution is to ping-test every blade while damping all other blades. This procedure is very tedious and may take several days, depending on the number of blades. Further, it is very difficult to eliminate the influence of the disk and to obtain the pure blade-alone eigenfrequencies. In this paper a method for the analytical determination of the eigenfrequency distribution due to geometric imperfections based on optical measurements is described. Starting from the point-cloud from the optical measurements a procedure to obtain a FEM-Model of all blades of a blisk is presented. As the procedure can partly be run as a batch-job, the time to determine the eigenfrequency distribution is drastically reduced compared to the experimental way. The procedure is applied to a real blisk and the calculated eigenfrequencies are compared with the measured frequencies. Then mistuning calculations are performed based on this eigenfrequency distribution.
Meanline Modeling of Radial Inflow Turbine With Variable Area Nozzle
Authors: Qiu Xuwen , Anderson Mark R. , Baines Nicholas C.
Published: February 2010

A meanline model of a radial inflow turbine with a variable geometry nozzle is presented. The existence of a clearance gap in a variable geometry nozzle presents a significant challenge in the prediction of turbine performance. First, the nozzle clearance carries a portion of the flow that is not turned by the nozzle vanes. The amount of flow in the clearance region is related to the size of the clearance as well as the nozzle setting angle or the throat area. This under-turned flow influences the power output and turbine efficiency. Furthermore, the maximum flow rate that is allowed to pass the nozzle is increased because of the presence of the clearance, altering the turbine map in turbine operation.
Analysis of Gas Turbine Rotating Cavities by an One-Dimensional Model
Authors: Da Soghe Riccardo , Facchini Bruno , Innocenti Luca , Micio Mirko
Published: February 2010

Reliable design of secondary air system is one of the main tasks for the safety, unfailing and performance of gas turbine engines. To meet the increasing demands of gas turbines design, improved tools in prediction of the secondary air system behavior over a wide range of operating conditions are needed. A real gas turbine secondary air system includes several components, therefore its analysis is not carried out through a complete CFD approach. Usually, that predictions are performed using codes, based on simplified approach which allows to evaluate the flow characteristics in each branch of the air system requiring very poor computational resources and few calculation time. Generally the available simplified commercial packages allow to correctly solve only some of the components of a real air system and often the elements with a more complex flow structure cannot be studied; among such elements, the analysis of rotating cavities is very hard. This paper deals with a design-tool developed at the University of Florence for the simulation of rotating cavities. This simplified in-house code solves the governing equations for steady one-dimensional axysimmetric flow using experimental correlations both to incorporate flow phenomena caused by multidimensional effects, like heat transfer and flow field losses, and to evaluate the circumferential component of velocity. Although this calculation approach does not enable a correct modeling of the turbulent flow within a wheel space cavity, the authors tried to create an accurate model taking into account the effects of inner and outer flow extraction, rotor and stator drag, leakages, injection momentum and, finally, the shroud/rim seal effects on cavity ingestion. The simplified calculation tool was designed to simulate the flow in a rotating cavity with radial outflow both with a Batchelor and/or Stewartson flow structures. A primary 1D-code testing campaign is available in the literature [1]. In the present paper the authors develop, using CFD tools, reliable correlations for both stator and rotor friction coefficients and provide a full 1D-code validation comparing, due to lack of experimental data, the in house design-code predictions with those evaluated by CFD.
Unsteady Vortices and Blade Loading in a High-Pressure Turbine
Authors: Chang Dongil , Tavoularis Stavros
Published: February 2010

Unsteady flow in a transonic, single-stage, high-pressure, axial turbine has been investigated numerically by solving the URANS (Unsteady Reynolds-Averaged Navier-Stokes) equations with the SST (Shear Stress Transport) turbulence model. Interest has focused on the identification and effects of the quasi-stationary vane and blade horseshoe vortices, vane and blade passage vortices, vane and blade trailing edge vortices, and blade tip leakage vortices. Moreover, two types of unsteady vortices, not discussed explicitly in the previous literature, have been identified and termed “axial gap vortices” and “crown vortices”. All vortices have been clearly and distinctly identified using a modified form of the Q criterion, which is less sensitive to the set threshold than the original version. The use of pathlines and iso-contours of static pressure, axial vorticity and entropy has been further exploited to distinguish the different types of vortices from each other and to mark their senses of rotation and strengths. The influence of these vortices on the entropy distribution at the outlet has been investigated. The observed high total pressure losses in the turbine at blade midspan have been connected to the action of passage vortices. The formation and disappearance processes of unsteady vortices located in the spacing between the stator and the rotor have been time-resolved. These vortices are roughly aligned with the leading edges of the rotor blades and their existence depends on the position of the blade with respect to the upstream vanes. In addition, the present study focuses on the unsteady blade loading that influences vibratory stresses. Contours of the time-dependent surface pressure on the rotor blade have demonstrated the presence of large pressure fluctuations near the front of the blade suction sides; these pressure fluctuations have been associated with the periodic passages of shock waves originating at the vane trailing edges.
Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System Due to Intermittent Shocks
Authors: San Andre´s Luis , Ryu Keun
Published: February 2010

Gas bearings in microturbomachinery (MTM) offer significant system level benefits, such as improved fuel efficiency, reduction in weight and number of components, extending life cycle and maintenance intervals, and reducing NOX emissions with a lower CO2 footprint. Emerging opportunities for gas bearings applications range from automotive turbochargers to engines for business jet aircraft, for example. Gas bearings, because of the inherently low gas viscosity, have low damping relative to oil-lubricated bearings and are prone to wear during rotor start-up and shut down procedures. The lack of damping brings concerns about rotor-gas bearing system robustness and endurance to tolerate shock induced loads, sudden while landing in jet engines, or intermittent in vehicles while moving across a rough terrain, for example. The paper demonstrates the reliability of a hybrid gas bearing system from rotor vibration measurements induced by sporadic shock loads acting on the base of a test rig and while the rotor is coasting down from a top speed of 60 krpm (1000 Hz). In the tests, (1) an electromagnetic pusher delivers impacts to the rig base, or (2) the whole rig is manually tilted and dropped. The test rig consists of a rigid rotor, 0.825 kg and 28.6 mm in diameter, supported on two flexure pivot tilting pad type, hybrid gas bearings, each with four pads and 60% pivot offset and 0.6 mm feeding holes. The bearings are supplied with feed pressures of 2.36, 3.72, and 5.08 bar (ab). Intermittent shocks, up to 30 g pk-pk and exciting a broad frequency range to 400 Hz, produce a remarkable momentary increase of the overall rotor response amplitude, up to 50 μm (pk-pk). The shocks readily excite the fundamental natural frequency of the rotor-bearing system (150–200 Hz), and on occasion the natural frequency (40 Hz) of the whole test rig. For operation at rotor speeds above the system critical speed, the rotor synchronous response is isolated; with transient motions induced by a shock, subsynchronous in whirl frequency, quickly disappearing. Full recovery takes place in ∼0.10 second. The measurements demonstrate that the hybrid gas bearings have enough damping to rapidly attenuate rotor transient motions and to dissipate the energy induced from intermittent shocks. Note that the shocks acted while the rotor traversed its critical speeds. The reliability of engineered gas bearings to forced transient events is no longer in question.
Multiharmonic Forced Response Analysis of a Turbine Blading Coupled by Nonlinear Contact Forces
Authors: Siewert Christian , Panning Lars , Wallaschek Jo¨rg , Richter Christoph
Published: February 2010

The rotor blades of a low pressure (LP) steam turbine stage are subjected to high static and dynamic loads during operation. The static loads are mainly due to the centrifugal force and thermal strains, whereas the dynamic loads are caused by fluctuating gas forces resulting in forced vibrations of the blades. The forced vibrations can lead to high cycle fatigue (HCF) failures causing substantial damage and high maintenance effort. Thus, one of the main tasks in the design of LP steam turbine blading is the vibration amplitude reduction in order to avoid high dynamic stresses that could damage the blading. The vibration amplitudes of the blades in a LP steam turbine stage can be reduced significantly to a reasonable amount if adjacent blades are coupled by shroud contacts that reinforce the blading, see Fig. 1. Furthermore, in the case of blade vibrations, relative displacements between neighboring blades occur in the contacts and friction forces are generated that provide additional damping to the structure due to the energy dissipation caused by micro- and macroslip effects. Therefore, the coupling of the blades increases the overall mechanical damping. A three-dimensional structural dynamics model including an appropriate spatial contact model is necessary to predict the contact forces generated by the shroud contacts and to describe the vibrational behavior of the blading with sufficient accuracy. To compute the nonlinear forced vibrations of the coupled blading, the nonlinear equations of motion are solved in the frequency domain owing to the high computational efficiency of this approach. The transformation of the nonlinear equations of motion into the frequency domain can be carried out by representing the steady-state displacement in terms of its harmonic components. After that transformation, the nonlinear forced response is computed as a function of the excitation frequency in the frequency domain.