bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of RANS and ZDES Methods for the Prediction of Three-Dimensional Separation in Axial Flow Compressors
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo 
Published: August 2015

Regions of three-dimensional separations are an inherent flow feature of the corner formed by the suction surface and endwall of axial compressors. RANS turbulence models, common in industrial CFD codes, often struggle in these regions. This paper investigates the use of two hybrid RANS/LES methods as alternatives to pure RANS methods.
SA and SST based Zonal DES (ZDES) are applied to a linear blade cascade case, studied experimentally by Gbadebo [1]. The time-averaged results are compared to steady SA, SST and RSM RANS results. SA model corrections for streamline curvature, anisotropy and non-equilibrium effects are also examined. For the ZDES computations the solver is modified to reduce dissipation at low Mach numbers.
Significant uncertainty is observed in the RANS results, with the origin of the suction surface corner separation occurring too far upstream, and the extent of the corner separation significantly over-predicted. The laminar separation bubble and the turbulent reattachment are also missed. Consequently the surface pressure distribution, exit flow angle and total pressure loss predictions are poor. Conversely, the ZDES results were encouraging; with much better predictions of the pressure distribution, exit flow angle and trailing edge boundary layer displacement thickness. Some RANS corrections proved effective, such as the SA model with Rotation/Curvature correction (SA-RC), however all had deficiencies in some areas.
Although the ZDES results are encouraging it is noted that these computations were two orders of magnitude more computaionally expensive due to the high mesh densities and small time-steps required. For the ZDES results quality indexes are examined in order to determine whether the computational mesh used is sufficient in different flow regions. Mesh generation strategies based on using a pre-cursor RANS solution to obtain a modelled energy spectrum and various turbulent length scales to guide mesh refinement are considered. These can provide a quick estimate of the potential computational cost of LES or hybrid RANS/LES computations from a RANS solution.
Heat Transfer and Pressure Drop in a Rotating Two-Pass Square Channel With Different Ribs at High Rotation Numbers
Authors: Li Yang , Deng Hongwu , Xu Guoqiang , Tian Shuqing 
Published: August 2015

Rotation effects on heat transfer and pressure drop in a rotating two-pass square channel with ribs is experimentally investigated. The cooper plate heating technique is applied to obtain the regional average heat transfer coefficients. The Reynolds number and rotation number varies from 10000 to 60000, and 0 to 2.0, respectively. Rib turbulators are placed on the leading and trailing walls of the channel at an angle of 90 deg or 45 deg to the flow direction. The rib pitch-to-height (P/e) ratio is 10 and the height-to-hydraulic diameter (e/Dh) ratio is 0.1 for all tests.
The detailed comparisons between smooth wall case and ribbed wall cases are presented. At stationary, increasing the Reynolds number decreases heat transfer and thermal performance ratios, but raises the friction factor ratios dramatically. Rotation shows the strongest effect on heat transfer in smooth case, and then 90 deg rib case, and the least in 45 deg rib case. Channel friction in smooth case is increased by rotation monotonously, but decreases with Ro in ribbed case when Ro increases up to 0.5. The similar thermal performances trends are observed for smooth and ribbed cases at rotation but with different peak point. The 45 deg rib channel has the superior thermal performance because it incurs the highest heat transfer and moderate pressure penalty.
Transient Analysis of a Transonic Compressor Rotor With Aeroelastic Effects
Authors: Tan Yan Han , van Rooij Michel , Prananta Bimo 
Published: August 2015

High fidelity aeroelastic analysis of gas turbine blading is becoming increasingly common. It is used in vibration analysis and prevention, to increase accuracy of off-design flow analysis and performance prediction, and in damage investigation. Here, an aeroelastic analysis is performed of the transient response of a transonic rotor to a change in operating point.
An existing aeroelastic method is used that was originally developed and validated for aircraft applications. The method consists of a time-accurate CFD-method coupled with a modal approach for geometry deformation. The validity of the aeroelastic method is confirmed using the standard aeroelastic test case STCF4. Next, the transient behavior of a transonic rotor due to a change in operating point is investigated. Two scenarios are analyzed: from design point to near stall, and from design point to near choke conditions. These scenarios were analyzed using time-accurate U-RANS calculations with rigid and deformable blading, using six vibration modes to describe the blade deformation in the latter case.
In the case of a rigid blade, the shock quickly moves from the original position to the position associated with the new operating point. The duration of this process is approximately one rotor revolution, but a small oscillatory movement remains after three rotor revolutions. With deformable blading, the changing pressure distribution deforms the blade shape during the transient process. The geometric displacement is very small, on the order of 10 μm, and has only a minor effect on the observed shock movement. The final extent of deformation is reached within 0.5 rotor revolutions, but the blade continues to vibrate after three rotor revolutions.
The oscillatory displacements of both the shock and the blade are very small for this particular geometry. For different configurations, the blade deformations might be large enough to influence the shock motion, possibly giving rise to noise and fatigue problems.
Premixed Pilot Flames for Improved Emissions and Flexibility in a Heavy Duty Gas Turbine Combustion System
Authors: York William D. , Romig Bryan W. , Hughes Michael J. , Simons Derrick W. , Citeno Joseph V. 
Published: August 2015

Operators of heavy duty gas turbines desire more flexibility of operation in compliance with increasingly stringent emissions regulations. Delivering low NOx at base load operation, while at the same time meeting aggressive startup, shutdown, and part load requirements for NOx, CO, and unburned hydrocarbons is a challenge that requires novel solutions in the framework of lean premixed combustion systems. The DLN2.6+ combustion system, first offered by the General Electric Company (GE) in 2005 on the 9F series gas turbines for the 50 Hz market, has a proven track record of low emissions, flexibility, and reliability. In 2010, GE launched a program to incorporate the DLN2.6+ into the 7F gas turbine model. The primary driver for the introduction of this combustion system into the 60 Hz market was to enable customers to capitalize on opportunities to use shale gas, which may have a greater Wobbe range and higher reactivity than traditional natural gas.
The 7F version of the DLN2.6+ features premixed pilot flames on the five outer swirl-stabilized premixing fuel nozzles (“swozzles”). The premixed pilots have their roots in the multitube mixer technology developed by GE in the US Department of Energy Hydrogen Gas Turbine Program. A fraction of air is extracted prior to entering the combustor and sent to small tubes around the tip of the fuel nozzle centerbody. A dedicated pilot fuel circuit delivers the gas fuel to the pilot tubes, where it is injected into the air stream and given sufficient length to mix. Since the pilot flames are premixed, they contribute lower NOx emissions than a diffusion pilot, but can still provide enhanced main circuit flame stability at low-load conditions. The pilot equivalence ratio can be optimized for the specific operating conditions of the gas turbine.
This paper presents the development and validation testing of the premixed pilots, which were tested on E-class and F-class gas turbine combustion system rigs at GE Power & Water’s Gas Turbine Technology Lab. A 25% reduction in NOx emissions at nominal firing temperature was demonstrated over a diffusion flame pilot, translating into more than 80% reduction in CO emissions if increased flame temperature is employed to hold constant NOx. On the new 7F DLN2.6+, the premixed pilots have enabled modifications to the system to reduce base load NOx emissions while maintaining similar gas turbine low-load performance and bringing a significant reduction in the combustor exit temperature at which LBO occurs, highlighting the stability the pilot system brings to the combustor without the NOx penalty of a diffusion pilot. The new combustion system is scheduled to enter commercial operation on GE 7F series gas turbines in 2015.
Vibration Modeling and Experimental Results of Two Phase Flow Twin-Screw Pump
Authors: Muhammed Ameen R. A. , Childs Dara W. 
Published: August 2015

In turbomachines, the transfer of energy between the rotor and the fluid does not — in theory — result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving and stationary components usually results in unbalanced pressure fields and forces. In [1] the authors developed a model to predict the dynamic forces in twin screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed.
The work presented here attempts to validate the model in [1] using a clear-casing twin screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 KPa and a flow rate 0.6 liter per second. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted in [1].
The predictions were found in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model.
The pump rotor’s calculated critical speed was at 24.8 krpm, roughly 14 times the rotor’s running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the 1st critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped 1st critical speed should be considered.
Centrifugal Compressors Return Channel Optimization by Means of Advanced 3D CFD
Authors: De Bellis Fabio , Guidotti Emanuele , Rubino Dante Tommaso 
Published: August 2015

In the Oil&Gas industry, the quest for turbomachinery high efficiency is continuously pushing technology towards new improvements. Rotor (impeller) optimization is a rather established practice in the centrifugal compressors design both in the scientific literature and in the industrial experience, but the same focus is not always applied to statoric components optimization. This is due to the smaller impact of plenums and return channels on the overall compressor performance in comparison to the impeller. However, further improvements in the design of centrifugal compressors stage have to deal with the loss minimization of statoric parts, also considering the advanced level of aerodynamic detail reached by Original Equipment Manufacturers (OEMs).
In the present paper, the optimization of the return channel is performed by means of 3D Computational Fluid Dynamics (CFD) with the objective of loss coefficient minimization. The CFD simulations are run with a non-commercial proprietary software (Tacoma) considering steady flow with Reynolds Averaged Navier Stokes (RANS) approach and turbulence k-ω model with strain correction; full validation of the employed method was performed in the past against experimental campaigns and is available in the literature.
In order to reproduce as much as possible full stage operating conditions, simulations should include impeller, diffuser and return channel, but the computational cost of an optimization with many iterations required the reduction of the domain. In order to preserve simulation accuracy at the same time, flow profiles at impeller exit have been imposed at the considered computational domain inlet (i.e. diffuser inlet), whilst cavity effects and secondary flows have been considered adding source terms taken from the full stage simulation of the baseline geometry.
Return channel blades have been parameterized in terms of angle distributions with Bézier curves at hub and shroud, for a total of 18 Bézier poles. Each different design has been simulated with its speedline consisting of 7 operating conditions, whereas progressive optimization based on response surfaces have been considered starting from an initial Design of Experiment (DOE). Over 100 designs have been simulated and the most efficient allows a 20% loss coefficient reduction on a real case stage design at design point.
Structural and Functional Adaptation of Vancomycin Resistance VanT Serine Racemases
Authors: Meziane-Cherif Djalal , Stogios Peter J. , Evdokimova Elena , Egorova Olga , Savchenko Alexei , Courvalin Patrice 
Published: August 2015

ABSTRACT

Vancomycin resistance in Gram-positive bacteria results from the replacement of the
d
-alanyl–
d
-alanine target of peptidoglycan precursors with
d
-alanyl–
d
-lactate or
d
-alanyl–
d
-serine (
d
-Ala-
d
-Ser), to which vancomycin has low binding affinity. VanT is one of the proteins required for the production of
d
-Ala-
d
-Ser-terminating precursors by converting
l
-Ser to
d
-Ser. VanT is composed of two domains, an N-terminal membrane-bound domain, likely involved in
l
-Ser uptake, and a C-terminal cytoplasmic catalytic domain which is related to bacterial alanine racemases. To gain insight into the molecular function of VanT, the crystal structure of the catalytic domain of VanT
G
from VanG-type resistant
Enterococcus faecalis
BM4518 was determined. The structure showed significant similarity to type III pyridoxal 5′-phosphate (PLP)-dependent alanine racemases, which are essential for peptidoglycan synthesis. Comparative structural analysis between VanT
G
and alanine racemases as well as site-directed mutagenesis identified three specific active site positions centered around Asn
696
which are responsible for the
l
-amino acid specificity. This analysis also suggested that VanT racemases evolved from regular alanine racemases by acquiring additional selectivity toward serine while preserving that for alanine. The 4-fold-lower relative catalytic efficiency of VanT
G
against
l
-Ser versus
l
-Ala implied that this enzyme relies on its membrane-bound domain for
l
-Ser transport to increase the overall rate of
d
-Ser production. These findings illustrate how vancomycin pressure selected for molecular adaptation of a housekeeping enzyme to a bifunctional enzyme to allow for peptidoglycan remodeling, a strategy increasingly observed in antibiotic-resistant bacteria.

IMPORTANCE
Vancomycin is one of the drugs of last resort against Gram-positive antibiotic-resistant pathogens. However, bacteria have evolved a sophisticated mechanism which remodels the drug target, the
d
-alanine ending precursors in cell wall synthesis, into precursors terminating with
d
-lactate or
d
-serine, to which vancomycin has less affinity.
d
-Ser is synthesized by VanT serine racemase, which has two unusual characteristics: (i) it is one of the few serine racemases identified in bacteria and (ii) it contains a membrane-bound domain involved in
l
-Ser uptake. The structure of the catalytic domain of VanT
G
showed high similarity to alanine racemases, and we identified three specific active site substitutions responsible for
l
-Ser specificity. The data provide the molecular basis for VanT evolution to a bifunctional enzyme coordinating both transport and racemization. Our findings also illustrate the evolution of the essential alanine racemase into a vancomycin resistance enzyme in response to antibiotic pressure.
A 1,000-Year-Old Antimicrobial Remedy with Antistaphylococcal Activity
Authors: Harrison Freya , Roberts Aled E. L. , Gabrilska Rebecca , Rumbaugh Kendra P. , Lee Christina , Diggle Stephen P. 
Published: August 2015

ABSTRACTPlant-derived compounds and other natural substances are a rich potential source of compounds that kill or attenuate pathogens that are resistant to current antibiotics. Medieval societies used a range of these natural substances to treat conditions clearly recognizable to the modern eye as microbial infections, and there has been much debate over the likely efficacy of these treatments. Our interdisciplinary team, comprising researchers from both sciences and humanities, identified and reconstructed a potential remedy forStaphylococcus aureusinfection from a 10th century Anglo-Saxon leechbook. The remedy repeatedly killed establishedS. aureusbiofilms in anin vitromodel of soft tissue infection and killed methicillin-resistantS. aureus(MRSA) in a mouse chronic wound model. While the remedy contained several ingredients that are individually known to have some antibacterial activity, full efficacy required the combined action of several ingredients, highlighting the scholarship of premodern doctors and the potential of ancient texts as a source of new antimicrobial agents.IMPORTANCEWhile the antibiotic potential of some materials used in historical medicine has been demonstrated, empirical tests of entire remedies are scarce. This is an important omission, because the efficacy of “ancientbiotics” could rely on the combined activity of their various ingredients. This would lead us to underestimate their efficacy and, by extension, the scholarship of premodern doctors. It could also help us to understand why some natural compounds that show antibacterial promise in the laboratory fail to yield positive results in clinical trials. We have reconstructed a 1,000-year-old remedy which kills the bacteria it was designed to treat and have shown that this activity relies on the combined activity of several antimicrobial ingredients. Our results highlight (i) the scholarship and rational methodology of premodern medical professionals and (ii) the untapped potential of premodern remedies for yielding novel therapeutics at a time when new antibiotics are desperately needed.
Knee kinematics and joint moments during gait following anterior cruciate ligament reconstruction: a systematic review and meta-analysis
Authors: Hart Harvi F , Culvenor Adam G , Collins Natalie J , Ackland David C , Cowan Sallie M , Machotka Zuzana , Crossley Kay M 
Published: August 2015

BackgroundAbnormal gait after anterior cruciate ligament reconstruction (ACLR) may contribute to development and/or progression of knee osteoarthritis.ObjectiveTo conduct a systematic review and meta-analysis of knee kinematics and joint moments during walking after ACLR.MethodsWe searched seven electronic databases and reference lists of relevant papers, for cross-sectional, human-based observational studies comparing knee joint kinematics and moments during level walking in individuals with ACLR, with the uninjured contralateral knee or healthy individuals as a control. Two independent reviewers appraised methodological quality (modified Downs and Black scale). Where possible, data were pooled by time post-ACLR (RevMan), otherwise narrative synthesis was undertaken.ResultsThirty-four studies were included. Meta-analysis revealed significant sagittal plane deficits in ACLR knees. We found greater knee flexion angles (standardised mean difference: 1.06; 95% CI 0.39 to 1.74) and joint moments (1.61; 0.87 to 2.35) <6 months post-ACLR, compared to healthy controls. However, lower peak knee flexion angles were identified 1–3 years (−2.21; −3.16 to −1.26) and ≥3 years post-ACLR (−1.38, −2.14 to −0.62), and lower knee flexion moment 6–12 months post-ACLR (−0.76; −1.40 to −0.12). Pooled data provided strong evidence of no difference in peak knee adduction moment >3 years after ACLR (vs healthy controls) (0.09; −0.63 to 0.81). No transverse plane conclusions could be drawn.ConclusionsSagittal plane biomechanics, rather than the knee adduction moment, appear to be more relevant post-ACLR. Better understanding of sagittal plane biomechanics is necessary for optimal post-operative recovery, and to potentially prevent early onset and progression of knee OA after ACLR.Trial registration numberPROSPERO systematic review protocol registration number CRD4201400882 2.
Alcohol consumption and risk of incident heart failure in older men: a prospective cohort study
Authors: Wannamethee S Goya , Whincup Peter H , Lennon Lucy , Papacosta Olia , Shaper A Gerald 
Published: August 2015

AimsLight-to-moderate drinking has been associated with reduced risk of heart failure (HF). We have examined the association between alcohol consumption and incident HF in older British men.Methods and resultsProspective study of 3530 men aged 60–79 years with no diagnosed HF or myocardial infarction (MI) at baseline and followed up for a mean period of 11 years, in whom there were 198 incident HF cases. Men were divided into 6 categories of alcohol consumption: none, <1, 1–6, 7–13, 14–34 and ≥35 drinks/week. There was no evidence that light-to-moderate drinking is beneficial for risk of HF. Heavy drinking (≥35 drinks/week) was associated with significantly increased risk of HF. Using the large group of men drinking 1–6 drinks/week as the reference group, the relative HRs (95% confidence interval) for HF adjusted for age, lifestyle characteristics, blood pressure, atrial fibrillation and renal dysfunction were 0.97 (0.59 to 1.63), 1.39 (0.86 to 2.25), 1.00, 0.94 (0.64 to 1.43), 1.16 (0.78 to 1.71) and 1.91 (1.02 to 3.56) for the 6 alcohol groups, respectively. The increased risk associated with heavy drinking was attenuated after adjustment for N-terminal pro-brain natriuretic peptide (NT-proBNP) (HR=1.43 (0.76 to 1.69)). Stratified analysis showed heavy drinking was associated with increased HF risk only in those with ECG evidence of myocardial ischaemia.ConclusionsThere was no evidence that light-to-moderate drinking is beneficial for the prevention of HF in older men without a history of an MI. Heavier drinking (≥5 drinks/day), however, was associated with increased risk of HF in vulnerable men with underlying myocardial ischaemia.
Industrial structural geology: principles, techniques and integration: an introduction
Authors: Richardson Nicholas J. , Richards Francis L. , Rippington Stephen J. , Bond Clare E. , Wilson Robert W. 
Published: August 2015

Abstract
This volume explores how structural geology can be applied to industrial activities. It includes case studies that exhibit the state of the art and provides an overview of current and future trends in structural geology. The constituent papers cover a wide range of topics, including regional tectonics; trap and prospect definition; fault, fold and fracture analysis; seal analysis; interpretation of geophysical, borehole, core and outcrop data. The volume demonstrates how structural concepts ultimately create value and how academic institutions, specialist consultants and operating companies work together at a variety of scales and in varied geological settings to explore for and produce natural resources for the economic benefit of society.