bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method
Authors: Rakut Christian , Diefenthal Mathias , Wirsum Manfred , Heuer Tom 
Published: September 2016

The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of turbine wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the turbine wheel as early as possible in the design process for steady state operating points and transient operation.
This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial turbine wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger turbine wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the turbine wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a turbine wheel is developed based on the numerical results. To model the local different heat transfer coefficients the turbine wheel is divided in several surface segments which correspond to the geometry of a radial turbine wheel.
To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the turbine wheel are possible for steady state operating points.
An Innovative Method for the Evaluation of Particle Deposition Accounting for the Rotor/Stator Interaction
Authors: Aldi Nicola , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio 
Published: September 2016

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system can cause deposits on blading and, consequently, result in a performance drop of the compressor.
This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0.15 μm – 1.50 μm) in a transonic axial compressor stage, carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase.
A particular computational strategy is adopted in order to take into account the presence of two subsequent annular cascades (rotor and stator) in the case of particle ingestion. The proposed strategy allows the evaluation of particle deposition in an axial compressor stage thanks to its capability of accounting for the rotor/stator interaction. NASA Stage 37 is considered as a case study for the numerical investigation. The compressor stage numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in literature.
The blade zones affected by particle impact and the kinematic characteristics of the impact of micrometric and sub-micrometric particles with the blade surface are shown. Both blade zones interested by particle impact and deposition are analyzed.
The particle deposition is established by using the quantity called sticking probability, adopted from literature. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon.
The results show that micro-particles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side of rotor blade and stator vane. Both rotor blade and stator vane suction side are affected only by the impact of smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, shock waves and tip leakage vortex, strongly influence the impact location of the particles. The kinematic analysis shows a high tendency of particle adhesion on the suction side of the rotor blade, especially for particles with a diameter equal to 0.15 μm.
Hermetic 40-kW-Class Steam Turbine System for the Bottoming Cycle of Internal Combustion Engines
Authors: Kraus Michael H. , Deichsel Michael , Hirsch Peter , Opferkuch Frank , Heckel Christoph 
Published: September 2016

An entirely new 40-kW-class steam turbine prototype has been constructed and successfully tested for more than 6,500 hours. The two-stage Curtis wheel with a nominal pressure ratio of about 130 has been designed for applications in bottoming water/steam cycles. The axial turbine runs at a rated rotational speed of 36,000 rpm, utilizing magnetic bearings and a permanent magnet synchronous generator which is coupled to the grid by frequency inverters. The integral turbine-generator set has been designed as a hermetically sealed assembly group. The turbine design allows both the turbine’s oil supply system and the bottoming cycle’s feed-water treatment system to be eliminated. The turbine has been designed to allow unmanned operation of the entire cycle with minimum maintenance requirements and reduced costs.
Extensive turbine testing, including rated power, overload and load rejection tests was carried out to verify functionality. Long-term operational capability was also demonstrated, giving particular attention to generator performance. Exemplarily a bottoming cycle, utilizing the turbine, matching the exhaust conditions of internal combustion engines was designed, increasing electrical efficiency from 40.4% to 43.4%, which represents a relative net improvement of 7.5%. In this application a turbine isentropic efficiency of more than 55% is expected, based on the congruence of measurement and calculation.
The Influence of Non-Equilibrium Wet Steam Effects on the Aeroelastic Properties of a Turbine Blade Row
Authors: Fuhrer Christopher , Grübel Marius , Vogt Damian M. , Petrie-Repar Paul 
Published: September 2016

Turbine blade flutter is a concern for the manufacturers of steam turbines. Typically, the length of last stage blades of large steam turbines is over one meter. These long blades are susceptible to flutter because of their low structural frequency and supersonic tip speeds with oblique shocks and their reflections. Although steam condensation has usually occurred by the last stage, ideal gas is mostly assumed when performing flutter analysis for steam turbines.
The results of a flutter analysis of a 2D steam turbine test case which examine the influence of non-equilibrium wet steam are presented. The geometry and flow conditions of the test case are supposed to be similar to the flow near the tip in a steam turbine as this is where most of the unsteady aerodynamic work contributing to flutter is done. The unsteady flow simulations required for the flutter analysis are performed by ANSYS CFX. Three fluid models are examined: ideal gas, equilibrium wet steam (EQS) and non-equilibrium wet steam (NES), of which NES reflects the reality most.
Previous studies have shown that a good agreement between ideal gas and EQS simulations can be achieved if the prescribed ratio of specific heats is equal to the equilibrium polytropic index of the wet steam flow through the turbine.
In this paper the results of a flutter analysis are presented for the 2D test case at flow conditions with wet steam at the inlet. The investigated plunge mode normal to chord is similar to a bending mode around the turbine axis for a freestanding blade in 3D. The influence of the overall wetness fraction and the size of the water droplets at the inlet are examined. The results show an increase of aerodynamic damping for all investigated interblade phase angles with a reduction of droplet size. The influence of the wetness fraction is in comparison of less importance.
Parametrically Induced Damping in a Cracked Rotor
Authors: Kulesza Zbigniew , Sawicki Jerzy T. 
Published: September 2016

The tendency to higher speeds in turbomachinery results in the design of more flexible shafts, which run at speeds above several of their natural frequencies. Due to stress concentration and high spin speed, the rotor dynamic system is more prone to cracks that propagate faster due to low-cycle fatigue loading. The propagating shaft crack usually leads to sudden machine failure, its damage and a serious accident. Therefore, an early shaft crack detection and warning is an important research task.
A transverse shaft crack in a rotor is usually modeled as a local change in the shaft stiffness. It is commonly assumed that this local stiffness change is not constant and varies as a result of a so-called breathing mechanism. This mechanism is explained with periodical opening and closing of crack faces under the load of external forces applied to the rotor. The rotor with a periodically varied stiffness can be modeled as a parametrically excited linear system.
In the presence of a parametric excitation, the vibrations of the system can be amplified or damped at specific excitation frequencies. Usually, the frequencies at which the vibrations are amplified are important, since they can affect stability of the system, and the frequencies at which the vibrations are damped seem to not be of interest. However, the increased damping at specific frequencies is a significant feature of a parametrically excited system that can have some potentially useful applications. The results of earlier studies demonstrate that one of the possible applications of the parametrically-induced damping can be an early detection of a shaft crack.
The unique feature of the increased damping in parametrically excited systems is that this phenomenon can appear only at specific excitation frequencies and at other specific conditions that are not always met. This paper presents the results of a numerical analysis of the influence of Rayleigh’s damping and gyroscopic effects on the increase in damping in a parametrically excited rotor with a cracked shaft. It is shown that the increase in damping in a parametrically excited system is a rare phenomenon that can be observed only at properly selected values of the excitation frequency and Rayleigh’s damping. Furthermore, gyroscopic effects influence the exact values of anti-resonance frequencies at which the phenomenon appears.
The Effects of Signal Erosion and Core Genome Reduction on the Identification of Diagnostic Markers
Authors: Sahl Jason W. , Vazquez Adam J. , Hall Carina M. , Busch Joseph D. , Tuanyok Apichai , Mayo Mark , Schupp James M. , Lummis Madeline , Pearson Talima , Shippy Kenzie , Colman Rebecca E. , Allender Christopher J. , Theobald Vanessa , Sarovich Derek S. , Price Erin P. , Hutcheson Alex , Korlach Jonas , LiPuma John J. , Ladner Jason , Lovett Sean , Koroleva Galina , Palacios Gustavo , Limmathurotsakul Direk , Wuthiekanun Vanaporn , Wongsuwan Gumphol , Currie Bart J. , Keim Paul , Wagner David M. 
Published: September 2016

ABSTRACT
Whole-genome sequence (WGS) data are commonly used to design diagnostic targets for the identification of bacterial pathogens. To do this effectively, genomics databases must be comprehensive to identify the strict core genome that is specific to the target pathogen. As additional genomes are analyzed, the core genome size is reduced and there is erosion of the target-specific regions due to commonality with related species, potentially resulting in the identification of false positives and/or false negatives.

IMPORTANCE
A comparative analysis of 1,130
Burkholderia
genomes identified unique markers for many named species, including the human pathogens
B. pseudomallei
and
B. mallei
. Due to core genome reduction and signature erosion, only 38 targets specific to
B. pseudomallei
/mallei were identified. By using only public genomes, a larger number of markers were identified, due to undersampling, and this larger number represents the potential for false positives. This analysis has implications for the design of diagnostics for other species where the genomic space of the target and/or closely related species is not well defined.
A Regulatory Circuit Composed of a Transcription Factor, IscR, and a Regulatory RNA, RyhB, Controls Fe-S Cluster Delivery
Authors: Mandin Pierre , Chareyre Sylvia , Barras Frédéric 
Published: September 2016

ABSTRACT

Fe-S clusters are cofactors conserved through all domains of life. Once assembled by dedicated ISC and/or SUF scaffolds, Fe-S clusters are conveyed to their apo-targets via A-type carrier proteins (ATCs).
Escherichia coli
possesses four such ATCs. ErpA is the only ATC essential under aerobiosis. Recent studies reported a possible regulation of the
erpA
mRNA by the small RNA (sRNA) RyhB, which controls the expression of many genes under iron starvation. Surprisingly,
erpA
has not been identified in recent transcriptomic analysis of the iron starvation response, thus bringing into question the actual physiological significance of the putative regulation of
erpA
by RyhB. Using an sRNA library, we show that among 26 sRNAs, only RyhB represses the expression of an
erpA-lacZ
translational fusion. We further demonstrate that this repression occurs during iron starvation. Using mutational analysis, we show that RyhB base pairs to the
erpA
mRNA, inducing its disappearance. In addition, IscR, the master regulator of Fe-S homeostasis, represses expression of
erpA
at the transcriptional level when iron is abundant, but depleting iron from the medium alleviates this repression. The conjunction of transcriptional derepression by IscR and posttranscriptional repression by RyhB under Fe-limiting conditions is best described as an incoherent regulatory circuit. This double regulation allows full expression of
erpA
at iron concentrations for which Fe-S biogenesis switches from the ISC to the SUF system. We further provide evidence that this regulatory circuit coordinates ATC usage to iron availability.

IMPORTANCE
Regulatory small RNAs (sRNAs) have emerged as major actors in the control of gene expression in the last few decades. Relatively little is known about how these regulators interact with classical transcription factors to coordinate genetic responses. We show here how an sRNA, RyhB, and a transcription factor, IscR, regulate expression of an essential gene,
erpA
, in the bacterium
E. coli
. ErpA is involved in the biogenesis of Fe-S clusters, an important class of cofactors involved in a plethora of cellular reactions. Interestingly, we show that RyhB and IscR repress expression of
erpA
under opposite conditions in regard to iron concentration, forming a regulatory circuit called an “incoherent network.” This incoherent network serves to maximize expression of
erpA
at iron concentrations where it is most needed. Altogether, our study paves the way for a better understanding of mixed regulatory networks composed of RNAs and transcription factors.
Cathelicidin Antimicrobial Peptides with Reduced Activation of Toll-Like Receptor Signaling Have Potent Bactericidal Activity against Colistin-Resistant Bacteria
Authors: Kao Cheng , Lin Xiaoyan , Yi Guanghui , Zhang Yunliang , Rowe-Magnus Dean A. , Bush Karen 
Published: September 2016

ABSTRACT
The world is at the precipice of a postantibiotic era in which medical procedures and minor injuries can result in bacterial infections that are no longer effectively treated by antibiotics. Cathelicidins are peptides produced by animals to combat bacterial infections and to regulate innate immune responses. However, cathelicidins are potent activators of the inflammatory response. Cathelicidins with reduced proinflammatory activity and potent bactericidal activity in the low micromolar range against Gram-negative bacteria have been identified. Motifs in cathelicidins that impact bactericidal activity and cytotoxicity to human cells have been elucidated and used to generate peptides that have reduced activation of proinflammatory cytokine production and reduced cytotoxicity to human cells. The resultant peptides have bactericidal activities comparable to that of colistin and can kill colistin-resistant bacteria.

IMPORTANCE
Cathelicidins are antimicrobial peptides that can also increase inflammatory responses. This combination of activities can cause complications in the treatment of bacterial infections despite the pressing need for new antimicrobials. We have identified cathelicidins with decreased activation of inflammatory responses. The peptides kill Gram-negative bacteria at low micromolar concentrations by binding to and perturbing the integrity of the bacterial membrane. The peptides were also engineered to further decrease lysis of human red blood cells. The peptides have activities comparable to those of the polymyxins, a class of antibiotics to which plasmid-borne resistance is rapidly spreading and can kill colistin-resistant bacteria. These peptides are promising candidates for the development of novel antibacterial agents.
Heterogeneity among Isolates Reveals that Fitness in Low Oxygen Correlates with Aspergillus fumigatus Virulence
Authors: Kowalski Caitlin H. , Beattie Sarah R. , Fuller Kevin K. , McGurk Elizabeth A. , Tang Yi-Wei , Hohl Tobias M. , Obar Joshua J. , Cramer Robert A. 
Published: September 2016

ABSTRACT

Previous work has shown that environmental and clinical isolates of
Aspergillus fumigatus
represent a diverse population that occupies a variety of niches, has extensive genetic diversity, and exhibits virulence heterogeneity in a number of animal models of invasive pulmonary aspergillosis (IPA). However, mechanisms explaining differences in virulence among
A. fumigatus
isolates remain enigmatic. Here, we report a significant difference in virulence of two common lab strains, CEA10 and AF293, in the murine triamcinolone immunosuppression model of IPA, in which we previously identified severe low oxygen microenvironments surrounding fungal lesions. Therefore, we hypothesize that the ability to thrive within these lesions of low oxygen promotes virulence of
A. fumigatus
in this model. To test this hypothesis, we performed
in vitro
fitness and
in vivo
virulence analyses in the triamcinolone murine model of IPA with 14 environmental and clinical isolates of
A. fumigatus
. Among these isolates, we observed a strong correlation between fitness in low oxygen
in vitro
and virulence. In further support of our hypothesis, experimental evolution of AF293, a strain that exhibits reduced fitness in low oxygen and reduced virulence in the triamcinolone model of IPA, results in a strain (EVOL20) that has increased hypoxia fitness and a corresponding increase in virulence. Thus, the ability to thrive in low oxygen correlates with virulence of
A. fumigatus
isolates in the context of steroid-mediated murine immunosuppression.

IMPORTANCE
Aspergillus fumigatus
occupies multiple environmental niches, likely contributing to the genotypic and phenotypic heterogeneity among isolates. Despite reports of virulence heterogeneity, pathogenesis studies often utilize a single strain for the identification and characterization of virulence and immunity factors. Here, we describe significant variation between
A. fumigatus
isolates in hypoxia fitness and virulence, highlighting the advantage of including multiple strains in future studies. We also illustrate that hypoxia fitness correlates strongly with increased virulence exclusively in the nonleukopenic murine triamcinolone immunosuppression model of IPA. Through an experimental evolution experiment, we observe that chronic hypoxia exposure results in increased virulence of
A. fumigatus
. We describe here the first observation of a model-specific virulence phenotype correlative with
in vitro
fitness in hypoxia and pave the way for identification of hypoxia-mediated mechanisms of virulence in the fungal pathogen
A. fumigatus.
Emergence of a Potent Multidrug Efflux Pump Variant That Enhances
Campylobacter
Resistance to Multiple Antibiotics
Authors: Yao Hong , Shen Zhangqi , Wang Yang , Deng Fengru , Liu Dejun , Naren Gaowa , Dai Lei , Su Chih-Chia , Wang Bing , Wang Shaolin , Wu Congming , Yu Edward W. , Zhang Qijing , Shen Jianzhong 
Published: September 2016

ABSTRACT

Bacterial antibiotic efflux pumps are key players in antibiotic resistance. Although their role in conferring multidrug resistance is well documented, the emergence of “super” efflux pump variants that enhance bacterial resistance to multiple drugs has not been reported. Here, we describe the emergence of a resistance-enhancing variant (named RE-CmeABC) of the predominant efflux pump CmeABC in
Campylobacter
, a major zoonotic pathogen whose resistance to antibiotics is considered a serious antibiotic resistance threat in the United States. Compared to the previously characterized CmeABC transporters, RE-CmeABC is much more potent in conferring
Campylobacter
resistance to antibiotics, which was shown by increased MICs and reduced intracellular accumulation of antibiotics. Structural modeling suggests that sequence variations in the drug-binding pocket of CmeB possibly contribute to the enhanced efflux function. Additionally, RE-CmeABC expands the mutant selection window of ciprofloxacin, enhances the emergence of antibiotic-resistant mutants, and confers exceedingly high-level resistance to fluoroquinolones, an important class of antibiotics for clinical therapy of campylobacteriosis. Furthermore, RE-CmeABC is horizontally transferable, shifts antibiotic MIC distribution among clinical isolates, and is increasingly prevalent in
Campylobacter jejuni
isolates, suggesting that it confers a fitness advantage under antimicrobial selection. These findings reveal a new mechanism for enhanced multidrug resistance and an effective strategy utilized by bacteria for adaptation to selection from multiple antibiotics.

IMPORTANCE
Bacterial antibiotic efflux pumps are ubiquitously present in bacterial organisms and protect bacteria from the antibacterial effects of antimicrobials and other toxic compounds by extruding them out of cells. Thus, these efflux transporters represent an important mechanism for antibiotic resistance. In this study, we discovered the emergence and increasing prevalence of a unique efflux pump variant that is much more powerful in the efflux of antibiotics and confers multidrug resistance in
Campylobacter
, which is a major foodborne pathogen transmitted to humans via the food chain. Unlike other specific resistance determinants that only allow bacteria to resist a particular antimicrobial, the acquisition of a functionally enhanced efflux pump will empower bacteria with simultaneous resistance to multiple classes of antibiotics. These findings reveal a previously undescribed mechanism for enhanced multidrug resistance and open a new direction for us to understand how bacteria adapt to antibiotic treatment.