bluuebunny/crossref_metadata_2025_split huggingface dataset:
Leakage Degradation of Straight Labyrinth Seal due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove
Authors: Dogu Yahya , Sertçakan Mustafa C. , Gezer Koray , Kocagül Mustafa , Arıcan Ercan , Ozmusul Murat S. 
Published: September 2016

In this paper, labyrinth seal leakage is numerically quantified for an acute trapezoidal rub-groove accompanied with a rounded tooth, as a function of rub-groove sizes and tooth-groove axial positions. Analyses parameters include clearance, pressure ratio, number of teeth, and rotor speed.
Labyrinth seals wear during engine transients. Radial incursion and axial movement of the rotor-stator pair cause the labyrinth teeth to rub against the unworn stator surface. The labyrinth teeth and/or stator wear depending on their material hardness. Wear damage in the form of material loss or deformation permanently increases seal clearance, and thus, leakage. This leakage is known to be dependent on the shape and geometry of the worn tooth and the stator rub groove.
There are two types of reported tooth tip wear. These can be approximated as a mushroom shape and a round shape. The stator rub-groove shapes can be approximately simulated in five forms: rectangle, trapezoid (isosceles and acute), triangle, and ellipse.
In this paper, the acute trapezoidal rub-groove shape is specifically chosen, since it is the most similar to the most commonly observed rub-groove form. The tooth tip is considered to be rounded, because the tooth tip wears smoothly and a round shape forms during rub-groove formation. To compare the unworn tooth, the flat stator is also analyzed as a reference case. All analyzed parameters for geometric dimensions (groove width, depth, wall angle, tooth-groove axial position,) and operating conditions (flow direction, clearance, pressure ratio, number of teeth, rotor speed) are analyzed in their practical ranges.
CFD analyses are carried out by employing a compressible turbulent flow solver in a 2-D axi-symmetrical coordinate system. CFD analyses show that the rounded tooth leaks more than an unworn sharp-edged tooth, due to the formation of a smooth and streamlined flow around the rounded geometry. This smooth flow yields less flow separation, flow disturbance, and less of vena contract a effect. The geometric dimensions of the acute trapezoidal rub-groove (width, depth, wall angle) significantly affect leakage. The effects of clearance, pressure ratio, number of teeth, and rotor speed on the leakage are also quantified. Analyses results are separately evaluated for each parameter.
Labyrinth Seal Leakage Degradation due to Various Types of Wear
Authors: Dogu Yahya , Sertçakan Mustafa C. , Gezer Koray , Kocagül Mustafa , Arıcan Ercan , Ozmusul Murat S. 
Published: September 2016

This paper systematically presents a complete leakage comparison for various types of wear experienced by labyrinth seals. Labyrinth seals used in turbine engines are designed to work at a clearance during steady-state engine operations. The tooth tip rubs the stator and wears either itself or the stator surface during transient operations, depending on the material properties of the tooth and stator. Any type of wear that increases clearance or deforms the tooth tip will cause permanent and unpredictable leakage degradation. This negatively affects the engine’s overall efficiency, durability, and life.
The teeth have been reported to wear into a mushroom profile or into a rounded profile. A rub-groove on the opposing surface may form in several shapes. Based on a literature survey, five rub-groove shapes are considered in this work. They are: rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this work, leakage degradation due to wear is numerically quantified for both mushroomed and rounded tooth wear profiles. It also includes analyses on rounded teeth with the formation of five rub-groove shapes. All parameters are analyzed at various operating conditions (clearance, pressure ratio, number of teeth, rotor speed).
CFD analyses are carried out by employing compressible turbulent flow in a 2-D axi-symmetrical coordinate system. CFD analyses show that the following tooth-wear conditions affect leakage from least to greatest: unworn, rounded, and mushroomed. These are for an unworn flat stator. It is also observed that rub-groove shapes considerably affect the leakage depending on the clearance. Leakage increases with the following groove profiles: triangular, rectangular, acute trapezoidal, isosceles trapezoidal, and elliptical. The results show that any type of labyrinth seal wear has significant effects on leakage. Therefore, leakage degradation due to wear should be considered during the engine design phase.
Non-Axisymmetric Endwall Profile Optimization of a High-Pressure Transonic Turbine Using Approximation Model
Authors: Kim Inkyom , Kim Jinuk , Cho Jinsoo , Kang Young-Seok 
Published: September 2016

Secondary loss of low aspect ratio turbines takes as much as 50% of the total loss. Non-axisymmetric endwall profile optimization was conducted for the nozzle hub and shroud of a 1-stage high-pressure transonic turbine. The endwalls of the hub and the shroud were individually optimized using an approximation model. Kriging model was used for response surface generation and the optimum solution was searched using Genetic Algorithm with stage efficiency as the objective function.
Optimized endwall profiles reduced nozzle losses and shocks, thereby improving stage efficiency. The shroud endwall profile showed higher performance, because it influenced the flow over the whole span, whereas the influence of the hub endwall profile was limited close to the hub.
The stage efficiency was improved by 0.39%p when both the hub and the shroud endwall profiles were applied. However, the mass flow rate exceeded the design limit and the efficiency had no benefit to the single shroud endwall profile, showing the limitations of individually optimized endwall profiles.
An Energy Based Fouling Model for Gas Turbines: EBFOG
Authors: Casari Nicola , Pinelli Michele , Suman Alessio , di Mare Luca , Montomoli Francesco 
Published: September 2016

Fouling is a major problem in gas turbines for aero-propulsion. The aerodynamics and heat load of the blades are severely affected by this phenomenon with local geometrical variations due to deposition and erosion. Currently two major models are available in literature for the evaluation of fouling effects in CFD: the first one is based on a critical threshold for the viscosity, whereas the second is characterized by the normal velocity to the surface. Both models aim to define a likelihood coefficient which estimates the probability a particle has to stick to a surface, known as sticking coefficient. However current models lack of generality being application specific.
This work presents an innovative model for the estimation of the sticking probability. The fouling effect is defined as function of particle velocity, temperature and size through an energy based approach. Expressing the energy involved in the impact through an Arrhenius’ type equation a general formulation for the sticking coefficient is obtained. The method, named EBFOG (Energy Based FOulinG), is the first “energy” based model presented in the open literature that can account any common deposition effect in gas turbines.
The EBFOG model is implemented into a Lagrangian tracking procedure, coupled to a full three-dimensional CFD solver. Particles are tracked inside the domain and the velocity, size and temperature of each ones are calculated. The local geometry of the blade is modified accordingly to the deposition rate, the mesh is modified and the CFD solver updates the flow field.
The application of this model to particle deposition in high pressure turbine vanes is investigated showing the flexibility of the proposed methodology. Such model is particular important in aircraft engines where the effect of fouling for the turbine, in particular the reduction of the HP nozzle throat area, influences heavily the performance: the energy based approach is thus used to quantify the area modification and estimate the variation of the compressor performance. The compressor map as a function of the operating hours in a severe environment can be in this way predicted to estimate, for example, the time that an engine can fly in a cloud of volcanic ashes. For this reason the impact of the fouling on the throat area of the nozzle is quantified for different conditions.
Flameless Oxidation Combustor Development for a Sequential Combustion Hybrid Turbofan Engine
Authors: Levy Y. , Erenburg V. , Sherbaum V. , Gaissinski I. 
Published: September 2016

A promising method of reducing NOx emissions in combustion systems is the Flameless oxidation (FO), which is based on significant dilution of the oxygen concentration in the reactant stream and elevating its temperature to above auto ignition level.
The present work is aimed at developing an FO based combustor for a sequential combustion turbofan engine, where the primary combustor is fuelled with H2 and the secondary combustor with hydrocarbon (jet or bio-jet) fuel. The work was performed within the framework of the European project AHEAD (www.ahead-euproject.eu). Being situated between the high pressure and the low pressure turbines, the inlet conditions to the FO combustor are non-conventional.
CHEMKIN simulations revealed the theoretical feasibility of a combustion system to operate in the FO mode of combustion under the specific Take off and Cruise operating conditions. Several design iterations were conducted to find an appropriate geometrical configuration that would allow for such a system to operate in a stable manner. The design iterations were followed by intensive CFD simulations (FLUENT) and a final design was a achieved where the predictions indicated nearly uniform internal temperature distribution with low mass fraction of CO (14.4ppm) and NOx (0.5 ppm) at the exhaust.
A separate experimental verification study was performed and confirmed the ability of the CFD model to predict the behaviour of such a combustion configuration within the hybrid turbofan engine and its results will be published elsewhere.
Foreign Object Damage and Fatigue After Impact Simulations on Flat and Curved Hi Nicalon and Hi Nicalon Type S (MI SiC) Specimens at Room and 1200°C Using Building Block Approach
Authors: Abdi Frank , Godines Cody , Morscher Gregory N. , Choi Sung , Villa Montero Marc , Han Zipeng , Presby Michael 
Published: September 2016

SiC-based ceramic matrix composites (CMC) in turbine engine applications must sustain fatigue residual life after foreign object impacts that might occur in services. Experiments, nondestructive evaluations (NDE), and simulations have illustrated good correlations between impact energy and foreign object damage (FOD) and fatigue life after impact at room and 1200°C temperatures. Flat and curved five-harness satin (5HS) woven CMCs specimens, consisting of Hi-Nicalon Type S (Goodrich) and Hi-Nicalon (Rolls Royce) in MI SiC matrix, were tested and simulated. Tests measured electrical resistivity (ER), acoustic emission (AE), and microscopy. Simulations used a building block validation strategy and the Multi-Scale Progressive Failure Analysis (MS-PFA) method. Simulations complemented experiments in understanding and predicting the damage states, of impact, and fatigue residual strength after impact of CMCs to form a more complete understanding of the damage mechanisms involved in such events. The GENOA software developed by Alpha STAR Corporation [1, 2, 3] is capable of Durability and Damage Tolerance (D&DT), life, and reliability predictions by means of multi-scale progressive failure analysis (damage and fracture evolution). In general, CMCs are modeled using effective fiber, matrix, and interface constitutive behaviors, from which the lamina stiffness, strengths, and the strain rate effect can be derived. Similarly, the fatigue strength and stiffness degradation, and the effect of defects in a matrix micro crack density, voids, as well as fibers waviness, and damages after impact can be characterized. The final simulation is static loading and impact on a generic CMC SiC/SiC (Sylramic MI 5HS) blade which is to be used in future blade optimization based on minimizing damage incurred.
The GENOA software platform supports FAA recommended ASTM standard Building-Block Validation Strategy with reduced tests conducting: 1) Material Calibration and Qualification, and 2) FEM Verification, Validation, and 3) Blind Predictions (Accreditation). The simulation and test comparisons performed included the damage size for both the CMC (fracture) and the steel impactor (plastic deformation), rebound velocities, SN curves for fatigue of pristine and impacted specimens at room and high temperatures. All simulations showed good correlation. The MS-PFA tool demonstrated a great potential for CMC post FOD fatigue life for part certification supported with reduced tests.
Using a Tracer Gas to Quantify Sealing Effectiveness for Engine Realistic Rim Seals
Authors: Clark Kenneth , Barringer Michael , Thole Karen , Clum Carey , Hiester Paul , Memory Curtis , Robak Christopher 
Published: September 2016

As overall pressure ratios increase in gas turbine engines, both the main gas path and cooling temperatures increase leading to component durability concerns. At the same time effective use of the secondary air for both cooling and sealing becomes increasingly important in terms of engine efficiency. To fully optimize these competing requirements, experiments at engine-relevant conditions are required to validate new designs and computational tools. A test turbine has been commissioned in the Steady Thermal Aero Research Turbine (START) lab. The test turbine was designed to be a 1.5 stage turbine operating under continuous flow simulating engine-relevant conditions including Reynolds and Mach numbers with hardware true to engine scale. The first phase of research conducted using the test turbine, which was configured for a half-stage (vane only), was to study hot gas ingestion through turbine rim seals.
This paper presents a series of facility benchmarks as well as validation experiments conducted to study ingestion using a tracer gas to quantify the performance of rim seals and purge flows. Sensitivity studies included concentration levels and sampling flow rates in flow regimes that ranged from stagnant to compressible depending upon the area of interest. The sensitivity studies included a range of purge and leakage flow conditions for several locations in the rim seal and cavity areas. Results indicate reasonable sampling methods were used to achieve isokinetic sampling conditions.
A Combined Power Plant Fueled by Syngas Produced in a Downdraft Gasifier
Authors: Fortunato Bernardo , Camporeale Sergio Mario , Torresi Marco , Fornarelli Francesco , Brunetti Gianluigi , Pantaleo Antonio Marco 
Published: September 2016

In this paper different gas-steam combined-cycles fueled by syngas produced in a local downdraft gasifier, are analyzed. At first, the downdraft gasifier model is briefly described, where waste biomass is transformed into syngas, which can be used more efficiently than the original solid biomass to generate useful power, and can be transported much more easily. The gasifier model is able to estimate, with good approximation, the composition of the produced syngas, taking separately into account the biomass drying and the pyrolysis, oxidation and reduction processes. The gasifier operates at ambient pressure using air as gasification agent and biomass as input. Among others, pomace has been considered, since, in Italy (where the plant is supposed to be located) there are many regions, like Apulia, where this biomass is largely available. Three different plant configurations have been proposed and compared in terms of overall performance. The first two, named REXC (Regenerative cycle with EXternal Combustor) and CR (Conventional Regenerative cycle), burn the syngas in an internal combustor, whereas the third one, named SyEXC (Syngas External Combustion), considers an externally fired configuration for the syngas combustion.
In the REXC cycle, a secondary external combustion system, fed by cellulosic biomass, is connected to a heat exchanger in order to increase the air temperature, as in a regenerative cycle. The combustion products pass through a primary heat exchanger placed in the external combustion system, heating the compressed air, which flows into the primary internal combustion chamber, where a defined quantity of syngas reacts with the compressed air. The turbine exhaust gas (TEG), before going back into the external combustion, partially transfers its enthalpy content to a Heat Recovery Steam Generator (HRSG) of a bottoming Rankine cycle.
The second plant configuration (CR cycle) is characterized by a main internal combustor fueled by the produced syngas and implements a conventional regenerative process. The TEG is reheated by an externally fired combustion before flowing in the HRSG of a bottoming Rankine cycle.
The last plant configuration (SyEXC) differs from the CR one only for the main externally fired gas turbine fueled by syngas, thus avoiding any costly cleanup operation and cooling.
A Multilaboratory, Multicountry Study To Determine MIC Quality Control Ranges for Phenotypic Drug Susceptibility Testing of Selected First-Line Antituberculosis Drugs, Second-Line Injectables, Fluoroquinolones, Clofazimine, and Linezolid
Authors: Kaniga Koné , Cirillo Daniela M. , Hoffner Sven , Ismail Nazir A. , Kaur Devinder , Lounis Nacer , Metchock Beverly , Pfyffer Gaby E. , Venter Amour 
Published: September 2016

ABSTRACT

Our objective was to establish reference MIC quality control (QC) ranges for drug susceptibility testing of antimycobacterials, including first-line agents, second-line injectables, fluoroquinolones, and World Health Organization category 5 drugs for multidrug-resistant tuberculosis using a 7H9 broth microdilution MIC method. A tier-2 reproducibility study was conducted in eight participating laboratories using Clinical Laboratory and Standards Institute (CLSI) guidelines. Three lots of custom-made frozen 96-well polystyrene microtiter plates were used and prepared with 2× prediluted drugs in 7H9 broth-oleic acid albumin dextrose catalase. The QC reference strain was
Mycobacterium tuberculosis
H37Rv. MIC frequency, mode, and geometric mean were calculated for each drug. QC ranges were derived based on predefined, strict CLSI criteria. Any data lying outside CLSI criteria resulted in exclusion of the entire laboratory data set. Data from one laboratory were excluded due to higher MIC values than other laboratories. QC ranges were established for 11 drugs: isoniazid (0.03 to 0.12 μg/ml), rifampin (0.03 to 0.25 μg/ml), ethambutol (0.25 to 2 μg/ml), levofloxacin (0.12 to 1 μg/ml), moxifloxacin (0.06 to 0.5 μg/ml), ofloxacin (0.25 to 2 μg/ml), amikacin (0.25 to 2 μg/ml), kanamycin (0.25 to 2 μg/ml), capreomycin (0.5 to 4 μg/ml), linezolid (0.25 to 2 μg/ml), and clofazimine (0.03 to 0.25 μg/ml). QC ranges could not be established for nicotinamide (pyrazinamide surrogate), prothionamide, or ethionamide, which were assay nonperformers. Using strict CLSI criteria, QC ranges against the
M. tuberculosis
H37Rv reference strain were established for the majority of commonly used antituberculosis drugs, with a convenient 7H9 broth microdilution MIC method suitable for use in resource-limited settings.
Multiple Antibody Lineages in One Donor Target the Glycan-V3 Supersite of the HIV-1 Envelope Glycoprotein and Display a Preference for Quaternary Binding
Authors: Longo Nancy S. , Sutton Matthew S. , Shiakolas Andrea R. , Guenaga Javier , Jarosinski Marissa C. , Georgiev Ivelin S. , McKee Krisha , Bailer Robert T. , Louder Mark K. , O'Dell Sijy , Connors Mark , Wyatt Richard T. , Mascola John R. , Doria-Rose Nicole A. 
Published: September 2016

ABSTRACT
One of the goals of HIV-1 vaccine development is the elicitation of neutralizing antibodies against vulnerable regions on the envelope glycoprotein (Env) viral spike. Broadly neutralizing antibodies targeting the Env glycan-V3 region (also called the N332 glycan supersite) have been described previously, with several single lineages each derived from different individual donors. We used a high-throughput B-cell culture method to isolate neutralizing antibodies from an HIV-1-infected donor with high serum neutralization breadth. Clonal relatives from three distinct antibody lineages were isolated. Each of these antibody lineages displayed modest breadth and potency but shared several characteristics with the well-characterized glycan-V3 antibodies, including dependence on glycans N332 and N301, VH4 family gene utilization, a heavy chain complementarity-determining region 2 (CDRH2) insertion, and a longer-than-average CDRH3. In contrast to previously described glycan-V3 antibodies, these antibodies preferentially recognized the native Env trimer compared to monomeric gp120. These data indicate the diversity of antibody specificities that target the glycan-V3 site. The quaternary binding preference of these antibodies suggests that that their elicitation likely requires the presentation of a native-like trimeric Env immunogen.

IMPORTANCE
Broadly neutralizing antibodies targeting the HIV-1 glycan-V3 region with single lineages from individual donors have been described previously. Here we describe three lineages from a single donor, each of which targets glycan-V3. Unlike previously described glycan-V3 antibodies, these mature antibodies bind preferentially to the native Env trimer and weakly to the gp120 monomer. These data extend our knowledge of the immune response recognition of the N332 supersite region and suggest that the mode of epitope recognition is more complex than previously anticipated.
Ex vivo study of human visceral nociceptors
Authors: McGuire Cian , Boundouki George , Hockley James R F , Reed David , Cibert-Goton Vincent , Peiris Madusha , Kung Victor , Broad John , Aziz Qasim , Chan Christopher , Ahmed Shafi , Thaha Mohamed A , Sanger Gareth J , Blackshaw L Ashley , Knowles Charles H , Bulmer David C 
Published: September 2016

ObjectiveThe development of effective visceral analgesics free of deleterious gut-specific side effects is a priority. We aimed to develop a reproducible methodology to study visceral nociception in human tissue that could aid future target identification and drug evaluation.DesignElectrophysiological (single unit) responses of visceral afferents to mechanical (von Frey hair (VFH) and stretch) and chemical (bradykinin and ATP) stimuli were examined. Thus, serosal afferents (putative nociceptors) were used to investigate the effect of tegaserod, and transient receptor potential channel, vanilloid 4 (TRPV4) modulation on mechanical responses.ResultsTwo distinct afferent fibre populations, serosal (n=23) and muscular (n=21), were distinguished based on their differences in sensitivity to VFH probing and tissue stretch. Serosal units displayed sensitivity to key algesic mediators, bradykinin (6/14 units tested) and ATP (4/10), consistent with a role as polymodal nociceptors, while muscular afferents are largely insensitive to bradykinin (0/11) and ATP (1/10). Serosal nociceptor mechanosensitivity was attenuated by tegaserod (−20.8±6.9%, n=6, p<0.05), a treatment for IBS, or application of HC067047 (−34.9±10.0%, n=7, p<0.05), a TRPV4 antagonist, highlighting the utility of the preparation to examine the mechanistic action of existing drugs or novel analgesics. Repeated application of bradykinin or ATP produced consistent afferent responses following desensitisation to the first application, demonstrating their utility as test stimuli to evaluate analgesic activity.ConclusionsFunctionally distinct subpopulations of human visceral afferents can be demonstrated and could provide a platform technology to further study nociception in human tissue.