bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lubricant Inertia in Water Lubricated Bearings
Authors: Deng Xin , Watson Cori , Weaver Brian , Wood Houston , Fittro Roger 
Published: October 2017

Oil-lubricated bearings are widely used in high speed rotating machines such as those used in the aerospace and automotive industries. However, with some applications including underwater machinery and environmentally friendly applications, water lubricated bearings have become increasingly used. Due to the different fluid properties between oil and water — namely viscosity — the use of water increases the Reynolds numbers drastically and, therefore, makes water-lubricated bearings prone to turbulence and fluid inertia effects. In other words, the linear approximation of the fluid film reaction forces due to the stiffness and damping parameters — as suggested in the traditional Reynolds equation — is not adequate and should be amended to include lubricant added mass. This is because water-lubricated bearings exhibit large lubricant inertia forces on the order of viscous forces. Additionally, stiffness and damping coefficients should be calculated with the turbulence effects included. The aim of this study was to investigate the methodology of modifying the traditional Reynolds equation to include lubricant inertia effects. This paper reviews the current status of research in the lubricant inertia of bearings and explores the development of methodologies to modify the Reynolds equation to include lubricant inertia in bearings.
The Reynolds equation is a partial differential equation governing the pressure distribution of thin viscous fluid films in lubrication theory. The thin film hypothesis is used to directly relate the bearing film thickness to the lubricant film pressure. Adding lubricant inertia to the Reynolds equation is vital to improving the accuracy of the bearing model and more specifically its film pressure which is essential to predicting load carrying capabilities. The film pressure relates the gradient of the velocity tensor through the Reynolds equation, and resulting shear stresses then allow the turbulent momentum equations to be written in terms of an eddy-viscosity value. An extended Reynolds equation should be developed which takes into account turbulence and both convective and temporal inertia. The most complete form of the temporal inertia effect model should be developed and applied to the turbulent regime, consisting of both primary and secondary temporal inertia terms. The convective inertia model follows Constantinescu’s approach. This analysis develops a lubricant inertia model applicable to water-lubricated bearings. The results of this study could aid in improving future designs and models of water-lubricated bearings.
Vortical Flow Structure of Hub-Corner Separation in a Stator Cascade of a Multi-Stage Transonic Axial Compressor
Authors: Saito Seishiro , Furukawa Masato , Yamada Kazutoyo , Tamura Yuki , Matsuoka Akinori , Niwa Naoyuki 
Published: October 2017

In this study, the hub-corner separation in a multi-stage transonic axial compressor has been investigated using a large-scale detached eddy simulation (DES) with about 4.5 hundred million computational cells. The complicated flow field near the hub wall in a stator with partial tip clearances was analyzed by data mining techniques extracting important flow phenomena from the DES results. The data mining techniques applied in the present study include vortex identification based on the critical point theory and topological data analysis of the limiting streamline pattern visualized by the line integral convolution (LIC) method.
It is found from the time-averaged flow field in the first stator that the hub-corner separation vortex formed near the solid part of the stator tip interacts with the leakage flow and secondary flow on the hub wall, resulting in a complicated vortical flow field. Near the leading edge of the stator, the leakage flow from the front partial clearance generates the tip leakage vortex, which produces loss from the leading edge to 10 percent chord position. At the mid-chord, the hub-corner separation vortex suffers a breakdown, resulting in the widespread huge loss production. It is shown from limiting streamlines on the suction surface of the stator that a reverse flow region expands radially from the solid part of the stator tip toward the downstream. From 50 percent chord position to the trailing edge of the stator, the leakage flow through the rear partial clearance interacts with the secondary flow on the hub wall. The leakage vortex generated along the rear partial clearance becomes a major loss factor there.
Lattice Boltzmann Method Simulation of Turbulent Indoor Airflow Using Hybrid LES/RANS Model
Authors: Sajjadi H. , Salmanzadeh M. , Ahmadi G. , Jafari S. 
Published: October 2017

In this study the hybrid RANS/LES turbulence model within the framework of the Lattice Boltzmann method (LBM) was used to study turbulent indoor airflows. In this approach the near wall region was simulated by the RANS model, while the bulk of the domain was analyzed using the LES model with the LBM approach. In the near wall layer where RANS was used, the k-ε turbulence model was employed. For the k-ε turbulence model in conjunction with the LBM two population balance equations for k and ε were used.
The present simulation results for the airflow showed good agreement with the experimental data and the earlier numerical results for the hybrid RANS/LES. The results showed that the hybrid model properly predicted the large scale turbulence fluctuation velocities in the bulk of the flow region. In addition, the computational time for the hybrid model is less than that of the LES method.
CFD Analysis of the Effect of Rolling Motion on the Characteristic of Labyrinth Seal
Authors: Huang Ning , Li Zhenlin , Li Shiyao , Zhang Ning , Dong Zhihui 
Published: October 2017

With the development of offshore oil and gas industry, LNG turbo expanders are widely used in Floating Liquid Natural Gas equipment (FLNG) for natural gas transportation. The performance characteristic of the turbo expander is significant affected by the rolling motion caused by the ocean conditions. As an important part of expander, the labyrinth seal is directly related to the safety of the expander, so it is necessary to study the performance characteristic of labyrinth seal under rolling motion.
In this paper, CFD is used to simulate the internal flow field of labyrinth seals under different rolling periods and sloshing amplitudes conditions. The distribution of the pressure drop is obtained, and the influence of rolling motion on different labyrinth seal radial clearances and cavity depths are discussed.
The results indicate that variation periods of the pressure drop are consistent with the rolling periods, and the larger the rolling amplitude is, the larger pressure drop fluctuation can be observed. Additionally, the fluctuation characteristic is significantly affected by gap widths and cavity depths.
Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making
Authors: Baglietto Emilio , Demarly Etienne , Kommajosyula Ravikishore 
Published: October 2017

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off.
Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.
Research on Heat-Transfer and Cooling Performance of Gas Turbine Endwall
Authors: Kakio Kazuto , Kawata Y. 
Published: October 2017

Recently, the number of gas turbine combined cycle plants is rapidly increasing in substitution of nuclear power plants. The turbine inlet temperature (TIT) is being constantly increased in order to achieve higher efficiency. Therefore, the improvement of the cooling technology for high temperature gas turbine blades is one of the most important issue to be solved.
In a gas turbine, the main flow impinging at the leading edge of the turbine blade generates a so called horseshoe vortex by the interaction of its boundary layer and generated pressure gradient at the leading edge. The pressure surface leg of this horseshoe vortex crosses the passage and reaches the blade suction surface, driven by the pressure gradient existing between two consecutive blades. In addition, this pressure gradient generates a crossflow along the endwall. This all results into a very complex flow field in proximity of the endwall. For this reason, burnouts tend to occur at a specific position in the vicinity of the leading edge. In this research, a methodology to cool the endwall of the turbine blade by means of film cooling jets from the blade surface is proposed. The cooling performance and heat transfer coefficient distribution is investigated using the transient thermography method. CFD analysis is also conducted to know the phenomena occurring at the end wall and calculate the heat transfer distribution.
Exit Loss Model for Plain Axial Seals in Multi-Stage Centrifugal Pumps
Authors: Bruurs K. A. J. , van Esch B. P. M. , van der Schoot M. S. 
Published: October 2017

Plain axial seals are often used in centrifugal pumps as a means to achieve acceptable sealing against leakage flow without the much higher friction losses that are associated with mechanical seals. Examples of their application are the front seals in shrouded radial and mixed-flow pumps and the inter-stage seals in multi-stage pumps. Knowledge about the relation between leakage flow rate and pressure drop over the seal is vital, not only for estimating the volumetric losses, but also for calculating the axial thrust and shaft power of a pump.
Investigations up till now have mainly concentrated on the frictional pressure drop in the seal (e.g. Yamada [1], Weber [2]), and hardly on the expansion losses at the exit of the seal. These exit losses are commonly modelled by a kinetic loss coefficient equal to or close to 1, but recent measurements by Storteig [3] have shown that exit loss coefficients can have values well above 1.
This paper presents an analytical method to compute the exit loss coefficient of a plain axial seal. It is derived from energy and momentum balances and assumes power-law profiles for the velocity distribution in the seal. The power-law coefficients are computed using CFD and are found to only depend on the Reynolds numbers based on axial flow, Reax, and Couette flow in circumferential direction, ReΩ. The resulting exit loss coefficients are shown to range between 1 and 2, depending on the ratio of Reax and ReΩ. Results of the analytical model are compared with measurements and CFD calculations.
This new analytical model can help improve the prediction of rotor dynamic stability, efficiency and axial thrust of turbomachinery without the need for dedicated CFD calculations in these tight clearances.
Particle-Cluster Formation and Vorticity in Gas-Solid Flows
Authors: Guda Sai Satish , Celik Ismail B. 
Published: October 2017

Fluidized beds are widely used in industry for combustion, gasification, catalytic cracking and several other purposes. Pneumatic conveying of air is popularly used in industry to transport materials such as pulverized coal through pipelines. A common observation in gas-solid flow dynamics in both of the above systems is the formation of high concentration regions of particles; known as clusters in fluidized beds and rope like structures in pipe bends and ducts. Both the clustering and roping phenomenon were clearly observed in some experiments and in simulations of both fluidized beds and gas-solid flows in pipe bends. It has been found from these simulations that there is a strong correlation between vorticity and concentration. The high particle concentration regions are bounded by vortices of clockwise and counter clockwise direction of roughly the same order of magnitude and there is very low vorticity at the high concentration regions.
The goal of this study is to find the cause and effect relation between the gas vorticity and the high particle concentration regions; in particular whether the gas vorticity causes particle agglomeration into clusters or vice-versa. Numerical study has been performed on a vertical pipe by creating a vortex field. In this regard, very large eddy simulations with Lagrangian Discrete Phase model have been performed using Ansys FLUENT and MFIX software packages. The influence of particles on the vorticity has been studied. Influence of several factors such as particle size, injection velocity etc. have also been studied. Correlations among turbulent kinetic energy, vorticity, and particle clustering and/or roping are illustrated.
A Multicolor Grid Technique for Volumetric Velocity Measurements
Authors: Dennis Kadeem , Siddiqui Kamran 
Published: October 2017

Turbulent flows are three-dimensional by nature. A major challenge in turbulence research is the simultaneous measurement of all three velocity components in three-dimensional space. Recently, Rainbow Volumic Velocimetry (RVV) has emerged as a promising technique to visualize and measure three-dimensional flow fields. The RVV technique projects a multicolor light beam in the measurement region. Currently, the technique utilizes beam color variations in one plane i.e. perpendicular to the camera field of view but is restricted to small measurement volumes.
In this paper, a new approach of light beam projection using a multicolor grid is proposed that allows beam color variations in multiple planes relative to the camera field of view. This enables the extension of the light beam width through multiple color combinations. Details of the technique and its implementation are presented along with the preliminary results that demonstrates the viability of this technique.
Wind-Turbine Vibration Reduction Using Flow Control Devices
Authors: Kim Ho-Young , Han Jae-Hung 
Published: October 2017

The size of wind turbine blades has been continuously increased for better aerodynamic efficiency. However, the large scale blades induce loud noise and vibration as well as the increased difficulty in maintenance; all of these eventually causes the increase in the cost of energy. The vibration of wind turbines is mainly caused by wind turbulence, wind shear, and tower shadow. These causes change in local angle of attack of wind turbine blades and create mostly periodic vibration.
In this work, a flow control device is applied for vibration reduction of wind turbine blades. The conventional role of flow control devices is to increase lift coefficient and to reduce drag coefficient by flow separation delay. In this research, flow control device is used to make a flat slope of lift coefficient in specific angle of attack range for vibration reduction; lift coefficient is not always increased but also decreased, too.
To manipulate the lift coefficient slope, several types of flow separation controller are considered. Finally, a plasma actuator is selected because the minimal structural modification is necessary while providing sufficient lift coefficient control. The plasma actuator is attached to an airfoil to blow the jet upwind to decrease the lift. Computational fluid dynamics simulation is conducted to estimate the flow control performance of the plasma actuator. Experiments are conducted on a DU35-A17 airfoil to verify the lift coefficient manipulation performance of the plasma actuator.
Oral Tobramycin Prophylaxis Prior to Colorectal Surgery Is Not Associated with Systemic Uptake
Authors: Mulder T. , Kluytmans-van den Bergh M. F. Q. , Crolla R. M. P. H. , Ermens A. A. M. , Romme J. , van‘t Veer N. E. , Kluytmans J. A. J. W. 
Published: October 2017

ABSTRACT
Preoperative oral prophylaxis with nonabsorbable antibiotics has been reported to reduce the risk of surgical site infections after colorectal surgery. This prospective study was conducted to evaluate the risk of toxic side effects by measuring postoperative serum tobramycin levels in patients who received a 3-day prophylaxis with tobramycin and colistin prior to colorectal surgery. In all patients, serum tobramycin concentrations were below the detection limit (0.3 mg/liter), implying a low risk of toxicity.
Antimicrobial Activities of Aztreonam-Avibactam and Comparator Agents against Contemporary (2016) Clinical Enterobacteriaceae Isolates
Authors: Sader Helio S. , Mendes Rodrigo E. , Pfaller Michael A. , Shortridge Dee , Flamm Robert K. , Castanheira Mariana 
Published: October 2017

ABSTRACT

A total of 10,451 contemporary (2016)
Enterobacteriaceae
isolates from 84 U.S. medical centers and 116 metallo-β-lactamase- and/or OXA-48-like-producing
Enterobacteriaceae
isolates from other countries were tested against aztreonam-avibactam and comparators. All U.S. isolates were inhibited at aztreonam-avibactam MICs of ≤8 μg/ml (MIC
50
, ≤0.03 μg/ml; MIC
90
, 0.12 μg/ml), including
Klebsiella pneumoniae
carbapenemase-producing isolates (
n
= 102; MIC
50
, 0.25 μg/ml; MIC
90
, 0.5 μg/ml), multidrug-resistant isolates (
n
= 876; MIC
50
, 0.06 μg/ml; MIC
90
, 0.25 μg/ml), and extensively drug-resistant isolates (
n
= 111; MIC
50
, 0.12 μg/ml; MIC
90
, 0.5 μg/ml). The highest aztreonam-avibactam MIC value among ex-U.S. isolates was 4 μg/ml.
Suppression of a Thermosensitive
zipA
Cell Division Mutant by Altering Amino Acid Metabolism
Authors: Vega Daniel E. , Margolin William 
Published: October 2017

ABSTRACT

ZipA is essential for cell division in
Escherichia coli
, acting early in the process to anchor polymers of FtsZ to the cytoplasmic membrane. Along with FtsA, FtsZ and ZipA form a proto-ring at midcell that recruits additional proteins to eventually build the division septum. Cells carrying the thermosensitive
zipA1
allele divide fairly normally at 30°C in rich medium but cease dividing at temperatures above 34°C, forming long filaments. In a search for suppressors of the
zipA1
allele, we found that deletions of specific genes involved in amino acid biosynthesis could partially rescue cell growth and division at 34°C or 37°C but not at 42°C. Notably, although a diverse group of amino acid biosynthesis gene deletions could partially rescue the growth of
zipA1
cells at 34°C, only deletions of genes related to the biosynthesis of threonine, glycine, serine, and methionine could rescue growth at 37°C. Adding exogenous pyridoxal 5-phosphate (PLP), a cofactor for many of the enzymes affected by this study, partially suppressed
zipA1
mutant thermosensitivity. For many of the deletions, PLP had an additive rescuing effect on the
zipA1
mutant. Moreover, added PLP partially suppressed the thermosensitivity of
ftsQ
and
ftsK
mutants and weakly suppressed an
ftsI
mutant, but it failed to suppress
ftsA
or
ftsZ
thermosensitive mutants. Along with the ability of a deletion of
metC
to partially suppress the
ftsK
mutant, our results suggest that perturbations of amino acid metabolic pathways, particularly those that redirect the flow of carbon away from the synthesis of threonine, glycine, or methionine, are able to partially rescue some cell division defects.

IMPORTANCE
Cell division of bacteria, such as
Escherichia coli
, is essential for their successful colonization. It is becoming increasingly clear that nutritional status and central metabolism can affect bacterial size and shape; for example, a metabolic enzyme (OpgH) can moonlight as a regulator of FtsZ, an essential cell division protein. Here, we demonstrate a link between amino acid metabolism and ZipA, another essential cell division protein that binds directly to FtsZ and tethers it to the cytoplasmic membrane. Our evidence suggests that altering flux through the methionine-threonine-glycine-serine pathways and supplementing with the enzyme cofactor pyridoxal-5-phosphate can partially compensate for an otherwise lethal defect in ZipA, as well as several other cell division proteins.
Transcatheter occlusion of the patent ductus arteriosus in premature infants weighing less than 1200 g
Authors: Morville Patrice , Douchin Stephanie , Bouvaist Helene , Dauphin Claire 
Published: October 2017

ObjectivesOver the last few decades different strategies have been proposed to treat persistent ductal patency in premature infants. The advent of the Amplatzer Duct Occluder II Additional Size (ADOIIAS) provided the potential to close the patent ductus arteriosus (PDA). Opinions differ on the significance and treatment of PDA in premature neonates. Because surgical ligation and medical therapy both have their drawbacks, interventional catheterisation can be considered as an alternative means of closing the ductus arteriosus. Our aim was to analyse the feasibility, safety and efficacy of this device in premature infants weighing <1200 g at procedure.MethodsEighteen premature infants underwent transcatheter closure. The procedure was performed in the catheterisation laboratory by venous cannulation without angiography. The position of the occluder was directed by X-ray and ultrasound. We looked at procedural details, device size selection, complications and short-term and mid-term outcomes.ResultsEighteen infants born at gestational ages ranging between 23.6 and 29+6 weeks (mean±SD 25+6±3 weeks) underwent transcatheter PDA closure. Their mean age and weight at the time of the procedure was 20 days (range 8–44 days) and 980 g (range 680–1200 g), respectively. The mean PDA and device waist diameters were 3.2±0.6 mm (range 2.2–4 mm) and 4.5±0.6 mm, respectively, and the mean PDA and device lengths were 4.3±1.2 mm (range 2–10 mm) and 2.5±0.9 mm, respectively. Complete closure was achieved in all but one patient. There was no device migration. One patient developed a left pulmonary artery obstruction. Three infants died. Two deaths were related to complications of prematurity and one to the procedure.ConclusionsTranscatheter closure of a PDA is feasible in very low weight infants with ADOIIAS and is an alternative to surgery. Success requires perfect selection and placement of the occluder.