bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exuberance, attention bias, and externalizing behaviors in Chinese preschoolers: A longitudinal study
Authors: He Jie , Li Pengchao , Wu Weiyang , Zhai Shuyi 
Published: September 2016

AbstractExuberance, a temperament type influenced by approach motivation, has been found to be associated with maladaptive behaviors such as more externalizing behaviors in early childhood. A possible mechanism underlying it is children's selective attention to environmental cues. However, few studies have investigated the effect of attention bias on the relation between exuberance and externalizing behaviors. This longitudinal study examined the association of temperamental exuberance (as assessed by behavioral observation and parental report) at 3 years old with attention bias to reward and punishment (as assessed by a spatial cueing task) and teachers' reports of externalizing behaviors at 5 years old in 153 Chinese preschool‐age children. As predicted, externalizing behaviors were positively predicted by exuberance and attention bias to reward. However, novel findings were that attention bias to punishment moderated the relation between exuberance and externalizing behaviors, such that exuberant children showed an increased risk of externalizing behaviors when they did not have high punishment bias. The results highlight attention bias to punishment as an important factor for the development of behavioral problems in exuberant children.
Modular embeddings of Teichmüller curves
Authors: Möller Martin , Zagier Don 
Published: September 2016

Fuchsian groups with a modular embedding have the richest arithmetic properties among non-arithmetic Fuchsian groups. But they are very rare, all known examples being related either to triangle groups or to Teichmüller curves. In Part I of this paper we study the arithmetic properties of the modular embedding and develop from scratch a theory of twisted modular forms for Fuchsian groups with a modular embedding, proving dimension formulas, coefficient growth estimates and differential equations. In Part II we provide a modular proof for an Apéry-like integrality statement for solutions of Picard–Fuchs equations. We illustrate the theory on a worked example, giving explicit Fourier expansions of twisted modular forms and the equation of a Teichmüller curve in a Hilbert modular surface. In Part III we show that genus two Teichmüller curves are cut out in Hilbert modular surfaces by a product of theta derivatives. We rederive most of the known properties of those Teichmüller curves from this viewpoint, without using the theory of flat surfaces. As a consequence we give the modular embeddings for all genus two Teichmüller curves and prove that the Fourier developments of their twisted modular forms are algebraic up to one transcendental scaling constant. Moreover, we prove that Bainbridge’s compactification of Hilbert modular surfaces is toroidal. The strategy to compactify can be expressed using continued fractions and resembles Hirzebruch’s in form, but every detail is different.
Optimization of a Steam Turbine Blade’s Double-T Root Through Contact Surface Convexity
Authors: Ehlers Johanna , Ressing Henning , von Karstedt Wulf-Christof , Rixen Daniel , Gadala Mohamed S. 
Published: September 2016

The turbine blade is one of the most critical components of a steam turbine. The high thermal loads and large centrifugal forces cause extreme stresses on the blade, especially on its root.
This paper focuses on improving the double-T root of a turbine blade of the control stage by decreasing the root’s peak equivalent von-Mises stress. An 18% reduction was achieved in the peak stress by changing the convexity of the contact surface between the root and the groove. The equivalent von-Mises stress was determined in a static structural analysis of a three dimensional finite element model (3D FEM-model) using ANSYS Workbench. This numerical model was developed to include one blade and the associated part of the shaft, whereas the complete circle of blades was considered by applying cyclic symmetry. Furthermore, this paper includes a modal analysis comparing the natural frequencies of the initial FEM-model with the frequencies of the optimized one. The results were established by an investigation of the influence of the FEM-model’s parameters, its material properties, thermal effects, and an additional damping wire in the shroud.
Two Years of Improvement and Experience in PEMS for Gas Turbines
Authors: Bainier Francis , Alas Pascal , Morin Florian , Pillay Tony 
Published: September 2016

Due to environmental regulations, Nitrogen oxides (NOx), Carbon Monoxide (CO) and Sulfur Dioxide (SO2) emissions are key issues for gas turbine plants. Regulators are becoming more and more involved and they often require complete and real-time emission information.
The measurements can be done with gas analyzers, this technology is called CEMS: Continuous Emissions Monitoring System. An alternative method [1][2] is to use a calculation based on the turbine instrumentation. This technology is called PEMS: Predictive Emissions Monitoring System. But these technologies do not provide all the information required by the regulator.
GRTgaz, the main gas transmission company in France managing 44 turbines spread over 27 stations across France, has decided to monitor its emissions by PEMS for many years. Two years ago, GRTgaz developed successfully its own PEMS equations, organized answers to regulators around this technology and decided to spread the technology across its gas turbine fleet. The complete intellectual path followed is described in the paper GT2014-25242. This 2016 3-part paper describes the PEMS project steps forward.
In the first part of the paper, a review is done of the PEMS equations used at GRTgaz for NOx and CO concentrations. The various lean premixed combustion turbines differ in terms of combustion design, control and instrumentation. These differences are analyzed considering their influence on combustion and their impact on the PEMS results accuracy.
In order to comply with regulators requirements a calibration of the PEMS results is done every quarter. The results of the first 2 stations equipped with PEMS are described in this first part.
The second part of the paper introduces the smoke developed and the neutral air flow to complete the real time calculation required by the regulators: SO2 concentration and the mass flowrates for NOx, CO and SO2. The final calculation integrates the mass flowrate in order to elaborate the total mass emitted into the atmosphere over different time periods.
The last part deals with developing personnel involvement, managing the data and compiling the results given to regulators. These aspects were more difficult to implement than expected. The importance of these aspects should not be underestimated because the scientific credibility of PEMS cannot be confirmed without them.
Measurements Versus Predictions for a Hybrid (Hydrostatic Plus Hydrodynamic) Thrust Bearing for a Range of Orifice Diameters
Authors: Childs Dara W. , Esser Paul 
Published: September 2016

A fixed-geometry hybrid thrust bearing is investigated with three different supply-orifice diameters, (1.63, 1.80, and 1.93 mm). The test rig uses a face-to-face thrust bearing design, with the test bearing acting as the rotor loading mechanism. A hydraulic shaker applies the static axial load, which is reacted by a second (slave) thrust bearing. The rotor is supported radially by two water-lubricated fluid film journal bearings and is attached to a 30,600 rpm motor via a high speed coupling with very low axial stiffness. Thrust bearings are tested for a range of supply pressures (5.17, 10.34, 17.34 bars), fluid film thicknesses, and speeds (7.5, 12.5, and 17.5 krpm). The water-lubricated test bearings have eight pockets, with feed orifices located centrally in each pocket. Experimental results are comparted to predictions found using the bulk-flow model HYDROTHRUST®.
Analysis of the data reveals generally good agreements between predictions and measurements. Thrust-bearing inlet supply and inner radius flow rates all decreased with decreasing orifice diameters and bearing axial clearances. In most cases, the bearings with larger orifice diameters exhibit higher recess pressure ratios, operating clearances, and flow rates. The 1.93 mm orifice diameter configuration does not display higher recess pressure ratios or operating clearances at high speeds for some supply pressures, but it does continue to require additional lubricant flow rate compared to the smaller orifice bearings. In these cases, the results are not reflected in predictions, which otherwise correlate very well with experimental measurements. Estimations of static loading axial stiffness are obtained using experimental results.
An optimum hybrid thrust bearing orifice diameter will depend on the conditions of individual applications. Larger orifices generally provide larger operating clearances and higher stiffnesses, but also require higher flow rates. For most applications, a compromise of bearing performance parameters will be desired. The test results and comparisons presented will aid in sizing orifice diameters for future hybrid thrust bearing designs and in validating and improving models and predictions.
Micro-Turbojet to Turbofan Conversion via Continuously Variable Transmission: Thermodynamic Performance Study
Authors: Kadosh K. , Cukurel B. 
Published: September 2016

In this study, the viability, performance, and characteristics of a turbojet-to-turbofan conversion through the use of a continuously variable transmission (CVT) are investigated. By an in-house thermodynamic simulation code, the performance of the simple cycle turbojet, a direct shaft joined turbofan, and a CVT coupled turbofan with variable bypass are contrasted. The baseline turbojet and turbofan findings are validated against a commercial software. The comparison indicates high quantitative agreement.
Analyzing the results of the turbofan engine equipped with a variable bypass and CVT, it is observed that both the thrust and the efficiency are increased. The augmented thrust is observed to be an artifact of enhanced component matching and wider operational range introduced by variable bypass capability. On the other hand, the introduction of CVT contributes to the reduction in fuel consumption. Therefore, the current research suggests that adaptation of a micro-turbojet into a variable cycle micro turbofan will greatly improve the performance and efficiency of existing engines, in addition to providing a pathway towards extended use in various applications.
Rotating Heat Transfer Measurements on a Multi-Pass Internal Cooling Channel: II — Experimental Tests
Authors: Pagnacco Fabio , Furlani Luca , Armellini Alessandro , Casarsa Luca , Davis Anthony 
Published: September 2016

The present contribution is focused on heat transfer measurements on internal cooling channels of a high pressure gas turbine blade in static and rotating conditions.
A novel rig designed for the specific purpose was used to assess the heat transfer coefficients on a full internal cooling scheme of an idealized blade. The channel has a multi-pass design. Coolant enters at the blade hub in the leading edge region and move radially outwards inside a two-sided ribbed channel. The second passage is again a two-sided ribbed channel with a trapezoidal cross section of high aspect ratio, while inside the third leg low aspect-ratio cylindrical pin fins are arranged in a staggered configuration to promote flow turbulence. Inside the third passage, the coolant is progressively discharged at the blade trailing edge and finally at the blade tip. The test model differs with respect to the real design only because there is no curvature due to the blade camber. Conversely, the correct stagger angle of the real blade with respect to the rotation axis is preserved.
Experiments were performed for static and rotating conditions with engine similar conditions of Re=21000 and Ro=0.074, both defined at the channel inlet. Transient liquid crystal technique was used for the measurement of the heat transfer coefficient (HTC) on both pressure and suction sides internal surfaces of the channel. From the spatially resolved HTC maps available, it is possible to characterize the thermal performances of the whole passage and to highlight the effect of rotation.
Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Authors: Diefenthal Mathias , Hopfinger Michael , Rakut Christian , Wirsum Manfred , Heuer Tom 
Published: September 2016

In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial turbine wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the turbine wheel came more into focus. In order to account for the thermally induced stresses in the turbine wheel as a part of the standard design process, a fast method is required for predicting metal temperatures.
In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures.
With this understanding, a fast method to calculate the transient temperatures in a radial turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.
Design and Performance Evaluation of an Economical Vertical Axis Wind Turbine
Authors: Himri Abdelghani , Göttlich Emil 
Published: September 2016

Nowadays, ensuring access to energy is one of the serious challenges the world confronts. For those who live in poverty, a shortage of access to energy services desperately influences and undermines health, affects education and development. The problem of energy access for the poor countries has become even more intense because of the impacts of climate change, the global financial crisis and volatile energy prices. Then a use of another sources of energy such as wind power could be a good alternative in these countries.
This paper represents a design of a vertical axis wind turbine that will produce an output power of 883 W for 9 m/s wind speed from a synchronous generator. The project involves the design and the sizing of all the components of this wind turbine. Oil barrels will be used as blades, Filippini was one of the first ones who developed a wind turbine architecture with half cylinders. Later, some modifications were introduced which leads to Thiès rotor and C-rotor.
A simple design was established to facilitate its implementation and reduce its cost. This wind turbine was designed to be used in developing countries. These facts had led to think about an uncomplicated conception and use accessible and cheap equipment which could be available all over the world.
Afterwards, a scaled prototype was realized to make some tests in order to examine its efficiency, some modifications were done to observe the feedback. The procedure of the design of the wind turbine was accomplished from the beginning to the end, no step has been skipped. Later, an estimation of cost was completed. The initial cost remains lower than the cost of a wind turbine in the market. Finally, this wind turbine could be constructed easily with accessible materials. An implementation of this machine in developing countries could help people in their lives. An economical model applied to an African country shows that using one turbine could save about 1400 € per year.
Numerical and Experimental Investigation of Axial Gap Variation in High Pressure Steam Turbine Stages
Authors: Bellucci Juri , Rubechini Filippo , Arnone Andrea , Arcangeli Lorenzo , Maceli Nicola , Paradiso Berardo , Gatti Giacomo 
Published: September 2016

This work aims at investigating the impact of axial gap variation on aerodynamic performance of a high-pressure steam turbine stage.
Numerical and experimental campaigns were conducted on a 1.5-stage of a reaction steam turbine. This low speed test rig was designed and operated in different operating conditions. Two different configurations were studied, in which blades axial gap was varied in a range from 40% to 95% of the blade axial chord. Numerical analyses were carried out by means of three-dimensional, viscous, unsteady simulations, adopting measured inlet/outlet boundary conditions. Two set of measurements were performed. Steady measurements, from one hand, for global performance estimation of the whole turbine, such as efficiency, mass flow, stage work. Steady and unsteady measurements, on the other hand, were performed downstream of rotor row, in order to characterize the flow structures in this region.
The fidelity of computational setup was proven by comparing numerical results to measurements. Main performance curves and span-wise distributions shown a good agreement in terms of both shape of curves/distributions and absolute values. Moreover, the comparison of two dimensional maps downstream of rotor row shown similar structures of the flow field.
Finally, a comprehensive study of the axial gap effect on stage aerodynamic performance was carried out for four blade spacings (10%, 25%, 40% and 95% of S1 axial chord), and five aspect ratios (1.0, 1.6, 3, 4 and 5). The results pointed out how unsteady interaction between blade rows affects stage operation, in terms of pressure and flow angle distributions, as well as of secondary flows development. The combined effect of these aspects in determining the stage efficiency is investigated and discussed in detail.
Design and Numerical Analysis of a New Type of Pre-Swirl Nozzle
Authors: Liu Yuxin , Liu Gaowen , Kong Xiaozhi , Feng Qing 
Published: September 2016

Pre-swirl nozzle is regarded as an important part of preswirl system. Theoretical analysis shows that the temperature drop of pre-swirl system directly relates to the pre-swirl effectiveness of nozzle. When the inlet and outlet pressure are given, there are three ways to improve the nozzle pre-swirl effectiveness. Firstly, increase the discharge coefficient by optimizing the geometry of nozzle; secondly, decrease the preswirl angle; thirdly, minimize the deviation angle of outlet flow to decrease the actual throat area and then increase the tangential velocity.
A new kind of pre-swirl nozzle called vane shaped hole (VSH) nozzle was presented and designed in this paper. The vane height/ pitch ratio of VSH nozzle could be adjusted to an appropriate value, which made its performance of acceleration and deflection better than that of cascade vane nozzle. With the same throat area, radial location and pre-swirl angle (15°), the performance of VSH nozzle was numerically analyzed and compared with three other traditional ones at pressure ratio range 1.1∼1.9, and Reynolds number range 1×105∼5×105. The three traditional nozzles were the simple drilled nozzle, aerodynamic nozzle and cascade vane nozzle. To consider the mixing and rotating influence in the pre-swirl cavity downstream of nozzle, the rotating pre-swirl cavity and receiver hole were included in the computational models. Entropy generation analysis was also made for each nozzle to assess the source of irreversibility.
Numerical results show that the discharge coefficient of aerodynamic nozzle increase 13.7% compared with that of simple drilled nozzle owing to the smaller pressure gradient at nozzle inlet. For cascade vane nozzle, pressure gradient generated in the course of acceleration and deflection would decrease due to the well-designed vane profile. The discharge coefficient of cascade vane nozzle can be as high as 0.97, whereas the preswirl effectiveness is only 0.86 because of a large deviation angle ( 2.42°). For VSH nozzle, higher vane height/pitch ratio and close to zero trailing edge radius lead to a further decrease of endwall secondary flow loss and trailing edge loss, which results in a very small deviation angle ( 0.56°). Consequently, the pre-swirl effectiveness of VSH nozzle is about 8% higher than that of cascade vane nozzle, though the discharge coefficient is about 5% lower. Since the volume of solid block in VSH is bigger than the volume of vane in cascade vane nozzle, which could reduce the difficulty in manufacturing but increase the total weight. Thus, the final nozzle design should comprehensively consider the aerodynamic performance, cost, manufacturing, and stress constraints.
CFD Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions
Authors: Rutledge James L. , Polanka Marc D. , Greiner Nathan J. 
Published: September 2016

The hostile turbine environment requires that film cooling designs are tested in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods is best suited to provide scaled film cooling performance. Furthermore, precise matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched.
A computational simulation of an engine scale film cooled leading edge geometry at high temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low temperature experimental conditions with a 10x scale model. Matching was performed with three common coolant types used in low temperature film cooling experiments — room temperature air, CO2, and cold air to match density ratio. Results indicate that matched momentum flux ratio is the most appropriate for matching adiabatic effectiveness for the case of room temperature air coolant, but also matching density ratio through either CO2 or cold coolant has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches density ratio.