bluuebunny/crossref_metadata_2025 huggingface dataset:
Status and recommendations for sustainable freshwater aquaculture in Brazil
Authors: Nobile André B. , Cunico Almir M. , Vitule Jean R. S. , Queiroz Jamile , Vidotto‐Magnoni Ana P. , Garcia Diego A. Z. , Orsi Mário L. , Lima Felipe P. , Acosta Aline A. , da Silva Reinaldo J. , do Prado Fernanda D. , Porto‐Foresti Fábio , Brandão Heleno , Foresti Fausto , Oliveira Claudio , Ramos Igor P.
Published: November 2019

Brazil is a megadiverse country and is participant of fundamental environmental agreements for biodiversity conservation. However, the internal politics and the cultures that affect negatively the ecological integrity in Brazilian freshwater need to be improved on the condition of sustainable management. Scientific community, the government and stakeholders are in constant conflicts of goals. Meanwhile, the current model for Brazilian aquaculture shows problems of ecological impact due to the lack of appropriated planning and legislation to the aquatic biota. The non‐recognition of sustainable census incorporated in its environmental politics reflects in an archaic and unsustainable management, with the following characters: a non‐specific approach for technical management, the indiscriminate use of interspecific hybrids and non‐native species and the lack of skilled labour. The potential impact on native species and the introduction of pathogens are the main negative effects on aquatic biota. This way, the aim of this article is to elucidate the conflicts of interests and ecological effects of fish aquaculture in Brazil, besides providing good practices and sustainable alternatives for management.
Electronic cigarettes: Tumultuous times
Authors: Peters Matthew J.
Published: November 2019

See related Article
Penal and welfare conditionality: Discipline or degradation?
Authors: McNeill Fergus
Published: November 2019

This paper aims to complement analyses of welfare conditionality by examining what can be learned from studies of conditional punishment in the criminal justice system. Drawing on a range of recent studies, I explore lived experiences of the conditionality attendant on penal forms of supervision; penal forms that have expanded rapidly in recent decades. I argue that, to paraphrase Stan Cohen, such supervision is as much about the dispersal of degradation as it is about the dispersal of discipline. Indeed, in contemporary western societies, both in punishment and in welfare systems, I suggest that conditionality functions less to discipline poor and marginalised people and more to disqualify them from the entitlements of ordinary citizenship. In so doing, conditionality constructs them as denizens, thus serving to limit the liabilities for the state that arise from social inequalities. Extending Delroy Fletcher and Sharon Wright's metaphor, the abusive slaps now meted out in concert by both hands of the penal state are as much about degrading and denying the entitlements of “needy” denizens as they are about influencing their conduct. But crucially, even within the increasingly restrictive context created by these developments, penal practitioners can and do provide care and assistance.
Performance of methods to conduct mediation analysis with time‐to‐event outcomes
Authors: Burgos Ochoa Lizbeth , Rijnhart Judith J.M. , Penninx Brenda W. , Wardenaar Klaas J. , Twisk Jos W.R. , Heymans Martijn W.
Published: November 2019

Previous studies have discouraged the use of the Cox proportional hazards (PH) model for traditional mediation analysis as it might provide biased results. Accelerated failure time (AFT) models have been proposed as an alternative for Cox PH models. In addition, the use of the potential outcomes framework has been proposed for mediation models with time‐to‐event outcomes. The aim of this paper is to investigate the performance of traditional mediation analysis and potential outcomes mediation analysis based on both the Cox PH and the AFT model. This is done by means of a Monte Carlo simulation study and the illustration of the methods using an empirical data set. Both the product‐of‐coefficients method of the traditional mediation analysis and the potential outcomes framework yield unbiased estimates with respect to their own underlying indirect effect value for simple mediation models with a time‐to‐event outcome and estimated based on Cox PH or AFT.
Interculturality and GTA Training in the Age of Globalization
Authors: Chalupa Cynthia , Hoecherl‐Alden Gisela
Published: November 2019

German, and increasingly French and Spanish, programs are by nature global because they attract graduate students and faculty from around the world. Most have studied the language and “big C” cultural products during their graduate studies, but they have not necessarily learned approaches for fostering intercultural communicative competence in the classroom. The demands of communication in the global age require not only that language learners examine cultural products and practices but also that they investigate the unique perspectives that underlie them. This need suggests that graduate teaching associates (GTAs) receive training in how to foster intercultural communicative competence and that the responsibility lies with language program directors to incorporate new aspects of teacher training into graduate student professional development. With that in mind, this conversation explores (1) how to promote interculturality within individual language programs that are characterized by global teaching staffs and (2) the training of GTAs on strategies for cultivating intercultural communicative competence in the classroom. Through added modules during pre‐service orientations and ongoing professional training, graduate teaching associates can be better prepared to meet the needs of 21st century students.
Opening our Imaginations: A Dialogue on Graduate Education
Authors: Mittman Elizabeth , Santos Krsna
Published: November 2019

Graduate education in the humanities struggles with weighty traditions, constrained (fiscal) resources, and a legacy of elitism and cultural homogeneity. As the makeup of graduate students becomes ever more diverse in terms of income, ethnicity, sexuality, citizenship, and disability, graduate programs are working through the challenges and opportunities non‐traditional students bring to light. An openness to rethinking the mission of German Studies at Michigan State University (MSU) – a large Midwestern, land‐grant institution – has made possible a series of specific changes, including the hybrid dissertation, faculty‐student research collaboration, uniquely transdisciplinary approaches, and explicit preparation for non‐academic career pathways. In this conversation, a professor and a doctoral student in the German Studies program at MSU reflect on these reforms in their program, and embed them within a broader framework of questions facing graduate education more generally: (1) the changing face of the discipline of German Studies, and indeed of German culture as an object of our study, (2) issues raised by the phenomenon of globalization and the emergence of Global Studies as an area of critical inquiry, and (3) the changing needs, knowledges, and aspirations of students today. We close with a call to embrace the promise of change.
Gender differences in nutritional status, diet and physical activity among adolescents in eight countries in sub‐Saharan Africa
Authors: Darling Anne Marie , Sunguya Bruno , Ismail Abbas , Manu Abubakar , Canavan Chelsey , Assefa Nega , Sie Ali , Fawzi Wafaie , Sudfeld Chris , Guwattude David
Published: November 2019

Objective

The objective of this study was to evaluate gender differences in nutritional status, dietary intake, physical activity and hand hygiene among adolescents from diverse geographical settings in sub‐Saharan Africa.

Methods

This study utilised cross‐sectional data from six countries (Burkina Faso, Ethiopia, Ghana, Nigeria, Tanzania and Uganda) within the ARISE Adolescent Health Survey (n = 7625). Body mass index (BMI) was calculated using measured heights and weights, and z‐scores were calculated based on the 2007 WHO growth standards for age and sex. Information on demographics, diet and health behaviours was collected through face‐to‐face interviews using a standardised questionnaire. Site‐specific and pooled prevalence ratios were determined.

Results

The prevalence of underweight, overweight and stunting pooled across sites was 14.3%, 6.8% and 18.1%, respectively. Female sex was associated with a lower risk of being underweight (pooled prevalence ratio 0.66, 95% 0.57, 0.77) and stunted (pooled PR 0.63, 95% CI 0.55, 0.71), but a higher risk of being overweight (pooled PR 1.60, 95% CI 1.26, 2.06). Females were also less likely to exercise for 1 h or more per day (pooled PR 0.77, 95% CI 0.67, 0.88), and more likely to wash hands after using toilets or latrines and to wash hands with soap (pooled PRs 1.13, 95% CI 1.05, 1.21 and 1.35, 95% CI 1.23, 1.45, respectively).

Conclusion

Our results emphasise that sex is a key predictor of nutritional status among sub‐Saharan African adolescents and suggest that gender‐specific interventions may be required to reduce the double burden of under‐ and overnutrition.
From Event Representation to Linguistic Meaning
Authors: Ünal Ercenur , Ji Yue , Papafragou Anna
Published: November 2019

A fundamental aspect of human cognition is the ability to parse our constantly unfolding experience into meaningful representations of dynamic events and to communicate about these events with others. How do we communicate about events we have experienced? Influential theories of language production assume that the formulation and articulation of a linguistic message is preceded by preverbal apprehension that captures core aspects of the event. Yet the nature of these preverbal event representations and the way they are mapped onto language are currently not well understood. Here, we review recent evidence on the link between event conceptualization and language, focusing on two core aspects of event representation: event roles and event boundaries. Empirical evidence in both domains shows that the cognitive representation of events aligns with the way these aspects of events are encoded in language, providing support for the presence of deep homologies between linguistic and cognitive event structure.
Photoperiod sensing of the circadian clock is controlled by EARLY FLOWERING 3 and GIGANTEA
Authors: Anwer Muhammad Usman , Davis Amanda , Davis Seth Jon , Quint Marcel
Published: November 2019

ELF3 and GI are two important components of the Arabidopsis circadian clock. They are not only essential for the oscillator function but are also pivotal in mediating light inputs to the oscillator. Lack of either results in a defective oscillator causing severely compromised output pathways, such as photoperiodic flowering and hypocotyl elongation. Although single loss of function mutants of ELF3 and GI have been well studied, their genetic interaction remains unclear. We generated an elf3 gi double mutant to study their genetic relationship in clock‐controlled growth and phase transition phenotypes. We found that ELF3 and GI repress growth differentially during the night and the day, respectively. Circadian clock assays revealed that ELF3 and GI are essential that enable the oscillator to synchronize the endogenous cellular mechanisms to external environmental signals. In their absence, the circadian oscillator fails to synchronize to the light–dark cycles even under diurnal conditions. Consequently, clock‐mediated photoperiod‐responsive growth and development are completely lost in plants lacking both genes, suggesting that ELF3 and GI together convey photoperiod sensing to the central oscillator. Since ELF3 and GI are conserved across flowering plants and represent important breeding and domestication targets, our data highlight the possibility of developing photoperiod‐insensitive crops by adjusting the allelic combination of these two key genes.
Control of Period-Doubling and Chaos in Varying Compliance Resonances for a Ball Bearing
Authors: Zhang Zhiyong , Rui Xiaoting , Yang Rui , Chen Yushu
Published: November 2019

Varying compliance (VC) is an inevitable parametrical excitation to rolling bearing systems due to time-varying stiffness from rolling element revolution. Period-doubling instability in the VC primary resonances of ball bearing is presented in many studies. Recently, this instability was demonstrated to be a probable indicator of occurrence of strong one to two internal resonances and chaotic motions, which has potential effects on the stability and safety of the bearing-rotor system. However, few studies have directly attempted to suppress this bifurcation instability. Here, a dynamic stiffness evaluating method is presented for assessing the threshold of the period-doubling and complex motions in VC primary resonances of ball bearings, where the elaborate evolution of the bifurcating process is obtained by harmonic balance and alternating frequency/time domain (HB-AFT) method and using Floquet theory. Our analysis indicates that by introducing certain additional stiffness, the period-doubling and corresponding subharmonic internal resonances can be suppressed. Besides, the evolution and mechanism of type I intermittency chaos in ball bearings will be clarified in depth. It is also shown that extensive chaotic motions for large bearing clearances (e.g., 40 μm) can vanish perfectly by action of additional stiffness.
Dynamic Performance Optimization of a Novel 8-SPU Parallel Walking Mechanism
Authors: Wan Xiao-Jin , Yang Junqiang , Zhang Yan
Published: November 2019

Dynamic performance as one of the important properties of the parallel mechanism cannot be ignored, which is usually illustrated through dynamic performance analysis with the aid of index. Therefore, to develop reasonable dynamic performance indices is of great theoretical and practical significance for the parallel mechanism. In this paper, the above issues are discussed by taking the parallel mechanism designed by our research group as a study object. First, on the basis of considering the driving motor, kinematics dexterity and dynamic dexterity based on the global kinematics condition index and the global dynamic condition index are analyzed, respectively, in the workspace. Second, a novel diagonally dominant index (DDI) is presented in terms of the equivalent inertia parameter in joint space, and the proposed approach gives full consideration to minimize the inter-chain coupling effects. Furthermore, the parallel mechanism is optimized by means of taking the volume of the workspace, the global kinematics condition index, the global dynamic condition index, and the diagonally dominant index as objective functions. The optimization result shows that the larger workspace, higher dexterity, and smaller DDI are obtained to further improve the work capability and dynamic property of the mechanism. Finally, a real and novel 8-SPU (spherical pair, prismatic pair, and universal pair) parallel walking mechanism is manufactured in terms of the optimized architecture parameters.
An Integrated Target Acquisition Approach and Graphical User Interface Tool for Parallel Manipulator Assembly
Authors: Chen Haodong , Teng Zhiqiang , Guo Zheng , Zhao Ping
Published: November 2019

In this paper, two integrated target identification and acquisition algorithms and a graphical user interface (GUI) simulation tool for automated assembly of parallel manipulators are proposed. They seek to identify the target machine part from the workspace, obtain its location and pose parameters, and accomplish its assembling task while avoiding the collision with other items (obstacles). Fourier descriptors (FDs) and support vector machine (SVM) are adopted in this approach. The image of task area of workspace is obtained through machine vision, and the target assembling parts are identified. To acquire the location and pose information of the target, a modulus-shift matching (MSM) algorithm is proposed and integrated into the FD and SVM approaches, which could efficiently obtain the pose parameters while eliminating the effect of choice of starting point. The simulation results of two integrated algorithms, FD-MSM and SVM-MSM, are then compared and analyzed. In addition, a GUI is designed to visualize and assist the assembly process. An application on delta parallel robot with an extra rotational degree of freedom (DOF) is presented.
Formation Mechanisms of Exit-Chippings in Rotary Ultrasonic Drilling and Conventional Drilling of Glass BK7
Authors: Lv Dongxi , Liu Dong , Chen Gang , Song Leilei , Yan Chun , Wu Xiaofei , Zhu Yingdan
Published: November 2019

This paper presented a fundamental investigation on the exit-chipping formation mechanisms involved in rotary ultrasonic drilling (RUD) and conventional drilling (CD) of glass BK7. It was found that the mutual tool-material extrusion initially activated the subsurface crack with the maximum depth (incipient crack) at the margin of the machined surface, and its penetration of the undrilled thickness brought about the emergence of the exit-chipping at Region I. Subsequently, the opposite propagations of two ring-cracks along the circumferential direction of the drilled hole were conducive to the collapse of the machined cylinder, thus leading to the appearance of the exit-chipping at Region II. Ultrasonic superposition significantly decreased the actual undrilled thickness of the machined surface, while slightly increased the exit-chipping width. All the exit-chippings, generated with and without ultrasonic, exhibited the elliptic and symmetrical morphologies accompanied by the corrugated stripes winding the entire chipping surfaces. The quantitative relationship between the instantaneous extrusion pressure and the propagation direction of the incipient crack was proposed, revealing that the propagation angle was inversely proportional to the extrusion pressure. Ultrasonic superimposition augmented the extrusion pressure exerted the machined surface, which reduced the propagation angle of the incipient crack. The elliptic morphology characteristics of the exit-chipping were attributed to the parabolic variation of the additional bending moment with the circumferential spreading of the ring-crack. Ultrasonic superposition increased the propagation angle of the ring-crack, thus deteriorating the exit quality of the drilled hole.
Dynamic Characteristics Analysis and Finite Element Simulation of Steel–BFPC Machine Tool Joint Surface
Authors: Shen Jiaxing , Xu Ping , Yu Yinghua
Published: November 2019

The dynamic performance of the steel–Basalt fiber polymer concrete (BFPC) machine tool joint surface (referred to as the joint surface) has a significant impact on the overall BFPC machine tool performance; however, its dynamic characteristics remain unclear. In order to solve this problem, the influence of roughness and surface pressure on the dynamic performance of joint surface was studied experimentally, and a neural network prediction model for the dynamic performance of the joint surface was established. A BFPC bed was designed and manufactured, and BFPC bed’s dynamic performance was tested experimentally. The finite element simulation model of BFPC bed was established with equivalent spring-damper element. The BFPC bed’s dynamic performance without considering the influence of the joint surface and considering the influence of the joint surface was studied separately. The results show that the maximum error of the natural frequency of the BFPC bed was 6.937% considering the influence of the joint surface, which was much lower than the error without considering the influence of the joint surface. The maximum amplitude error of the X-axis and Z-axis acceleration of the BFPC bed was 6.917% and 5.15%, which were much smaller than the error without considering the influence of the joint surface. It proves the accuracy of the neural network prediction model for dynamic performance of the joint surface and the validity of the finite element simulation method for the joint surface. It provides theoretical support for the design analysis of BFPC machine tool.
Effects of Varying Dynamics of Flexible Workpieces in Milling Operations
Authors: Kiss Adam K. , Bachrathy Daniel , Stepan Gabor
Published: November 2019

In this study, surface error calculations and stability conditions are presented for milling operations in case of slender parts. The dynamic behavior of the flexible beam-type workpiece is modeled by means of finite element method (FEM), while the varying dynamical properties related to the feed motion as well as the material removal process are incorporated in the model. The FEM-generated direct frequency response function is verified through a closed-form solution based on the distributed transfer function method. Relative errors and convergence of the FEM are investigated based on the analytical solutions of the continuum model, from which appropriate element size and mode number can be selected for modal coordinate transformations. The pattern in the variation of the natural frequencies is explored using the analytical model in case of high radial depth of cut relative to the original cross section of the beam-like workpiece. Both the stability conditions and the resulted surface errors are predicted as a function of the tool position. The presented approach and the results are validated by laboratory tests.
Development and Verification Tests of Titanium 50-Inch and 60-Inch Last Stage Blades for Steam Turbines
Authors: Senoo Shigeki , Kudo Takeshi , Fukushima Hisataka , Segawa Kiyoshi , Sakakibara Kazuya
Published: November 2019

Increasing the annulus area of the last stage in steam turbines provides an effective way of increasing power output and improving the efficiency by reducing the amount of lost kinetic energy. The 50-inch and 60-inch last stage blades, which provide some of the world’s largest exhaust annulus areas, have been developed for 3600 rpm and 3000 rpm units respectively. The blades are designed to suppress the increase in losses caused by the supersonic inflow, and to ensure reliability. This paper describes the verification of the aerodynamic performance through four-stage model steam turbine tests. In addition, the unsteady flow phenomena caused by shock wave interactions near the tip between the last stage stator and rotor are clarified by unsteady flow measurements and calculations.

The characteristic of total-to-static efficiencies and flow distributions measured with pneumatic five-hole probes are obtained as designed. Static pressure recovery is also confirmed by static pressure measurement on the exhaust hood walls and three-dimensional turbulent flow analysis.

Regarding the unsteady stator-rotor interactions, the flow fluctuations such as static pressures and flow angles become relatively larger, when the travelling bow shock waves emanating from upstream of the rotor leading edge impinge near the stator trailing edge, because the axial distance between the emanating and impinging position of the shock wave is smaller. The static pressure on the suction surface of the rotor blade becomes locally large when it comes to the same circumferential portion as the stator trailing edge. However, the mass flow rate and loss variations caused by the unsteadiness are small, because the inlet relative Mach number is as small as 1.25, so that the strength of the shock wave is small.
Investigation on the Internal Cooling of Two-Passage Channels With Parallel Ribs and Guide Vanes
Authors: Amano Ryoichi S. , Saravani Mandana S. , DiPasquale Nicholas
Published: November 2019

The present work investigates the effects of various guide vane designs on the heat transfer enhancement of rotating U-Duct configuration with parallel 45-deg ribs. The ribs were installed on the bottom wall of the channel which has a constant heat flux boundary condition. The channel has a square cross-section with a 5.08 cm (2 in) hydraulic diameter. The first and second passes are 514 mm and 460 mm, respectively. The range of Reynolds number for turbulent flow is up to 35,000. The channel rotates in various speed up to 600 rpm which brings the maximum rotation number of 0.75. Several computational fluid dynamics simulations are carried out for this study to understand the effect of guide vanes on flow and heat transfer in serpentine channels under various operating conditions.
Aerodynamic Excitation Analysis of a Radial Turbine Featuring a Multi-Channel Casing Design
Authors: Hassan Ahmed Farid , Blackburne Jennifer , Kovachev Nikola , Schatz Markus , Vogt Damian M.
Published: November 2019

Partial admission using Multi-channel Casing (MC) is a technique under investigation for controlling the operation of radial inflow turbines. The MC has different admission configurations according to the number of open channels which control the relation between the mass flow and expansion ratio at different operating speeds in order to provide the advantage of operational controllability. These different casing configurations will excite the structure in different manners and may cause high cycle fatigue on the rotor. Consequently, the source of excitation for a multi-channel casing is not only the casing asymmetries but also the different admission configurations.

The current study investigates the effect of different MC admission configurations on the aerodynamic excitation mechanisms of the turbine rotor blades. The Generalized Pressure (GP) and Generalized Force (GF) approach is used to compare the aerodynamic forcing field acting on the rotor blade for different admission arrangements. First, a 3D unsteady numerical simulation of a radial turbine featuring four channel casing is performed for different admission configurations to provide the raw unsteady pressure. In conjunction with this, a finite element modal analysis is applied to the turbine rotor to calculate the natural frequency and the mode shapes. Finally, the results from the unsteady simulation and the modal analysis are superimposed to calculate and compare the GP and GF.

It is found that using different MC admission configurations has a significant effect on the aerodynamic forces acting on the radial turbine featuring MC. One of the applied configurations increases the generalized force by up to 2.6 times compared to the full admission configuration, MC 4, at engine order 8. While another configuration reduces it by a factor of 0.7 compared with the same base case.
Experimental Film Cooling Effectiveness of Multi-Row Patterns on Flat and Step-Down Surfaces
Authors: Baldino Filippo , Taslim Mohammad E.
Published: November 2019

Multiple rows of film cooling holes have been widely used for the protection of gas turbine airfoils and other hot sections. In the common approach, however, the streamwise surfaces between the film holes may not receive enough protection. The objective of this research was to overcome this issue by introducing a new layout of film cooling, the step-down surfaces. Pressure-sensitive paint technique was used to test three pairs of geometries. Each pair consists of a flat and a step-down surface for back to back comparisons, under otherwise identical conditions. Two rows of 30° angled cylindrical holes of 3.175 mm diameter, exiting at the step bottom corner, introduced the coolant to the surface. Two spanwise pitch-to-diameter ratios of 2 and 4, two row distance to hole diameter of 4 and 8, four blowing ratios of 0.25, 0.5, 0.75 and 1, all at a constant density ratio of 1 were tested. Adding a step-down of the order of 0.8 hole-diameter proved to significantly increase the overall film cooling effectiveness. Two major improvements compared to a flat surfaces were observed: (a) longer streamwise film cooling effectiveness (b) more uniform spanwise distribution of coolant. The main reason of all the improvements is the aerodynamic phenomenon governing the flow evolution, the Coanda effect. The latter, indeed, enhances the flow attachment to the airfoil surface downstream the step.
Effect of Non-Axisymmetric Endwall Profiling on Heat Transfer and Film Cooling Effectiveness of a Transonic Rotor Blade
Authors: Li Jinjin , Yan Xin , He Kun
Published: November 2019

Effects of non-axisymmetric endwall profiling on total pressure loss, heat transfer and film cooling effectiveness of a transonic rotor blade were numerically investigated. The numerical methods, including the turbulence model and grid sensitivity, were validated with the existing experimental data. To reduce thermal load on endwall, non-axisymmetric endwall profiling near leading edge and at pressure-side corner area were performed with a range of contour amplitudes. Heat transfer and flow fields near the profiled endwalls were analyzed and also compared to the plain endwall configuration. On the profiled endwall, three kinds of cooling-holes, i.e. cylindrical holes, rounded-rectangular holes and elliptical holes, were arranged, and film cooling effect was investigated at three blowing ratios. Results indicate that, with endwall profiling, the area-averaged Stanton number on endwall is reduced by 7.71% and total pressure loss in cascade is reduced by 11.07%. Among three kinds of cooling holes, arrangement of elliptical hole performs the best film cooling effect on profiled endwall. Compared with plain endwall, non-axisymmetric endwall with elliptical cooling holes improves film cooling coverage by 10.87%, reduces the Stanton number by 8.88% and increases the net heat flux reduction performance by 4% at M = 0.7.
Investigation and Prediction Models of the Axial Thrust in Centrifugal Compressors
Authors: Younsi Mohand , Hypolite Eric
Published: November 2019

The purpose of this paper is to provide an overview of the prediction methods used to accurately determine the axial rotor thrust in centrifugal compressors. Thus, semi-empirical models were developed to estimate the aerodynamic forces acting on each side of the rotating impeller. In addition to this, a numerical approach based on Computational Fluid Dynamics (CFD) technique was carried out to simulate the 3D steady flow in the centrifugal compressor. The numerical simulations consider the entire geometry details. The resulting axial thrust, estimated by the semi-empirical approach and the CFD calculations, were compared to experimental data. The application of these approaches was extended and discussed at different operating conditions. Furthermore, the effect of the expeller vanes (pump-out-vanes) on the axial thrust was highlighted.
Ignition Delay Times of Syngas and Methane in sCO2 Diluted Mixtures for Direct-Fired Cycles
Authors: Barak Samuel , Pryor Owen , Ninnemann Erik , Neupane Sneha , Lu Xijia , Forrest Brock , Vasu Subith
Published: November 2019

In this study, a shock tube is used to investigate combustion tendencies of several fuel mixtures under high carbon dioxide dilution and high fuel loading. Individual mixtures of oxy-syngas and oxy-methane fuels were added to CO2 bath gas environments and ignition delay time data was recorded. Reflected shock pressures maxed around 100 atm, which is above the critical pressure of carbon dioxide in to the supercritical regime. In total, five mixtures were investigated within a temperature range of 1050–1350K. Ignition delay times of all mixtures were compared with predictions of two leading chemical kinetic computer mechanisms for accuracy. The mixtures included four oxy-syngas and one oxy-methane combinations. The experimental data tended to show good agreement with the predictions of literature models for the methane mixture. For all syngas mixtures though the models performed reasonably well at some conditions, predictions were not able to accurately capture the overall behavior. For this reason, there is a need to further investigate the discrepancies in predictions. Additionally, more data must be collected at high pressures to fully understand the chemical kinetic behavior of these mixtures to enable the supercritical CO2 power cycle development.
Large-Eddy Simulation of Shaped Hole Film Cooling With the Influence of Cross Flow
Authors: Wang Qingsong , Li Yifei , Bian Xiutao , Su Xinrong , Yuan Xin
Published: November 2019

In the modern highly-loaded gas turbine, due to the large pressure difference between the suction side and the pressure side of the turbine blade, strong cross flow is formed and it strongly affects the aerodynamic and cooling performances in the end-wall region. The film cooling behavior in the environment of strong cross flow is different from the straight channel environment widely studied in the literature. In this research, the effect of cross flow on film cooling is investigated by Large Eddy Simulation (LES) using subgrid-scale (SGS) model. Numerical simulation is carried out in a curved passage to simulate the turbine blade passage. Shaped cooling hole with blowing ratio 1 is studied. The time-averaged friction line results are compared with existing experimental ink trace results. The vortex structures, both time-averaged and instantaneous, are analyzed to study the effect of cross flow on film cooling. At the exit of the cooling hole, the hanging vortices with negative y-vorticity are more flat in shape and closer to the wall in position in contrast to hanging vortex with positive y-vorticity, which is caused by cross flow and results in the asymmetry of hairpin vortices downstream as well as the asymmetry of the distribution of coolant. It has been shown that the vortices from mainstream have a significant impact on the field near the exit of the cooling hole. Those vortices interact with the hairpin vortices from the cooling hole and directly lead to the asymmetry of the hairpin vortices. Proper Orthogonal Decomposition (POD) analysis is further conducted to extract the dominant flow structures and the physical mechanisms of primary POD modes are given to explain the distribution of film cooling effectiveness affected by cross flow. Based on the specific situation in this work, a fast incremental POD (iPOD) approach is adopted since the rank of the field matrix is far less than the rows, which is caused by the tall and thin character of the matrix, which makes the analysis less costly and more effective. This research helps to understand the cooling performance in the real turbine blade passage and to explain the coolant mixing process based on the instantaneous flow field obtained using high precision LES simulation and powerful iPOD.
Laser Thermal Gradient Test of a Thermal Barrier Coating and Failure Analysis
Authors: Wu Yingsang , Wang Yao , Hsu Pei-feng , McCay Mary Helen , Croy Ed , Moreno David , He Lei , Wang Chao , Zhang Hongqi
Published: November 2019

Thermal barrier coatings (TBC) are used to protect the hot components of gas turbine engines to enhance thermal efficiency and component service life. It is critical for TBC development that a testing method be used to understand the potential and limitation of coating’s durability and integrity under the gas turbine engine operation conditions. In this paper, laser high heat flux testing with an applied temperature gradient across TBC coated buttons is presented. The ceramic coating is ZrO2-8 wt.% Y2O3 applied via the air plasma spraying process on top of a NiCoCrAlY bond coating and an Inconel alloy substrate button of 25.4 mm diameter. The coated button is subject to precisely-controlled laser heating on the top side (1150°C) and temperature gradient of 63.9°C/mm through the button overall thickness. The TBC button lasts 160.9 hr or 570 cycles of laser heating. Analysis of void fraction change before and after the test, thermal conductivity change during the laser test, and failure assessment are presented. After the test, the top coating has cracks in vertical or oblique directions and significant horizontal cracks near the top coating and bond coating interface. Significant horizontal top coating cracks close to the interface between the top coating and bond coating appear near the button center. Although the coating delamination has not occurred yet, at the end of the laser testing the button is close to delamination. Based on the horizontal cracks and the thermally grown oxide layer geometry, a finite element analysis is conducted to calculate the residual stress and the strain energy release rate. A possible approach to combine laser rig test result and finite element computation for developing a TBC service life model is discussed.
Improving Accuracy and Comparability of Turbocharger Performance Measurements
Authors: Schinnerl Mario , Bogner Mathias , Ehrhard Jan
Published: November 2019

The reduction of fuel consumption and emissions is the most dominant challenge in powertrain development. Therefore, engine and turbocharger have to be matched with high accuracy to achieve optimum powertrain efficiencies.

With respect to relevant engine operating points, compressor maps can be measured in full operating range on a standard hot gas test bench. Even though there is no need for extrapolation of the operating range, they have to be corrected for the impact of heat transfer to represent the adiabatic performance of the compressor stage.

The common approach to evaluate the turbine efficiency is to apply the energy balance of the entire turbocharger where the turbine power is the sum of the compressor power and the friction losses of the radial and axial journal bearings. The adiabatic compressor power in combination with the calculation of the friction losses by using validated run-up simulations enables the evaluation of the isentropic turbine efficiency and the comparability to CFD simulations of the turbine stage.

For reasons of comparability to CFD simulations, which can predict a wide operating range of the turbine stage, the limited measureable turbine operating range is enhanced by a so-called compressor closed loop unit (CCLU). This additional test device enables to vary the demand of compressor power for the same operating points as in the standard mapping and therefore to enlarge the measureable turbine operating range. In combination with proper extrapolation methods, the isentropic turbine efficiency can now be compared to CFD simulations.
Autoignition Study of “Gas-to-Liquid” Fischer-Tropsch Jet Fuels
Authors: Alturaifi Sulaiman A. , Atherley Tatyana , Mathieu Olivier , Guo Bing , Petersen Eric L.
Published: November 2019

In recent years, there has been an interest in finding a jet fuel alternative to the crude oil-based kerosene. Gas-to-liquid (GtL) fuel is being derived via Fischer-Tropsch synthesis processes by converting natural gas to longer-chain hydrocarbons which form the basis for jet fuel. In this study, new experimental ignition delay time measurements of GtL jet fuels have been determined at elevated pressures and temperatures. The measurements were conducted in a heated, high-pressure shock-tube facility capable of initial temperatures up to 200°C. Two GtL jet fuels were investigated, Shell GTL and Syntroleum S-8, which can be used in aviation applications at concentrations up to 50% blended with conventional oil-based kerosene. The ignition delay time measurements were conducted behind reflected shock waves for gaseous-phase fuel in air at a pressure around 10 atm and over a temperature range of 966 to 1266 K for two equivalence ratios, fuel lean (ϕ = 0.5) and stoichiometric (ϕ = 1.0). Ignition delay time was determined by observing the pressure and electronically excited OH chemiluminescence around 307 nm at the endwall location. Similar ignition delay times were observed for the two fuels at the fuel lean condition, while Syntroleum S-8 showed shorter ignition delay times at the stoichiometric condition. Comparisons are made with ignition delay time measurements for Jet-A previously conducted in the same facility and showed reasonable agreement over the tested conditions. The predictions from the available literature for GtL fuel surrogate kinetics models were obtained and compared with the experimental measurements.
Economy and Emission Analysis of the Effects of Different Diluents in Syngas for Gas Turbine Using Low Heating Value Syngas Through Numerical Model
Authors: Mu Yanfei , Shi Shaoping , Qin Ye , Zhang Bo , Yan Shu , Liu Xin , Chen Xinming
Published: November 2019

Integrated Gasification Combined Cycle (IGCC) combines gasifier, gas turbine, and steam turbine to increase the electricity production efficiency while having lower emissions compared to conventional coal fired power plants. The syngas produced from coal gasification differs from natural gas in terms of composition, heating value, as well as combustion characteristics. Typically, syngas has much lower heating value than natural gas, thus the flow rates of the syngas are higher than that of natural gas for a similar size gas turbine. In addition, the hydrogen in the syngas may lead to more rapid combustion and higher flame temperature compared to natural gas, which may result it more NOx emission. Thus, to address these issues, syngas could be diluted with nitrogen, steam or carbon dioxides to lower the flame speed and temperature. The effects of different diluents on the fuel economy and emissions are investigated by a combined thermodynamic and computational fluid dynamics (CFD) model. The thermodynamic model was first established and validated by the industrial operational data. More power output and better fuel economy can be achieved using N2 and CO2 as diluent instead of steam from calculation with the thermodynamic model. A numerical case study was done to estimate the profit using nitrogen instead of the steam considering in industrial operation conditions as well as all other costs. Next, the CFD model was employed to further examine the combustion stability and NOx emissions. The results show that changing diluent from steam to nitrogen will not impact the combustion stability and may lead to slightly lower NOx emissions. Finally, the partial replacement of steam by nitrogen as diluent has been realized and the industrial operational performance has also been reported.
The Influence of Non-Axisymmetric End Wall in a High-Load Compressor Stage With Tandem Stator
Authors: Li Xiangjun , Chu Wuli
Published: November 2019

The application of tandem blade in compressors has been study for decades. According to the open literature, using tandem blade can effectively extend the working range of the compressor under high incidence. Many earlier researches focused on the two-dimensional influence of tandem blade, and revealed that a proper arrangement on the positions of the front and the rear blade would allow the boundary layer on the suction side to develop in a more favourable way to control the two-dimensional separation. However, because of the serious corner separation and higher loss in the end wall region of high-load compressors. Some recent researches started to focus on the three-dimensional flow for further understanding the effect of the tandem setup.

As an effective way to influence the end wall flow, the profiled end wall can be applied to both turbines and compressors to reduce the end wall loss. However, the co-work of tandem blade and profiled end wall was seldom reported. In this paper, a numerical research was carried out based on a single-stage high-load compressor with a tandem stator. After a numerical study for the hub separation. A series of optimization design were carried out for the hub end wall of the rotor, stator and the stage to improve the overall efficiency. The discussion revealed the positive effects of the optimum profiled end wall on the tandem stator were on one hand to limit the extension of the recirculation region of the front passage and on another hand to suppress the suction side corner separation in the rear passage. The efficiency of the upstream rotor was also reduced in small value because the variation of the through flow. After that, the indirect influence of the rotor profiled end wall on the stator and the stage profiling case were also analysed. The optimum stage hub profiling did not equal to the simple combination of the optimum stator and the rotor hub end wall. It is found that in the stage profiling case, the variation of loss in stator and rotor are very well adjusted and balanced by the optimization algorithm. The improvement of efficiency therefore achieved the highest value.
Laboratory and On-Site Findings Demonstrating the Greater Effectiveness of Biphase Water-Based Compressor Cleaners Over Monophase Cleaners
Authors: Kloter Simon , Ashford Neil F. , Fitchett Duncan R.
Published: November 2019

Compressor washing is a widely applied method to reduce the fouling rate of compressor blades by on-line washing and restore lost power by off-line washing. One of the factors influencing the effectiveness of a wash procedure is the efficiency of the detergent used for washing. This especially in the presence of hydrophobic contamination such as oily and carbon type deposits that can be difficult to penetrate and loosen by water-based detergents.

In this paper, a comparison of cleaning performance is made between monophase water-based compressor cleaners and a biphase water-based compressor cleaner.

Most of the currently used water-based compressor cleaners are monophase solutions. Their main active ingredients are surfactants which lower surface tension and interfacial tension allowing detachment and emulsification of foulant from a compressor blade. Biphase compressor cleaners are also formulated with surfactants, however due to their sub-micron heterogeneous nature they not only provide detachment and emulsification but a much more effective capability to solubilize even hydrocarbon type contamination.

Cleaning efficiencies of these cleaners were evaluated in the laboratory using various test methods including US MIL-PRF-85704C. All of these performed tests confirm the significantly higher effectiveness of the biphase compressor cleaner.

To validate the results from the laboratory tests a direct comparison of a monophase cleaner and a biphase cleaner was performed at a power station in the UK. After about four years of frequent washing with the monophase cleaner on two engines, one GT was then washed three times consecutively offline within a time period of six months with the biphase cleaner. In the second GT, washing was continued with the monophase cleaner. The visual inspection during a major overhaul very clearly showed a significantly higher removal of contamination from the GT washed with the biphase compressor cleaner.