1,720,956 research outputs found
Numerical Study of Unsteady Rotating Structures in a Turbine Disk Cavity
No full textThe improvement of modern cooling systems in aero-engines has led to an increase in the turbine inlet temperature to improve cycle efficiency. In particular, the use of purge flow within the cavity between the stator rim and rotor platform has considerably reduced hot gas ingestion from the main flow and has ensured the maximum metal components operating life. The mechanisms governing axial turbine rim seal flow are complex and influenced by various factors, firstly by the geometry of the cavity. The resulting flow has a three-dimensional structure and a pattern that varies over time. For a wide axial cavity, hot gas ingestion zones can be mainly attributed to three phenomena. The first one is the disc pumping effect generated by the shaft rotation, which induces a radial outflow in the rotor disc boundary layer, creating a recirculation within the cavity that leads to ingestion in the stator disc area. The second one is the vane/blade relative position, which determines a circumferential pressure profile where the higher and lower pressure zones define the flow ejection or ingestion. The third phenomenon is the purge/mainstream flow interaction and its inherent instability that leads to large-scale unsteady flow features developing within the cavity. The formation of such rotating structures and their impact on the ingestion zones is a key research topic in this area. This study presents the results of unsteady numerical simulations (URANS) of an axial turbine's first-stage cavity with a focus on the analysis of 3D-unsteady flow structures. The simulations have been performed by imposing a circumferential pressure periodicity at the outlet, extracted from previous simulations of the stage. The static pressure values within the cavity have been validated by comparison with experimental data. Three purge flow rates have been tested, namely high purge, low purge, and ingestion flow. The paper provides a new perspective on the topic by performing a SPOD analysis on a characteristic plane to identify the main energy modes that dominate the flow and their influence on the ingestion phenomenon
Analysis on the Effect of Cavity Flows on the Aerothermal Performance of a High-Pressure Turbine Stage
No full textIn aero-engines, the turbine entry temperature profile determines the characteristics of the cooling system, including the flow field occurring in the cavity positioned between the stator rim and the rotor platform, which is used to provide end-wall cooling while ensuring no flow ingestion to prevent harmful configurations. The local flow field depends on the relative position between the blade rows, on the geometry of the cavity, on the rotational speed, and on the mass flow. The flow structures within the cavity may be described by high-fidelity simulations, which are still too onerous at engine-relevant conditions. However, unsteady Reynolds-averaged Navier–Stokes solvers provide information about integral-scale structure development and interaction. In this article, the results obtained from three unsteady simulations of a high-pressure turbine stage considering different cavity flowrates and rotational speeds are presented. The comparison between the experimental data obtained at the von Karman Institute for Fluid Dynamics, and the numerical results allows for analyzing the interaction between the cavity flow and the main flow. Pressure and velocity fields are analyzed to describe both the sealing mechanism and the formation of secondary flows in the presence of secondary air. It is demonstrated that the occurrence of ingestion regions depends on the potential interaction between the vanes and the blades and that the wake shed by the vane trailing edge determines the intensity of the phenomena. The secondary flows’ analysis shows that the purge flow exiting the cavity impacts the arrangement and strength of the hub-passage vortex
Film Cooling Modeling in a Turbine Working under the Unsteady Exhaust Flow of Pulsed Detonation Combustion
Full text linkPressure gain combustors (PGCs) have demonstrated significant advantages over conventional combustors in gas turbine engines by increasing the thermal efficiency and reducing the pollution emission level. PGCs use shock waves to transfer energy which contributes to the increase in outlet total pressure. One of the major obstacles in the actual implementation of PGCs in the gas turbine cycle is the exploitation of the highly unsteady flow of the combustor outlet with the downstream turbine. Because of the higher outlet temperature from the PGCs, the turbine blade cooling becomes essential. Due to the highly fluctuating unsteady flow of PGCs, 3D CFD simulation of turbines becomes very expensive. In this work, an alternative approach of using a 1D unsteady Euler model for the turbine is proposed. One of the novel aspects of this paper is to implement the turbine blade cooling in the unsteady 1D Euler model. The main parameters required for the turbine blade cooling are the cooling air mass flow rate, temperature, and pressure. Due to the introduction of coolant flow, the blades are no longer adiabatic and the mass flow rate across the turbine is not constant. Comparing the 1D Euler results against zero-dimensional calculation and 3D CFD approach showed a very good match for both steady and unsteady simulations confirming the applicability of the 1D method
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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