1,720,960 research outputs found
Analysis of the water injection process in industrial gas turbines axial compressor
Get PDFIn this work, the water injection process in the AXial COmpressor (AXCO) of industrial Gas Turbines (GT) has been analyzed to identify the benefits on the GT operation and the associated risks for GT and AXCO mechanical integrity. Water injection is a technique in which a flow of water is injected and dispersed at the suction of industrial Gas Turbines. This technique has been largely used either for washing purposes or to improve GT output power in specific conditions. In the water washing application, the water injection allows to recover the performance losses due to fouling of the GT internals, while in the power augmentation application, water injection is used to increase GT power output. Although the water injection has shown to be effective in both applications, site experiences demonstrated that it could yield to components erosion with most of the damages detected in the Leading Edge section of the AXCO first stage rotor blades. Since the control and reduction of performance detriment due to AXCO fouling is of paramount importance for an industrial GT operation, the present work is focused on the water washing application; however, some of the results could be extended also to power augmentation application. Through the analyses of the present work, the leading design parameters of the water injection system have been identified to provide a design guideline for the optimized design and optimized operation of the water washing devices. The effects of the water washing have also been assessed in terms of carbon footprint reduction of a typical industrial GT. To identify the effects of the water injection on the GT AXCO, a dedicated Water Droplets Erosion (WDE) model has been developed and assessed against the available models. The WDE has been
developed considering the effects of a wide range of droplets diameters combined with the introduction of specific materials properties characterized through a dedicated experimental campaign. The model demonstrated a clear improvement compared to the models available in literature, improving the main limitations related to the droplets’ dimeters and blades material selection. The novel WDE has shown consistency with experimental results when considering a wide range of droplets diameters and when considering specific GT AXCO material characteristics. To reduce the number of variables to be considered in the performance and design space definition, a sensitivity analysis on the WDE leading parameters has been performed on simplified GT geometries through means of CFD simulations. The results highlighted the role of the injection time and of the angle and velocity of injection as the parameters with larger effect on the washing efficiency. The injection location and the droplet size distribution seem to be the leading parameters to control the water droplets distribution on the AXCO blade.
Based on the results of the sensitivity analyses, the novel WDE has been applied on a real case where the complete geometry of a real GT has been considered form the inlet plenum up to the outlet of the first AXCO rotor. The results of CFD analyses coupled with the new WDE have been compared with field data and the shop analyses of a GT subjected to several water washing cycles. The comparison of the numerical results with the experimental field data has shown good 4 qualitative agreement, with the ability of highlight the impact regions and of predicting the overall component erosion. Based on the design and operations space highlighted through the simplified geometry analyses and based on the experimental verification of the model, a complete mapping of the water washing design and operation has been created. This mapping is currently being used to create a design tool for the design optimization of the water washing devices and a monitoring and diagnostic analytic to provide indications on the optimum settings of the water washing during operation. This analytic, will be able to provide real time guidance on the optimum water washing cycles, predicting GT efficiency recovery, highlighting mechanical integrity risks and, thanks to the LCA analyses and mapping, providing information on the resulting carbon footprint of the GT
Effects of Water-to-Air Mass Ratio on Long-Term Washing Efficiency and Erosion Risk in an Axial Compressor Under Online Washing Conditions
No full textOne of the main reasons of gas turbines performance losses is the deposition of dirt on the compressor blades. Dirt deposit has to be periodically removed to keep the engine performance as high as possible. This is the reason motivating the presence of online water washing systems (WWS) in most of the compressor gas turbines. Such systems aim at cleaning the compressor blades to recover efficiency; thus, the larger the water flow the better it is assumed the compressor is cleaned (fixing all the other conditions). In the present work we simulate the long-term behaviour of a real axial compressor, from the inlet to the first-stage rotor, subject to online water washing with different water flow rates. The frozen rotor approach is adopted to solve the flow field in the rotor region. Simulations are performed by using the unsteady k-ε realizable model coupled with a Lagrangian tracking of the injected liquid phase. Water droplets erosion is handled by using a semi-empirical model developed by the authors. In each simulation 504000 parcels have been tracked, providing statistically reliable predictions. To simulate long-term evolution of the washing process, a discrete mesh morphing technique coupled with the use of specific scale factors is adopted. Each of the tested configuration is composed of three successive erosive steps up to the blade compressor end-of-life. Six different injection configurations are here assessed in terms of long-time average washing efficiency and erosion risk. Results predicted, show the dependence of the considered washing indices on water mass flow rate and set the stage for the development of a washing optimization tool, which helps the design and management processes. In the present simulations the optimal configurations are WAMF*=0.250 in the case that a small weight is given to the washing indices, and WAMF*=0.750 for high weights
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
