1,720,959 research outputs found
Performance Improvement in a Helical Savonius Wind Rotor
No full textAbove all vertical axis wind turbines, for their lower cost and independent on wind direction, Savonius rotor takes the advantage to be more suitable for some implementation. Thus, many investigations have been carried out to improve its efficiency. This study emphasizes on the effect of the overlap distance and the blade shape on a helical Savonius wind turbine performance. Assessment methods based on the flow field characterizations, the variation of torque and power coefficient are performed. Thus, transient simulations using the SSTk-omega turbulence model are carried out. The numerical model is validated using wind tunnel tests. Results indicate that the non-overlapped helical Savonius rotor highlights higher maximum power coefficient of 0.124 at a tip speed ratio of 0.73 over rotors with overlap distance of 10 mm, 15 mm and 20 mm, respectively. In addition, the delta-bladed rotor improves the performance of the helical Savonius rotor by 14.51%. With the novel blade shape, the maximum power coefficient reaches a value of 0.142 at a tip speed ratio of 0.78. The obtained results present an interesting data that could provide the aerodynamic characteristics of the airflow for the designers and engineers to enhance the efficiency of the helical Savonius turbine
Numerical and experimental investigation for helical savonius rotor performance improvement using novel blade shapes
No full textWind energy is extensively invested as a renewable and clean energy source. Savonius wind rotor, as an energy converter, has the merit of being appropriate for specific applications. The current paper centers on the performance enhancement of a helical Savonius wind rotor through the blade shape modification. The basic objective is to assess and compare, numerically and experimentally, the performance of two rotors with novel blade shapes named delta bladed and two-stage delta bladed shapes in relation to a helical Savonius rotor. Numerical study was conducted using Ansys Fluent software. 3-D unsteady simulations were carried out through the use of the SST k-ω turbulence model based on the finite volume method solver. Aerodynamic flow and performance characteristics were investigated. Static and dynamic experimental tests were undertaken on a wind tunnel. An improvement in Cp by 22.58 % and 29.5 % for the two-stage delta bladed rotor and 19.35 % and 16.4 % for the delta bladed rotor over the helical Savonius rotor was recorded, respectively, numerically and experimentally. In addition, the self-starting ability as well as the aerodynamic flow characteristics of the helical rotor were enhanced with the novel blade shapes
Numerical Model Parameters Choice of Helical Savonius Wind Rotor: CFD Investigation and Experimental Validation
No full textElectrical power is essential for human beings welfare. The available wind as a clean and renewable source of energy has whetted extensive interest over decades. Savonius vertical axis wind rotor as an energy converter has the merit of being adequate for specific implementations owing to its lower cost and independency on wind direction. From this perspective, multiple studies have been conducted to boost its efficiency. This research work emphasizes on the helical Savonius wind rotor (HSWR). The basic objective is to investigate the impact of selecting the numerical model parameters on its aerodynamic and performance characteristics. Experimental tests were realized with a 3D printed HSWR in a wind tunnel. The experimental performances in terms of power, static and dynamic torque coefficients were addressed. Next, a numerical study was undertaken through Ansys Fluent 17.0 software. Grid, turbulence model and rotating domain size tests were examined. Good accordance was obtained, which validated the numerical model with an averaged error of 5%. The maximum power coefficient proved to be equal to 0.124 at a tip speed ratio of 0.73 and 0.1224 at a tip speed ratio of 0.69, respectively, numerically and experimentall
Performance enhancement of a twisted Savonius hydrokinetic turbine with an upstream deflector
No full textThe conventional Savonius turbine is one of the most used rotors to convert the kinetic energy of natural water resources instead of potential energy. However, this rotor presents low efficiency. A twisted Savonius turbine was appeared which is considered most performant by twisting the blades of the conventional Savonius turbine along theirs spans. In fact, various experimental and numerical investigations were carried out to enhance the efficiency of the twisted Savonius turbine which has not been completely explored. In this study, an experimental investigation was carried out to assess the performance characteristics of a twisted Savonius turbine in an irrigation canal. In order to improve the efficiency of the Savonius turbine, three deflector designs were investigated numerically based on a CFD 3D numerical model. The peak value of the turbine power coefficient reaches 0.166 at a tip-speed ratio value of 0.78 without using a deflector upstream the turbine. Using the deflector design showing the highest efficiency, the peak value of the power coefficient was increased by 17.47%. The use of the proposed deflector is expected to provide toward a more effective employment of flowing water like tidal currents, river streams or other man-made water channels for electrical energy production in rural regions
Performance improvement of a Savonius water rotor with novel blade shapes
No full textSavonius water rotor is a prominent drag based turbine able to extract energy available in flowing water with low
velocity like river streams, tidal currents or other man made water canals. However, in view of its low perfor-
mance, an enhanced design of the rotor blades is necessary to better its efficiency. Therefore, the present study
aims to improve the efficiency of Savonius rotor by changing the blade design. Different blade shapes were
investigated numerically using computational fluid dynamics (CFD). Using conventional design, the peak power
coefficient was found to be 0.166 at tip-speed ratio of 0.78. However, the peak power coefficient reaches 0.184
using the optimal blade design. This work may be an important towards further improvement of the Savonius
rotor’s efficienc
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
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