1,720,964 research outputs found
Performance and midspan wake measurements on a H-Darrieus in controlled conditions
Full text linkPerformance and wake measurements on a H-Darrieus vertical axis wind turbine are discussed on the basis of an extensive experimental campaign performed at the large scale, high speed wind tunnel of the Politecnico di Milano (IT). The paper proposes a combined mechanical and fluid-dynamic investigation by virtue of an advanced measurement system that allows to reconstruct both phase-resolved thrust and torque acting on the machine and the phase-resolved multi-dimensional velocity field in the wake. The aerodynamic torque is presented as a function of the azimuthal angle of revolution, while the velocity field in the wake is fully characterized by means of a point to point detailed measurement on the midspan plane, where the influence of both blade support struts and tip vortices is negligible. Particular care is taken in the description of the experimental setup as well as in the presentation of the measurements. The here proposed achievements can be considered as a benchmark for the validation of several classes of computational tools
Modeling Strategy and Numerical Validation for a Darrieus Vertical Axis Micro-Wind Turbine
No full textThis paper presents a model for the evaluation of optimal spatial grid node distribution in the CFD analysis of a Darrieus vertical axis micro wind turbine, by analyzing the trends over a 360° rotation of some indicators of near-blade mesh quality. To this purpose, a complete validation campaign has been conducted through a systematic comparison of numerical simulations with wind tunnel experimental data. Both two-dimensional and three-dimensional grids, characterized by average y+ values of 30 and 1, have been tested by applying some statistical techniques as a guidance in selecting the appropriate grid configuration and corresponding turbulence model. Finally, the tip downstream recirculation zone due to the finite blade extension and the influence of spokes have been analyzed, achieving a numerical quantification of the influence of induced drag and spokes drag on overall rotor performance
A review based on evaluation experiences with ten-years activity in VAWT experimental wind tunnel testing
No full textThe purpose of this paper is to provide guidance on the practice gained on vertical-axis wind turbine (VAWT) testing by a combined group of researchers from the Università di Trento (IT) and the Politecnico di Milano (IT), from early experiences dating back to 2007 up to the present day. The adopted operating procedures are discussed with particular care set to the achievement of high precision measurements to be used both as a benchmark for the validation of numerical codes and as a contribution to a deeper understanding of the flow field around VAWTs, to be converted into novel measurement procedures. As a matter of fact, by providing historical and technical information from the ongoing research activity, the lessons learned about the main obtained results could serve as a valuable tool for use by other research groups who are facing similar activities, providing information on which to help base their project plans
Experimental benchmark data for H-shaped and troposkien VAWT architectures
Full text linkMost of the experimental research on vertical axis wind turbines was carried out during 1970â1980s but, recently, the potential of wind energy harvesting in new environments has renewed the interest on VAWT technology. Unfortunately, this interest still collides with an immaturity of aerodynamic modelling tools and detailed experimental analyses are now highly recommended to convert flow field comprehension into novel design techniques. This paper critically revises the main extensive wind tunnel campaigns conducted on VAWTs during the last 15 years. Moreover, a direct comparison between two widely adopted lift-driven rotor architectures, i.e. H-shaped and troposkien, characterized by the same swept area and blade section, is presented. After being instrumented to characterize aerodynamic performance and thrust as well as flow characteristics in the wake, the rotors were tested in the Politecnico di Milano wind tunnel using an open configuration, allowing real-scale measurements of micro wind turbines. A complete characterization was obtained by recording steady-state torque, thrust and flow velocity in the wake as a function of the unperturbed wind speed, while the angular velocity of the rotors was kept constant. The measurements were conducted with high accuracy and can represent a useful experimental benchmark for the validation of computational tools
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
- …
