1,720,958 research outputs found
A new regulation system for Crossflow type turbines for water management industry
No full textMini-hydro hydropower plants have recently gained much attention from energy providers, more than traditional
turbines installed downstream of artificial hydrological basins. The reason is that mini-hydro plants do not
require significant water storage and the construction of dams or weirs with significant environmental impact.
However, the occurring large flow rate variability requires a great care in the design of the mobile parts of the
distributor, like guide-vanes in Kaplan and Francis turbine types, or the Cink flap in Crossflow type. In the
present work, a new regulation system for Crossflow turbines is proposed, which is aimed to maintain high
efficiency inside a large range of flow rate values. This goal is achieved by regulating the width of the inlet
section of the nozzle, which allows maintaining an almost constant velocity ratio without changing the rotational
velocity of the runner. The proposed system can be applied to all the Crossflow type turbines; in the present
research paper it is finalized to Power Recovery System (PRS) turbines, a Crossflow type turbine with pressurized
output, used for in-line installations. The new system was studied using CFD analysis and the results were
validated with laboratory tests on a 2 kW prototype
MAST-RT0 solution of the incompressible Navier–Stokes equations in 3D complex domains
Full text linkA new numerical methodology to solve the 3D Navier-Stokes equations for incompressible fluids within complex boundaries and unstructured body-fitted tetrahedral mesh is presented and validated with three literature and one real-case tests. We apply a fractional time step procedure where a predictor and a corrector problem are sequentially solved. The predictor step is solved applying the MAST (Marching in Space and Time) procedure, which explicitly handles the non-linear terms in the momentum equations, allowing numerical stability for Courant number greater than one. Correction steps are solved by a Mixed Hybrid Finite Elements discretization that assumes positive distances among tetrahedrons circumcentres. In 3D problems, non-Delaunay meshes are provided by most of the mesh generators. To maintain good matrix properties for non-Delaunay meshes, a continuity equation is integrated over each tetrahedron, but the momentum equations are integrated over clusters of tetrahedrons, such that each external face shared by two clusters belongs to two tetrahedrons whose circumcentres have positive distance. A numerical procedure is proposed to compute the velocities inside clusters with more than one tetrahedron. Model preserves mass balance at the machine error and there is no need to compute pressure at each time iteration, but only at target simulation times
DEVIATORE DI FLUSSO PER TURBINE IDRAULICHE IN LINEA
No full textUn deviatore di flusso per una turbina idraulica a flusso incrociato presenta una
sezione di uscita atta ad essere collegata alla sezione a valle della condotta idraulica
per l’immissione di un flusso in uscita del fluido liquido in pressione con un vettore di velocità di uscita avente modulo di uscita (Vo) e direzione di uscita (do)
predeterminati, un condotto di scarico per il ripristino del vettore velocità di detto
flusso in uscita al modulo in ingresso ed a una direzione di uscita sostanzialmente
parallela o coincidente con detta direzione di ingresso (di), in cui detto deviatore
comprende, un primo settore immediatamente a valle di detta girante ed atto a variare
la direzione del flusso in uscita dalla girante da radiale a tangenziale, un secondo
settore a valle di detto primo settore ed in continuità fluidica con lo stesso ed avente
una prima ed una seconda parete laterale opposte configurate per determinare
un’accelerazione costante del flusso, un terzo settore a valle di detto secondo settore
ed in continuità fluidica con lo stesso ed avente una prima ed una seconda parete
laterale opposte curvilinee ed in continuità rispettivamente con detta prima e detta
seconda parete laterale di detto secondo settore, un quarto settore a valle di detto
terzo settore ed in continuità fluidica con lo stesso ed avente una sezione di uscita in
collegamento con il tratto a valle della condotta per lo scarico del fluido con detta
velocità di uscita, in cui dette prima e seconda pareti laterali di detto terzo settore
comprendono ognuna un primo ed un secondo tratto curvilinei e definenti archi di
cerchio di circonferenze reciprocamente concentriche ed in cui detto primo tratto di
detta prima parete laterale di detto terzo settore e detta prima parete laterale di detto
secondo settore definiscono un arco di cerchio di una stessa circonferenza avente un
primo raggio (Rp) predeterminato
Performance Investigation of a Twisted Savonius Wind Rotor
No full textFor human welfare, electrical power is necessary. For many years, there has been a great deal of interest in wind energy because it is a clean, sustainable energy source. Because of its cheaper cost and independence from wind direction, the Savonius vertical axis wind rotor has the advantage of being suitable for certain implementations as an energy converter. Several studies have been carried out to increase its efficiency. In this paper, a novel blade design of a twisted Savonius wind rotor has been investigated numerically with the intention of performance betterment. Three-dimensional unsteady simulations were performed deploying Ansys Fluent using the Shear Stress Transport k-ω turbulence model based on the finite volume method solver. The wind flow aerodynamic characteristics in addition to the rotor performance properties were acquired and analyzed. The numerical model was validated based on findings taken from experimental tests performed on a 3-D printed twisted rotor in a wind tunnel. An improvement in the power coefficient by 22.58 % was recorded with the novel blade design over the twisted Savonius wind rotor. The obtained findings could provide further direction for researchers to use the twisted Savonius wind turbine in power generation
Low-Head Hydropower for Energy Recovery in Wastewater Systems
Full text linkHydraulic turbines for energy recovery in wastewater treatment plants, with relatively large discharges values and small head jumps, are usually screw Archimedes or Kaplan types. In the specific case of a small head jump (about 3 m) underlying a rectangular weir in the major Palermo (Italy) water treatment plant, a traditional Kaplan solution is compared with two other new proposals: a Hydrostatic Pressure Machine (HPM) located at the upstream channel and a cross-flow turbine (CFT) located in a specific underground room downstream of the same channel. The fluid mechanical formulations of the flow through these turbines are analyzed and the characteristic parameters are stated. Numerical analysis was carried out for the validation of the HPM design criteria. The efficiency at the design point of the CFT and HPM are estimated using the ANSYS CFX solver for resolution of 3D URANS analysis. The strong and weak points of the three devices are compared. Finally, a viability analysis is developed based on several economic indicators. This innovative study with a theoretical formulation of the most suitable turbomachine characterization, the potential energy estimation based on hydraulic energy recovery in a real case study of a wastewater treatment plant and the comparison of the three different low-head turbines, enhancing the main advantages, is of utmost importance towards the net-zero water sector decarbonization
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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