1,721,070 research outputs found
Multilevel model for flood wave propagation in flood-affected areas
No full textA hyperbolic model for the simulation of flood wave propagation on initially dry land is presented. The convective inertia terms are neglected in the momentum equations. This assumption allows the use of a finite element scheme with linear shape functions for the free surface elevations and constant unit discharges inside each element. An appropriate use of the explicit and implicit approximation of the spatial derivatives is able to avoid the introduction of internal boundaries in the case of vertical discontinuities of the terrain elevation. This is obtained without losing the desirable features of the system matrix or limiting the maximum Courant number. The efficiency and the reliability of the proposed method are investigated for a flood in the south of Sicily, Italy, where a detailed description of the ground morphology has been proved to be essential for obtaining a good match between measured and computed maximum water depths
Cost benefit analisys for hydropower production in water distribution networks by pump as turbine (PAT)
No full textREGOLAZIONE DELLE PRESSIONI MEDIANTE PRODUZIONE DI ENERGIA IDROELETTRICA NELLE RETI DI DISTRIBUZIONE IDRICA
No full textNegli ultimi anni, sempre più gestori di reti idriche hanno mostrato interesse nella realizzazione di micro e mini centrali idroelettriche poiché: È spesso disponibile un eccesso di pressione che viene oggi, frequentemente, dissipato mediante valvole PRV; La produzione di energia elettrica “propria” contribuirebbe a ridurre i costi energetici per la gestione della rete stess
Performance improvement of a novel combined water turbine
No full textNowadays, industrials and researchers are looking for renewable energy resources due to the increase of energy demand. Recently, the ability of combined turbines in harnessing energy from water current has increased their renewed interest. However, there still exist a big knowledge gap to select the optimal design of these turbines. In this paper, systematic studies of stand-alone helical Savonius and delta bladed Darrieus turbines were carried out using experimental methods as a precursor to analyze their roles in hybrid configuration. By varying the attachment angle, two hybrid configurations were tested experimentally. Using the optimal attachment angle, six hybrid configurations were investigated numerically based on the commercial software ANSYS FLUENT 17.0. From one configuration to another, only the design of the Savonius turbine was changed. The maximum power coefficient is found to be equal to 0.191 at tip-speed ratio of 0.63 using a helical bladed Savonius turbine with twist angle of 90°. However, the maximum power coefficient reaches 0.232 using a delta bladed Savonius turbine with the same twist angle. This optimization of the novel combined water turbine could be a solution to enhance the generated power
A telescopic wind tower with reduced environmental impact - The Perima Project
No full textA prototype of a telescopic pole for wind energy production with low environmental impact and its lifting system for a 60 to 250 kW turbine and a height of 30 m have been designed and manufactured. A telescopic tower, which is raised and lowered by automation or by remote control, allows to differentiate the presence of the generator within the landscape over time. Research target: the optimal design of the telescopic coupling, the design for maintaining the preload and for the rotational decoupling, the optimization of the pairs of sleeves, the design of the pegs and the bushes of the jack-up lifting system. All the components of the wind tower have been preliminary analyzed through FEM stress computational analysis. The prototype was installed in Caltanissetta, Italy, and successfully tested
Urban Flood Prediction through GIS-Based Dual-Coupled Hydraulic Models
Full text linkPropagation of pluvial floods in urban areas, occurring with return time periods of few years, can be well solved using dual models accounting for the mutual relationship between the water level in the streets and the discharges inside the sewer pipes. The extended WEC-flood model (EWEC), based on the use of unstructured triangular meshes and a diffusive formulation of the momentum equations in both the 2D and the 1D lower domains, is presented along with its novelty, limits, and advantages. The model is then applied to a small computational domain in the Palermo area, where only some ‘hard’ data given by one rain gauge has been used for calibration and validation, along with other ‘soft’ data like yes/no surcharge observations and water depths available from photos and interviews. Model input data are mainly geometrical parameters, and calibration parameters are restricted only to average Manning coefficients. In the test case a very good validation has been obtained of three historical events using the EWEC model, with only one average Manning coefficient calibrated using other two historical events
A New Cross-Flow Type Turbine for Ultra-Low Head in Streams and Channels
Full text linkIn the last few decades, hydropower production has been moving toward a new paradigm of low and diffused power density production of energy with small and mini-hydro plants, which usually do not require significant water storage. In the case of nominal power lower than 20 kW and ultra-low head H (H < 5 m), Archimedes screw or Kaplan type turbines are usually chosen due to their efficiency, which is higher than 0.85. A new cross-flow type turbine called Ultra-low Power Recovery System (UL-PRS) is proposed and its geometry and design criteria are validated in a wide range of operating conditions through 2D numerical analysis computed using the ANSYS Fluent solver. The new proposed solution is much simpler than the previously mentioned competitors; its outlet flow has a horizontal direction and attains similar efficiency. The costs of the UL-PRS turbine are compared with the costs of one Kaplan and one cross-flow turbine (CFT) in the case study of the main water treatment plant of the city of Palermo in Italy. In this case, the UL-PRS efficiency is estimated using a URANS 3D numerical analysis computed with the CFX solver
Cross-Flow turbine design for variable operating conditions
Full text linkThe potential energy hidden in water resources is becoming more and more a significant economic value. The value of the hydroelectric energy is often magnified by the proximity of the turbine to pumps or other energy sinks owned by the same water manager. Cross-flow or Banki-Michel turbines are a very efficient and economic choice that allows a very good cost/benefit ratio for energy production located at the end of conduits carrying water from a water source to a tank. In the paper the optimum design of a cross-flow turbine is sought after, assuming a flow rate variable in time.
Regulation of the discharge entering in the turbine is a key issue, which is faced adopting a shaped semicircular segment, moved inside the main case around the rotating impeller. The maximum efficiency of the turbine is attained by setting the velocity of the particles entering the impeller at about twice the velocity of the rotating system at the impeller inlet. If energy losses along the pipe are negligible, closing and opening the inlet surface with the semicircular segment allows always a constant hydraulic head and a constant velocity at the impeller inlet, even with different flow rate entering values. Observed reduction of the turbine efficiency along with the inlet surface reduction is first investigated; a design methodology, using also CFD simulations, is then proposed; finally, the same methodology is applied to a real site in Sicily, selected in the context of the HYDROENERGY P.O. - F.E.S.R. European project
Experimental study of Cross-Flow micro-turbines for aqueduct energy recovery
No full textAn important component of the management cost of aqueducts is given by the energy costs. Part of these costs can be recovered by transforming some of the many existing energy dissipations in electric energy by means of economic turbines. In this study an experimental work has been carried out: 1) to test the performance of an economic Cross-Flow turbine which maintains high efficiency within a large range of water discharges, and 2) to validate a new approximated formula relating main inlet velocity to inlet pressure. It is proved that the proposed formula, according to some simplifying assumption, exactly links inlet velocity to inlet pressure according to any possible geometry of the Cross-Flow turbine. A specific stand has been designed and constructed, inside the lab of the DICAM Department of the University of Palermo, to carry on the experiments. Results show a general good agreement between numerical simulation and results and a bit larger experimental efficiency values. The ratio between the inlet experimental velocity and the velocity provided by the new formula is almost constant with respect to the velocity ratio and falling in the range between 0.95 and 0.98
Impeller optimization in crossflow hydraulic turbines
Full text linkCrossflow turbines represent a valuable choice for energy recovery in aqueducts, due
to their constructive simplicity and good efficiency under variable head jump conditions. Several
experimental and numerical studies concerning the optimal design of crossflow hydraulic turbines
have already been proposed, but all of them assume that structural safety is fully compatible with
the sought after geometry. We show first, with reference to a specific study case, that the geometry
of the most efficient impeller would lead shortly, using blades with a traditional circular profile
made with standard material, to their mechanical failure. A methodology for fully coupled fluid
dynamic and mechanical optimization of the blade cross-section is then proposed. The methodology
assumes a linear variation of the curvature of the blade external surface, along with an iterative use of
two-dimensional (2D) computational fluid dynamic (CFD) and 3D structural finite element method
(FEM) simulations. The proposed methodology was applied to the design of a power recovery system
(PRS) turbine already installed in an operating water transport network and was finally validated
with a fully 3D CFD simulation coupled with a 3D FEM structural analysis of the entire impeller
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