Extensible Wind Towers

The diffusion of wind energy generators is restricted by their strong landscape impact. The PERIMA project is about the development of an extensible wind tower able to support a wind machine for several hundred kW at its optimal working height, up to more than 50 m. The wind tower has a telescopic structure, made by several tubes located inside each other with their axis in vertical direction. The lifting force is given by a jack-up system confined inside a shaft, drilled below the ground level. In the retracted tower configuration, at rest, tower tubes are hidden in the foundation of the telescopic structure, located below the ground surface, and the wind machine is the only emerging part …

Progettazione di una cassa d’espansione e determinazione della riduzione del rischio idraulico con modellazione 2D

Nell’articolo si studia l’effetto di una cassa d’espansione posta a monte di un’area fluviale soggetta a rischio idraulico. Lo strumento utilizzato è un software bidimensionale sviluppato per simulare la propagazione delle piene fluviali. Il dominio di calcolo è rappresentato da una mesh triangolare non strutturata con una maggiore densità di elementi all’interno dell’alveo e nelle zone immediatamente limitrofe. Per facilitare gli accumuli temporanei di parte dei volumi di piena, si ipotizza la costruzione di un restringimento dell’alveo per mezzo di due pareti verticali che avvicinano le sponde fluviali. Durante la piena, il passaggio per lo stato critico nel restringimento provoca un rigu…

Coupled hydraulic and electronic regulation of cross-flow turbines in hydraulic plants

The potential benefit of coupling hydraulic and electronic regulation to maximize the energy production of a cross-flow turbine in hydraulic plants is analyzed and computed with reference to a specific case. Design criteria of the cross-flow turbine inside hydraulic plants are first summarized, along with the use of hydraulic regulation in the case of constant water head and variable discharge. Optimal turbine impeller rotational speed is derived, and traditional as well as innovative systems for electrical regulation are presented. A case study is analyzed to evaluate the potential energy production according to the expected monthly mean flow distribution and two possible choices: CFT1 wit…

The MAST-edge centred lumped scheme for the flow simulation in variably saturated heterogeneous porous media

A novel methodology is proposed for the solution of the flow equation in a variably saturated heterogeneous porous medium. The computational domain is descretized using triangular meshes and the governing PDEs are discretized using a lumped in the edge centres numerical technique. The dependent unknown variable of the problem is the piezometric head. A fractional time step methodology is applied for the solution of the original system, solving consecutively a prediction and a correction problem. A scalar potential of the flow field exists and in the prediction step a MArching in Space and Time (MAST) formulation is applied for the sequential solution of the Ordinary Differential Equation of…

Analisi fluidodinamica e sperimentale su una turbina Cross-Flow

L'energia idroelettrica è una forma di energia rinnovabile che oggi sta subendo un profondo processo di trasformazione passando da un sistema centralizzato di produzione ad un sistema di tipo distribuito. Tale processo ha dato un forte impulso alla costruzione di impianti di produzione idroelettrici su piccola scala. Questi impianti si possono realizzare: 1) lungo piccoli corsi d'acqua con piccoli salti disponibili, 2) alla fine di lunghe condotte di adduzione in corrispondenza della sezione di consegna ad un serbatoio cittadino, 3) nelle reti di distribuzione idriche dove il carico piezometrico in eccesso si dissipa con valvole di regolazione, 4) a valle di impianti di depurazione nel caso…

A NEW SOLVER FOR NON-ISOTHERMAL FLOWS IN NATURAL AND MIXED CONVECTION

Most thermal fluid flow of real-life practical problems fall in the category of low Mach-number or incompressible flow (e.g., industrial flows inside ducts, or around stationary/moving objects, flows in biological/biomedical problems, or atmospheric flows). Several numerical techniques have been proposed for simulation of thermal flows, Finite Difference (FDM), Finite Element (FEM), Finite Volume (FVM) and Lattice Boltzmann (LBM) methods. Unlike the FVMs and FEMs, the classical FDMs show some difficulties in handling irregular geometries. Conventional formulation of FEMs (e.g., Galerkin FEMs) suffers from the lack of local mass balance, recovered by modified formulations (Narasimhan & W…

ASSESSMENT OF RIVER FLOW WITH SIGNIFICANT LATERAL INFLOW THROUGH REVERSE ROUTING MODELING

The discharge hydrograph estimation in rivers based on reverse routing modeling and using only water level data at two gauged sections is here extended to the most general case of significant lateral flow contribution, without needing to deploy rainfall-runoff procedures. The proposed methodology solves the Saint-Venant equations in diffusive form also involving the lateral contribution using an ‘head driven’ modeling approach where lateral inflow is assumed to be function of the water level at the tributary junction. The procedure allows to assess the discharge hydrograph at ends of a selected river reach with significant lateral inflow, starting from the stage recorded there and without n…

AN EFFICIENT SOLUTION OF HETEROGENEOUS ANISOTROPIC CONVECTION/DIFFUSION TRANSPORT PROBLEMS

Experimental and Numerical Analysis of a Cross-Flow Turbine

An important component of the management cost of aqueducts is the energy costs. Part of these costs can be recovered by transforming some of the many existing energy dissipations into electric energy by means of economical turbines. This paper describes an experimental study that has been carried out in order to (1) test the performance of an economical cross-flow turbine that maintains high efficiency within a large range of water discharges, and (2) validate a new approximate formula relating main inlet velocity to inlet pressure. It is demonstrated that the proposed formula, on the basis of some simplifying assumptions, exactly links inlet velocity to inlet pressure with any possible geo…

A New Cross-Flow Type Turbine for Ultra-Low Head in Streams and Channels

In 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…

Cross-Flow Turbine Design For Energy Production And Discharge Regulation

Cross-flow turbines are very efficient and cheap turbines that allow 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 this paper a new design procedure for a cross-flow turbine working with a variable flow rate is proposed. The regulation of the head immediately upstream the turbine is faced by adopting a shaped semicircular segment moving around the 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, the semicircular …

MAST-RT0 SOLUTION OF 3D NAVIER STOKES EQUATIONS ON UNSTRUCTURED MESHS. PRELIMINARY RESULTS IN THE LAMINAR CASE

Computation of vertically averaged velocities in irregular sections of straight channels

Abstract. Two new methods for vertically averaged velocity computation are presented, validated and compared with other available formulas. The first method derives from the well-known Huthoff algorithm, which is first shown to be dependent on the way the river cross section is discretized into several subsections. The second method assumes the vertically averaged longitudinal velocity to be a function only of the friction factor and of the so-called "local hydraulic radius", computed as the ratio between the integral of the elementary areas around a given vertical and the integral of the elementary solid boundaries around the same vertical. Both integrals are weighted with a linear shape f…

UN’EFFICIENTE METODOLOGIA PER LA SOLUZIONE DEI PROBLEMI DI TRASPORTO ANISOTROPI ETEROGENEI

Flooding in the Digital Twin Earth: The Case Study of the Enza River Levee Breach in December 2017

The accurate delineation of flood hazard maps is a key element of flood risk management policy. Flood inundation models are fundamental for reproducing the boundaries of flood-prone areas, but their calibration is limited to the information available on the areas affected by inundation during observed flood events (typically fragmentary photo, video or partial surveys). In recent years, Earth Observation data have supported flood monitoring and emergency response (e.g., the Copernicus Emergency Service) thanks to the proliferation of available satellite sensors, also at high spatial resolution. Under this umbrella, the study investigates a levee breach that occurred in December 2017 along t…

Numerical and experimental investigation of a cross-flow water turbine

ABSTRACTA numerical and experimental study was carried out for validation of a previously proposed design criterion for a cross-flow turbine and a new semi-empirical formula linking inlet velocity to inlet pressure. An experimental test stand was designed to conduct a series of experiments and to measure the efficiency of the turbine designed based on the proposed criterion. The experimental efficiency was compared to that from numerical simulations performed using a RANS model with a shear stress transport (SST) turbulence closure. The proposed semi-empirical velocity formula was also validated against the numerical solutions for cross-flow turbines with different geometries and boundary c…

Experimental Study of Cross-flow Micro-turbines for Aqueduct Energy Recovery

An 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 Cros…

PROGETTAZIONE DI UNA OPERA DI PRESA A BASSO IMPATTO AMBIENTALE PER UN IMPIANTO MINI IDROELETTRICO IN SICILIA

EXTERNAL RECIRCULATION IN PRS TYPE TURBINE: EXPERIMENTAL AND NUMERICAL RESULTS.

Cavitation is a relevant phenomenon for structural safety and noise level in hydraulic turbines, occurring when water pressure falls below the vapor value at a given temperature. In this case bubbles of vapor grow inside the liquid and move along with it. When the pressure returns above the vapor value the bubble collapses, and the pressure can locally achieve very high values, up to 7000 bars (Kumar & Saini, 2010). Moreover, if the bubble was confined also by the solid wall of a blade, the solid particles suspended in the fluid can be transported by the fluid ones and hit the solid wall at very high velocity, generating erosion. Cavitation is also the source of high frequency noise, ve…

Utilizzo di un modello diffusivo 2D di acque basse PER LA simulazione in tempo reale di scenari di inondazioni

I recenti cambiamenti climatici e le sempre più frequenti inondazioni rendono particolarmente attuale l’utilizzo di sistemi di allerta per facilitare l’evacuazione precoce della popolazione e la messa in sicurezza dei beni. I suddetti sistemi sono basati in parte sulla previsione a breve termine delle piogge, in parte sulla stima del processo di trasformazione afflussi-deflussi e della propagazione dell’onda di piena. Nella presente memoria il modello diffusivo MAST 2D ad avanzamento spaziale e temporale già proposto da alcuni degli autori viene ulteriormente migliorato per una più rapida soluzione ed una migliore adattabilità all’uso del calcolo parallelo. Viene introdotta una nuova soluzi…

Scala delle portate in sezioni naturali di forma irregolare

Calcolo della portata di piena con modello bidimensionale non lineare

Si propone un modello bidimensionale di trasformazione afflussi-deflussi per il calcolo della piena in una sezione di un corso d’acqua. Il bacino idrografico è rappresentato da una mesh triangolare non strutturata. L’input del modello è costituito dalle piogge lorde, trasformate in piogge nette mediante l’equazione integrata di Horton. Il calcolo della propagazione idraulica nei diversi rami della rete idrografica consente di abbandonare le ipotesi di stazionarietà e di linearità, ordinariamente adottate nell’idrologia delle piene. Il modello proposto viene calibrato ed applicato ad un bacino idrografico di un affluente del fiume Tevere per il quale si dispongono di alcuni idrogrammi di pie…

Energy recovery from rectangular weirs in wastewater treat-ment plants

Hydraulic turbines for energy recovery in wastewater treatment plants, with relatively large discharges and small head jumps, are usually screw or Kaplan types. In the specific case of a small head jump (about 3 m) underlying a rectangular weir in the major Palermo (Italy) treat-ment plant, a traditional Kaplan solution is compared with two other ones: a Hydrostatic Pres-sure Machine (HPM) located in the upstream channel and a cross-flow turbine located in a specif-ic underground room downstream the same channel.

A New Device for Pressure Control and Energy Recovery in Water Distribution Networks

The potential energy of the water in Water Distribution Networks (WDNs) usually exceeds the amount needed for delivery and consumption and, at the present time, it is mainly dissipated through Pressure Reducing Valves (PRVs) or Open Water Tanks. The present study suggests the use of a new energy-producing device, a Cross-flow turbine with positive outlet pressure named PRS (Power Recovery System), which can provide the same service as PRVs and water tanks, with additional significant hydropower production. After a short presentation of the PRS, the management rules of the proposed device are laid out, according to two possible modes. In the ‘passive’ mode, the piezometric level downstream o…

Cross-flow Turbine Design for Variable Operating Conditions

Abstract The 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 se…

Monotonic solution of flow and transport problems in heterogeneous media using Delaunay unstructured triangular meshes

Transport problems occurring in porous media and including convection, diffusion and chemical reactions, can be well represented by systems of Partial Differential Equations. In this paper, a numerical procedure is proposed for the fast and robust solution of flow and transport problems in 2D heterogeneous saturated media. The governing equations are spatially discretized with unstructured triangular meshes that must satisfy the Delaunay condition. The solution of the flow problem is split from the solution of the transport problem and it is obtained with an approach similar to the Mixed Hybrid Finite Elements method, that always guarantees the M-property of the resulting linear system. The…

A paradigm of extreme rainfall pluvial floods in complex urban areas: the flood event of 15 July 2020 in Palermo (Italy)

Abstract. In the last years, some regions of the Mediterranean area are witnessing a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and severe extreme rainfall events and their ground effects, which are often exacerbated by ever-growing urbanization. In such a context, the traditional defense of urban areas, which are usually based on urban drainage systems designed without regard to the impacts of urbanization and climate change on natural systems, may not be sufficient to deal with the risk deriving from the occurrence of such events. This study focuses on a very recent and particularly intense urban flood that occurred i…

Coupled Electric and Hydraulic Control of a PRS Turbine in a Real Transport Water Network

Although many devices have recently been proposed for pressure regulation and energy harvesting in water distribution and transport networks, very few applications are still documented in the scientific literature. A new in-line Banki turbine with positive outflow pressure and a mobile regulating flap, named Power Recovery System (PRS), was installed and tested in a real water transport network for the regulation of pressure and flow rate. The PRS turbine was directly connected to a 55 kW asynchronous generator with variable rotational velocity, and coupled to an inverter. The start-up tests showed how automatic adjustment of the flap position and the runner velocity variation are able to c…

Numerical analysis of a new cross-flow type hydraulic turbine for high head and low flow rate

Cross-flow turbines have recently been proposed for energy recovery in aqueducts when the outlet pressure is greater than zero, owing to their constructive simplicity and good efficiency within a large range of flow rates and head drops. In the case of high head drop (higher than 150 m) and relatively small discharge (lower than 0.2 m3/s), the traditional design of these turbines leads to very small widths of the nozzle and the runner; as a consequence, friction losses grow dramatically and efficiency drops down to very low values. Standard Pelton turbines require zero outlet pressure and cannot be used as alternatives. A new counter-pressure hydraulic turbine for high head and low flow rat…

Costruzione e sperimentazione di una turbina cross-flow per acquedotti

La memoria descrive una nuova micro turbina idraulica con capacità di regolazione della portata, per installazioni in piccoli corsi d’acqua, su acquedotti esistenti o a valle di impianti di depurazione delle acque. Viene inoltre descritta l’installazione del prototipo della turbina nella rete idropotabile di un comune siciliano.

A new solver for incompressible non-isothermal flows in natural and mixed convection over unstructured grids

Abstract In the present paper we propose a new numerical methodology for the solution of 2D non-isothermal incompressible flows for natural and mixed convection in irregular geometries. The governing equations are the Incompressible Navier-Stokes Equations and the Energy Conservation Equation. Fluid velocity and temperature are coupled in the buoyancy term of the momentum equations according to the Oberbeck–Boussinesq approximation. The governing equations are discretized over unstructured triangular meshes satisfying the Delaunay property. Thanks to the Oberbeck–Boussinesq hypothesis, the flow and energy problems are solved in an uncoupled way, and two fractional time step procedures are s…

Analisi del moto di filtrazione in rilevati arginali mediante tomografia di resistivià elettrica

An Evaluation Matrix to Compare Computer Hydrological Models for Flood Predictions

In order to predict and control the impacts of floods in torrents, it is important to verify the simulation accuracy of the most used hydrological models. The performance verification is particularly needed for applications in watersheds with peculiar climatic and geomorphological characteristics, such as the Mediterranean torrents. Moreover, in addition to the accuracy, other factors affect the choice of software by stakeholders (users, modellers, researchers, etc.). This study introduces a &ldquo

Simulazione idraulica bidimensionale per la perimetrazione in tempo reale delle aree a rischio di inondazione

A COST BENEFIT ANALISYS FOR HYDROPOWER PRODUCTION IN WATER DISTRIBUTION NETWORKS BY PUMP AS TURBINE (PAT)

The use of micro hydroelectric plant in urban pipe networks, based on the combination of a PAT, two regulating valves and two pressure meters, is proposed along with simple automation rules. Its economic benefit is tested on a small pipe network, where the network geometry, as well as the demand coefficient variation in time and space have been inferred from previously collected data and existing analysis. A similar analysis has been also carried out for different scenarios, where the reduction of pipe installation cost due to a diameter reduction is compared with the increased benefit in energy production. The case study shows that a small increment of the pipe installation cost, with resp…

MAST-RT0 solution of the incompressible Navier–Stokes equations in 3D complex domains

A 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 tetrahedr…

Impeller optimization in crossflow hydraulic turbines

Crossflow 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 …

Performance Improvement of a Drag Hydrokinetic Turbine

Hydropower is at present in many locations, among all the other possible renewable energy sources, the best one for net cost per unit power. In contrast to traditional installation, based on water storage in artificial basins, free flow river turbines also provide a very low environmental impact due to their negligible effect on solid transport. Among them, kinetic turbines with vertical axis are very inexpensive and have almost zero impact on fish and local fauna. In application to tidal waves and sea waves, where vertically averaged velocities have alternate direction, a Savonius rotor also has the advantage of being productive during the whole time cycle. In this work, the effect of an u…

Urban Flood Prediction through GIS-Based Dual-Coupled Hydraulic Models

Propagation 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 ot…

Experimental and numerical analysis of a backpressure Banki inline turbine for pressure regulation and energy production

Abstract Water distribution networks have become, in recent years, a major opportunity for the harvesting of renewable energy, which is otherwise dissipated though hydrovalves installed for discharge and pressure regulation. Mini and micro hydroturbines have the capability of providing the same functionality of hydrovalves, producing at the same time a relevant amount of electric power. In this paper a 10 kW prototype of a new compact in-line turbine, named Power Recovery System (PRS), has been designed, constructed and tested in the hydraulic laboratory of the University of Palermo. The proposed device is a Banki-type micro-turbine, with positive outflow pressure and a mobile regulating fl…

Extensible Wind Tower

The diffusion of wind energy generators is restricted by their strong landscape impact. The PERIMA project is about the development of an extensible wind tower able to support a wind machine for several hundred kW at its optimal working height, up to more than 50 m. The wind tower has a telescopic structure, made by several tubes located inside each other with their axis in vertical direction. The lifting force is given by a jack-up system confined inside a shaft, drilled below the ground level. In the retracted tower configuration, at rest, tower tubes are hidden in the foundation of the telescopic structure, located below the ground surface, and the wind machine is the only emerging part …

Anisotropic potential of velocity fields in real fluids: Application to the MAST solution of shallow water equations

In the present paper it is first shown that, due to their structure, the general governing equations of uncompressible real fluids can be regarded as an "anisotropic" potential flow problem and closed streamlines cannot occur at any time. For a discretized velocity field, a fast iterative procedure is proposed to order the computational elements at the beginning of each time level, allowing a sequential solution element by element of the advection problem. Some closed circuits could appear due to the discretization error and the elements involved in these circuits could not be ordered. We prove in the paper that the total flux of these not ordered elements goes to zero by refining the compu…

MAST-2D diffusive model for flood prediction on domains with triangular Delaunay unstructured meshes

Abstract A new methodology for the solution of the 2D diffusive shallow water equations over Delaunay unstructured triangular meshes is presented. Before developing the new algorithm, the following question is addressed: it is worth developing and using a simplified shallow water model, when well established algorithms for the solution of the complete one do exist? The governing Partial Differential Equations are discretized using a procedure similar to the linear conforming Finite Element Galerkin scheme, with a different flux formulation and a special flux treatment that requires Delaunay triangulation but entire solution monotonicity. A simple mesh adjustment is suggested, that attains t…

Coupled Hydraulic and Electronic Regulation for Banki Turbines

Abstract The potential benefit of coupling hydraulic and electronic regulation to maximize the energy production of a Bank turbine in hydraulic plants is analyzed and computed with reference to a specific case. Design criteria of the Banki turbine inside hydraulic plants are first summarized, along with the use of hydraulic regulation in the case of constant water head and variable discharge at the end of aqueducts feeding water distribution systems. Optimal turbine impeller rotational speed is derived and traditional, as well as innovative systems for electricity production according to controlled rotational speed of the generator are presented. The study case at the purification plant nam…

Discharge estimation in natural channels with significant lateral inflow

The indirect measurement technique for discharge estimation, based on water level data analysis in two different river sections, is extended to the case of existing significant tributary flow between the two sections. The methodology is based on the calibration of a numerical flow routing algorithm, solving the Saint-Venant equations in diffusive form along the main channel between the two measurement sections. The first calibration parameter is the average Manning's roughness coefficient holding in the main channel, the other ones are relative to the rating curve of each tributary channel, estimated per unit roughness coefficient and per unit slope immediately before the junction of the tr…

Fast solution of diffusive shallow water equations for real time flood prediction

Unsteady State Water Level Analysis for Discharge Hydrograph Estimation in Rivers with Torrential Regime: The Case Study of the February 2016 Flood Event in the Crati River, South Italy

Discharge hydrograph estimation during floods, in rivers with torrential regime, is often based on the use of rating curves extrapolated from very low stage-discharge measurements. To get a more reliable estimation, a reverse flow routing problem is solved using water level data measured in two gauged stations several kilometers from each other. Validation of the previous analysis carried out on the flood event of February 2016 at the Europa Bridge and Castiglione Scalo sections of the Crati River (Cosenza, Italy) is based on the use of 'soft' discharge measurement data and the comparison of the water level data computed in the downstream gauged section by three different hydraulic models w…

Utilizzo di un modello diffusivo 2D di acque base per la simulazione in tempo reale di scenari di inondazione

Investigation of the hemodynamic flow conditions and blood-induced stresses inside an abdominal aortic aneurysm by means of a SPH numerical model.

The estimation of blood flow-induced loads occurring on the artery wall is affected by uncertainties hidden in the complex interaction of the pulsatile flow, the mechanical parameters of the artery, and the external support conditions. To circumvent these difficulties, a specific tool is developed by combining the aorta displacements measured by an electrocardiogram-gated-computed tomography angiography, with the blood velocity field computed by a smoothed particle hydrodynamics (SPH) numerical model. In the present work, the SPH model has been specifically adapted to the solution of the 3D Navier-Stokes equations inside a domain with boundaries of prescribed motion. Images of the abdominal…

Inserimento di restringimenti e ponti in un modello diffusivo 2D di acque basse

Gli effetti su una corrente, causati dalle pile di un ponte, o più in generale da strutture che riducono la sezione trasversale dell’alveo, risultano di particolare interesse per le variazioni idrometriche che comportano alla corrente stessa. Nonostante i numerosi studi teorici e sperimentali di letteratura, l’attuale modellistica numerica diffusiva non integra la presenza di tali manufatti nelle proprie tecniche risolutive. Nella presente memoria viene presentata la metodologia implementata nel modello diffusivo bidimensionale FLOW2D per la valutazione del rigurgito provocato da restringimenti della sezione trasversale, nonché dalla presenza delle campate. I profili di rigurgito ottenuti c…

Low-Head Hydropower for Energy Recovery in Wastewater Systems

Hydraulic 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 ana…

Un modello 1D-2D di acque basse per il calcolo della propagazione di piene naturali

Le equazioni 2D del Saint-Venant (SV), o delle acque basse (shallow water), si utilizzano ampiamente per le simulazioni idrodinamiche in fiumi, laghi, zone di estuari e zone golenali. Come ampiamente descritto in letteratura, in base ai termini che si trascurano nell'equazione del momento, si possono distinguere modelli completi, cinematici, diffusivi e a zero inerzia convettiva. Escludendo eventi estremi di shock, nella normalità dei casi relativi a fenomeni di inondazione, si possono trascurare i termini inerziali nell'equazione del momento, ottenendo il modello diffusivo. La scelta del modello da utilizzare dipende anche dalla disponibilità e dall'accuratezza dei dati di input (Smith et …

A Self-Contained and Automated Method for Flood Hazard Maps Prediction in Urban Areas

Water depths and velocities predicted inside urban areas during severe storms are traditionally the final result of a chain of hydrologic and hydraulic models. The use of a single model embedding all the components of the rainfall&ndash

Un sistema informativo territoriale per la simulazione di una rete di drenaggio urbano con Flow1D

Si propone un modello di simulazione monodimensionale delle reti di drenaggio urbano che operi all’interno di un software GIS e che consenta la realizzazione amichevole di un sistema informativo territoriale (SIT) della rete di drenaggio. Il modello, fisicamente basato, simula la formazione e la propagazione idraulica dei deflussi che si realizzano in ogni sottobacino, nonché la propagazione idraulica all’interno della sottostante rete fognaria. La connessione fra le due reti viene ricostruita attraverso il calcolo dei flussi verticali che si realizzano in corrispondenza dei pozzetti. Il modello è di tipo duale, in quanto rispetta l’interazione idrodinamica fra i deflussi nella rete stradal…

Cost-Benefit Analysis for Hydropower Production in Water Distribution Networks by a Pump as Turbine

AbstractThe use of microhydroelectric plants in urban pipe networks, based on the combination of a pump as turbine (PAT), two regulating valves, and two pressure meters, is proposed along with simple automation rules. Its economic benefit is tested on a small pipe network, where the network geometry as well as the demand coefficient variation in time and space have been inferred from previously collected data and existing analysis. A similar analysis has been also carried out for different scenarios in which the reduction of pipe installation cost due to a diameter reduction is compared with the increased benefit in energy production. The case study shows that a small increment of the pipe …

A novel pressure regulation system based on Banki hydro turbine for energy recovery under in-range and out-range discharge conditions

Abstract Efficiency improvement of water distribution networks needs to be in place to guarantee a long life period under suitable operating conditions. Excessive pressure is among the well-known issues encountered in water distribution networks which can cause strength damages to the piping system. In order to overcome this drawback and to reach a suitable water pressure delivery, the present work suggests a novel pressure regulation system. This regulation system is consisting of a Banki turbine equipped with a mobile flap as a control device. The suggested pressure regulation system was experimentally and numerically investigated under in-range i.e. like actual water distribution network…

Progettazione di un'opera di presa a basso impatto ambientale per un impianto mini idroelettrico in Sicilia

An improved numerical solver of the 2D diffusive shallow waters equations over unstructured triangular meshes

A Banki–Michell turbine for in-line water supply systems

The design of a novel Banki-Michell type turbine, to be located in existing water pipelines, is proposed. The turbine has a very efficient diffuser which allows the turbine to be compact and, most important, to have in-line flanges for minimal piping modifications at existing sites. This turbine combines a simple geometry with stable efficiency in a wide range of water discharges. The design procedure estimates the outer diameter of the impeller, its width and the geometry of the diffuser. A series of experimental tests has been carried out to measure the efficiency of the proposed turbine prototype. The turbine was tested in two different configurations, with and without rotational velocit…

OTTIMIZZAZIONE FLUIDO-MECCANICA DI TURBINE IDRAULICHE CROSSFLOW

A paradigm of extreme rainfall pluvial floods in complex urban areas: the flood event of 15 July 2020 in Palermo (Italy)

Abstract. In the last few years, some regions of the Mediterranean area have witnessed a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and severe extreme rainfall events, which are often exacerbated by the ever-growing urbanization. In such a context, the urban drainage systems may not be sufficient to convey the rainwater, thus increasing the risk deriving from the occurrence of such events. This study focuses on a particularly intense urban flood that occurred in Palermo (Italy) on 15 July 2020; it represents a typical pluvial flood due to extreme rainfall on a complex urban area that many cities have experienced in rece…

MAST-RT0 solution of 3D Navier Stokes equations in very irregular domains. Preliminary results in the laminar case

A 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 tetrahedr…

The FLO Diffusive 1D-2D Model for Simulation of River Flooding

An integrated 1D-2D model for the solution of the diffusive approximation of the shallow water equations, named FLO, is proposed in the present paper. Governing equations are solved using the MArching in Space and Time (MAST) approach. The 2D floodplain domain is discretized using a triangular mesh, and standard river sections are used for modeling 1D flow inside the section width occurring with low or standard discharges. 1D elements, inside the 1D domain, are quadrilaterals bounded by the trace of two consecutive sections and by the sides connecting their extreme points. The water level is assumed to vary linearly inside each quadrilateral along the flow direction, but to remain constant …

Design of Reliable and Efficient Banki-Type Turbines

A new shape for the external surface of the Crossflow turbine blades is proposed, which allows for the preservation of hydraulic efficiency in spite of a significant maximum blade thickness providing mechanic robustness and reliability. The final shape of the blades is assessed using an iterative solution for two uncoupled models: a 2D computational fluid dynamic (CFD) and a structural 3D finite element method (FEM) analysis of a single blade. Application of the proposed methodology to the design of a power recovery system (PRS) turbine, a new backpressure Crossflow-type inline turbine for pressure regulation, and energy production in a real Sicilian site follows.