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Given the current practice to perform lean-premixed combustion to decrease NOx emissions, thermoacoustic instabilities have become one of the major drawbacks in gas turbine combustors. The necessity to control and limit such a deleterious phenomenon is mandatory to avoid structural damage of the burner. It has been demonstrated that perforated liners, if conveniently designed, can be very effective in reducing acoustic oscillations inside gas turbine combustors. Studying perforated plates traversed by bias flow can give a useful insight on sound absorption properties of liners, rather than investigate complex geometries. The present paper aims to carry out a numerically cost-effective, but reliable, CFD analysis to predict the acoustic impedance of perforated plates traversed by bias flow, and to grasp the details of the sound dissipation process. 2D axisymmetric simulations have been carried out and the governing equations solved by using the commercial code ANSYS Fluent®. Hypotheses, boundaries and operating conditions are described, focusing on the role of the Non-Reflecting-Boundary-Condition (NRBC) and the Transparent-Flow-Forcing condition (TFF) in treating acoustic waves. Numerical results are compared both with linear analytical models and experimental data from a case study, by proving a fast and reliable prediction of the acoustic response. Furthermore, effects of increasing bias flow temperature on the sound absorption property have been investigated, showing an increase in acoustic power losses as temperature rises. The proposed CFD model (2D-axisymmetric) proved to be a valid and versatile tool in evaluating the acoustic response of perforated plates under different operating conditions.

Hydrogen is gaining momentum in the current global energy transition framework. In fact a great and widespread enthusiasm is growing up towards it, as indicated by the current worldwide economic and political strategies, which endorse the carbon neutrality by 2030 and a fast transition to clean energy. Green hydrogen has the potential to create a virtuous cycle for the future renewables-based electricity grids, as it can provide the much-needed flexibility to power systems, acting as a buffer to non-dispatchable renewable generation. Indeed, the excess energy, provided by conventional and renewable power plants, can be stored as hydrogen and then employed to produce electricity (fuel cells or power systems), heat (combustion) or both (co-generation), abating drastically the greenhouse gas production. In this scenario, it is important to understand what benefits could derive from the use of hydrogen. For this reason, the present work not only aims at reviewing the recent updates on hydrogen economy (in terms of the main advantages and drawbacks) but also focuses on determining the impact that this hydrogen may have in various sectors (transport, industry and power generation). Different assessments have been carried out showing how hydrogen can effectively contribute to the carbon neutrality goal. This work points out that hydrogen can be really sustainable if produced via electrolysis powered by renewable energies. Furthermore, for the mobility, the use of fuel cells currently turns out to be less efficient than the adoption of Li-ion batteries, but at the same time far less polluting ( CO 2 , eq ) and labor intensive. Finally, a near-term solution to contrast the power generation carbon footprint, namely the blending of fossil fuels with hydrogen, has been investigated. Thus, a real Combined Cycle Gas Turbine power plant has been selected as a case study, in order to assess the impact of the hydrogen employment in terms of power output and emissions with respect to the current status of the plant fueled with 100% natural gas. As a result, using a mixture with 70% CH 4 and 30% H 2 a remarkable reduction of CO 2 can be achieved (0.28 Mt CO 2 / year ).

Water Distribution Networks (WDNs) are subject to leakages due to pipes aging, resulting in water and pressure losses. These issues are solved by installing Pressure Reduction Valves (PRVs) to decrease the pressure in WDNs. Depending on the application, PRVs can waste large amount of energy, hence the substitution of PRVs with Pumps used as Turbines (PaTs) can be a good compromise in terms of economic and technical aspects to reduce leakages and recover energy. Currently the share of PaT is not yet fully developed due to the certain technical challenges yet to be addressed, as providing an affordable control strategy closer to the real working conditions in a WDN. Hence, more experimental activities are required. For these reasons, in this work an experimental campaign was carried with the aim to investigate the behavior of a PaT according to a possible layout that could be embedded into a WDN. Firstly, the machine was characterized both in pump and turbine modes. Moreover, the machine working conditions limits have been analysed in terms of runaway and blocked-rotor curves. Then, turbine tests were carried out at constant speed with a typical hydraulic control scheme by means of a PRV installed in series to the PaT and a second one installed on a bypass. As a result, this analysis highlighted the feasibility to recover a consistent amount of hydraulic energy otherwise wasted under typical WDN daily pressure and flow rate patterns, with promising results in terms of the operating point control of the machine.

In the context of reducing carbon dioxide ([Formula: see text]) emissions, hydrogen is gaining momentum as a possible fuel for Internal Combustion Engines (ICEs). In-cylinder direct injections allow for a higher specific power density while enabling different levels of charge stratification. The high-pressure injection leads to the onset of under-expanded jets, characterized by complex patterns of shock waves and expansion fans. In ICEs simulations, such physics needs to be correctly solved to obtain a reliable assessment of the mixture formation. In this paper, the main features of hydrogen under-expanded jets are examined under the conditions typically found in turbocharged engines. Improved correlations are provided for the assessment of the Mach disk height and diameter, up to a Nozzle Pressure Ratio (NPR) equal to 60. The dependency of the hydrogen-air mixing on the cylinder temperature has been analyzed, and the unsteady jet dynamics has been examined by continuously varying the combustion chamber pressure. To the authors’ knowledge, no studies of this kind can be found in the literature for the specific case of hydrogen. Lastly, a preliminary investigation of the jet-jet interaction (a Coanda-like effect) is reported. This phenomenon is observable when multi-hole injectors are employed, and it may have a great impact on the mixture formation.

The European Green Deal for halving greenhouse gases emissions by 2030, compared to those of 1990s, and the resulting conversion in road transport from 2035 imply the need for the automotive field. Hydrogen-fueled internal combustion engines show a good potential to satisfy the transition towards the carbon neutrality. In particular, direct injection of hydrogen in spark-ignited internal combustion engines have great efficiency potentialities, nonetheless the design optimization of the injection systems needs extensive analysis for the evaluation of the hydrogen-air mixing processes under different engine operating conditions. Transient simulations of the gas-exchange process and fuel injection and mixing are fully described within this paper for two different commercial CFD codes namely, AVL-Fire and Ansys-Fluent. Both codes use the finite-volume approach to discretize the governing equations. Numerical results from the two commercial codes have been compared against the experimental data provided by the Argonne National Laboratories in terms of contours of fuel mole-fractions and velocity-field vectors, resulting from applying laser-based techniques on an optically accessible, single-cylinder engine.

The purpose of this work is to build a model of diesel engine useful for studying new hybrid solutions for power generation. This kind of study is of significant interest particularly for the marine sector, due to recent limitations on fuel consumption and constraints imposed on the minimum powertrain efficiency. In this paper a variable-speed diesel generator model is presented. The model simulates both the dynamic behavior of the engine and the fuel consumption during the operating cycle. This model was developed using experimental results of bench tests conducted on the VL1716C2-MLL engine by Isotta Fraschini Motori (IFM) SpA. Diesel engine dynamics is based on the formulation found in the technical literature on mean value models and then adjusted through experimental data. Special attention was paid to developing the procedure to find the minimum specific fuel consumption for a given load. Initially, the presented resutls concern the correct response of the model under different load conditions. Then, the improvement in specific fuel consumption (obtained by adjusting the engine speed according to the load), in comparison with fixed speed operation, is shown.

The effects of climate change and global warming are arising a new awareness on the impact of our daily life. Power generation for transportation and mobility as well as in industry is the main responsible for the greenhouse gas emissions. Indeed, currently, 80% of the energy is still produced by combustion of fossil fuels; thus, great efforts need to be spent to make combustion greener and safer than in the past. For this reason, a review of the most recent gas turbines combustion strategy with a focus on fuels, combustion techniques, and burners is presented here. A new generation of fuels for gas turbines are currently under investigation by the academic community, with a specific concern about production and storage. Among them, biofuels represent a trustworthy and valuable solution in the next decades during the transition to zero carbon fuels (e.g., hydrogen and ammonia). Promising combustion techniques explored in the past, and then abandoned due to their technological complexity, are now receiving renewed attention (e.g., MILD, PVC), thanks to their effectiveness in improving the efficiency and reducing emissions of standard gas turbine cycles. Finally, many advances are illustrated in terms of new burners, developed for both aviation and power generation. This overview points out promising solutions for the next generation combustion and opens the way to a fast transition toward zero emissions power generation.

This book chapter is focused on how to study the fluid dynamic behavior of a Wave Energy Converter (WEC) of the Oscillating Water Column (OWC) type by means of Computational Fluid Dynamics (CFD). The U-OWC plant installed in the harbor of Civitavecchia (Italy) is chosen as the case study. The CFD approach is described referring to ANSYS Fluent, release 17.2. The model is mainly oriented to investigate the interaction of single harmonic waves with the OWC device and allows the user to perform a preliminary wave-to-wire energy conversion process analysis. To limit the computational cost, a 2D model is developed. The presence of the Power Takeoff (PTO) system generally breaks the 2D configuration of this kind of device, and here an approach to overcome this problem is described in detail. The solution is the introduction of a porous medium region in the 2D computational domain, which emulates the effect of the PTO system on the fluid dynamic behavior of the flow inside the WEC.

Double suction centrifugal pumps are the main devices involved in the feedwater system of nuclear power plants and they are responsible for a significant share of their energy consumption (by affecting the balance of both the gross and net electrical energy production), hence even an efficiency increase of only a few percentage points could be substantial in their economy. Herein a novel impeller designed for low-medium specific speed double suction centrifugal pumps ( n q 60 ) is proposed showing an efficiency improvement with respect to conventional designs in the order of 1–2% associated to a slip factor increase, secondary losses reduction and impeller outflow homogeneity improvement. The novel double suction impeller is characterized by a new arrangement of its flow channels, which come up alternately on the same circumferential exit even if they start from the two different sides. The flow field through the impeller is investigated via numerical simulations run by means of the open source CFD code OpenFOAM and its performance is compared against experimental results. The CFD model set-up, in terms of grid size and discretization schemes, has been previously assessed against results of consolidated CFX simulations on a conventional centrifugal pump.

Hydrogen combustion is one of the most promising solution to achieve a global decarbonization in power production and transports. Pure hydrogen combustion is far from becoming a standard but, during the energy transition, hydrogen co-firing can be a feasible and economically attractive shortterm measure. The use of hydrogen blending gives rise to several issues related to flashback, NOx emissions and thermo-acoustic instabilities. To improve the understanding of the effect of hydrogen enrichment, herein a numerical analysis of lean premixed hydrogen enriched flames is performed by means of 3D unsteady CFD simulations. The numerical model has been assessed against experimental results for both cold and reacting flows in terms of velocity profile (average) and flame shape (mean OH* radical fields). The burner under investigation is the swirl stabilized PRECCINSTA studied at the Deutsches Zentrum für Luft-und Raumfahrt (DLR). The DLR’s researchers have shown the effect of hydrogen addition on the flame topology and combustion instabilities at various operating conditions in terms of thermal power, equivalence ratio and H2 volume fraction. Simulations are in good accordance with experimental data both in terms of velocity and temperature profiles. The numerical model provides a qualitative estimation of the flame shape.

The hydrodynamics and heat transfer of a binary mixture of sand and biomass in a fluidized bed have been numerically investigated. The Eulerian multi-fluid model MFM incorporating kinetic theory of granular flow was used to numerically investigate fluidized bed. A commercial code has been used together with user-defined functions to correctly predict the hydrodynamics and the heat transfer. Numerical results were validated against the experiment in terms of pressure drop across the bed and concentration of biomass at different heights of the bed. Influence of additional parameters, such as superficial gas velocity and sand sizes on hydrodynamics were investigated. Additionally, heat transfer in the fluidized bed was also studied highlighting the influence of the temperature dependent properties of air on the results. The present results reveal that better mixing is achieved for smallest sand size, also promoting more uniform temperature of biomass.

This paper expands on the results of the technical and economic feasibility analysis of substituting existing pressure reduction valves (PRVs) with pumps used as turbines (PaTs) in two real Italian water distribution networks (WDN), chosen as case studies, aiming at effective energy recovery. Water demand variability makes complex the selection of the right pump to be used as a turbine in a WDN maximizing its annual electric energy yield. Hence, this study describes an effective approach that permits us to identify the most suitable pumps, starting from the definition of the best efficiency points at which they should operate in reverse mode.

Water Distribution Networks (WDNs) are becoming an attractive area of application for small hydropower, which can contribute to the development of distributed energy generation from renewable sources. Indeed, WDNs experience considerable water leakages due to their age and water management authorities often divide the WDNs by inserting Pressure Reducing Valves (PRVs), which waste a potentially recoverable hydraulic head. The replacement of PRVs with Pump as Turbines (PaTs) can be considered as an economically feasible solution to achieve both an effective pressure control and a throttling energy recovery. The selection, installation and control strategy of a PaT in a WDN must consider the variability of the pressure and the flow rate demand. Starting from the evaluation of the available head and the water demand, in this work, we describe a methodology to select from pump catalogues the most suitable PaT and the best control criteria for a specific WDN. Then, knowing the pump geometry, it is possible to predict the characteristic curve of the pump operating as a turbine by using a 1-D performance prediction model. The WDN of a town in the Apulia region (Southern Italy) has been used as a case study. Finally, a techno-economic evaluation has been carried out by considering both economic and environmental benefits.

Even if researchers are working on the exploitation of marine energy for more than thirty years, blue energy is not yet a consolidated reality and still contributes marginally to the world energy mix. For this reason, in the last years, the effort of the scientific community has been significantly intensified to further improve the know-how on marine energy harvesting. The goal is to allow ocean energy to effectively contribute to a more sustainable energy production in the next future. In the wide range of technologies for wave energy harvesting, Oscillating Water Column (OWC) devices are counted among of the most mature ones. Due to the oscillating nature of the generated air flow, which continuously inverts its direction, OWC devices need to be coupled with self-rectifying turbines, such as Wells, impulse, or biradial turbines. Wells turbines can reach high efficiencies, but their performance can show a hysteretic behaviour due to dynamic stall phenomena, especially in presence of high amplitude flow rate oscillations. Moreover, under dynamic stall conditions, during the flow deceleration, the shaft torque evidence the presence of gradually damped fluctuations, which delay the flow reattachment, superposed to the hysteresys loop. In order to better characterize this phenomenon, a new experimental campaign was performed in the open wind tunnel of the Polytechnic University of Bari on a 3D-printed Wells turbine model. The interest is mainly focused on the dependency of these torque fluctuations on the amplitude and frequency of the oscillating flow.

The regulatory restrictions, currently acting, impose a significant reduction of the Greenhouse Gas (GHG) emissions. After the coal-to-gas transition of the last decades, the fossil fuel-to-renewables switching is the current perspective. However, the variability of energy production related to Renewable Energy Sources requires the fundamental contribution of thermal power plants in order to guaranty the grid stability. Moving toward a low-carbon society, the industry is looking at a reduction of high carbon content fuels, pointing to Natural Gas (NG) and more recently to hydrogen-NG mixtures. In this scenario, a preliminary study of the BERL swirled stabilized burner is carried out in order to understand the impact of blending natural gas with hydrogen on the flame morphology and CO emissions. Preliminary 3D CFD simulations have been run with the purpose to assess the best combination of combustion model (Non Premixed and Partially Premixed Falmelets), turbulence model (Realizable k ɛ and the Reynolds Stress equation model) and chemical kinetic mechanism (GriMech3.0, GriMech 1.2 and Frassoldati). The numerical results of the BERL burner fueled with natural gas have been compared with experimental data in terms of flow patterns, radial temperature profiles, O2, CO and CO2 concentrations. Finally, a 30% hydrogen in natural gas mixture has been considered, keeping fixed the thermal power output of the burner and the global equivalence ratio.

In the present contribution the authors investigate by means of numerical simulations the thermal performance of two geometries of Latent Heat Thermal Energy Storage (LHTES). The numerical model takes into account the mass, momentum and energy equations for the PCM together with an Entalphy-Porosity model for the phase change and a Bussinesq approximation for the buoyancy force. Indeed in such a system the convective motion within the melted PCM plays an important role, as confirmed by several studies. The scope of the research has been the enhancement of heat transfer performance of LHTES increasing the convection by means of modifications on the shape of the PCM enclosure. In particular, in this study two geometries have been considered to investigate the influence of the convective motion on the overall melting time. The first case consists of two concentric cylinders with the axis aligned with the vertical direction, in order to realize an internal heating of the Phase Change Material (PCM) that is confined between the internal and the external cylinder. It is a well-known ”shell-and-tube” configuration, generally adopted in LHTES systems, even in CSP applications. In the second case, the authors propose a simple cylindrical geometry filled with the PCM, with the cylinder axis aligned with the vertical position. Thus, the heated surface corresponds to the external lateral surface of the cylinder. The PCM volume (V) and the net heat transfer surface (A) have been kept constant in the two cases, in order to be able to compare them under the same operative conditions. The tests reveal a sensible difference between the thermal performance of the two proposed solutions. The external heating configuration shows an important enhancement of the convective motion within the PCM that induces a more efficient heat transfer with respect to the standard ”shell-and-tube” configuration. The complete melting time of the PCM with external heating is reduced by about 50%.

Oscillating Water Column (OWC) devices, both the fixed structures and the floating ones, are an important class of Wave Energy Converter (WEC) devices. In this work, we carried out a numerical investigation aiming to give a deep insight into the fluid dynamic interaction between waves and a U-shaped OWC breakwater, focusing on the energy conversion process. The U-OWC breakwater under consideration, represents the full-scale plant installed in the Civitavecchia (near Rome) harbour. The adopted numerical method is based on the solution of the unsteady Reynolds Averaged Navier-Stokes equations (URANS). The water-air interaction is taken into account by means of the Volume Of Fluid (VOF) model. A two-dimensional domain has been adopted to investigate the unsteady flow outside and inside the OWC device. In order to simulate the action of an air turbine of the Wells type, the air chamber has been connected to the atmosphere by means of a porous medium able to reproduce its linear relationship between pressure drop and flow rate of the air turbine. Several simulations have been carried out considering periodic waves of different amplitudes in order to analyze the performance of the plant and, in particular to analyze the resonance with incoming waves, when the U-OWC is expected to absorb more energy. In order to characterize the plant efficiency, we split the energy conversion process into three main steps, 1) the primary conversion from wave energy to hydraulic energy the water discharge flowing inside the U-duct; 2) the secondary conversion from the OWC inlet to the oscillating pneumatic power made available to the turbine and, finally, 3) the turbine mechanical power output. To this purpose, the simulations of three different cases, varying wave period and height, have been carried out to quantify the energy captured by the plant and the fluid dynamic losses both in the water and in the air.

Anthropogenic Greenhouse Gases (GHG) emissions have increased since the pre-industrial era, driven by the economic and population growth. In the last decades, significant efforts have been made to develop cleaner and more efficient technologies able to control GHG emissions. In the field of combustion burners, this commitment strongly relies on the development of new and detailed numerical models, which allow a deep investigation of complex burner performance and a significant reduction of full-scale experimental costs. The knowledge previously acquired on the TEA-C coal burner CFD study is here expanded in the framework of the Be4GreenS project, targeting to the development of a new generation of burners. The new implemented model accounts for the detailed chemical and kinetic characterization of the pulverized coal together with the exact inner volume geometry of the experimental combustion chamber and the actual extension of the heat exchanging and refractory surfaces. In addition, the secondary and tertiary air registers are here numerically investigated. The outcome from the CFD analysis is validated against the experimental data. The NOx formation analysis is also provided.

In this paper a gas-steam combined-cycle, partially fueled by syngas (produced in an embedded downdraft gasifier fed with pomace), is considered. In addition, an auxiliary combustion system is directly fed by ligno-cellulosic biomass. The thermodynamic model of the entire system is developed by means of the Cycle-Tempo software. The gasification process is supposed to occur at ambient pressure and air is used as gasifying agent. An optimization process has been introduced by means of the Design of Experiment ( DoE ) technique. The design variables and their corresponding ranges have been chosen by using a heuristic criterion. The power plant performance is represented by the thermal efficiency, _ η I , the exergetic efficiency, η II , the cost of electricity, COE, and the net return, R net . The DoE technique provided the so-called Pareto barrier, which isolates all the non-dominated solutions.

A NOx Storage Catalyst (NSC) has been studied by means of reactive CFD simulations. In the scenario of automotive pollutant emission reduction, due to the stringent regulation, the detailed description of the chemical and physical phenomena within catalysts represents a key point in order to improve their conversion efficiency. The active part of the catalyst has been simulated as a porous medium. In this zone, surface reactions take place, which are modelled by means of an Arrhenius chemical kinetic approach, involving the Pt and BaO sites on the active surface of the matrix. Actually, two chemical mechanisms are considered, the simplest involves only BaO site, the other one includes both BaO and Ptsites. Both models are validated against data available in the literature and then applied to a real automotive catalyst geometry. Thus, a detailed description of the spatial distribution of the species is provided for both models. Lean condition is simulated in order to check the catalyst behaviour according to experimental results.

This paper focuses on the thermodynamic modelling and parametric optimization of an Organic Rankine Cycle (ORC) which recovers the heat stored in a thermal energy storage (TES). A TES with two molten-salt tanks (one cold and one hot) is selected since it is able to operate in the temperature range useful to recover heat from different sources such as exhaust gas of Externally Fired Gas Turbine (EFGT) or Concentrating Solar Power (CSP) plant, operating in a network for Distributed Generation (DG). The thermal storage facilitates a flexible operation of the power system operating in the network of DG, and in particular allows to compensate the energy fluctuations of heat and power demand, increase the capacity factor of the connected plants, increase the dispatchability of the renewable energy generated and potentially operate in load following mode. The selected ORC is a regenerative cycle with the adoption of a Heat Recovery Vapour Generator (HRVG) that recovers heat from molten salts flowing from the Hot Tank to the Cold Tank of the TES. By considering the properties of molten salt mixtures, a ternary mixture able to operate between 200 and 400 °C is selected. The main ORC parameters, namely the evaporating pressure/temperature and the evaporator/condenser pinch point temperature differences, are selected as variables for the thermodynamic ORC optimization. An automatic optimization procedure is set up by means of a genetic algorithm (GA) coupled with an in-house code for the ORC calculation. Firstly, a mono-objective optimization is carried out for two working fluids of interest (Toluene and R113) by maximization of the cycle thermal efficiency. Afterwards, a multi-objective optimization is carried out for the fluid with the best performance by means of a Non-dominated Sorting Genetic Algorithm (NSGA) in order to evaluate the cycle parameters which maximize the thermal efficiency and minimise the heat exchanger surface areas. Toluene results able to give the best trade-off between efficiency and heat exchanger dimensions for the present application, showing that by with respect to the best efficiency point, the heat exchange area can be reduced by 36% with only a penalty of 1% for the efficiency.

This paper provides the reader with guidelines for the definition of coarse but effective meshes on reduced computational domains in order to accurately evaluate the drop curves and the NPSH3% of centrifugal pumps by means of CFD. The procedure has been validated against experimental data, carried out on single stages of multi-stage centrifugal pumps, and numerical data obtained by a monodimensional model. Thanks to the proposed procedure, without any detriment to the accuracy, a significant computational cost reduction has been experienced with respect to simulations performed on complete stages.

The slip phenomenon consists in the deviation of the fluid fl ow (r elative ve locity ve ctor) wi th re spect to th e blade congruent angles and is mainly due to the finite number of blades. For this reason, slip becomes significant in pumps operating as turbines (PaTs) being characterized by a lower number of blades compared to conventional turbines highlighting a shortcoming of these devices in energy recovery applications. Even though this topic has been widely investigated in the past for centrifugal pumps, it has been often neglected for hydraulic turbine applications. As described in the literature, a counter rotating vortex (known as eddy vortex) develops inside each vane of a rotating machine and its effect can be superimposed to the main flow characteristics. Moreover, the relative vorticity magnitude, which is twice the angular velocity under the hypothesis of inviscid, incompressible and irrotational flow, is constant regardless of the number of vanes. In this work, 3D inviscid steady flow numerical simulations of a purely radial impeller with zero-thickness blades, being designed according to a logarithmic spiral law, have been carried out with the purpose of bringing out the relationship between the flow deviation and the number of blades, neglecting viscous effects which could hinder the inertial ones. The results show a local deviation of the streamline downstream of the trailing edge when the flow is not confined by the blades. The effect of the flow deviation has been also evaluated by calculating the hydraulic performance of the runners. Four different runners have been investigated (with 28, 14, 7 and 3 blades) at their design point and rotating at two different angular velocities. This allowed to correlate the deviation with the inertial effect and to propose a least-squares fitting curve. As shown in previous works, the inclusion of the slip correction factor in 1-D PaT performance prediction models enhances their accuracy.The slip phenomenon consists in the deviation of the fluid fl ow (r elative ve locity ve ctor) wi th re spect to th e blade congruent angles and is mainly due to the finite number of blades. For this reason, slip becomes significant in pumps operating as turbines (PaTs) being characterized by a lower number of blades compared to conventional turbines highlighting a shortcoming of these devices in energy recovery applications. Even though this topic has been widely investigated in the past for centrifugal pumps, it has been often neglected for hydraulic turbine applications. As described in the literature, a counter rotating vortex (known as eddy vortex) develops inside each vane of a rotating machine and its effect can be superimposed to the main flow characteristics. Moreover, the relative vorticity magnitude, which is twice the angular velocity under the hypothesis of inviscid, incompressible and irrotational flow, is constant regardless of the number of vanes. In this work, 3D inviscid steady flow nume...

Nowadays, a great effort is increasingly put by the scientific community into a more sustainable energy management, which requires a higher harvesting of renewable energy sources with respect to conventional ones. In the framework of distributed electricity production, Pumps as Turbines (PaTs), i.e. pumps operated in reverse mode, are becoming more and more tempting, being very cost effective with respect to customized hydro turbines. For instance, Water Distribution Networks (WDNs) are equipped by pressure relief valves (PRVs) in order to regulate flow rates and to reduce leakages. The replacement of PRVs with PaTs could be a feasible practice to achieve both an effective pressure control and a throttling energy recovery. The preliminary identification of specific speed of a pump to be used as a turbine is fundamental in order to find the best suitable solution. However, the insertion of a PaT must consider the variability of water demand and pressure patterns. The hydraulic variability in a water distribution network does not permit to define a unique operating point for a PaT and this aspect is a further obstacle for the functional planning of such a system. In this framework, the present work aims at proposing a methodology to find the more suitable PaT for a specific WDN, starting from the analysis of the pressure and flow rate patterns. The methodology is based on the selection of an existing machine from a pump catalogue. Then, knowing its geometrical information, it is possible to predict the characteristic curve of the pump operating as turbine by using a 1-D performance prediction model. The WDN of a town in the Apulia region (Southern Italy) has been used as a case study, in order to select a PaT useful for throttling energy recovery. Finally, a techno-economic evaluation has been carried out.

Due to the mismatching between the renewable energy source and the energy demand, the energy storage devices have attracted the attention of the scientific community in order to maximize their performance. Several technologies have been developed and applied in laboratory scale and prototypes in the last decades. The energy storage devices can be mainly defined according to the average working temperature, the storage material, and the geometrical configuration. This work is focused on the 2D axisymmetric finite volume multiphase numerical simulations of the fluid flow and heat transfer within a shell-and-tube type latent heat thermal energy storage (LHTES). The effect of the geometrical parameters on the thermal performance of such systems is investigated. The influence of the LHTES shape is highlighted keeping constant the heat exchange area, the total storable heat and the heated surface temperature. Detailed description of the liquid fraction and temperature distribution during the solidification phase are reported. The solidification phase appears strongly influenced by the geometry. The geometries have been chosen according to fixed volume and heat exchange area condition. The ratio between the external and the internal radius (re/ri) has been changed and its effect on the thermal performance of the thermal storage device is considered. Thus, according to the application requirement, particular care should be taken in the design of the shape of the LHTES device.

A novel impeller, designed for double suction centrifugal pumps, has been recently proposed, showing higher performance than the baseline with a back-to-back configuration. The impeller is characterized by a new arrangement of its vanes, which come up alternately on the same circumferential exit actually, doubling the number of blades at the outlet. These characteristics may be helpful to effectively harness energy when the pump is used as a turbine, since the higher number of blades improves the flow guidance at the inlet of the runner and the new shape of the vanes reduces the losses inside the channels. This work aims to quantify the improvement in terms of performance as a PaT of the new design with respect to the baseline. Both configurations have been investigated by means of 3D U-RANS simulations. Furthermore, the rotary stagnation pressure inside the vanes at their best efficiency points and their characteristic curves have been calculated and compared. Eventually, advantages in terms of power coefficient and space saving have been pointed out by scaling the novel geometry.

Nowadays, the increasing energy demand represents a priority issue to be faced on social, economic, political and technical points of view. For a sustainable development, renewable energy sources should be preferred to the conventional ones. In water distribution networks, Pumps as Turbines (PaTs) can represent a cost-effective alternative to conventional turbines for the recovery of the throttling energy. In this framework, a preliminary assessment of the installation of a PaT in the water distribution network of Casamassima, a town in the Apulia region (Southern Italy), has been conducted. A PaT, suitable for this application, has been tested in both direct and reverse modes at the test rig of the Department of Mechanics, Mathematics and Management of the Polytechnic University of Bari. Then, starting from the analysis of the pressure and flow rate patterns during the day and the night, three installation cases have been evaluated and compared in terms of hydraulic energy harvesting and power output useful to supply an electrical charging station.

In the open wind tunnel of the Polytechnic University of Bari a new 3D-printed prototype of a Wells turbine is investigated under steady-state and pulsating flow conditions. The flow rate is modified by changing sinusoidally the frequency of the control drive, hence the rotational speed of the suction fan. The Wells turbine is a scaled prototype designed to operate in a 1:10 scaled model of a REWEC3 breakwater for ocean application. The Wells turbine characteristics are evaluated in terms of torque coefficient and pressure drop coefficient vs. flow coefficient. A delayed onset of stall can be observed, with a clockwise hysteretic loop, when the turbine experiences large sinusoidal variation of the flow coefficient at high mass flow rates. The variation of the turbine performance under dynamic flow conditions is crucial for a correct design of the Wells turbine.

Starting from a previously proposed Integrated Gasification Combined Cycle power plant with an externally fired gas turbine and a bottoming heat recovery steam generator, in this paper a new plant scheme is proposed. The main changes concern, on one hand, a plant layout simplification by removing a regenerative heat exchanger, on the other hand, the replacement of the Water Rankine Cycle with an Organic one. The thermodynamic model of the entire system has been developed by means of the Cycle-Tempo software. The gasification process has been supposed to occur at ambient pressure and air is used as gasifying agent. Moreover, considering the small size (below 1 MW) of this Combined Cycle power plant, the new configuration embodying an Organic Rankine Cycle appears to be more suited for the biomass conversion process even though shows a slightly lower conversion efficiency.

Nowadays hydrogen is gaining more and more attention by Industry, Academia and Politics. Being a carbon free fuel, it is supposed to have a key role in the future energy scenario, especially if produced by renewable sources. The use of mixtures of hydrogen and conventional hydrocarbons in gas turbines is one of the most promising technical solutions for obtaining a sustainable combustion during the transition toward a full decarbonization. For this reason, it is fundamental to investigate the behaviour of fuels enriched with hydrogen in combustion processes. In this work, a lab-scale swirled premixed burner has been investigated by means of a fully 3D URANS approach. Firstly, a numerical simulation with cold flow has been performed to validate the model against experimental data. Then, reactive flow simulations have been performed. Initially, a combustion with 100% methane was considered. Then, a 30% by volume hydrogen blending has been investigated. The partially premixed combustion model has been implemented to take into account the inhomogeneities of the mixture at the chamber inlet. The variation of the flame structure due to the hydrogen enrichment will be described in terms of the temperature and species concentration distributions.

A latent heat storage system for concentrated solar plants (CSP) is numerically examined by means of CFD simulations. This study aims at identifying the convective flows produced within the melted phase by temperature gradients and gravity. Simulations were carried out on experimental devices for applications to high temperature concentrated solar power plants. A shell-and-tube geometry composed by a vertical cylindrical tank, filled by a Phase Change Material (PCM) and an inner steel tube, in which the heat transfer fluid (HTF) flows, from the top to the bottom, is considered. The conjugate heat transfer process is examined by solving the unsteady Navier-Stokes equations for HTF and PCM and conduction for the tube. In order to take into account the buoyancy effects in the PCM tank the Boussinesq approximation is adopted. The results show that the enhanced heat flux, due to natural convective flow, reduce of about 30% the time needed to charge the heat storage. A detailed description of the convective motion in the melted phase and the heat flux distribution between the HTF and PCM are reported. The effect of the mushy zone constant is also investigated. © 2015 Elsevier Ltd.

In the present work three-dimensional steady and unsteady numerical simulations of the flow field and chemical reactions within aNOx Storage Converter (NSC) diesel catalyst have been made. In the first part of the paper, only the flow characteristics within a catalyst have been investigated by mean of a steady three-dimensional Reynolds-Averaged Navier-Stokes approach and a transport equation for each of the incoming chemical species. For flow simulations, the catalyst volume has been split in three zones: inlet, catalytic monolith, treated as porous media, and outlet, medium. The results have been reported in three different working points. Evidences on how the non-uniform flow distribution affects the catalyst efficiency have been described. In the second part, the fluid-dynamic solver has been coupled with a chemical reaction mechanism in order to catch the chemical surface reaction within a NSC catalyst. This coupled model has been validated according to the literature. Volumetric and superficial species concentration have been calculated imposing the site density and the kinetic of the reactions on a substrate Ba/Al2O3. NOx spatial distributions within the catalyst during a dsorption phase are reported. The model represent a reliable tool to investigate in detail the complex flow/chemistry interaction within the modern diesel engine catalysts.