Papers by Giovanna Cavazzini
Techno-economic benefits deriving from optimal scheduling of a Virtual Power Plant: Pumped hydro combined with wind farms
Journal of Energy Storage, 2021
Abstract Wind and solar are renewable sources characterized by a great potential but a variable a... more Abstract Wind and solar are renewable sources characterized by a great potential but a variable and unpredictable nature. Characteristics that provoke mismatch between power supply and demand which in turns are the source of network control issues. Problems manageable with the installation of large-scale energy storage like Pumped Hydro Energy Storage (PHES). To this purpose, the paper presents a techno-economic analysis for assessing the benefits deriving from the hybridization of a seawater PHES (sPHES) plant with an in-operation wind farm. Plants work as a Virtual Power Plant (VPP) instead of two separate unit. The hybridization aims to avoid the unbalances of the wind farm, having negative impact on both the grid and the wind farm owner itself. The unbalances cause unpredictable deviations from the predicted production and, hence, power production fluctuations faced by the grid with curtailments and/or calls in operation of fossil-fuelled power plants. A VPP techno-economic optimization on a daily bases is performed using the ASD-PSO algorithm while the optimization aim is the revenue maximization. Results show that a VPP composed by a sPHES and a wind farm and with a single owner, is able to manage the wind farm production, improving the revenue of 6.8% compared to plants acting separately on the market. The VPP approach is also convenient in the case of a joint venture between the plants owners. But, in this case, the revenue is increased only of 0.4% compared to plants working separately. Finally, results also highlight that, in the Italian electricity market, a sPHES plant alone is not able to generate sufficient revenue to guarantee a reasonable payback time while coupling it with a wind farm increases incomes and working days and avoid cost and grid issues in managing the unpredictable wind farm production.
Growing environmental concerns, and the need for better power balancing and frequency control hav... more Growing environmental concerns, and the need for better power balancing and frequency control have increased attention in renewable energy sources, such as, the reversible pumpturbine which can provide both power generation and energy storage. Pump-turbine operation along the hump-shaped curve can lead to unusual increases in water pressure pulsations, which lead to machine vibrations. Measurements of wall pressure in the stators were performed together with high-speed flow visualizations. Starting from the best efficiency point (BEP) and by decreasing the flowrate, a significant increase of the pressure fluctuations was observed mainly in the wicket gates channels. The analyses in frequency and time-frequency domains showed a rise of low frequency components. High-speed movies revealed a quite uniform flow pattern in the guide vanes channels at the normal operating range, whereas, the flow was highly disturbed by rotating stall passage at part load. The situation was more critical in the dump flow rate range, where backflow and vortices in the guide vanes channels developed during the stall cell passage.
Both calculations and measurements detected the periodic fluctuations at impeller discharge which... more Both calculations and measurements detected the periodic fluctuations at impeller discharge which were found to be coherent from blade to blade and possessed a rich harmonic content. ABSTRACT The objective of the study was the experimental and computational investigation of the unsteady flow in the centrifugal pumps. This paper analysed the effect of the vaneless stator interference on the exit flow field of a radial pump operated in the DIM facility. INTRODUCTION During the last decades several research groups were involved in the aero investigation of unsteady flows in single and multi-stage turbomachine. The unsteadiness generated by stator-rotor interactions were often classified into potential inviscid interactions, viscous effects and shock wave passing.
Indagine Sperimentale dell'Interazione Rotore-Statore in una Pompa Centrifuga
Sustainability, 2021
The drive for sustainable societies with more resilient infrastructure networks has catalyzed int... more The drive for sustainable societies with more resilient infrastructure networks has catalyzed interest in leakage reduction as a subsequent benefit to energy recovery in water distribution systems. Several researchers have conducted studies and piloted successful energy recovery installations in water distribution systems globally. Challenges remain in the determination of the number, location, and optimal control setting of energy recovery devices. The PERRL 2.0 procedure was developed, employing a genetic algorithm through extended period simulations, to identify and optimize the location and size of hydro-turbine installations for energy recovery. This procedure was applied to the water supply system of the town of Stellenbosch, South Africa. Several suitable locations for pressure reduction, with energy recovery installations between 600 and 800 kWh/day were identified, with the potential to also reduce leakage in the system by 2 to 4%. Coupling the energy recovery installations...
Lagrangian Analysis of Unsteady Partial Cavitating Flow Around a Three-Dimensional Hydrofoil
Journal of Fluids Engineering, 2021
This study employs an incompressible homogeneous flow framework with a transport-equation-based c... more This study employs an incompressible homogeneous flow framework with a transport-equation-based cavitation model and shear stress transport turbulence model to successfully reproduce the unsteady cavitating flow around a three-dimensional hydrofoil. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 23 ms. By monitoring the motions of the seeding trackers, growth-up of attached cavity and dynamic evolution of U-type cavity are clearly displayed, which indicating the trackers could serve as an effective tool to visualize the cavitating field. Repelling Lagrangian coherent structure (RLCS) is so complex that abundant flow patterns are highlighted, reflecting the intricacy of cavity development. The formation of cloud cavities is clearly characterized by the attracting Lagrangian coherent structure (ALCS), where bumbling ...
Water, 2020
Excess pressure within water distribution systems not only increases the risk for water losses th... more Excess pressure within water distribution systems not only increases the risk for water losses through leakages but provides the potential for harnessing excess energy through the installation of energy recovery devices, such as turbines or pump-as-turbines. The effect of pressure management on leakage reduction in a system has been well documented, and the potential for pressure management through energy recovery devices has seen a growth in popularity over the past decade. Over the past 2 years, the effect of energy recovery on leakage reduction has started to enter the conversation. With the theoretical potential known, researchers have started to focus on the location of energy recovery devices within water supply and distribution systems and the optimization thereof in terms of specific installation objectives. Due to the instrumental role that both the operating pressure and flow rate plays on both leakage and potential energy, daily variation and fluctuations of these paramet...
A new generation of small hydro and pumped-hydro power plants: Advances and future challenges
Renewable and Sustainable Energy Reviews, 2014
Hydropower is not only a renewable and sustainable energy source, but its flexibility and storage... more Hydropower is not only a renewable and sustainable energy source, but its flexibility and storage capacity also makes it possible to improve grid stability and to support the deployment of other intermittent renewable energy sources such as wind and solar power. As a result, a renewed interest in pumped-hydro energy storage plants (PHES) and a huge demand for the rehabilitation of old small hydropower plants are emerging globally.
Using splitter blades to improve suction performance of centrifugal impeller pumps
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2014
A comparison between centrifugal impeller pumps with and without splitter blades in terms of suct... more A comparison between centrifugal impeller pumps with and without splitter blades in terms of suction performance is presented by experimental tests and numerical analyses. The design of both pumps was carried out by preserving the impeller meridional shape, number of blades, and volute casing. Blade shapes were obtained by adopting a 1D inverse design method. The same blade loading distribution was assumed for the full blades of both impellers, while the loading distribution of the splitter blades was modified until a close matching between the two head-capacity curves was achieved. The fulfilment of this performance requirement and the use of the same number of blades were needed to describe accurately the role played by the splitter blades in cavitation inception and development. Differently from other experimental comparisons, where previous requirements were not met, a noticeable improvement in suction performance was found at large flow rates but not at partial ones, where a sm...
Optimal Design and Management of a Hybrid Photovoltaic-Pump Hydro Energy Storage System
Volume 2: Dynamics, Vibration and Control; Energy; Fluids Engineering; Micro and Nano Manufacturing, 2014
The exploitation of renewable sources is an opportunity to increase the number of people who have... more The exploitation of renewable sources is an opportunity to increase the number of people who have access to electricity. To assure better living conditions, the free and simple access to water is another fundamental key point in many developing countries. Stand-alone photovoltaic pumping systems are often installed in remote areas where the grid is not available: they are used for irrigation and/or other local water needs and can supply also electricity to small consumers. In this paper a system aimed at supplying electricity and water to an isolated small village has been studied. Ground water is pumped into a storage reservoir and can be used both for irrigation and domestic use. The system is composed by a photovoltaic plant, a pump as turbine (PAT), a diesel internal combustion engine for integration purposes and a battery storage. By means of an optimization model based on the Particle Swarm Theory, the size of the system and its managing strategy have been optimized in order to fulfill the requirement of the users, to improve the system efficiency and minimize the overall costs. The most suitable hourly-based profile of the flow rates of a pump-as-turbine as well was found.© 2014 ASME
Pressure instabilities in a vaned centrifugal pump
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2011
This article reports the acoustic and fluid-dynamical analyses of large-scale instabilities in a ... more This article reports the acoustic and fluid-dynamical analyses of large-scale instabilities in a vaned centrifugal pump. The unsteady pressure fields at full/part load were measured by dynamic piezoresistive transducers placed at the impeller discharge and on an instrumented diffuser vane. To spectrally characterize the inception and the evolution of the unsteady phenomena, spectral analyses of the pressure signals were carried out both in frequency and time–frequency domains. Numerical analyses were carried out on the same pump with the help of the commercial code CFX. All the computations were performed using the unsteady ‘transient’ model with a time step corresponding to about 1° of the impeller rotation. The turbulence was modelled by the detached eddy simulation model. Numerical pressure signals were compared with the experimental ones to verify the development of the same pressure instabilities. The unsteady numerical flow fields were analysed to study the fluid-dynamical evo...
Influence of the bucket geometry on the Pelton performance
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2013
The increasing share of hydropower in world electricity production requires the development of st... more The increasing share of hydropower in world electricity production requires the development of standardized and optimized design procedures leading to increasingly higher efficiency values. To date, despite a certain amount of support from computational fluid dynamics, Pelton turbines are still characterized by semiempirical design criteria that do not make it possible to optimize the jet–bucket interaction in order to maximize turbine performance. Based on an analysis of particle flow tracks, this paper presents a hybrid Eulerian–Lagrangian method to investigate the influence of bucket geometry on the Pelton efficiency at two different operating conditions. Jet–bucket interaction was numerically analyzed by means of a traditional mesh-based numerical approach, using a transient multi-phase homogeneous model. Subsequently, the numerical results were integrated using a predictor–corrector algorithm, combining a fourth order Adams-Bashforth method as predictor and a fourth order Adams...
Numerical characterization of pressure instabilities in a vaned centrifugal pump under partload condition
IOP Conference Series: Materials Science and Engineering, 2013
ABSTRACT This paper studies the hysteresis/saddle phenomena of the head-drop in a scaled model pu... more ABSTRACT This paper studies the hysteresis/saddle phenomena of the head-drop in a scaled model pump turbine using CFD methods. This lag was induced by complicated flow patterns, which influenced the reliability of rotating machine that was analysed by a commercial code with DES model for computing turbulence. Analyses were carried out on the pressure signals both in frequency and time-frequency domains at full and part load conditions. The results highlighted the remarkable interaction between the unsteady structures in diffuser and return.
Experiments in Fluids, 2011
This paper presents an experimental analysis of the unsteady phenomena developing in a vaneless d... more This paper presents an experimental analysis of the unsteady phenomena developing in a vaneless diffuser of a radial flow pump. Partial flow operating conditions were investigated using 2D/3C high repetition rate PIV, coupled with unsteady pressure transducers. Pressure measurements were acquired on the shroud wall of the vaneless diffuser and on the suction pipe of the pump, whereas PIV flow fields were determined on three different heights in the hub to shroud direction, inside the diffuser. The classical Fourier analysis was applied to both pressure signals to identify the spectral characteristics of the developing instabilities, and the high-order spectral analysis was exploited to investigate possible non-linear interaction mechanisms between different unsteady structures. A dedicated PIV averaging procedure was developed and applied to the PIV flow fields so as to capture and visualize the topology of the spectrally identified phenomena. The influence of these phenomena on the diffuser efficiency was also investigated.
Energy Conversion and Management, 2011
This paper presents a method for the capacity sizing of a small hydropower plant on the basis of ... more This paper presents a method for the capacity sizing of a small hydropower plant on the basis of technoeconomical analyses of the flow duration curve. Seven technical and economical parameters were considered: the turbine type, the turbine dimensions, the annual energy production, the maximum installation height to avoid cavitation inception, the machine cost, the Net Present Value (NPV) and the Internal Rate of Return (IRR). A proper model was proposed to study the effects of the design operating conditions on these parameters. The model, applied to the flow duration curve, allowed to analyse the feasibility, the profitability and the performance of the plant in the available flowing range of the site. To verify the effectiveness of the proposed method, three sites having different flow duration curves were analysed.
Analysis of Unsteady Flow Velocity Fields Inside the Impeller of a Radial Flow Pump: PIV Measurements and Numerical Calculation Comparisons
ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011, 2011
ABSTRACT PIV measurements were performed at mid hub to shroud section inside the impeller of a va... more ABSTRACT PIV measurements were performed at mid hub to shroud section inside the impeller of a vaned diffuser pump model working with air. The measurements were restricted to the outlet section of the impeller where the diffuser blades interacted with the impeller flow. Each PIV measuring plane was related to one particular impeller blade to blade channel and analysed according to different relative positions of the vaned diffuser. Two frame change models were considered: the so-called frozen rotor approach for different impeller passage positions relative to the vaned diffuser and a fully unsteady calculation of the whole pump. Comparisons between numerical and experimental results are presented and discussed for a specific mass flow rate corresponding to an off-design point for the impeller and a design point for the vaned diffuser.
Fluid Leakage Effect on Analysis of a Vaned Diffuser of Shf Pump
ABSTRACT The paper presents the results of numerical analysis on the local and global internal fl... more ABSTRACT The paper presents the results of numerical analysis on the local and global internal flow behaviour at the inlet of the vaned diffuser of a radial flow pump model, taking into account the effect of fluid leakages for various flow rates and a given rotation of speed. For each flow rate, numerical calculations were performed both with two different boundary conditions: -Without any leakage effects. -With calculated leakage effects The numerical simulations were realized with the two commercial codes: i-Star CCM+ 8.02.011 (at LML), ii-CFX 10.0 (at University of Padova). RANS unsteady calculations, with a k- RNG model were performed with Star CCM+. Fully unsteady calculations of the whole pump were done with CFX with DES turbulentmethod (Cavazzini [1]). For each flow rate, different angular positions of the impeller are considered. First part of the paper shows global comparisons between numerical and experimental results already presented in ref [2-3], for which the effects of fluid leakage due to the gap between the rotating and fixed part of the pump model were found to be interesting to be analysed. Second part is devoted to the local comparisons of flow structures at the inlet section of the diffuser, without and with leakages only with Star CCM+. Leakage modeling Two sources of fluid leakage occur (Fig. 1): -The first one between the inlet and the impeller (leakage1) -The second one between the impeller and the diffuser (leakage 2) Fig.1 Numerical model The two fluid leakages are taken account with the two codes: -In CFX (Fig.2) , the seal systems both at the impeller inlet and outlet were modelled (At the labyrinth of the seal system close to the impeller inlet the mass flow rates determined from the experimental data was prescribed. At the impeller outlet the leakage mass flow rate was controlled by the known experimental pressure in the large plenums upstream the labyrinth).
Uncertainty Quantification and Missing Data for Turbomachinery With Probabilistic Equivalence and Arbitrary Polynomial Chaos, Applied to Scroll Compressors
This work presents a framework for predicting unknown input distributions for turbomachinery appl... more This work presents a framework for predicting unknown input distributions for turbomachinery applications starting from scarce experimental measurements. The problem is relevant to turbomachinery where important parameters are obtained using indirect measurements. In this paper a scroll compressor is used as example but the suggested framework is completely general and can be used to infer missing data on material composition (carbon fiber properties, laser melted specimens for additive manufacturing etc) or input data (such as the turbine inlet temperature). Scroll compressors are small devices with a very complex geometry that is difficult to measure. Moreover these compressors are highly sensitive to manufacturing errors and clearances. For these reasons we have chosen this example as an ideal candidate to prove the effectiveness of the framework. An input probability distribution for the scroll height is recovered based on a scarce, synthetic data set. The scroll height is used ...
The paper presents the analysis of the performance and the internal flow behaviour in the vaned d... more The paper presents the analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV technique, pressure probe traverses and numerical simulations. PIV measurements have been performed at different heights inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, PIV measurements have been made for different angular positions of the impeller. For each angular position, instantaneous velocities charts have been obtained on two simultaneous views, which allows, firstly, to cover the space between the leading edge of the impeller and the diffuser throat and secondly, to get a rather good evaluation of phase averaged velocity charts and "fluctuating rates ". Probe traverses have also been performed using a 3 holes pressure probe from hub to shroud diffuser width at different radial locations in between the two diffuser geometrical throats. The numerical simulations...
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Papers by Giovanna Cavazzini