Emanuele Quaranta- PhD
- Project Officer Scientific Research at European Commission
Emanuele Quaranta
- PhD
- Project Officer Scientific Research at European Commission
About
88
Publications
78,493
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,868
Citations
Introduction
Current institution
Additional affiliations
July 2019 - July 2019
January 2017 - July 2019
October 2015 - present
Education
January 2014 - December 2016
October 2011 - July 2013
September 2008 - October 2011
Publications
Publications (88)
In low head sites and at low discharges, water wheels can be considered among the most convenient hydropower converters to install. The scope of this work is to improve the performance of an existing breastshot water wheel changing the blades shape, using Computational Fluid Dynamic (CFD) simulations. Three optimal profiles are investigated: the pr...
Il presente documento include la relazione tecnico-descrittiva del progetto relativo a un impianto per l’utilizzo della risorsa idrica ai fini della produzione di energia idroelettrica sul fiume Tione delle Valli nel comune di Villimpenta (MN).
Nella parte finale viene trattata la progettazione idraulica della ruota idraulica, le verifiche idrauli...
MHP is a renewable energy technology that transforms the kinetic energy of flowing water into electrical power. With the rising interest in sustainable energy, there is a potential for enhanced integration of micro-hydropower (MHP) with water distribution networks (WDNs) for energy generation and pressure regulation. The deployment of this technolo...
The six Western Balkan countries (WB6), which include Albania, Bosnia and Herzegovina, Kosovo, Montenegro, North Macedonia, and Serbia, are in a critical phase of their development and face various economic, political and environmental challenges. Political uncertainties, economic imbalances, and institutional weaknesses have hindered their progres...
This study examines recent energy transition policies and the conceptual framework of energy justice, emphasizing the role of hydropower, in ensuring the equitable distribution of energy services and burdens. The analysis focuses on the EU’s energy mix, highlighting the capacity of hydropower and its impact on energy justice, and examines the relat...
Water storage and water reservoirs are key to the Water-Energy-Food-Ecosystem (WEFE) nexus, especially when they store water for hydropower. However, there is not a uniform view on existing energy storage capacity and on the potential for future deployment of pumped-storage hydropower (PSH) and conventional reservoir storage hydropower (RSHP) acros...
FREE DOWNLOAD here
https://publications.jrc.ec.europa.eu/repository/handle/JRC139225
------------------------------------------------------------------------------------------------------------------------------------
///
The energy crisis has highlighted the key role of hydropower in providing grid stability and dispatchable generation. Pumped-...
Nature-based solutions (NBSs) and urban greening are well-established strategies used in various planning and policy instruments to promote the sustainability of cities and mitigate the effects of climate changes. Within this context, green roofs are emerging as an effective NBS in urban areas where space is often limited. The estimation of green r...
The green energy transition and its boost to the deployment of renewable energy can offer a unique opportunity for rural areas to benefit from their natural resources. The present study aims to provide a quantitative assessment of the technical potential of renewable energy sources in the EU’s rural areas, focusing on solar, wind and hydropower. Th...
Soil erosion is both a major driver and consequence of land degradation with significant on-site and off-site costs which are critical to understand and quantify. One major cost of soil erosion originates from the sediments delivered to aquatic systems (e.g., rivers, lakes, and seas), which may generate a broad array of environmental and economic i...
Very low head hydropower is a sector in rapid expansion due to the untapped potential in hydraulic infrastructures and at non-powered weirs. However, the space availability is often a limitation. In this contribution, numerical simulations are performed to improve the performance of a double-regulated low head Kaplan turbine, at a head difference o...
FREE DOWNLOAD the 2024 version HERE
https://publications.jrc.ec.europa.eu/repository/handle/JRC139225
------------------------------------------------------------------------------------------------------------------------------------New developments in the renewable and clean energy sector came on the back of the energy crisis, brought on by the...
More information here: https://setis.ec.europa.eu/hydropower-and-pumped-hydropower-storage-european-union-0_en
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
The installed hydro capacity in the EU is 152 GW, contributing to about 12 per cent of the EU’s net elec...
Hydropower structures are typically made of materials that are available in most parts of the world, such as steel, concrete, and—to a lesser extent—copper, and do not use critical materials. The weight of hydropower structures is an important input data, as it is used to perform Life Cycle Assessments and to estimate the cost and the economic valu...
The increasing utilization of wind and solar power sources to lower CO2 emissions in the electric sector is causing a growing disparity between electricity supply and demand. Consequently, there is a heightened interest in affordable energy storage solutions to address this issue. Pumped Hydropower Storage (PHS) emerges as a promising option, capab...
Very low head (VLH) turbines are axial turbines with the capability of extracting power at a high efficiency of over 80% from very low heads (less than 4.5 m) and high flow rates of up to 30 m3/s per unit, with a significant reduction in construction costs, compared to conventional hydropower turbines. At no-load conditions, the turbine reaches its...
Microgrids are decentralized power production systems, where the energy production and consumption are very close to each other. Microgrids generally exploit renewable energy sources, encountering a problem of storage, as the power production from solar and wind is intermittent. This research presents a new integrated methodology and discusses a co...
According to the WSHPDR 2022, the global installed SHP capacity for plants of ≤10 MW is estimated at approximately 79.0 GW
and the total known potential for SHP ≤10 MW (including developed capacities) is estimated at 221.7 GW. Thus, despite the
appeal and benefits of SHP solutions, much of the world’s SHP potential remains untapped (64 per cent). I...
: There has been an ever-increasing demand for energy from the past decades. Renewable energy technologies play a major role in satisfying the energy demand as well as in a decreased CO2 emissions. Solar and Wind energies are the major upcoming technologies in renewable energies. Decentralized power production is a system where the energy productio...
During the Digital Decade, the European Union (EU) is facing two important challenges: the green (and energy) transition and the digital transition, which are interconnected with one another. These transitions are of high relevance in the water sector, as water is always becoming more vulnerable to climate change (e.g., droughts and floods) and hum...
In the hydropower sector, the weight of electro-mechanical equipment is an important input data. During the design stage, it allows to estimate material cost, to perform Life Cycle Assessments and to consider adequate load factors on the supporting structures. At the end of the lifetime, in case of dismantling or retrofitting, the estimation of the...
Hydropower globally represents the main source of renewable energy, and provides several benefits, e.g., water storage and flexibility; on the other hand, it may cause significant impacts on the environment. Hence sustainable hydropower needs to achieve a balance between electricity generation, impacts on ecosystems and benefits on society, support...
We present a preliminary estimation of the gross potential of hydropower that can be harnessed from drainpipes of residential buildings in the European Union (EU) and UK. Aggregated data available from the Copernicus Urban Atlas website is used to determine the building height of 25 major European cities that, combined with rainfall data relative t...
![Oil consumption in hydropower units [11].](publication/367023208/figure/tbl1/AS:11431281112765167@1673529749674/Oil-consumption-in-hydropower-units-11_Q320.jpg)
Lubricant oil is used in hydropower units to minimize friction, improving the turbine efficiency and reducing the wear. However, oil production is a pollutant process, while eventual spills may affect water quality and damage freshwater ecosystems. In this study, the lubricant oil consumption of the European hydropower fleet was estimated (consider...
There is a hidden energy potential in existing hydropower plants, and this was assessed for Europe. • Heat recovery from generators can reach 5 TWh/y, and can be used either for powerhouse heating or for district heating. • The harvesting of the tailrace water energy can increase European generation by 0.43 %, equivalent to thousands of micro hydro...
FREE DOWNLOAD the 2024 version HERE
https://publications.jrc.ec.europa.eu/repository/handle/JRC139225
------------------------------------------------------------------------------------------------------------------------------------
Hydropower, with its 1,360 GW of global installed capacity and 4,260 TWh/year in 2021, is currently the giant of...
The objective of this report is to establish a scoreboard to assess the EU’s competitive position in carbon-neutral solutions across important industrial ecosystems related to the energy transition. The 2021 annual report of the European Climate Neutral Industry Competitiveness Scoreboard (CIndECS) provides an assessment of 20 climate-neutral solut...
The Banki turbine is a crossflow turbine suitable for sites with heads below 200 m and flow rates below 10 m³/s, with maximum efficiency around 80%. Its flexible operation and easy manufacturing make it a suitable hydropower technology for different geographic areas and hydraulic contexts. However, the design procedure proposed in literature is not...
Combined sewer overflows (CSOs) may represent a significant source of pollution, but they are difficult to quantify at a large scale (e.g. regional or national), due to a lack of accessible data. In the present study, we use a large scale, 6-parameter, lumped hydrological model to perform a screening level assessment of different CSO management sce...
The development of a hydropower facility has, in nearly all cases, some impact on natural river flows and the wider environment. This impact often includes the effect on fish, most notably curtailment of migration routes and changes to their natural habitat and ecosystem services fish is dependent on.
The general relationship between fish and hydro...
The Very Low Head turbine (VLHT) is an axial flow turbine developed for heads below 4.5 m and flow rates up to 30 m³/s. In this work, the state of the art, the technological advancements and the scientific gaps were discussed and generalized, with a special focus on design, ecological behavior, costs, performance at different flows, heads and rotat...
Study region
Combined Sewer Overflows (CSO) of 671 Functional Urban Areas (FUAs) throughout the European Union + UK (EU28), representing almost half of the EU28 population.
Study focus
CSO loads can be quantified at the local scale through measurements, or with calibrated hydrological models. However, they are difficult to quantify at a large scal...
The problem of ingested bodies and sediments in hydropower plants is one of the current research trends in the hydropower sector, since sediments can generate several problems such as abrasion, increased maintenance costs, reduction of storage capacity. However, most researches focus on the effects of fine sediments rather than on the effects of co...
Small hydropower plants (installed power below 10 MW) are generally considered less impacting than larger plants, and this has stimulated their rapid spread, with a developing potential that is not exhausted yet. However, since they can cause environmental impacts, especially in case of cascade installations, there is the need to operate them in a...
The powering of nonpowered dams and barriers and the modernization of the aged hydropower plants are emerging practices of hydropower development, due to the minimal impacts on ecosystems and the fact that most of the infrastructure is already in place. The modernization of existing plants also allows to increase safety, resilience to climate chang...
The noise generated by free surface hydropower machines, e.g., water wheels, has led to complaints and to restrictions in their operation in urban areas. This problem generally occurs when water wheels are not well designed and are installed without expertise. Despite the relevance of the problem, and the growing interest in the use of water wheels...
The Pelton turbine is the most widespread and efficient impulse hydropower turbine. The Pelton casing is a static, but key component: the internal hydrodynamic phenomena affect the performance of the hydropower plant, the vibration of the equipment and water quality (dissolved oxygen downstream). However, the literature information is very fragment...
In this chapter, some innovative case studies in the hydropower sector are discussed , highlighting how novel technologies and operational practices can make it more efficient, sustainable and cost-effective. Some practices to reduce hydropeaking effects, improving fish habitat, and turbines with higher survival rate, allowing to bring fish surviva...
Lifting water is crucial to irrigate agricultural terraces in the Mediterranean region. But the energy demand and emissions of modern forms of water pumping have increased, while many traditional water wheels, which lift water at zero direct emissions, have been abandoned. We explored the state of preservation and the potential for the deployment o...
Environmentally enhanced turbines (EETs) have gained attention in the past two decades in order to reduce environmental impacts of hydropower plants on fish communities and on water quality. In this mini-review the main EETs are discussed, focusing on the Alden and Minimum Gap Runner turbines to reduce fish injury and on self-aerating and self/free...
Environmentally enhanced turbines (EETs) have gained attention in the past two decades in order to reduce environmental impacts of hydropower plants on fish communities and on water quality. In this mini-review the main EETs are discussed, focusing on the Alden and Minimum Gap Runner turbines to reduce fish injury and on self-aerating and self/free...
About 50% of all hydropower plants (HPPs) worldwide were originally commissioned more than 40 years ago, so that the advanced age of the fleet is a major concern across all continents, and especially in Europe. The modernization of HPPs can generate several benefits in terms of generation, flexibility, safety, operation, and may have neutral or eve...
The hydropower sector is currently experiencing several technological developments. New technologies and sustainable practices are emerging to make hydropower more flexible and eco-friendly. Novel materials have also been recently developed to increase performance, durability, and reliability; however, no systematic discussions can be found in the...
Purpose
The paper presents a techno-economic analysis of the electromechanical equipment of traditional vertical axis water mills (VAWMs) to help investors, mill owners and engineers to preliminary estimate related benefits and costs of a VAWM repowering.
Design/methodology/approach
Two sustainable repowering solutions were examined with the addit...
The MesoHABitat SImulation Model (MesoHABSIM) is the preferred method to calculate spatio-temporal variation in the fish habitat availability in Italian rivers. With the aim of improving the applicability of the MesoHABSIM approach in the Italian territory, we carried out a systematic review of physical habitat preferences for 31 freshwater fish sp...
The Indus basin has a large hydropower untapped potential for electricity generation and to regulate the Indus river flow, which could reduce flooding events and provide water supply during drought periods. In this paper, a computational module is developed to localize potential sites for hydropower generation and seasonal pumped hydropower storage...
Introduction Hydropower development is a key renewable source to reach the European climate targets (2030 climate and energy framework, the 2050 long-term strategy) and it is encouraged by the Renewable Energy Directive 2009/28/EC (and its recast 2018 /2001/EU also known as RED II). Hydropower enables energy storage and stabilization of the electri...
Urban greening is an effective mitigation option for climate change in urban areas. In this contribution, a European Union (EU)-wide assessment is presented to quantify the benefits of urban greening in terms of availability of green water, reduction of cooling costs and CO 2 sequestration from the atmosphere, for different climatic scenarios. Resu...
Study region
This study considers daily time series of 14 years of weather parameters (temperature, wind speed, rainfall, vapor pressure and radiation) for 671 functional urban areas (FUA) across Europe, from a latitude of 35° (Cyprus) to 65° (Finland).
Study focus
Quantification of urban greening effects usually requires relatively complex and in...
Water wheels are low head hydropower converters considered fish friendly, although their ecological behavior has not been scientifically assessed. The results presented in the available reports are not generalized (thus hardly applicable in engineering applications), and they have not been performed at different hydraulic conditions or wheel charac...
Hydropower is a sector in rapid development, with new technologies and best practices aimed at making it more sustainable and with the required flexibility to support the spread of wind and solar plant and the frequent instabilities of the electric grid. In this review, study cases and technologies are discussed in this context, with focus on flexi...
Hydropower remains a key renewable energy source in the pursuit of the decarbonization of the economy, although the relatively high potential impact of the hydro-morphological alterations it may cause poses significant concerns for aquatic ecosystems. In the last years, new technologies and practices have been increasingly adopted to minimize the i...
The Deriaz hydraulic machine is a diagonal pump-turbine; it has adjustable blades and can be used in pump mode. In this paper, a dimensional analysis was performed by applying the Buckingham-π-theorem to achieve an equation to estimate the design rotational speed of Deriaz turbines. The equation was calibrated on a dataset of 19 full scale cases, w...
![FIGURE 8 Concept of the HPM. Source: University of South Hampton [15].](profile/Emanuele-Quaranta/publication/343587713/figure/fig1/AS:923434557136896@1597175363901/Concept-of-the-HPM-Source-University-of-South-Hampton-15_Q320.jpg)
In recent years, renewable energy sources have increasingly contributed to global energy
production with a total supplement of around 2,200 GW (approximately 34% of global
installed power capacity). Hydropower is the largest contributor, with approximately 1,200
GW (approximately 18% of global installed power capacity). It is hence a key energy sou...
Overshot water wheels are hydropower converters generally employed for head differences up to 6 m and maximum flow rates of 150−200 L=s per meter width. The maximum hydraulic efficiency (80%-85%) is constant for rotational speeds below the critical speed, whereas the efficiency linearly decreases at higher rotational speeds due to the increase of w...
Hydropower is the most developed renewable energy technology. It has evolved over hundreds of years, with the highest growth in the Twentieth
century. Some technologies are continuously improving, while others have been forgotten. Four emerging hydropower turbines developed in the
past, but forgotten in the last century, are here presented: water w...
Water wheels are hydraulic machines that employ the water’s weight to rotate. Because of their large diameter, the rotational speeds range from 2 to 10 revolutions per minute. Such conditions require ex-pensive power take off systems. For this paper, a wa-ter wheel with an innovative power transmission was tested, showing maximum global efficiency...
A rotary hydrostatic pressure machine (RHPM) is a hydropower converter for very low head applications (less than 2.5 m). An RHPM can be installed in straight canals, because its wheel can generate a hydraulic head as a result of the created dam effect. Some new experimental results on an RHPM are presented in this paper. Because of the asymmetric s...
KEY POINTS Artificial Vegetation Patches (VP) can be used for the design of fish passes. The drag coefficient of VP depends on the patch solidity (SVF). The drag coefficient vs SVF is explained by bleeding effects. RANS-based CFD allows for a satisfactory prediction of VP drag.
The rotational speed estimation of Francis and Kaplan turbines is of primary importance in the design of hydropower plants. However, most rotational speed equations were conceived for power outputs higher than 1 MW, i.e., for heads typically higher than 10 m for Kaplan turbines and 50 m for Francis turbines. Therefore, the accuracy of these equatio...
Undershot water wheels are hydropower converters for head differences between 0.5 and 1.5 m. The Zuppinger and Sagebien types are the most used and efficient. Optimal rotational speeds depend on the head difference and on the flow rate: hence, in variable flow rate applications, the variable rotational speed is needed to optimize the performance, r...
The paper reviews recent research and development activities in the field of hydropower technology. It covers emerging and advanced technologies to mitigate flow instabilities (active and passive approach) as well as emerging magneto-rheological control techniques. Recent research findings on flow instabilities are also presented , especially conce...
Vertical slot fishways (VSFs) are the most efficient and least selective typology of technical fish passage, due to their ability to remain effective even when significant upstream and/or downstream water level fluctuations occur. Fishway construction costs can be reduced by increasing its bed slope, but this affects the flow field inside the pools...
Buoyancy forces can be found in several hydraulic
phenomena, and they are the driving force in the most
of wave energy converter power plants. In this work
a theoretical model and numerical simulations were
presented to estimate the performance of a new buoyancy driven turbine, finding a maximum hydraulic
theoretical efficiency of up to 77%.
![Fig. 2. Historic representations of gravity water wheels [49]: (a) low...](profile/Roberto-Revelli/publication/327551766/figure/fig1/AS:669595996282882@1536655534209/Historic-representations-of-gravity-water-wheels-49-a-low-breastshot-undershot-b_Q320.jpg)
![Fig. 3. Historic pictures of a Sagebien water wheel [83] and a...](profile/Roberto-Revelli/publication/327551766/figure/fig2/AS:669595996270595@1536655534258/Historic-pictures-of-a-Sagebien-water-wheel-83-and-a-Zuppinger-water-wheel-74_Q320.jpg)
![Fig. 6. The number of blades proposed by Pacinotti [54], Weisbach [48]...](profile/Roberto-Revelli/publication/327551766/figure/fig5/AS:669595996286981@1536655534869/The-number-of-blades-proposed-by-Pacinotti-54-Weisbach-48-and-Cullen-55-as-a_Q320.jpg)
Nowadays, due to the need for clean energy and sustainable electricity production, hydropower plays a central role in satisfying the energy demand. Particularly, use of low head micro hydropower plants is spreading worldwide, due to their low payback periods and good environmental sustainability. Gravity water wheels are micro hydropower converters...
Water wheels were the earliest hydraulic machines used in antiquity to convert water energy into mechanical one. Due to their simple installation, low maintenance costs, and thanks to the possibility to use local manpower and material for their construction, nowadays water wheels are again used as energy supply, especially in remote localities and...
In rivers and at old mill sites there is a substantial amount of very low-head hydropower with head differences from 0.3 to 1.5 m. Much of this potential is unused since in these conditions modern hydropower technology is not cost effective. In the mid-nineteenth century, the Sagebien and Zuppinger wheels were developed for such situations. Recent...
Sagebien and Zuppinger undershot water wheels are hydropower converters for head differences between 0.3-1.5 m. Today, because of the renewed demand for micro hydropower utilisation, these undershot low-head water wheels may offer an attractive solution. In this paper, comparative model tests at approximately 1:10 scale are reported. The Sagebien w...
Fishways are hydraulic structures that allow passage of fish across obstructions in rivers. Vertical slot fishways—VSFs—are considered the most efficient and least selective type of technical fishway solutions, especially due to their ability to remain effective even when significant upstream and/or downstream water level fluctuations occur. The sc...
At low head sites and at low discharges, water wheels can be considered among the most convenient hydropower converters to install. The aim of this work is to improve the performance of an existing breastshot water wheel by changing the blade shape using computational fluid dynamic (CFD) simulations. Three optimal profiles are investigated: the pro...
In low head sites and at low discharges, water wheels can be considered among the most convenient hydropower converters to install. The scope of this work is to improve the performance of an existing breastshot water wheel changing the blades shape, using Computational Fluid Dynamic (CFD) simulations. Three optimal profiles are investigated: the pr...
In low head sites and at low discharges, water wheels can be considered among the most convenient hydropower converters to install. The scope of this work is to improve the performance of an existing breastshot water wheel changing the blades shape, using Computational Fluid Dynamic (CFD) simulations. Three optimal profiles are investigated: the pr...
Breastshot water wheels are gravity hydraulic machines employed in low head sites. The scope of this work is to test the performance of a breastshot water wheel with two geometric inflow configurations: a sluice gate at different openings and two vertical overflow weirs. With the sluice gate, the maximum efficiency of the plant is 75%, constant ove...
Breastshot water wheels are gravity hydraulic machines employed in low head sites. The scope of this work is to test the performance of a breastshot water wheel with two geometric inflow configurations: a sluice gate at different openings and two vertical overflow weirs. With the sluice gate, the maximum efficiency of the plant is 75%, constant ove...
- Vertical slot fishways are hydraulic structures that allow fish to pass over an obstacle. Several experimental tests have been performed, but fewer numerical simulations have been explored.
- The standard design of a vertical slot fishway and a modified version were investigated using CFD simulations, in order to simulate the turbulent flow field...
- Vertical slot fishways are hydraulic structures that allow fish to pass over an obstacle. Several experimental tests have been performed, but fewer numerical simulations have been explored.
- The standard design of a vertical slot fishway and a modified version were investigated using CFD simulations, in order to simulate the turbulent flow field...
Thanks to their efficiency and simplicity of contruction, breastshot water wheels represent an attractive low head hydropower converter. In this work, a breastshot wheel is investigated by numerical simulations, and the results are validated with experimental tests. The average discrepancy between the numerical shaft torque and the experimental tor...
Water wheels can be efficient hydropower converters at low heads and low discharges. The paper presents the results of a study of a breastshot water wheel in a laboratory experimental channel. The obtained data show that breastshot water wheels can reach a maximum efficiency of about 75%, at a rotational velocity which is about 60% of the runaway v...
Questions
Question (1)
There is a micro Kaplan hydro plant:
Flow rate: 0.58 mc/s
Head: 4.85 m
RPM: 625
Max electrical power: 16.5 kW
Generator+gearbox efficiency: 0.89
Maximum Turbine efficiency: 0.67
Draft tube: vertical/conical, 1.5 m high
The problem is the decrease in electrical power (measured during operation) with the time up to an asymptotic value, although all the external conditions (head, flow rate, rpm, blades configurations) remain constant.
I summarize here better, by using a picture (in attach). The picture depicts the power in kW versus the time in minutes.
Let's suppose that the turbine is switched off. Then it is switched on and the ELECTRICAL power reaches in few seconds 16.5 kW. But, as you can see from the picture, then it starts to decrease approaching, over three days, 13.65 kW, and remains at 13.65 kW. Then, suppose that it is again switched off and switched on (process that last few minutes, not again plotted in the figure), again the ELECTRICAL POWER reaches 16.5 kW as at the beginning, but then it decreases approaching 13.65 kW (after 3 days) and remains 13.65 kW. If we repeat again the switch on/off (process done in few minutes), again it reaches 16.5 kW, and then decreases up to 13.65 kW. If the turbine is not switched on/off, the power remains 13.65 kW “forever” ….. until a new switched off/on is made. Therefore, the switched off/on process last few minutes, while the decreasing trend until the lowest power value of 13.65 kW lasts few days.
Have you got general ideas?
1) Formation of a big vortex in the draft tube. If this would occur, the decreasing trend should last few minutes (the time needed for the vortex development), and the power would immediately approach 13 kW. This phenomenun should last few minutes, not days. Furthermore, by CFD simulations, the vortex in the draft tube is not powerful, and at the outlet of the draft tube flow velocities are vertical.
2) Possible inclusion of air from the conical (vertical) draft tube towards the turbine. The draft tube is immersed of slightly more than 1.1 D into the downstream water level (D is maximum turbine diameter), as recommended by engineering practice. From CFD simulations flow velocities are downward, so this point should be ok.
3) Possible electro-mechanics/electrical load problem.
4) Cavitation: during operation there are not noise, neither appreciable vibrations, but there is hub erosion due to cavitation. But cavitation should reduce the maximum power output, not generate a decreasing trend during the time.
Thanks
