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Advances and Challenges in Hydropower

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics and Hydrodynamics".

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 51172

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Special Issue Editors

Prof. Dr.-Ing. Jochen Aberle

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Guest Editor

Leichtweiß Institute for Hydraulic Engineering and Water Resources, Technische Universität Braunschweig, Germany
Interests: hydraulic engineering; hydraulic structures; environmental hydraulics; ecohydraulics; experimental methods; sediment transport
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Prof. Dr. Robert Boes

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Guest Editor

Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich, Switzerland
Interests: dam hydraulics; dam safety; reservoir sedimentation; impulse waves; hydropower and environment; sediment monitoring; hydro-abrasive wear of hydraulic structures and machinery; flood protection
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The European Energy Research Alliance (EERA) aims to catalyze European energy research to accelerate the development and deployment of low-carbon technologies. Hydropower plays an important role in this regard and the EERA Joint Programme Hydropower aims to facilitate a new role for hydropower as enabler of a renewable energy system by aligning and targeting research efforts in Europe. The importance of hydropower is also reflected by a number of large research projects and programmes on a national level, such as the Tunnelroughness project in Norway (funded by the Norwegian Research Council) or the work package hydropower within the Swiss Competence Center for Energy Research – Supply of Electricity (SCCER-SoE), funded by the Swiss Innovation Agency Innosuisse. These projects are led by the editors of this special issue, who act also as coordinators within the above-mentioned Joint Programme Hydropower.

This special issue focuses on hydraulic structures such as dams, weirs, intakes, tunnel systems, power stations, spillways, and outlets from the waterways, which in turn represent one of the backbones for the generation of hydroelectricity. Contributions are invited which address the development of novel and innovative solutions for improving the reliability, efficiency, safety, and environmental friendliness of hydropower infrastructure and reservoirs. This includes contributions focusing on analytical considerations, scale model investigations, numerical simulations and field investigations. Special emphasis is placed on the further development of hybrid modelling strategies, i.e. the combined application of hydraulic scale models, numerical models and/or field investigations to make full use of the advantages and to minimize the uncertainties associated with the different modelling strategies.

Prof. Dr.-Ing. Jochen Aberle
Prof. Dr. Robert Boes
Guest Editors

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Keywords

Hydropower
Hydraulic Structures
Hydropower Structures
EERA (European Energy Research Alliance)
Environmental Hydraulics
Hydraulic Engineering
Dams
Reservoirs

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Published Papers (14 papers)

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Research

24 pages, 5543 KiB

Open AccessFeature PaperArticle

Design of Desanding Facilities for Hydropower Schemes Based on Trapping Efficiency

by Christopher Paschmann, David F. Vetsch and Robert M. Boes

Water 2022, 14(4), 520; https://doi.org/10.3390/w14040520 - 9 Feb 2022

Cited by 4 | Viewed by 5385

Abstract

Turbine wear caused by hydro-abrasion due to suspended sediment in the turbine water has a negative impact on the power production and revenue of hydropower schemes. Efficiency of desanding facilities that reduce suspended sediment load ahead of turbines is key to limiting hydro-abrasion. Existing facilities built according to common design approaches often show lack of performance, in particular under non-ideal site-specific inlet and outlet conditions. Consequently, a new design concept that allows for the optimized design of desanding facilities at hydropower schemes has been developed based on prototype field measurements and CFD modeling. The effects of facility layout and components, such as tranquilizing racks, transition zone and outflow weir and related design parameters on the flow field and involved particle settling have been investigated in a comprehensive numerical model study. Hence, length adjustment terms were deduced from resulting changes in trapping efficiency, which allow for the estimation of the required basin length and an optimized facility layout. Compared to design approaches considering linear settling trajectories of sediment particles, the proposed procedure leads to longer settling basins in general and thus to increased trapping efficiencies of desanding facilities. Furthermore, the findings about the effect of specific facility components may allow for the optimisation of existing desanding facilities in an economical way. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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24 pages, 16320 KiB

Open AccessFeature PaperArticle

Extreme Pressures and Risk of Cavitation in Steeply Sloping Stepped Spillways of Large Dams

by Jorge Matos, Carolina Kuhn Novakoski, Rute Ferla, Marcelo Giulian Marques, Mauricio Dai Prá, Alba Valéria Brandão Canellas and Eder Daniel Teixeira

Water 2022, 14(3), 306; https://doi.org/10.3390/w14030306 - 20 Jan 2022

Cited by 9 | Viewed by 3311

Abstract

Stepped spillways have been increasingly used to handle flood releases from large dams associated with hydropower plants, and it is important to evaluate the fluctuating pressure field on the steps. Hydraulic model investigations were conducted on three 53° (1V:0.75H) sloping and relatively large-stepped chutes to characterize the mean, fluctuating, and extreme pressures acting on the most critical regions of the step faces, near their outer edges. The pressure development along the chutes is presented, generally indicating an increase of the modulus of pressure coefficients up to the vicinity of the point of inception of air entrainment, and a decrease further downstream. The extreme pressure coefficients along the spillway are fitted by an empirical formula, and the critical conditions potentially leading to cavitation on prototypes are calculated. The correlation between the cavitation index and the friction factor is also applied for predicting the onset of cavitation on prototypes, and the results are compared with the pressure data-based method. Generally, the results obtained from those methods yield typical values for the cavitation index in the vicinity of the point of inception, varying approximately from 0.8 to 0.6, respectively. In light of these results, maximum unit discharges of about 15–20 m²/s are considered advisable on 53° sloping large-stepped spillways without artificial aeration, for step heights ranging from 0.6 to 1.2 m. For much higher unit discharges, a considerable reach of the spillway may potentially be prone to the risk of cavitation damage. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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22 pages, 19016 KiB

Open AccessArticle

Assessing Visual Preferences of the Local Public for Environmental Mitigation Measures of Hydropower Impacts—Does Point-of-View Location Make a Difference?

by Berit Junker-Köhler and Håkon Sundt

Water 2021, 13(21), 2985; https://doi.org/10.3390/w13212985 - 22 Oct 2021

Cited by 1 | Viewed by 2337

Abstract

Hydropower is a highly appreciated climate-friendly source of energy production. However, it has non-negligible negative impacts on the environment and landscape aesthetics where the energy is produced, affecting the recreational interests of the public using the respective local river spaces. The preferences of the local public are increasingly assessed and involved in the planning of mitigation measures for impacted rivers. Aesthetic assessment methods using a common user perspective, i.e., an “on-the-ground” perspective, could potentially be improved by using an aerial perspective facilitated by modern drone technology. Studies on the compatibility of these two perspectives of assessment in terms of public preference elicitation are lacking so far. In river Nea, Norway, we conducted a quantitative analysis of the visual preferences of the local public for different environmental mitigation measures related to weirs, minimum flow, and recreational infrastructure using both perspectives. The results indicate that there exist significant differences in the preferences for scenarios based on the two different visual perspectives, and that a compatibility between them cannot be assumed and therefore requires further investigation. Finally, based on our study setup and previous experience, we outline and propose a standardized procedure for the visualization of mitigation measures as an input to environmental design projects where public perception is incorporated. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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11 pages, 1578 KiB

Open AccessArticle

Dynamic Water-Level Regulation at Run-of-River Hydropower Plants to Increase Efficiency and Generation

by Stephan Heimerl and Niklas Schwiersch

Water 2021, 13(21), 2983; https://doi.org/10.3390/w13212983 - 22 Oct 2021

Cited by 2 | Viewed by 4159

Abstract

In times of the energy transition and the intensified expansion of renewable energy systems, this article presents an optimization approach for run-of-river power, i.e., dynamic water-level regulation. Its basic idea is to use river sections influenced by backwater more evenly via the operating regime of a hydropower plant. In contrast to conventional dam and weir water level management, the head of the reservoir is not shifted toward the weir while the discharge rate increases but is kept in position by temporarily raising the water level. This generates a greater head for higher discharge rates of an operating regime. As can be shown using an example, this has a direct effect on the performance and, in interaction with the discharge duration curve, on the annual work of the plant. The dynamic water-level regulation, thus, represents an environmentally compatible, energy-efficient optimization for run-of-river hydropower plants. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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27 pages, 9819 KiB

Open AccessArticle

Retrofitting of Pressurized Sand Traps in Hydropower Plants

by Wolfgang Richter, Kaspar Vereide, Gašper Mauko, Ola H. Havrevoll, Josef Schneider and Gerald Zenz

Water 2021, 13(18), 2515; https://doi.org/10.3390/w13182515 - 14 Sep 2021

Cited by 7 | Viewed by 3751

Abstract

Unlined pressure tunnels in sound rock, combined with pressurized sand traps at the downstream end, allow for low-cost construction of hydropower tunnel systems. This design concept is utilized in hydropower plants across the world. Currently, many such power plants are being upgraded with higher installed capacity, which may result in challenges with the sand trap efficiency. A physical scale model test, accompanied by 3D CFD simulations of a case study pressurized sand trap, has been studied for economic retrofitting. The geometric model scale is 1:36.67 while the velocity scale and sediment scale are 1:1 (same average flow velocity and sediment size in model and prototype). This is currently an uncommon scaling approach but with several advantages, as presented in this paper. Various options for retrofitting were investigated. A combined structure of ramp and ribs was found to significantly improve the sediment trap efficiency. The main novelties from this work are the proposed design of the combined ramp and rib structure. Secondary results include an efficient setup for physical scale models of pressurized sand traps and a methodology that combines the benefits of 3D CFD simulations with physical scale models testing for sand trap engineering and design. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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17 pages, 8397 KiB

Open AccessFeature PaperArticle

Submerged Wall Instead of a Penstock Shutoff Valve—Alternative Protection as Part of a Refurbishment

by Roman Gabl, Markus Wippersberger, Jakob Seibl, Christian Kröner and Bernhard Gems

Water 2021, 13(16), 2247; https://doi.org/10.3390/w13162247 - 17 Aug 2021

Cited by 3 | Viewed by 3525

Abstract

Hydropower is an important source of renewable energy. Due to ageing infrastructure, more and more existing hydropower plants have to be refurbished and modernised. This includes a complete review of the design parameters as well as the change of specific parts. Investments should be targeted to improve the overall performance of hydropower plants and ensure a long lasting life extension. This paper presents the concept of the submerged wall as a local high point in the headrace tunnel, which can—in combination with the intake gates—replace existing penstock shutoff valves. Such a replacement was conducted for the hydropower plant Schneiderau in Austria, which also allowed us to prove the concept based on measurements including a simulated break of the penstock. The presented solution can help to reduce investment costs and also minimise maintenance efforts and therefore is an attractive option for classic penstock shutoff valves for comparable projects. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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17 pages, 19606 KiB

Open AccessArticle

Enhanced Operational Flexibility of a Small Run-of-River Hydropower Plant

by Jean Decaix, Anthony Gaspoz, Vlad Hasmatuchi, Matthieu Dreyer, Christophe Nicolet, Steve Crettenand and Cécile Münch-Alligné

Water 2021, 13(14), 1897; https://doi.org/10.3390/w13141897 - 8 Jul 2021

Cited by 4 | Viewed by 2896

Abstract

Over the last two decades, the public policies for promoting new renewable energies allowed the growth of such energies around the world. Due to their success, the policies are changing, forcing the producers to adapt their strategy. For instance, in Switzerland, the feed-in tariff system has been modified in 2018 to promote an electricity production from renewable energies that matches the demand. For small hydraulic power plants owners, such a change requires to increase the flexibility of their fleet. The SmallFLEX project, led by HES-SO Valais, aims at demonstrating on the pilot site of Gletsch-Oberwald owned by Forces Motrices Valaisannes SA, the possibilities to increase the flexibility of the power plant and to provide new services. The paper focuses on the methodology followed to warranty the use of the settling basin, the forebay tank, and the third upper part of the headrace tunnel as a new smart storage volume. By combining laboratory tests, numerical simulations, and on-site measurements, the new range of operating conditions has been defined. These data can be used to foresee economic gains. The methodology and the outputs of the project can be useful for performing such a study on other power plants. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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23 pages, 9018 KiB

Open AccessArticle

Efficiency Assessment for Rehabilitated Francis Turbines Using URANS Simulations

by Philippe Martineau Rousseau, Azzeddine Soulaïmani and Michel Sabourin

Water 2021, 13(14), 1883; https://doi.org/10.3390/w13141883 - 7 Jul 2021

Cited by 2 | Viewed by 3120

Abstract

Due to the large number of aging hydraulic turbines in North America, rehabilitation is a growing market as these turbines have low efficiency compared to modern ones. Computational Fluid Dynamics identifies components with poor hydraulic performance. The models often used in industry are based on individually analyzing the sub-components of a turbine instead of full turbine simulations due to computational and time limitations. An industrial case has shown that such analyses may lead to underestimating the efficiency increases by modifying the stay vane. The unsteady full turbine simulation proposes to simulate all components simultaneously to assess this efficiency augmentation due to stay vane rehabilitation. The developed simulation methodology is used to evaluate the efficiency increase and the flow of two rehabilitated turbines with stay vane modifications. Comparison with model tests shows the accuracy of the simulations. However, the methodology used shows imprecision in predicting the efficiency increase compared to model tests. Further works should consider the use of more complex flow modeling methods to measure the efficiency increase by the stay vane modifications. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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20 pages, 6272 KiB

Open AccessArticle

Operation of Norwegian Hydropower Plants and Its Effect on Block Fall Events in Unlined Pressure Tunnels and Shafts

by Bibek Neupane, Kaspar Vereide and Krishna Kanta Panthi

Water 2021, 13(11), 1567; https://doi.org/10.3390/w13111567 - 1 Jun 2021

Cited by 5 | Viewed by 3541

Abstract

The main objective of this study is to investigate the effect of hydropower plant operation on the long-term stability of unlined pressure tunnels of hydropower plants in Norway. The authors analyzed the past production data of some hydropower plants to find out the number of starts/stops and the frequency and magnitude of load changes. The study demonstrates that an average of 200–400 start/stop events are occurring per turbine per year for the analyzed period, with an increasing trend. Currently, 150–200 large load changes per turbine smaller than 50 MW are occurring every year, and this is expected to increase by 30–45% between 2025 and 2040 for one of the studied power plants. Most importantly, the monitored pressure transients and pore pressure response in the rock mass during real-time operation at Roskrepp power plant are presented. A new method is proposed to calculate and quantify the hydraulic impact (HI) of pressure transients on rock joints and the effect of duration of shutdown/opening, which is found to be the most dominant parameter affecting the magnitude. The results show that faster shutdown sequences cause unnecessary stress in rock mass surrounding pressure tunnel. The hydraulic impact (HI) can be more than 10 times higher when the shutdown duration is reduced by 50 percent. The study recommends that duration of normal shutdowns/openings in hydropower plants should be slower so that hydraulic impacts on the rock joints are reduced and cyclic hydraulic fatigue is delayed, prolonging the lifetime of unlined pressure tunnels and shafts. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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16 pages, 3024 KiB

Open AccessArticle

Velocity Structure of Density Currents Propagating over Rough Beds

by Reza Nasrollahpour, Mohamad Hidayat Jamal, Zulhilmi Ismail, Zulkiflee Ibrahim, Mazlin Jumain, Mohd Ridza Mohd Haniffah and Daeng Siti Maimunah Ishak

Water 2021, 13(11), 1460; https://doi.org/10.3390/w13111460 - 23 May 2021

Cited by 4 | Viewed by 3004

Abstract

In most practical cases, density-driven currents flow over surfaces that are not smooth; however, the effects of bottom roughness on these currents have not been fully understood yet. Hence, this study aims to examine the velocity structure of density currents while propagating over rough beds. To this end, alterations in the vertical velocity profiles within the body of these currents were investigated in the presence of different bottom roughness configurations. Initially, laboratory experiments were carried out for density currents flowing over a smooth surface to provide a baseline for comparison. Thereafter, seven bottom roughness configurations were tested, encompassing both dense and sparse bottom roughness. The bottom roughness consisted of repeated arrays of square cross-section beams covering the full channel width and perpendicular to the flow direction. The primary results indicate that the bottom roughness decelerated the currents and modified the shape of velocity profiles, particularly in the region close to the bed. Additionally, a critical spacing of the roughness elements was detected for which the currents demonstrated the lowest velocities. For the spacings above the critical value, increasing the distance between the roughness elements had little impact on controlling the velocity of these currents. Moreover, using dimensional analysis, equations were developed for estimating the mean velocities of the currents flowing over various configurations of the bottom roughness. The findings of this research could contribute towards better parameterization and improved knowledge of density currents flowing over rough beds. This can lead to a better prediction of the evolution of these currents in many practical cases as well as improved planning and design measures for the control of such currents. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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23 pages, 4510 KiB

Open AccessArticle

Combined Dispatching of Hydropower and Wind Power Based on the Hedging Theory

by Kaoshe Zhang, Mengyan Xie, Gang Zhang, Tuo Xie, Xin Li and Xin He

Water 2021, 13(9), 1319; https://doi.org/10.3390/w13091319 - 9 May 2021

Viewed by 2408

Abstract

In order to improve the utilization rate of water resources in the flood season of the reservoir effectively and promote wind power consumption, this paper proposes an optimization model for the combined dispatching of wind power and hydropower based on the hedging theory. First, the conflicting relationship between the water storage benefits of hydropower stations, flood control risks, and the joint output of hydropower and wind power in joint dispatching is studied. The introduction of hedging theory divides the combined dispatching of wind power and hydropower into a two-stage dispatching problem including the decision-making stage and the remaining stage; Second, considering the uncertainty of water forecasting and wind power forecasting, a multi-objective optimal dispatching model of hydropower and wind power based on hedging theory is constructed. This model aims to minimize flood control risks, maximize water storage benefits, and minimize wind power and hydropower combined power output volatility. Finally, the non-dominated sorting genetic algorithm (NSGA2) is used to solve the specific examples. The results show that the model built in the article controls the flood control risk at each time period not to be higher than 1.63 × 10⁻³ (the flood control standard corresponding to the flood control risk in 50 years is 0.006). Additionally, the water level of the reservoir increased from the flood limit water level (583.00 m) to 583.70 m. It greatly increases the water storage capacity and effectively improves the utilization rate of water resources. At the same time, the optimized scheduling scheme reduced the peak-valley difference of joint output from 125.00 MW to 35.66 MW, and the peak-valley difference was greatly reduced. It effectively improves the volatility of wind power. The validity of the model is verified, and the obtained scheme can provide decision-making for the joint dispatch scheme of hydropower and wind power. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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15 pages, 2635 KiB

Open AccessArticle

Evaluating the Structure from Motion Technique for Measurement of Bed Morphology in Physical Model Studies

by Sanat Kumar Karmacharya, Nils Ruther, Ujjwal Shrestha and Meg Bahadur Bishwakarma

Water 2021, 13(7), 998; https://doi.org/10.3390/w13070998 - 5 Apr 2021

Cited by 1 | Viewed by 3391

Abstract

The selection of instrumentation for data acquisition in physical model studies depends on type and resolution of data to be recorded, time frame of the model study, available instrumentation alternatives, availability of skilled personnel and overall budget of the model study. The available instrumentation for recording bed levels or three-dimensional information on geometry of a physical model range from simple manual gauges to sophisticated laser or acoustic sensors. In this study, Structure from Motion (SfM) technique was applied, on three physical model studies of different scales and study objectives, as a cheap, quicker, easy to use and satisfactorily precise alternative for recording 3D point data in form of colour coded dense point cloud representing the model geometry especially the river bed levels in the model. The accuracy of 3D point cloud generated with SfM technique were also assessed by comparing with data obtained from manual measurement using conventional surveying technique in the models and the results were found to be very promising. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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22 pages, 3137 KiB

Open AccessArticle

Experimental and Numerical Determination of the Head Loss of a Pressure Driven Flow through an Unlined Rock-Blasted Tunnel

by Jochen Aberle, Pierre-Yves Henry, Fabian Kleischmann, Christy Ushanth Navaratnam, Mari Vold, Ralph Eikenberg and Nils Reidar Bøe Olsen

Water 2020, 12(12), 3492; https://doi.org/10.3390/w12123492 - 11 Dec 2020

Cited by 9 | Viewed by 3964

Abstract

The friction loss in a part of the rock-blasted unlined tunnel of the Litjfossen hydropower plant in Norway was determined from experimental and numerical studies. Remote sensing data from the prototype tunnel provided the input data for both the numerical model and the construction of a 1:15 scale model with an innovative milling approach. The numerical simulations were based on the solution of the Reynolds-averaged Navier–Stokes equations using the CFD program OpenFoam. Head loss measurements in the scale model were carried out by means of pressure measurements for a range of discharges and were compared against the results of the numerical model. The measured data were used to determine the Darcy–Weisbach and Manning friction factors of the investigated tunnel reach. The high-resolution remote sensing data were also used to test the applicability of existing approaches to determine the friction factor in unlined rock blasted tunnels. The results of the study show the usefulness of the chosen hybrid approach of experimental investigations and numerical simulations and that existing approaches for the determination of head losses in unlined tunnels need to be further refined. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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18 pages, 4738 KiB

Open AccessFeature PaperArticle

Holistic Design Approach of a Throttled Surge Tank: The Case of Refurbishment of Gondo High-Head Power Plant in Switzerland

by Mona Seyfeddine, Samuel Vorlet, Nicolas Adam and Giovanni De Cesare

Water 2020, 12(12), 3440; https://doi.org/10.3390/w12123440 - 8 Dec 2020

Cited by 3 | Viewed by 2935

Abstract

In order to increase the installed capacity, the refurbishment of Gondo high-head power plant required a modification of the existing surge tank by installing a throttle at its entrance. In a previous study, the geometry of this throttle was optimized by physical modeling to achieve the target loss coefficients as identified by a transient 1D numerical analysis. This study complements previous analyses by means of 3D numerical modeling using the commercial software ANSYS-CFX 19 R1. Results show that: (i) a 3D computational fluid dynamics (CFD) model predicts sufficiently accurate local head loss coefficients that agree closely with the findings of the physical model; (ii) in contrast to a standard surge tank, the presence of an internal gallery in the surge tank proved to be of insignificant effect on a surge tank equipped with a throttle, as the variations in the section of the tank cause negligible local losses compared to the ones induced by the throttle; (iii) CFD investigations of transient flow regimes revealed that the head loss coefficient of the throttle only varies for flow ratios below 20% of the total flow in the system, without significantly affecting the conclusions of the 1D transient analysis with respect to minimum and maximum water level in the surge tank as well as pressure peaks below the surge tank. This study highlights the importance of examining the characteristics of a hydraulic system from a holistic approach involving hybrid modeling (1D, 3D numerical and physical) backed by calibration as well as validation with in-situ measurements. This results in a more rapid and economic design of throttled surge tanks that makes full use of the advantages associated with each modeling strategy. Full article

(This article belongs to the Special Issue Advances and Challenges in Hydropower)

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