bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical investigation for intake and discharge conditions of horizontal multi-jet Pelton turbines
Authors: Mössinger Peter , Mack Reiner , Jörg Necker J 
Published: December 2024

Abstract
Modernization of existing Pelton turbines comes with a required increase in power and efficiency. At the same time, maintainability and accessibility should be improved. Here a replacement of the existing units with horizontal multi-jet turbines can achieve these requirements. Concurrently, the hydraulic inlet and outlet conditions are challenging as the penstock and tailwater are often reused. At two examples, one in operation, one in construction, the possibilities to design and improve the inflow and discharge situation with the aid of numerical methods is shown. Efficiency and flow conditions can be significantly improved when the turbine in- and outlet is designed for the specific on-site situation.
Multidisciplinary optimization of an axial turbine
Authors: Fraas S , Tismer A , Riedelbauch S 
Published: December 2024

Abstract
The results of three different optimization setups for an axial propeller turbine consisting of a guide vane, a runner and a draft tube are presented. The first setup only contains the efficiency as objective and the design head as a constraint. In the second setup, the minimization of the cavitation volume is added as a further objective while in the third, the compliance with a permissible stress is included as an additional constraint. Three operating points are simulated during the optimization. Comparing the results of the first two setups, the minimization of the cavitation volume leads to a lower plant efficiency at all operating points. Including structural mechanical aspects results in a further decrease of the plant efficiency at all operating points. Nevertheless, none of the best individuals from the setups have a maximum von Mises stress below the permissible stress without taking the structural stress limits into account. This points out the importance of considering both, structural as well as fluid mechanical aspects in the optimization process of hydraulic machines.
Comparison of discharge characteristics of Pelton injector estimated by empirical relation, numerical simulation and experiment
Authors: Shrestha Sajan , Pandey Arun , Satyal Sajan , Abregu Jim , Prasad Neopane Hari , Gunnar Dahlhaug Ole 
Published: December 2024

Abstract
It is difficult to define a general relationship for discharge characteristics of a Pelton injector due to high degree of variability in geometry of injector amongst different Pelton turbine designs. This study has been aimed to determine discharge characteristics of injector of Pelton rig at Waterpower Laboratory, NTNU. Three different approaches have been undertaken, viz. calculation based on empirical relations, numerical simulations, and experimental validation. For empirical calculation, the injector has been simplified into series of flow geometries with equivalent cross-sectional area and axial length for multiple stroke to constant aperture diameter ratio (s/D
0). Discharge coefficient has been calculated for a constant pressure difference between inlet and atmospheric outlet for each case of s/D
0, based on head loss estimated using empirical resistance coefficient (ζ - values) available in engineering handbooks. Discharge has been determined through numerical simulations for same s/D
0 values. Results from numerical and empirical calculations are compared and correction factor (CF) has been determined. It is found that the CF is almost constant, at value of 0.85, for all values of s/D
0. The discharge coefficient calculated by numerical simulation is around 0.02 lower than the values obtained by experimental observation.
Diagnosis of the unstable behaviour of a Kaplan turbine before synchronizing to the grid
Authors: Moraga G , Mut V , Hijón C , Girardelo J , Valentín D , Egusquiza M , Egusquiza E , Presas A 
Published: December 2024

Abstract
This work reports on a new Kaplan turbine that experienced an unstable behaviour during its start up. The unit experienced strong sound and vibration in that phase. To identify the origin of this unstable behaviour, a set of sensors were installed within the turbine. Subsequently, tests were performed to determine the response of the different sensors during the acceleration of the machine to the speed no load stage. Following a thorough analysis of the results, the problem was identified as the air admission openings of the head cover and their distribution. To address this issue, a reconfiguration of these openings was implemented and their performance was evaluated. Following this rearrangement, the vibrations in the head cover were significantly reduced and the unit was successfully commissioned.
Analysis of the flow interference on a Pelton turbine at different operating heads
Authors: Xiao Y , Min H , Liang Q , Liu Z , Wang X , Zhou H , Tang D 
Published: December 2024

Abstract
Flow interference is a phenomenon harmful for the Pelton turbines stable and high efficiency operation. In this paper, numerical simulation of unsteady multiphase flow on a Pelton turbine runner buckets and entire flow passage was carried out at three operating heads. Different types of flow interference were occurred for the turbine with larger nozzle opening: the water sheet interference on the same bucket surface from the adjacent jets, the bucket cutout-flow and jet flow interference, as well as the interference between bucket brim outflow and the following bucket rear surface. The highest turbine efficiency is about 88.0% appears at 1.00H
0, and efficiency decreases when deviating from the design head, especially at the low head decrease dramatically. The predicted unsteady flow patterns with bucket torque curves show that the self-designed Pelton turbine model with six nozzles opened at larger needle stroke is remains to be optimized. The relationship between the predicted flow interference and the decrease of runner torque and hydraulic performance is summarized.
Pump start instability on a low head pump turbine and testing with partial deaeration
Authors: Nennemann B , Bergweiler M , Herrero Prada C 
Published: December 2024

Abstract
Since 2019 Iberdrola has had an interest in enabling pump operation of the Valparaiso hydropower plant. Iberdrola contacted Andritz, the original manufacturer of the machines, and a collaboration for that purpose was started. This powerplant was equipped with two pump turbine units in the 1980ies but pump operation has not been possible since strong vibrations occurred during pump commissioning in 1995. Therefore, the units had only been operated in turbine mode since then. In 2020 Iberdrola and Andritz performed a renewed pump start test with a fully rewatered machine. This again led to high vibrations during the initial phase of guide vane opening. Subsequently, guide vane flutter (self-excitation) was investigated as a potential cause of the vibrations but could not be established as the cause. Instead, it was found, that due to a transient effect, the machine entered the unstable part of the pump characteristic. Partial deaeration before guide vane opening during pump start was then considered as a solution and successfully tested in 2021.
Numerical study of pressure fluctuation in vaneless space of variable speed reversible pump-turbine in turbine mode at maximum head
Authors: Rode Bhushan R , Kumar Arun , Segoufin Claire , Laurant Yann 
Published: December 2024

Abstract
Efficiency and grid stability of pumped storage plants with significant head variations can be enhanced by the implementation of variable speed operation. The reversible pump-turbine (RPT) operating in turbine mode is particularly prone to fatigue and vibrations when operating at maximum head conditions, primarily due to hydraulic instabilities caused by pressure fluctuations in vaneless space and thus, the performance of the RPT becomes increasingly critical under such operating conditions. It is, therefore, important to examine the pressure fluctuations in vaneless space of RPTs operating at higher heads. The findings indicate that the main source of pressure fluctuations across all operating conditions is rotor-stator interaction (RSI), where the dominant frequency is blade passing frequency (9fn
) and its harmonics.
Effect of wrap angle on performance of Pump As Turbine (PAT) in both pump and turbine modes
Authors: Bhukya N K , Rai A K 
Published: December 2024

Abstract
Pump as turbine (PAT) is used in small hydropower plants to generate electricity for remote hill regions and the integration of other renewable resources. Generally, the efficiency of centrifugal pumps operating in turbine mode is low. To improve efficiency, variables such as wrap angle, blade thickness, and blade count can be optimized for turbine mode; however, such changes may lead to a decrease in PAT performance in pump mode. To explore the effect of wrap angle on PAT performance in pump mode, flow simulations were carried out at conditions with wrap angle and discharge variations between 85°-120° and 8-16 kg/s, respectively. With a decrease in wrap angle in pump mode compared to the rated design condition, both efficiency and head rise were improved at the partial load condition. A design with a 120° wrap angle provided a 5.15 % improvement of efficiency in turbine mode compared with the available empirical relation; however, a minor decrease of 0.5% in pump mode was observed. Such zones with high efficiency in turbine mode with less compromise in pump mode should be identified for PAT.
Experimental investigation of a FSFC variable speed pump-turbine prototype – Part2: runner fatigue reduction
Authors: Biner D , Hasmatuchi V , Lecointre C L , Quarroz A , Nicolet C , Alligné S , Dreyer M , Hugo N , Dujic D , Münch-Alligné C 
Published: December 2024

Abstract
The demonstration of flexibility technologies to enhance ancillary services of Hydropower Plants (HPPs) is showcased by the XFLEX HYDRO H2020 European Project. The potential of Full Size Frequency Converters (FSFC) is numerically and experimentally assessed by a case study on the Z’Mutt HPP. The investigated unit is a 5 MW variable speed reversible Francis pump-turbine fed by a FSFC that provides full speed control from −100% to +100%, allowing for fast start-up and mitigation of damage caused to different components. In this context, several turbine start-up sequences with controlled guide vane opening and rotational speed are developed, implemented, and tested on prototype scale. The definition of the different sequences, their impact on penstock fatigue and further FSFC capabilities like fast active power control in pump mode and fast power reversion are presented in part 1 of this contribution. Part 2 deals with fatigue damage investigations of the runner with respect to variable speed operation in generating mode using coupled numerical and experimental techniques. Strain signals from the runner blades are extrapolated to the critical areas to assess the relative fatigue damage induced by each turbine start-up. The scaled normal stress approach is applied, which is a critical plane method, adapted for multiaxial stress states. The results reveal that runner damage is mitigated by more than two orders performing a variable speed start-up compared to a classical one with fixed speed technology. Simultaneously, the delay for active power provision is significantly shortened. Thus, the study approves that fast and frequent turbine start-ups are realizable without affecting the runner’s service life thanks to the FSFC.
Evaluation of the fatigue-related influence of start-ups on Pelton turbines based on reduced scale model stress measurements
Authors: Leonardo Alerci Aldo , Vagnoni Elena , Paolone Mario 
Published: December 2024

Abstract
In recent decades, the electricity industry has undergone a significant transformation from a vertically integrated supply system to a market-regulated structure. This shift, along with the intermittent nature of increasingly prevalent non-dispatchable renewable energy sources, induces system operators to redistribute portions of the power generation included in the market schedule to preserve the energy balance within the power system. For hydropower plants, this translates in increasingly frequent operations in transient condition, with significant fatigue-related consequences on the lifetime of hydraulic machines. The understanding of fatigue phenomena during transient operations requires therefore experimental investigations, modeling and optimization of such operations, representing today a relevant research subject. This paper proposes the comparison between two methodologies which aim to estimate and optimize the operational cost, with respect to the lifetime of a Pelton turbine, of the specific case of the back-to-back start-up of a multistage pump performed with the Pelton runner of the same ternary group. These methodologies are developed on data collected during an experimental campaign performed with the reduced scale model of the investigated turbine, homologous to the real test case pumped-storage power plant. Despite the substantial distinction in the adopted approaches, the two methodologies show common features in terms of the fatigue damage trend as a function of the turbine operating conditions, and of the optimal strategy minimizing the structural impact of start-up sequences.
On the modelling of the fatigue-induced damage in Francis turbines start-up sequences
Authors: Vagnoni E , Muser T , Seydoux M , Morabito A , Krymova E 
Published: December 2024

Abstract
The European Green Deal is prescribing a very ambitious rise in the annual production of renewable energy sources, and grid regulation services are increasingly important in the course of a massive integration of intermittent renewable energy sources. Although hydropower effectively regulates power, the growing demand for flexibility in the coming decades means that hydroelectric technologies must be adaptable, often operating in conditions for which they were not originally designed to ensure availability and system reliability. This also includes a significant increase of the number of start-ups per year. To address these challenges, this paper suggests a two-fold forecasting method to predict damage due to fatigue in the runner blades of Francis turbines. Firstly, stresses during transient operations are predicted using a quasi-steady approach that concatenates measurements from steady-state operations through Voronoi tessellation. Following that, a neural network is trained on an existing dataset of recorded blade stresses during transient operations. The effectiveness of both approaches is validated against measurements in a reduced scale model of a Francis turbine. The comparative analysis highlights the strengths and weaknesses of each method, offering a detailed understanding of dynamic damage accumulation during start-up sequences compared to steady-state operations.
Exploring the effects of operating time and sediment minerals on hydro abrasive erosion in Pelton turbine
Authors: Arora N , Kumar A , Singal S K 
Published: December 2024

Abstract
Hydro-abrasive erosion in the Pelton turbines is attributed to high jet velocity generated by high head and abrasive sediment particles in sediment laden flow. This study presents a part of the research study that focuses on investigating the effect of sediment minerals on hydro abrasive erosion in Pelton buckets. Experiments were conducted on a Pelton jet test rig with a Pelton runner of 10 kW equipped with 20 buckets of different material using four sediment minerals (muscovite, feldspar, garnet, and quartz), operating time (3 h, 6 h, 9 h, 12 h), erosion velocity (46.58 m/s), suspended sediment concentration (1500 mg/l), and sediment size range (90-150 μm). It was found that erosion increases with an increase in the operating time; however, the rate of erosion varies with the material. Among all the materials tested, 13Cr4Ni with WC-Co-Cr coating performed best under the action of sediment and offered the best resistance to erosion. The correlations between normalized erosion and operating time were developed for each bucket material corresponding to muscovite, feldspar, garnet, and quartz sediments, and the obtained exponents of operating time vary from 0.95 to 1.22.
Mitigation of high load flow instabilities using axial water jet injection in Francis turbines
Authors: Khullar Subodh , Singh Krishna M , Gandhi Bhupendra K 
Published: December 2024

Abstract
The high load (HL) operations in Francis turbines lead to the inception of unsteady phenomena causing pressure pulsations, vibrations, and cavitation. The flow instabilities at HL differ from that of part load operation (PL). At high load, an axisymmetric vortical structure, rotating opposite to the runner develops in the draft tube. The authors had previously successfully employed axial water jet injection in the draft tube to mitigate flow instabilities at different part loads. The present numerical work is performed to investigate the effect of water jet injection on flow instabilities at a high-load operating condition. The simulations are performed on a model Francis turbine unit installed at IIT Roorkee. The study presents changes in the velocity and pressure distribution along with turbine characteristics, such as efficiency, and pressure recovery with the water jet injection.
Numerical Analysis of Cavitation Characteristics of Francis Turbine at Different Runner Blade Numbers
Authors: Kumar Prashant , Singal S K , Gohil Pankaj P 
Published: December 2024

Abstract
The main objective of this study is to evaluate the hydraulic performance and cavitation characteristics of Francis turbine at different operating conditions by varying the number of runner blades 13, 15, and 17 using commercially available CFX code. The runner blade numbers have a significant impact on both the turbine’s hydraulic efficiency and cavitation characteristic performance. The turbine efficiency and cavitation characteristic of turbine has been analysed under the best efficiency point (BEP) condition in order to achieve the optimum number of runner blades for Francis turbine. The turbulent nature of water flow through the turbine passages is accurately captured by SST turbulent model. The numerical results obtained from the CFD analysis were validated by comparing them with turbine manufacturer data available in the literature. Based on the simulation results, the hydraulic efficiency of turbine has been found to be maximum with 15 runner blades as compared to 13 and 17 runner blades. However, the predicted zone of water vapour volume fraction becomes less on trailing edge suction side of blades with an increase in number of runner blades. The results of the suggested research could prove highly valuable to hydro turbine manufacturers.
Developing a customized laboratory setup to assess sensors for real-time suspended sediment monitoring
Authors: Friz Carolin , Felix David , Evers Frederic M , Boes Robert M 
Published: December 2024

Abstract
Sedimentation challenges water reservoir operations globally, particularly for storage hydropower plants (HPPs), necessitating effective management strategies. One such strategy, fine sediment venting through turbines, though effective in managing sediment continuity, increases hydro-abrasive erosion on turbines due to the additional sediment load. Hence, there is a need for precise real-time monitoring of suspended sediments. Existing systems, however, often lack the capability to measure suspended sediment mass concentration (SSC) and particle size distribution (PSD) with low uncertainty, particularly for coarser particles, such as sand. To maintain particles with sizes up to 2 mm in suspension, which is the size of particles vented through the power waterways of the turbines, this study developed a customized laboratory setup with an upward flow column and a closed pump circuit. To foster a homogeneous SSC distribution, the setup was hydraulically optimized by different diffusor designs at the inlet of the upward flow column. We tested particles ranging from 1500 - 2000 μm at SSCs up to 20 gl−1 with optical and acoustic sensors to prove our concept. First results yielded as expected mostly linear relationships between instrument outputs and nominal SSC, particularly for larger particles. This indicates that the setup allows keeping particles up to 2 mm in suspension, enabling further measurement series to better understand the impacts of sand particles in combination with silt on sensor performance. This is crucial for enhancing suspended sediment monitoring capabilities for fine sediment venting at HPPs.
On the Generation of Large-Scale Vortical Flow Structures in Pipe Multifurcations
Authors: Semlitsch Bernhard 
Published: December 2024

Abstract
In many hydraulic power plants, the water supplied through the penstock needs to be distributed to multiple turbines. The application of pipe multifurcations is motivated by economic and efficiency reasoning. However, flow instabilities and large-scale vortical flow structures can occur for some operating conditions, causing high-amplitude pressure and mass flow rate fluctuations. To enhance the understanding of the flow instability inception, we investigate the unsteady flow in a pipe multifurcation with six branches for different operating conditions. The unsteady flow is simulated employing the large eddy simulation approach, where the numerical mesh is constructed such that y
+ < 1 and a recycling-type boundary condition is utilised to provide the turbulent inflow conditions. While the general flow pattern are described by the time-averaged results, the work focuses on analysing the unsteady physical phenomena occurring in the pipe multifurcation. At part-load operation, the results clearly show the formation of large-scale vortical flow structures stretching into the active branches. The vortices are observed to move around and eventually burst. When one vortex breaks down, the other large-scale vortices reaching into the other active branches are likely to burst and the flow pattern changes. Such events come with decreased turbulence intensity propagating through the branch line, flow separation at the branch line junction, and mass flow rate fluctuations. After a short time, large-scale vortices were established again.
Achieving zero liquid discharge through water recycle in Muara Karang Combine Cycle Power Plant
Authors: Putra S A , Yasin T R , Hikmat P J 
Published: December 2024

Abstract
The study evaluates a water recycling program implemented at the Muara Karang Power Plant (MKPP), which plays a crucial role in reducing wastewater and enhancing the operational efficiency of the power plant. Water is an essential resource in power generation, but its quality has been declining over time, impacting plant performance. Regular checks on the boiler water at MKPP reveal that the plant collects around 1-1.4 m3/second, which was traditionally discarded after inspection. However, considering the quality and quantity of this water, the study explores its potential for recycling. Since 2023, approximately 2,741.46 m3 of water has been reused, improving efficiency by 160 m3 per month while reducing wastewater discharge. The program demonstrates that simple yet strategic water management interventions can significantly improve operational efficiency and environmental sustainability in power plants. By recycling boiler water within the system, the plant conserves valuable water resources and lowers pollution levels. This study introduces a pioneering approach to water recycling in power plant by utilizing boiler water that was previously discarded. This innovative approach not only reduces the environmental impact but also sets a new benchmark for sustainable water management in the energy sector, providing a model for other power plants to follow.