bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of the leakage flow in runner on flow characteristics of a Francis turbine model
Authors: Kim S J , Choi Y S , Cho Y , Choi J W , Hyun J J , Joo W G , Kim J H 
Published: June 2021

Abstract
In the Francis turbine, there are gaps between the runner and the stator structure as the labyrinth seals. The flows inside gaps have the complicated flow phenomena; these complicated flows can affect the hydraulic performance and the downstream of the Francis turbine as the leakage flow. Therefore, it is important to investigate the flow characteristics induced by the runner gaps. However, normally the runner gap that has very complicated flow structure is often disregarded by considering the time and cost of the numerical analysis. But, it is necessary to apply all flow structures correctly to confirm the more accurate and reliable flow phenomena. In this study, the flow characteristics of gaps at the hub and shroud of the Francis turbine model runner were investigated with adding the leakage flow in the runner cone. In addition, the internal flow characteristics were compared by considering with and without the runner gaps application. For observing the influence of the leakage flow on the hydraulic performance and flow characteristics, the three-dimensional steady Reynolds-averaged Navier-Stokes analyses were performed using the shear stress transport turbulence model. The efficiency was decreased by applying the runner gaps; and the complicated flow phenomena were captured in the runner gaps.
Numerical and experimental analysis of pressure fluctuations in the draft-tube of a Francis turbine using the swirl number
Authors: Khozaei M H , Favrel A , Masuko T , Yamaguchi N , Watanabe R , Miyagawa K 
Published: June 2021

Abstract
Pressure fluctuations in the draft-tubes of hydraulic turbines are the most dominant issues that may cause damages to a hydraulic power plant. When the frequency of the fluctuations coincides with one natural frequencies of the plant, resonance with high amplitude vibrations and pressure pulsations occurs, dramatically impacting the integrity of the plant. This research focuses on the part-load behaviour of a medium specific-speed Francis turbine (with specific speed 184 m.kW), designed by the authors in the framework of an industrial project. This paper combines the results of model tests with CFD simulation to investigate the part-load behaviour of the turbine. To do so, performance of the turbine is numerically simulated at one operating condition by solving the RANS equations via the commercial code ANSYS CFX 19.0. The k-ω SST turbulence model is used to predict the turbine performance. In addition, model tests are conducted in the range of 20% to 110% guide vane opening. To capture pressure fluctuations in the draft-tube, 12 static pressure sensors are installed in 4 different sections of the draft-tube. The no-swirl and other iso-swirl lines of the draft tube flow are first determined by using CFD results. Furthermore, pressure signals from model tests are analysed by performing cross spectral density analysis. Two transitions in the behaviour of the precessing vortex under part-load conditions occurring at given values of swirl number are observed. Finally, it is observed that linear correlations between the Strouhal number of the vortex rope frequency and the swirl number can be established within the 2nd and 3rd part-load regimes, independently of the values of the speed coefficient.
Numerical simulation of the unsteady cavitating flow in a Francis turbine draft tube at Upper-Part-Load (UPL) conditions
Authors: Liu Z. , Favrel A. , Takahashi W. , Miyagawa K. 
Published: June 2021

Abstract
At part-load conditions, Francis turbines experience the development of a precessing vortex rope in their draft tube (DT), rotating with a frequency between 0.2 and 0.5 times the runner frequency. It induces pressure pulsations at the precession frequency in the whole hydraulic system, undesirable vibrations and noise putting at risk the stability of the system and the lifetime of the machine components. In specific machines, a dramatic amplification of the noise and vibrations can be observed between 70% and 85% of the design conditions. In these cases, synchronous pressure pulsations with a high frequency, typically between 2 and 4 times the runner frequency, are observed, referred to as the so-called Upper-Part-Load (UPL) pulsations. These pulsations are induced by a self-excitation of the entire hydraulic system including the cavitation vortex rope at one of its high order eigenmodes. Besides, the cavitation vortex rope features an elliptical cross-section rotating around the vortex axis at a high frequency. In this manuscript, unsteady two-phase flow simulations using a Scaled-Adaptive-Simulation (SAS) turbulence model and ZGB cavitation model of a Francis turbine draft tube at 80% of the design condition are performed to clarify the mechanisms responsible for the formation of the elliptical shape of the vortex and the UPL pulsations. However, the numerical simulation with a constant inlet boundary condition cannot reproduce the UPL pulsation phenomenon since it is a self-excited oscillation at one eigenmode of the complete system, which is not considered. Therefore, the UPL pulsations component is extracted from the measured pressure fluctuations data by applying a band-pass filter and is then set as the inlet boundary condition in the numerical simulation. The flow field is therefore artificially excited which aims to confirm whether the same phenomenon can be observed and to compare with the flow field obtained with constant inlet boundary condition. The numerical simulations are validated by experimental results, and the wave propagation in the DT is clarified.
Efficiency measurement on horizontal Pelton turbine by thermodynamic method
Authors: Cao Dengfeng , Zhou Ye , Pan Luoping , Wang Junjie 
Published: June 2021

Abstract
Thermodynamic method is a practical solution to determine the turbine efficiency of heads in excess of 100m without need for discharge measurement directly. Efficiency measurement is performed on a horizontal Pelton turbine with 650m rated head and two jets by thermodynamic method in this paper. Determination of specific hydraulic energy, specific mechanical energy, discharge and efficiency of Pelton turbine are discussed accordingly. To avoid the uncertain impact from unstable flow and velocity profile at low pressure section, an improved method to determine the turbine discharge is introduced, in which discharge may be worked out without need for flow velocity measurement at low pressure section.
Transient TEHD Analysis of a Thrust Bearing Based on Two-Way Fluid-Solid-Thermal Interaction
Authors: Cao Jingwei , Zhai Liming , Luo Yongyao , Wang Zhengwei 
Published: June 2021

Abstract
Thrust bearing is a key component of hydroelectric generator and bears the axial load of the unit. During transient processes, such as start and stop of the unit, thrust bearing usually occurs wear phenomenon at pad surface, which affects the stable operation of the unit and reduces service life of the bearing. Based on two-way fluid-solid-thermal interaction, this paper did transient thermal-elastic-hydrodynamic (TEHD) analysis of a tilting pad thrust bearing under the pump mode. For the fluid region, the Reynolds equation and the viscosity-temperature equation are solved. For the solid region, transient heat conduction equation and basic thermal-elasticity equation are considered. The data transferred in the fluid-solid interface satisfy the fluid-solid-thermal interaction equation. The variation of the lubricant oil temperature, the oil film force, the pad surface inclination angle and axial velocity of pad and mirror plate are analysed, which provide theoretical basis for the design of bearing and the safe operation of the unit.
Numerical study of hydraulic axial force of prototype pump-turbine pump mode’s stop with power down
Authors: Mao Zhongyu , Tao Ran , Bi Huili , Luo Yongyao , Wang Zhengwei 
Published: June 2021

Abstract
Pumped storage power station is regarded as a key component in modern social power system. It usually requires pump-turbine start and stop frequently. The hydraulic axial thrust is one of the most essential effects on the stable operation during start and stop. The hydraulic axial thrusts of pump-turbine pump mode’s stop with power down based on 1D transient flow simulation and 3D CFD simulation were carried out in this paper. The hydraulic axial thrusts of two operation conditions show different trends in early stage. In later stage, results show similar characteristics with load-rejection process of turbine mode. The components of Fz
including the crown, band and blade reach an obvious peak value with unit operation status change. This study provides the reference for the safety and stable operation of pump storage power stations.
Electricité de France Hydro’s overview of the First Israeli Hydro-Electric Pumped Storage Power Plant: GILBOA PSPP
Authors: Maruzewski P. , Sautereau T. , Fauriel D. , Drommi J.-L. , Ciocan G. , Laffly E. , Sapir Y. , Barak H. 
Published: June 2021

Abstract
The Israeli Public Utilities Authority (PUA) has decided to increase the instantaneous power available on the grid by adding Pumped Storage Power Plants (PSPP) to the existing generation capacity. PSPP Investments Ltd. is a private investor that has decided to develop the GILBOA PSPP. The capacity of the GILBOA PSPP is 300MW (2x 150 MWe). The project performance has to comply with PUA regulation for PSPP, and with all relevant Israeli laws and standards. The GILBOA PSPP is located at the Gilboa Mountain, in the north of Israel, near the town of Beit She’an (about 120 km North of Tel Aviv). As during IAHR 2016, EDF Hydro presented different items from feasibility studies to installations on site including model tests and manufacturing process. This current paper will give an overview of the GILBOA PSPP through short descriptions of EDF Hydro feedback during the end of the installation, during commissioning and during meetings for preparation of acceptance tests with Israeli Electric Company. The main equipment from the 2 units (reversible Francis pumps-turbines, motor-generators and associated auxiliaries) to the hydraulic gates as well as units ‘control and protection systems are provided by GE Renewable Energy which will also ensure Operating and Maintenance of the PSPP. GE Renewable Energy has introduced several technical innovations that will be presented in this paper as for instance, a dedicated trolley for the installation and the maintenance of the main inlet valves, or the thrust bearing with composite material PolyPadTM. The GILBOA PSPP is capable of connecting on IECo grid in approximately one minute.
Low-frequency oscillations in hydroturbines caused by cavitation together with the phase transitions effects
Authors: Kuibin P A 
Published: June 2021

Abstract
Among the unsteady phenomena taking place in hydroturbines one can separate oscillations caused by a cavitation bubble behind the runner. Usually a concept of cavitation compliance is used to model the cavity pulsations (Chen et al.). There was demonstrated the destabilizing effect of the diffuser and swirl. Kuibin et al. had found that the effect of swirl on stability is much smaller than that described by Chen et al. In the present work, the same analysis is repeated, but taking into account influence of the evaporation and condensation on dynamics of the cavity appearing in the draft tube. During analysis a simplified spherical cavity form was considered.
Modal Decomposition of Large- and Small-Scale Cloud Cavitation
Authors: Hatzissawidis G , Ludwig G J , Pelz P F 
Published: June 2021

Abstract
Cavitation clouds cover a frequency ω and wavenumber k spectrum limited by an upper bound due to the span of a blade or the diameter of a nozzle. The lower bound is given by the size of the eddies of a turbulent flow. Interpreting cavitation clouds as ring vortices and the formation as a challenge between re-entrant jet and asymptotic sheet growth, this becomes clear. To investigate the temporal and spatial contain of cavitation clouds, experiments were conducted on an unmodified and a modified hydrofoil with an artificial roughness i.e. an obstacle. From the high-speed measurements, we observe two cavitation regimes, (i) periodic large-scale cloud cavitation for the modified and (ii) small-scale cloud cavitation for the unmodified hydrofoil. For the latter, a coherent pattern is not visible to the naked eye. Sparsity-Promoting Dynamic Mode Decomposition is applied to the high-speed measurements to capture the dominant coherent structures from the complex flow field. This allows us to identify the underlying physical mechanism leading to cloud detachments. Within the paper we give the temporal frequencies of cloud detachments in both observed cavitation regimes.
A new method for calculating transition process based on full characteristic modeling of turbine
Authors: Liu Xiao , Jiang Xiaoping , Xiao Yexiang 
Published: June 2021

Abstract
Hydropower units undertake the tasks of frequency modulation and peak load regulation, flood control and discharge in flood season. When the unit working condition changes greatly, the stability of unit output will be affected. Therefore, the study of the transient process is of great significance to maintain the stability of hydropower units. This paper introduces a calculation method of transition process based on comprehensive characteristic curve. Based on the data of the comprehensive characteristic curve of Chaijiaxia hydropower station, the full characteristic surface of the turbine is obtained by BP neural network algorithm. Finally, the differential algebraic equation of the transient process of the turbine is established, and the transient process is solved by combining with the full characteristics of the turbine.
Numerical simulation of air injection in part load operating point
Authors: Shcherbakov P , Chirkov D , Skorospelov V , Turuk P 
Published: June 2021

Abstract
The operation hydro turbines in the off-design operating points is often accompanied by pressure pulsations with a large amplitude. One way to deal with such pulsations is to inject the air into hydro turbine flow passage. The aim of this work is to simulate this process. Previously we carried out calculations in frames of homogeneous incompressible three-phase «liquid – vapor – non-condensable gas» mixture model. The computational domain consisted of wicket gate, runner and draft tube. The wicket gate and runner were considered in the periodic stage approach. The results obtained were in good agreement with experimental data at full load operating point. It was shown that the calculations on the previous model failed to accurately simulate influence of air flow rate on the amplitude and frequency of pressure pulsations in part load. Therefore the part load regime is studied carefully in this work: different computational domains are considered, different solvers are used, including ANSYS CFX and CADRUN, developed at the Institute of Computational Technologies. Different models of «liquid – gas» mixture are used in the calculations, compressibility is also taken into account. The flow rate of the injected air ranged from 0.5 to 2 percent of the water flow rate. The influence of the injected air on the flow pattern, including the vortex rope, is investigated. The results obtained are compared with experimental data.
Velocity profiles in a water jet of a Pelton nozzle: CFD simulations on both 2D and 3D geometries
Authors: Stivala D. , Rossi M. , Renzi M. 
Published: June 2021

Abstract
Hydropower is an important energy sector deployed all over the World with a significant share in the global electricity production. Due to the ongoing climate changes, the lack of water in summer periods compromises the performance of hydraulic machines, whose efficiency quickly decreases when they operate at strong part-load conditions.
Among the most known hydraulic turbines, Pelton is suitable to be used with high geodetic heights and relatively low flow rates. When dealing with flow rates 30% lower than the Best Efficiency Point (BEP), the efficiency drastically decreases mainly due to the non-uniform velocity profiles of the water jets coming out from the nozzles. The quality of the jet is affected by the distributor geometry, bending pipes and spear valves with the respective supports located upstream.
The aim of this work is to investigate different velocity profiles of the water jet coming out from a Pelton nozzle geometry by means of Computational Fluid Dynamics (CFD) simulations performed by ANSYS® Fluent solver. Four different spear valve angles were simulated on a 2D-axisymmetric geometry, starting from a reference case of = 50° with increasing steps of 5°, maintaining a fixed positioning of the spear valve that corresponds to a partial load operation of the machine.
In addition, also a 3D simulation has been carried out and the streamlines along a symmetry plane are shown. The results of the 3D simulations were compared to the 2D-axisymmetric ones taking into account the aforementioned reference case, showing how this last simplification of the computational domain leads to almost the same macroscopic results.
Digitalization in hydropower generation: development and numerical validation of a model-based Smart Power Plant Supervisor
Authors: Vagnoni E , Gerini F , Cherkaoui R , Paolone M 
Published: June 2021

Abstract
The paper presents the development of a model-based Smart Power Plant Supervisor, a digital tool targeting the optimization of the operation and maintenance of hydroelectric units to improve ancillary services provision to the power system. The paper focuses on a control-oriented modelling methodology which allows integrating the operational parameters of the hydroelectric unit in an optimization algorithm steering the advanced control of the units. The technique to develop analytical functions representing the behaviour of the hydropower plant is presented and validated by comparing numerical simulations with measurements of the real time operation of the run-of-river hydropower plant Vogelgrun. The results show a good performance of the modelling technique able to correctly predict the power generation of the power plant over one month of operation.
Multi-objective shape optimization of Francis runner using metamodel assisted genetic algorithm
Authors: Chirkov D , Filatova A , Polokhin S 
Published: June 2021

Abstract
Nowadays evolutionary optimization techniques become an integral part of the design process of hydraulic turbine runners. For optimization the shape of the runner is parameterized by a set of geometrical parameters. The objective functions of each runner geometry, being the efficiency and cavitation performance, are evaluated through CFD analysis of 3D flow-field. As usual, some kind of genetic algorithm is used for searching the Pareto front, due to its inherent possibility of parallel evaluation of different runner variants within one generation. This approach requires extensive CFD computations of hundreds and thousands of runner variants. In order to speed up the optimization process a metamodel (approximate, surrogate model) can be utilized. The metamodel provides an approximation of true dependency of the objective functions on the design parameters. The metamodel is built based on the known objective functions for some initial set of points randomly taken form the design space. Once built, it can be used to replace time consuming CFD computations during the optimization process. In the present paper a metamodel, based on Gaussian processes, is implemented and integrated into a multi-objective genetic algorithm. The obtained algorithm is applied for shape optimization of the Francis turbine runner. The number of the design parameters varied from 4 to 24. The objective functions are multi-point efficiency and cavitation characteristics. True values of the objective functions are evaluated using Reynolds averaged Navier-Stokes computations of the flow field in a reduced turbine domain, including wicket gate, runner and draft tube. These values are used to train the initial metamodel. In order to enhance predictive capabilities of the metamodel, it is retrained periodically during the optimization loop. The results of metamodel-assisted optimization runs are compared to that obtained without metamodel. It is shown that application of metamodel significantly reduces the number of actual CFD computations even for high number of design parameters and thus speeds up the overall optimization process.
Influence of the runner cone design on the pressure fluctuations in the draft tube of a low head Francis turbine
Authors: Khullar Subodh , Kumar Sandeep , Singh Krishna M , Cervantes Michel J , Gandhi Bhupendra K 
Published: June 2021

Abstract
This paper presents a preliminary numerical investigation on the design of the runner cone for a small turbine test rig under development at IIT Roorkee, India. The test rig is designed to study the formation and mitigation of rotating vortex rope (RVR) in the draft tube of a low head Francis turbine. The original runner cone design needs to be modified to include the provision for axial jet injection. Three different configurations, namely, a truncated cone and two original length cones with different nozzle positions, have been compared with the original cone to choose a suitable one for further investigations. The entire three-dimensional flow passage of the turbine unit has been simulated using the shear stress transport turbulence model after carrying out a mesh independence test on the original design. The proposed designs are compared at three different operating points. The amplitude and frequency of the pressure pulsations in the draft tube have been analyzed using the fast Fourier transform (FFT) method.
Stabilisation of the swirl exiting a Francis runner far from the best efficiency point
Authors: Susan-Resiga R F , Muntean S , Bosioc A , Stuparu A 
Published: June 2021

Abstract
The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge, far from the best efficiency point, develops self-induced instabilities featuring a precessing helical vortex (so-called vortex rope) which hinders the stable and safe turbine operation. This is an intrinsic characteristic of the swirl exiting the Francis runner, which at part load has a relatively large residual flux of moment of momentum as well as an imbalanced specific hydraulic energy with an excess near the band. We address in this paper the question of how one should alter this swirling flow in order to mitigate further instabilities in the discharge cone. In doing so, we consider an actuator disk located in the upstream part of the discharge cone that model a runaway runner which alter the hub-to-shroud angular momentum and specific head distributions without altering the turbine operating point. However, such a runaway runner provides a swirl stabilisation further downstream thereby effectively mitigating the vortex rope.