bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of a Novel Cavitation Monitoring System for Hydro Turbines Based on Machine Learning Algorithms
Authors: Amini Ali , Pacot Olivier , Voide Dominique , Hasmatuchi Vlad , Roduit Pierre , Münch-Alligné Cécile 
Published: October 2022

Abstract
Operating hydro turbines in off-design conditions increases the risk of cavitation occurrence, which in turn, leads to numerous problems such as performance degradations, structural vibrations, and most importantly, mechanical damage due to erosion. It is therefore crucial to develop a monitoring system that detects the occurrence and severity of cavitation in real time. For this purpose, a cavitation detection methodology has been developed that is based on the analysis of acoustic emissions of a turbine with machine learning algorithms. In this method, a conventional microphone is used to record the airborne noise emitted from a turbine under different working conditions, and then, a supervised learning algorithm is trained to classify the recorded noise signals into cavitating and non-cavitating categories. The detection system was developed based on laboratory tests and was validated in Ernen hydropower plant located in Canton of Wallis in southeast of Switzerland. This power plant consists of two identical double-flux Francis turbines each having a maximum power of 16 MW and a net head of 270 mWC. The preliminary results obtained from a two-day experimental campaign in the Ernen powerplant are very promising in terms of cavitation detection with a classification accuracy of more than 90 %. The system could be implemented either for real-time monitoring of cavitation occurrence allowing the operators to avoid such a condition or as a post processing tool to evaluate the number of hours a turbine has worked under severe conditions. Work is still ongoing to deploy more complex learning algorithms for this task to minimize expert intervention and/or interpretation during the setup process.
Evaluation of fish-related properties of Kaplan turbines at the design phase: simulation-based outcomes vs. experimental data
Authors: Romero-Gomez P , Salalila A , Deng D Z , Peyreder R 
Published: October 2022

Abstract
The development of turbine technology faces growing demands to maximize the survival of migratory fish entrained into turbine flows. In this context, two strategies have emerged for quantifying hazardous hydraulic conditions: computer-based evaluations at design stage and recordings with autonomous sensors deployed in prototypes. The former is a desktop evaluation with many modelling assumptions (idealization) and the latter is a field technique that introduces various unknown and uncontrollable factors (uncertainty.) The present work introduces and implements a third method based on test rig measurements and the corresponding computer-based predictions of conditions that negatively affect fish survivability. The experimental work was conducted in a five-bladed Kaplan turbine model in which miniaturized autonomous sensors (SF Mini, developed at the Pacific Northwest National Laboratory, U.S.) measured fish-relevant hydraulic features. The modelling work involved flow simulations according to industry practices and the representation of fish trajectories through the simulated flow conditions. We compared both the experimental measurements and CFD outcomes and discussed the challenges and advantages of the modelling strategies, as well as the benefits for turbine engineers in need of incorporating effective design concepts to mitigate fish mortality through turbines.
Experimental and numerical validation of a Francis turbine draft tube designed for mitigation of pressure fluctuations
Authors: Favrel Arthur , Irie Tatsuya , Ishii Yuya , Lee Nak-joong , Miyagawa Kazuyoshi 
Published: October 2022

Abstract
This paper presents an experimental and numerical investigation of the internal flow in a Francis turbine draft tube previously designed for minimizing pressure fluctuations and energy losses in off-design conditions. The design of the draft tube geometry is based on an original approach combining Design of Experiments and steady/unsteady Computational Fluid Dynamics (CFD) simulations of the draft tube internal flow. The proposed method provides new insight on the influence of the draft tube geometry on the flow dynamic behaviour on one hand and enables the determination of a geometry promoting flow stability and hydraulic performance on another hand. CFD simulations of the internal flow in the final geometry showed promising results in terms of flow stability compared with the initial geometry designed by conventional CFD-aided methods. A reduced-scale model of the prototype machine featuring the final draft tube geometry is finally installed and tested in laboratory. Tests include performance and pressure fluctuations measurements over the complete operating range. The analysis of the results shows that the draft tube flow remains globally stable over the complete part-load range with pressure fluctuations amplitude lower than 1% of the net head. It is also shown that the dominant pressure component at the runner outlet in the draft tube cone is of synchronous nature. The physical mechanisms of excitation are finally highlighted by analysis of unsteady CFD simulation results.
Hydroacoustic interaction between draft tube and penstock eigenmodes under Francis turbine full load instability
Authors: Alligné S. , Nicolet C. , Vaillant Y. , Lowys P-Y. , Heraud J. , Lecomte B. 
Published: October 2022

Abstract
At high load, Francis Turbines may experience self-sustained pressure surge leading to significant power swing and pressure fluctuations along the waterway. The physical mechanism initiating this instability phenomenon has been the subject of much research. The development of the axisymmetric cavitating vortex rope at the runner outlet modifies the hydroacoustic properties of the draft tube waterway. Very low wave speed due to high cavitation volume combined with a high swirling number initiates the unstable axial pulsations of the cavitating vortex rope which frequency corresponds to a penstock’s eigenfrequency. The 15 MW power plant of Monceaux-la-Virole in France, composed of two units fed by a single penstock, experiences such full-load surge. On-site tests have been carried out to analyze the envelope of pressure fluctuations along the penstock once instability occurs. Combined with a 1D SIMSEN model of the power plant, these measurements have allowed to enhance the understanding of this instability phenomenon. To achieve this, an advanced draft tube modelling taking into account distributed wave speed, convective terms and divergent geometry is used and frequency analysis is carried out. Unstable draft tube eigenmodes and stable penstock eigenmodes are predicted. The key draft tube model parameters such as wave speed and second viscosity are calibrated to set the draft tube eigenmode frequency to the unstable measured frequency for different operating points. This frequency analysis concludes that high load instability occurs when a matching between the draft tube and the penstock eigenfrequencies is experienced. Moreover, it is shown that the unstable draft tube eigenmode is able to interact with different order penstock eigenmodes as function of the operating point of the unit.
Influence of axial water jet size on RVR mitigation in draft tube of Francis turbine
Authors: Khullar S , Kumar S , Singh K M , Cervantes M J , Gandhi B K 
Published: October 2022

Abstract
The present work investigates the effect of the axial water jet nozzle size on the unsteady pressure fluctuations arising from RVR formation in the draft tube of a Francis turbine operating at part load. The results compare two different nozzle diameter jets for their effect on the pressure pulsations and pressure recovery in the draft tube. Simulations were carried out at four jet injections varying from 2% to 10% of the main discharge. The study also presents the changes in the net effective area and average swirl in the draft tube with the introduction of the water jet.
Optimization of Francis Turbine Runner for Variable Speed Operations with minimization of sediment erosion
Authors: Ghimire Amul , Gautam Saroj , Chitrakar Sailesh , Neopane Hari Prasad 
Published: October 2022

Abstract
Sediment erosion is one of the most notorious phenomenon damaging the turbines, in the Himalayan region. Francis turbine, which is one of the most used type of hydro turbine in the world as well as in Nepal, is affected quite severely, more so when operated in off design conditions. This study has taken a reference design of a Francis turbine from a hydropower in Nepal to optimize it for operation in variable speeds. Minimization of sediment erosion and maximization of efficiency are taken as the objective functions of the optimization, for which blade angles at trailing edge and blade angle distribution are taken as the design variables. The design space of the runner are constrained such that the optimized design could replace the existing runner in the turbine. Latin Hypercube Sampling technique is used to populate the design space such that the design variables are divided randomly to create required number of designs in the design space. Computational Fluid Dynamic analysis are performed on simplified numerical models of the samples to predict their performance and Sediment Erosion Rate Density (SERD), under various operating conditions. The results of output parameters, obtained from CFD, along with the design variables, are used to develop an approximation model relating the objective functions with the design parameters. NSGA-II optimization technique is used to search for the optimum design. The paper presents the comparison of the sediment erosion and efficiency of the reference runner and optimized runners under various operating conditions. It also presents an outline of the process used to optimize the runner for variable speed operation with minimum sediment erosion.
A Simulation Study of Hydraulic Vibration caused by Clearance Flow in a Pump Turbine
Authors: Hu H P , Xia M , Qiao M , Wang W , Wang J Z , Wang Z W 
Published: October 2022

Abstract
The pumped-storage power station needs to adjust the load to meet the needs of the power grid at any time and cannot always operate under the best working conditions. In practical operation, vibration phenomenon with complex inducements occasionally occurs. In the stable operation of the Baishan energy storage power station, the headcover vibrates obviously. To find the cause of vibration, this paper modeled the unit flow area, used the numerical simulation method for steady and unsteady calculation, extracted the pressure fluctuation information in the flow field, and then analyzed the possibility of strong vibration caused by the instability of the flow field. The results show that there is a low frequency component of pressure fluctuation caused by the spiral motion of the fluid in the sealing groove in the upper canopy clearance flow, which may be the inducer of the vibration of the headcover.
Evaluation of startup time for a model contra-rotating pump-turbine in pump-mode
Authors: Fahlbeck J , Nilsson H , Salehi S 
Published: October 2022

Abstract
A larger part of the electricity is today from intermittent renewable sources of energy. However, the energy production from such sources varies in time. Energy storage is one solution to compensate for this variation. Today pumped hydro storage (PHS) is the most common form of energy storage. Usually, it requires a large head, which limits where it can be built. In the EU project ALPHEUS, PHS technologies for low- to ultra-low heads are explored. One of the concepts is a contra-rotating pump-turbine (CRPT). The behaviour of this design at time-varying load conditions is today scarce. In the present work, the impact of the startup time for a CRPT is analysed through computational fluid dynamics (CFD) simulations. The analysis includes a comparison between a coarse and a fine CFD model. The coarse model produces acceptable results and is 50 times cheaper, this model is thus used to assess the startup time. It is found that longer startup times generate lesser loads and peak values. A startup time of 10 s may be a sufficient alternative as the peak loads are heavily reduced compared to faster startups. Furthermore, there is not much difference between a startup time of 20–30 s.
Experimental Analysis of a Centrifugal pump in pump mode and turbine mode
Authors: Pokharel N , Sapkota P , Ghimire A , Thapa B S , Thapa B 
Published: October 2022

Abstract
The national grid of Nepal faces several hurdles during its operation, especially in remote areas of hilly and mountain region. Citizens face blackouts of days to weeks, due disturbances caused in the grid in those regions. Micro hydro can be a very strategic backup for the national grid in those regions. However, due to lack of subsidy, which used to be provided in the past, for development of micro hydro, micro developers are unable to afford the construction cost of the micro hydro. Thus using Pumps that are readily available in the market at a much cheaper price, compared to custom built hydro turbines, as turbines can be a very economical alternative for such cases. But the concept of pump as turbine has not been utilized in Nepalese market. In this study, a centrifugal pump abundantly available in the Nepalese market has been used to evaluate its performance in turbine mode as well as in pump mode. A characteristic performance curve of the pump operated in turbine mode is obtained from the experimental data. The Best efficiency point and the operating regime is also determined based on the results obtained from experiments. The head conversion factor and discharge conversion factor calculated based on the data measured from the experiment, at various operating conditions, are compared to previous works done by other researchers. The performance obtained from the experimental analysis is comparable to the performance of the turbines installed in the micro hydro power projects. PAT can be a game changer in the micro hydro sector, by providing a very economical and technically viable option of expensive hydro turbines.
Parametric design and multi-objective optimization on blade high-pressure side of a pump-turbine
Authors: Qin Y L , Li D Y , Wang H J , Liu Z S , Wei X Z , Wang X H 
Published: October 2022

Abstract
High pressure side, as the runner outlet at pump mode and runner inlet at turbine mode, playing an important role in controlling hydraulic loss and flow characteristics in vaneless region, affecting both steady characteristics and unsteady characteristics. While when it comes to three-dimensional inverse design of a pump-turbine blade, scholars are forces on the design method in runner flow channel, ignoring the geometry profile of high-pressure side. Hence, in present paper, concepts “swept”, “bowed (lean)” and “twisted” are innovatively introduced, eight new parameters are proposed to control the profile of blade high pressure side. And then a multi-objective optimization design system consisting of geometry generation, computational fluid dynamics, design of experiment, approximation model, multi-objective genetic algorithm, and self-organization map is built. Efficiency at both pump mode and turbine mode and S margin at turbine mode are selected as optimization objectives in the first optimization step. Then, the hump margin is regard as the objective in the second optimization step. Based on the two-step optimization, a runner with optimized high-pressure side is obtained and CFD results show that compared with the original runner, the efficiency at rated points and the margin of unsteady characteristics can be increased. The parametric design method on high-pressure side presented in our paper can be regard as an essential supplement to the traditional design method in hydraulic machinery.
Pressure pulsation of a single-stage storage pump with 1300 m delivery head
Authors: Benigni H , Bodner C , Leithner S , Kirilowitsch C , Giefing D , Penninger G , Giese M , Jaberg H , Meusburger P 
Published: October 2022

Abstract
A new storage pump replaced 3 multistage pumps to transport water between the Kreuzeck and the Reisseck power plant sides. Located in the valley of the two reservoirs, it provides impressive performance data for single-stage operation at n = 3000 rpm. Hydraulics already utilised for significantly lower heads are the basis of this pump. The pump was adapted to the new location, and CFD-based development was applied. Within the scope of a model test, the performance data (Q-H-Eta and Q-H-Sigma) were to be confirmed and measured, including the inflow and outflow situation. In addition, the pressure pulsations had to be verified. Finally, installing air vessels should reduce pressure pulsations on the suction and pressure sides. Furthermore, modifications in the bladed areas of the impeller and the guide vane section should enhance this reduction.
Mesh dependence analysis for simulating unsteady cavitation around a plane convex hydrofoil
Authors: Puga D , Escaler X , Hidalgo V , Luo X 
Published: October 2022

Abstract
The mesh significantly influences the quality of the numerical results in computational fluid dynamics (CFD) problems due to its correlation with turbulence models. In the present paper a structured mesh was generated using Gmsh and two semi-structured meshes were generated using snappyHexMesh to determine the suitable mesh distribution for simulating unsteady cavitation around a plane convex hydrofoil. The numerical simulation was conducted by using the software OpenFOAM with the k-ω SST SAS turbulence model and the Zwart-Gerber-Belamri (ZGB) cavitation model. Besides, the experimental results obtained by the Laboratory for Hydraulic Machines of École Polytechnique Fédérale de Lausanne were used to validate the numerical results. The results showed that both structured and semi-structured meshes predicted the cavitation pattern and the maximum cavity length. The semi-structured mesh with suitable refinement reproduced in detail the dynamic behavior of unsteady cavitation, while the structured mesh efficiently reproduced the phenomenon.
Draft tube guide vane system to mitigate pressure pulsations
Authors: Joy J , Raisee M , Cervantes M J 
Published: October 2022

Abstract
The present study introduces the concept of mitigating pressure pulsations in a hydro-turbine draft tube. The concept refers to using an adjustable guide vane system in the draft tube. The adjustability relates to its ability to rotate around an axis. The test rig for the experimental study is a high-head Francis model turbine. Three sets of guide vanes are distributed evenly circumferentially in the draft tube. Each guide vanes consists of two hydrofoils. The upper hydrofoil can move around an axis. The lower hydrofoil is fixed. The turbine operating head for the experiments was 12 m. The operating condition considered is at part load, for Q/Q

BEP
= 0.71. The results indicate that using the guide vanes in the draft tube, the plunging mode of the rotating vortex rope becomes insignificant for nearly all upper hydrofoil configurations considered. The reduction in the rotating mode of the vortex rope is between 50% and 80%. The vortex rope frequency shifts from 0.307·f

0
and varies between 0.33·f

0
to 0.617·f

0
, which is a function of upper hydrofoil angles
Global linear stability analysis of the flow inside a conical draft tube
Authors: Mitruţ R , Bucur D M , Dunca G , Cervantes M J 
Published: October 2022

AbstractThe paper presents the numerical simulations of the flow inside the draft tube of Francis-99 turbine at the part load (PL) operating condition. The rotating vortex rope (RVR) is a phenomenon that occurs during the PL operating regime inside the draft tube of hydraulic turbines. To reduce the computational cost, the numerical simulations are carried out in two steps. Firstly, steady state numerical simulations are performed in a reduced geometry of the runner which is made of a runner passage and part of the draft tube. The velocity profiles from the steady state simulation are used as a boundary condition for unsteady numerical simulation on the inlet of the full draft tube geometry. The velocities from the numerical simulations are time-averaged over a period of 5 RVR rotations and validated with the experimental velocities averaged over the same period. Further, a two-dimensional (2D) linear global stability analysis is performed on a plane extracted from the cone of the draft tube using the time-averaged flow. The frequency of three-dimensional (3D) flow simulation and of the 2D stability analysis are found to be in good agreement with the experimental frequency.
Impact of runner crown shape modifications on the onset of the precessing vortex core
Authors: Lückoff F , Naster M , Müller J S , Sieber M , Litvinov I , Oberleithner K 
Published: October 2022

Abstract
In this experimental study, a passive flow control concept is provided to extend the stable part load operation regime by shifting the rise of the precessing vortex core (PVC), also known as vortex rope, toward lower mass flows respectively deeper part loads. A parametrized runner crown design working as a passive flow control device is derived. This control device aims for shifting the bifurcation point of the PVC to lower flow rates. To determine the most influential design parameters and derive an optimized runner crown design, a design of experiments (DoE) approach is used. This DoE approach is based on data obtained from differential pressure sensors inside the draft tube wall of a generic hydro turbine test rig using air as working fluid. By means of stochastic modeling, the growth rate of the PVC mode is derived from the statistics of the measured pressure signals. The growth rate is used to estimate the bifurcation point of the PVC characterized by a certain normalized flow rate. It is shown that the stable part load operation regime is extended by up to 25% due to the passive impact of the modified runner crown. Moreover, the operational range featuring considerable PVC-induced pressure oscillations is diminished and the pressure recovery of the draft tube is improved compared to the baseline case.
On the relevance of the runner crown for flow instabilities in a Francis turbine
Authors: Müller J S , Lückoff F , Kaiser T L , Oberleithner K 
Published: October 2022

Abstract
The precessing vortex core (PVC), also known as vortex rope, in a draft tube of a Francis-99 hydro turbine is investigated. The goal is to increase our comprehension of the root of the PVC in order to attenuate or suppress the PVC, thus extending the stable operational range below the best efficiency point at part load conditions. Unsteady Reynolds-averaged Navier– Stokes simulations are conducted and used as a basis for all the analyses performed in this work. The discrete Fourier transform (DFT) and the spectral proper orthogonal decomposition (SPOD) as data-driven methods and the linear stability analysis (LSA) as a physics-based, operator-driven method are used to examine the PVC in detail. With the DFT and SPOD, two dominant modes are found inside the draft tube. Likewise, the LSA reveals two distinct linear instabilities of single-helical and double-helical shape, which agree with the findings of the SPOD in terms of spatial shape and temporal frequency. A particular focus is laid upon the region upstream of the draft tube. An adjoint-based sensitivity analysis reveals that both instability modes are highly sensitive to mean flow modifications inside the transitional segment between runner and draft tube, such as induced by passive control devices. The knowledge of these sensitivities will guide to an optimized runner and draft tube design for controlling the PVC and the double-helical mode.