bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vortex rope interaction with radially protruded solid bodies in an axial turbine: a numerical study
Authors: Holmström H , Sundström J , Cervantes M J 
Published: October 2022

Abstract
Radially protruded solid rods and their interaction with the rotating vortex rope at part load condition are investigated numerically on an axial model turbine.
The commercially available software ANSYS CFX was used to perform the simulation, and the test case was the Porjus U9 Kaplan turbine model operating at a fixed runner blade angle at part load condition. Four rods, with a rod diameter equal to 15% of the runner diameter were evenly distributed in a horizontal plane in the draft tube cone and protruded to a length set to intercept the RVR in its unperturbed trajectory. It is shown that the RVR plunging (synchronous) mode is completely mitigated upstream and downstream of the protruded rods. The RVR rotating (asynchronous) mode is reduced by 47% and 63% at the two monitor positions located upstream of the protruding rods, while only a minor reduction occurs to the first RVR harmonic at the monitor positions located downstream of the protruded rods. The perturbed RVR experiences an increased angular velocity due to the flow area decrease caused by the protruding rods, thus increasing the RVR frequency by approximately 53% compared to the unperturbed value. Investigation of the swirling flow indicates a locally increased swirl in the center of the draft tube downstream of the protruded rods which could explain the reduction of the RVR pressure amplitude. The overall turbine efficiency with solid rods protruded causes a marginally efficiency reduction of 0.85%. However, as the RVR pressure pulsations are reduced significantly, a more comprehensive investigation of the rods impact on the turbine performance and life time should be performed to elucidate the suitability of using solid rod protrusion for RVR mitigation.
Application of wireless measurement technology in hydraulic turbine test
Authors: Deng Xiangping , Wang Xiuling , Liu Zhiyuan 
Published: October 2022

Abstract
At present, the measurement of internal characteristics of hydraulic machinery runner (blade pressure pulsation, pressure field and dynamic stress) and blade torque is difficult to be realized by the existing wired measurement methods due to the measurement object is a high-speed rotating part. This paper will introduce the system composition and application in hydraulic machinery of the wireless measurement technology one by one. In the measurement of model hydraulic machinery, it is mainly used to measure the rotating part. The sensors work in water, including measuring the internal characteristics of the runner (blade pressure pulsation, pressure field and dynamic stress) and blade torque. The wireless measurement technology that is by laying the corresponding measurement unit at the measured part, the signal sensed by the sensor is collected and stored by the node, and then wirelessly transmitted through the node, and the data is received through the wireless gateway and enters the computer acquisition system.
Comparison of fatigue loading in Francis turbine runners using extreme values interpolation
Authors: Pham Q H , Gagnon M , Page M 
Published: October 2022

Abstract
Extreme values of strain signals are important for hydroelectric turbine runners fatigue assessment. However, due to measurements limitations such as short data length and limited subset of measured operation conditions, the extreme values are rarely fully captured. Our study aims to estimate the extreme values of runner strain at non-measured operating conditions by interpolating the extreme components from the measured ones. The method is based on the peaks over threshold technique and the kriging interpolation. A case study with two similar Francis turbines (same design and power plant) is presented. The comparison is made between the use of independent interpolation models and a combined model for the two turbines. This helps assess the assumption that similar turbines share similar fatigue loading. If that is the case, a common model for the whole fleet of similar turbines design in a given facility could be considered, and thus contribute to reduce the uncertainties related to unmeasured loadings without the need for in-situ measurements on every runner.
Measurement and analysis on natural frequency of runner blade of hydraulic turbine by hammering method
Authors: Cao Dengfeng , Ding Jiaren , Zhou Ye , Jiang Cuiwei 
Published: October 2022

Abstract
Hammering method is a common solution to the measurement on natural frequency of solid components. Due to the difficulty to directly measure the natural frequency of a rotating runner in the water, numerical simulation is widely applied to predict the runner behaviours. To verify the influence coefficient of the natural frequency in the water than that in the air, specific measurements are taken on a model runner both in the water and air and a prototype runner by hammering method. Test results show that the ratio of natural frequency in the water to in the air lies in 0.692 ∼ 0.753 on the model runner, and 0.746 ∼ 0.812 on the prototype runner. Practice in this paper shows that hammering method is a helpful way to predict the natural frequency of runner blade in the water, then the operation risk of resonance may be avoided.
Approach to sediment monitoring in Hydro Power Plant
Authors: Almeida Vinícius , D’Agostini Neto Alexandre , Jung Alexander , Kratzsch Axel , Sozio Felipe , Gissoni Humberto , Papp Guilherme , Asencio Jaime Danus , Nieto Diaz Jose Manuel , Gonçalves Manuel , Garcés Octavio , Rohne Wolfgang 
Published: October 2022

Abstract
The presence of mineral sediments in water led to significant erosion damage to a power plant in the Chilean Andes. The plant is operated by Enel and is equipped with three vertical Francis power units, with approximately 25 MW each operating under a net head of around 120 m. The overall machine condition with reported significant damage on the turbine caused by erosion led to a modernization project with runner replacement and output and efficiency increase. In order to ensure a proper sediment measurement and quantification during the turbine operation, Voith developed, supplied and installed a sediment monitoring system in power unit #01. The monitoring system, developed using the OnCare.Health Hydro platform, applies optical sensors installed directly in the spiral case inlet section to measure the water turbidity. Other operational parameters are recorded, processed and stored together in the same database. Two optical sensors were installed in the spiral case inlet section and provide turbidity readings. The first one is positioned directly flush to the flow. The second one is located in a sampling pipe that collects water from four different points of the same cross section. An automatic water sampler installed in the sampling pipe collects water periodically, which is sent to a laboratory for particle analysis. The laboratory results allow an identification of important parameters such as sediments concentration, particle sizes and materials that are used for correlation with the indicated turbidities. The main data analysis shows that the power unit operated most of the time close to the rated condition. A comparison between turbidities indicated by both sensors shows an offset, probably associated to the particles distribution along the cross section. A system calibration process successfully correlated suspended sediment concentration and turbidity values to allow online indications of the sediment concentration. The system has been operating for almost two years in a close cooperation with the engineering teams of the plant owner and system provider. Main results and system findings for this application will be presented and discussed in this paper.
PIV measurements in the draft tube of a down-scale propeller turbine: uncertainty analysis
Authors: Sotoudeh Nahale , Shiraghaee Shahab , Andersson Robin , Sundstrom Joel , Raisee Mehrdad , Cervantes Michel 
Published: October 2022

Abstract
In this study, the flow in the conical section of the draft tube of a propeller turbine has been investigated at the best efficiency point and part-load operating conditions using 2D and stereoscopic 3D particle image velocimetry. Since the flow in the turbine is periodic, it is necessary to study the mean flow field rather than the instantaneous one to identify the flow characteristics from a statistical standpoint. However, the statistical convergence of the obtained mean velocity is questionable. Thus, the current work proposes a methodology for investigating the convergence of mean velocity profiles based on the central limit theorem. The methodology is applied to the best efficiency point and part-load results. The results show that 3D PIV results have lower uncertainty than 2D PIV results because measuring the tangential velocity component affects uncertainty, only measured in 3D PIV. The uncertainty difference is more significant, especially in part-load operation, due to the presence of the rotating vortex rope, and therefore a more accurate measurement is necessary to produce a reliable mean flow field. Furthermore, the convergence of the mean velocity profile is faster, with lower uncertainty for best efficiency point results since, at the part-load condition, the tangential velocity component of the flow is higher. In addition, the converged mean velocity profiles show a backflow region with minor rotation in the center, surrounded by a high rotational axial flow during the part-load operation of the turbine.
Research of Water Consumption Rate Measurement Based on Thermodynamic Method
Authors: Zhou Ye , Duan Lian , Cao Dengfeng , Li Ligang 
Published: October 2022

Abstract
As an important index which can be used to evaluate the economic operation result for hydropower station, the water consumption rate of hydropower unit can be acquired with hill chart curve of hydraulic turbine, the relationship curve between flow discharge of hydropower station and water level of reservoir. However, considering that the hill chart curve of turbine is calculated and converted by the model test, there are certain errors when used on the prototype machine, which also brings limitations to the applicability. According to the definition of water consumption rate, it can be determined by the unit’s net head and efficiency. The static water head of the unit can be obtained by measuring pressure for spiral case inlet and draft tube outlet. Therefore, the key issue for the measurement of unit water consumption rate is the measurement of turbine flow discharge. Therefore, according to the operating characteristics of high-head turbines, this article adopts thermodynamics to measure the flow discharge of turbine, studies the installation and implementation of high- and low-pressure section test instruments with the site condition of a hydropower project, and analyses of the water consumption rate of units under different conditions such as the multiple-unit’s operation, various water heads, etc. The analysis results show the relationship and trend for the water consumption rate and unit operation condition, which can provide references for the optimal dispatch operation of multi-units’ hydropower stations, achieving the purpose of reducing the water consumption rate of power generation and improving the efficiency of power generation.
Virtual sensors to generate turbine runner blade strains from indirect measurements
Authors: Gagnon Martin , Vouligny Luc , Cauchon Luc , Giroux Anne-Marie 
Published: October 2022

Abstract
Strain measurements on turbine blades are difficult and costly tasks. Such measurements, when carried out, generally only happen during the runner commissioning. This gives rise to two problems. The first is that some of the sensors often stop functioning properly during the measurement campaign, which leads to distorted data, and the second is that runner blade strains are not available for long-term monitoring after the measurement campaign. To alleviate the consequences of distorted or missing values, we propose the use of neural networks to automate the imputations of missing values in measurement campaign data using virtual sensors. Three types of network architecture are proposed: Long Short-Term Memory (LSTM) in different multi-stage/multi-layer configurations in Nonlinear Auto-Regressive Neural Networks with exogenous input (NARXNN), injector multi-scale attention network (Injector MA-Net), and a combined architecture using both. The performance of these architectures will be compared in four situations: the loss of strain gauge rosette branches; the loss of a complete strain gauge rosette; the loss of data on a complete blade; and the absence of strain data, which is related to the problem of identifying which sensors could be used for long-term monitoring. The performance of the proposed algorithms will be evaluated on real case scenarios from a measurement campaign during a recent unit commissioning.
Application of a Coupled Reynolds Stress Model to a Swirl-Driven Diffuser Flow
Authors: Del Rio A , Casartelli E , Mangani L , Roos Launchbury D 
Published: October 2022

Abstract
Swirling flow is a dominant feature in a significant number of technical applications. Hydraulic turbines at part-load are strongly affected by the related vortex rope phenomenon. Its dynamic behavior has a negative impact on the operating performance and durability of the machine.
CFD can be used to get additional insight in this complex phenomenon but requires a valid simulation model able to capture the relevant flow physics, which is driven by highly anisotropic turbulent structures. The simulation results are therefore strongly affected by the turbulence modeling. A swirl apparatus (AC6-14), for which extensive experimental data is available, is used in this work for the assessment and validation of different turbulence models. The state-of-the-art SST k-ω model, with and without curvature correction, is compared to a coupled full Reynolds stress model. All models are integrated into a pressure-based coupled flow solver.
The investigation revealed that both, SST k-ω with curvature correction and the full Reynolds stress model better predict the time-averaged velocity profiles in the diffuser compared to standard SST k-ω. The swirl component is thereby best captured with the Reynolds stress model. All models deliver a reasonable frequency spectrum for the dynamic behavior of the vortex rope. However, flow visualization shows that standard SST k-ω is not capable of predicting the shape and size of the vortex rope accordingly. Both, SST k-ω with curvature correction and the full Reynolds stress model, can be used in the future for more detailed flow investigations, which include also the assessment of flow control measures.
Comparison of mechanical stress in Pelton Buckets between simulation and measurement
Authors: Rentschler M , Weibel P , Isler P , Lais S , Gervais N 
Published: October 2022

Abstract
Thinner structures, lead to higher efficiencies, but also to higher mechanical stresses. The increase of the hydraulic performances of Pelton runners is hence limited by mechanical stress constraints. The design process of Pelton runner therefore includes stress and hydraulic assessment during profile development phase. This assessment is based on the combination of Finite Element Method (FEM) for the mechanical stress and computational fluid dynamics (CFD) for the hydraulic behavior of the machine. This combined approach enables the generation of hydraulic profiles with high efficiency while respecting defined limits for the stress. The validation of the combined simulation is achieved by comparison with prototype measurements. For several projects the runners have been equipped with strain gauges in the root and close to the cut-out to record the deformation for different operating points. The comparison with numerical simulation results shows some limitations of the approach but concludes with a satisfying agreement between numerical simulation and measurement.
Effect of blade layout on performance of low specific speed pump operating in turbine mode
Authors: Štefan David , Chabannes Lilian , Hudec Martin , Bezdíček Jiří , Rudolf Pavel 
Published: October 2022

Abstract
The very low specific speed pump (nq = 8.9) operated in turbine mode was analyzed. The experimental and numerical studies were carried out in order to show effect of different blade layout on pump-as-turbine (PaT) performance. In total three different impellers were analyzed. One impeller consisting of four main blades and two impellers consisting of four main blades and different arrangement of splitter blades. Either single splitter blade or two splitter blades are placed between each of main blades. While measurements pointed out the main PaT performance, the simulations enable to analyze internal flow fields and point out the mechanisms of performance variation using different impellers. The main aim of this study is to clarify usability of very low specific speed pump for energy recovery in terms of pump as turbine operation or for storage capability in terms of pump-turbine.
Eigenfrequencies of rotating discs in dense fluid: imposed modal motion approach
Authors: Nennemann B , Monette C , Braun O , Biner Daniel , Münch-Alligné Cécile 
Published: October 2022

Abstract
The mode split on disc like structures rotating in a dense fluid leads to a deviation of eigenfrequencies at high rotational speeds compared to their values in still water. Predicting eigenfrequencies correctly is essential to avoid fatigue cracks on prototype turbine runners. Analytical models for simple geometric configurations and complex numerical models using fully coupled fluid structure interaction to predict the mode split on arbitrary geometries exist. We are presenting a complementary approach of intermediate complexity applicable to arbitrary geometries. Mode shapes and modal parameters are computed by finite element analysis in still water. These mode shapes are imposed with a harmonic variation in time during an unsteady computational fluid dynamics computation. From the interaction between the flow and the modal motion, the modal force and the modal work can be computed. These can be converted into added modal mass and hydrodynamic damping and further into the shift of the eigenfrequency under rotation due to the fluid for a given mode. The tendencies of the frequencies with rotation compare reasonably well with experimental data. The numerical method can be applied to disc rotation speeds far beyond the range of experimental data revealing interesting tendencies and a phenomenological interpretation of the cause of the mode split.
Numerical investigation of the structural behaviour of a headwater bifurcation in hydraulic short circuit
Authors: Khalfaoui K , Tismer A , Riedelbauch S 
Published: October 2022

Abstract
Within the XFLEX HYDRO project, hydraulic short circuit operation (HSC) is being investigated as one of the possibilities to enhance the flexibility of pumped storage powerplants. Therefore, the structural behaviour of a headwater piping bifurcation of a pumped-storage power plant is investigated. Based on unsteady CFD simulations, time history mechanical simulations are carried out to assess the dynamic integrity of the structure in pump (PP), turbine (TT) and hydraulic short circuit operation. Since the plant at hand was initially designed for PP and TT operation, simulating these load conditions delivers a base of assessment for the admissibility of HSC loading. Herein, the focus of the assessment lays on the welded joints. First, a modal analysis of the rock-supported structure is conducted to identify the required numerical analysis method to be employed for the time-history structural simulations. The CFD pressure fluctuations are then applied to the structure within time history FE analyses. The dynamic structural simulations deliver low stress fluctuations which go hand in hand with the low pressure fluctuations previously determined using CFD. Besides, the structure exhibits comparable stress oscillations for all three loading conditions. The latter stress oscillations lie below the fatigue limit of the welds. The study herewith presents promising findings towards safe HSC operation ensuring more flexibility of the power plant at hand.
On the auto-oscillation effect of Kaplan rotors during load rejection
Authors: Weber W , Hübner B , Koutnik J 
Published: October 2022

Abstract
High vibrations due to auto-oscillation effects can occur at power units with Kaplan type runner during load rejection. These vibrations may be present in the turbine braking mode when the wicket gates are almost closed, and the rotating runner pushes the water towards the draft tube resulting in higher pressure below the runner blades. The upward leakage flow between runner blades and discharge ring is suspected to cause the vibration phenomenon.
Within this contribution, a fluid-structure-interaction (FSI) technique is applied to identify the mechanism of self-excitation. The investigation is carried out on a disk that represents the simplified geometry of a Kaplan runner. Computational fluid dynamics (CFD) simulations are used in order to obtain parameters in terms of stiffness, damping and inertia of the fluid to be applied in the following shaft line analysis. Damped modal analyses of the shaft line allow for evaluation of the stability of natural frequencies and corresponding mode shapes of the shaft line. A resulting negative damping indicates the occurrence of auto-oscillation behavior of the shaft line. For the operating condition under investigation, mode shapes with negative damping are obtained with this approach and a dynamic bending moment on the runner due to lateral movement in combination with a tilting at the runner in these mode shapes is identified as source of instability.
Based on these findings, an analytical approach for modeling the relevant effect is derived and compared to CFD result as well as results from acoustic finite element modelling. Finally, conclusions for avoidance of self-excited vibrations at Kaplan runners are proposed.
On the numerical assessment of flow losses and secondary flows in Pelton turbine manifolds
Authors: Hahn F J J , Semlitsch B , Bauer C 
Published: October 2022

Abstract
Different methods combining analytical guidelines, numerical simulations, and the manufacturer’s experience are employed to design and optimise the distributor manifold of a Pelton turbine. All these methods have in common to assume undisturbed straight inflow to the manifold, thus neglecting the upstream flow conditions. Our numerical simulations executed with the open-source code OpenFOAM v2012 show that the insufficient consideration of the upstream flow situation may lead to inaccurate predictions of the manifold flow. Five turbulence models were tested in our simulations, and the inflow turbulence intensity was varied from 1% to 10%. The flow quality was assessed by evaluating the head loss coefficient from total pressure drop, the head loss coefficient from the entropy production, the secondary velocity ratio upstream the injectors and the mass flow imbalances in the injectors. The study of turbulence models revealed that the k-ω Shear Stress Transport model predicted the head loss and secondary flows with reasonable accuracy. Also, the computationally less expensive model of Spalart-Allmaras leads to similar results and therefore emerges as an appropriate model for optimisation. The simulations with varying inflow turbulence intensity levels indicate a flow pattern change, if the specified inflow turbulence intensity is less than 4%. Below this value of inflow turbulence intensity, a significant increase of the secondary flow upstream of the injectors was observed.