bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selection and Optimization of Sensors for Monitoring of Francis Turbines
Authors: Valentín David , Presas Alexandre , Valero Carme , Egusquiza Mònica , Egusquiza Eduard 
Published: June 2021

Abstract
With the current demand of flexibility to hydraulic turbines, these are working under off-design conditions more than ever. Under these conditions different complex hydraulic phenomena appear, especially in Francis turbines, affecting the machine stability as well as reducing the useful life of its components. Hence, it is desirable to detect in real-time these hydraulic phenomena to assess the operation of the machine. In addition, the position and type of sensor to detect these phenomena is a key point for the monitoring of Francis units. In this paper, a large medium-head Francis turbine was instrumented with several sensors such as accelerometers, proximity probes, strain gauges, pressure sensors and a microphone. Results obtained with the different sensors in different locations are compared to know which hydraulic phenomenon is detected with every sensor. Furthermore, different signal analysis techniques are also compared. With this information, monitoring systems can be optimized with the most convenient sensors, locations and signal analysis techniques, reducing its difficulty to install and economic cost.
Analysis of hydro-abrasive erosion and efficiency changes measured on the coated Pelton turbines of HPP Fieschertal
Authors: Abgottspon A , von Burg M , Staubli T , Felix D 
Published: June 2021

Abstract
Geometrical changes and material loss of Pelton turbine runners as well as changes in turbine efficiency have been measured at HPP Fieschertal in Valais, Switzerland since 2012. The HPP is equipped with two horizontal axis Pelton units, with each 32 MW nominal power, 7.5 m3/s design discharge, 515 m head and two injectors. The nozzles and the buckets are hard-coated. Due to the relatively high hydro-abrasive erosion during the summer (sediment transport season), the splitters and cut-outs of the runner buckets are grinded and re-coated on-site usually every winter.
Turbine erosion was quantified based on repeated measurements on two runner buckets using 3d-scanning and a coating thickness meter. The detailed geometrical models showed amongst others that the splitter width distributions are similar for buckets of one runner, but differ considerably between runners. Changes in turbine efficiency were measured by the sliding needle procedure and continuously monitored based on operating data. From the efficiency monitoring over eight years of both turbines, efficiency differences were evaluated for each sediment season and for various refurbishment or replacement actions. The mean efficiency reduction was 0.4 % per sediment season. The on-site refurbishment works partly compensate the efficiency reductions due to erosion, leading to an efficiency drop of e.g. 2 % over six years, after which the runners are usually overhauled in the factory.
Fully automated multidisciplinary design optimization of a variable speed turbine
Authors: Tengs Erik , Charrassier Flora , Jordal Maria Rolstad , Iliev Igor 
Published: June 2021

Abstract
The future electricity market will have large contributions from renewable energy sources such as solar and wind. The intermittent nature of these energy sources creates a need for highly flexible operation of hydropower stations and changes the way we use hydraulic turbines to more off-design operation and more start-stop cycles. These changes challenge the structural integrity of the turbines in a way not seen before, and the next generation of hydro turbines will therefore have to be designed differently to meet this challenge. The goal of this article is to develop a framework for variable-speed Francis turbine design.
A fully automated multi-disciplinary design optimization procedure has been developed. As off-design operation is assumed, the runner do not only have to be optimized from a hydraulic point of view, the structural integrity is equally important. The design optimization is therefore based on a blending function of the hydraulic efficiency and the harmonic stress levels at a series of operating conditions. This is to ensure that the turbine is less prone to fatigue, even at off-design operation.
The process is fully automated, with no need for human interaction. A MATLAB design code is producing the raw design, every design is then meshed and tested at different operating points in a CFD solver. The pressure field from the fluid analysis is mapped onto the structure and evaluated in an acoustic-harmonic analysis to assess the fluctuating stresses in the turbine blades. A global optimization loop consisting of 15 design parameters is driving the process based on an overall optimization function.
The work has been performed as part of the HydroFlex project, and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 764011.
Influence of flow patterns on the performance of straight-through labyrinth seals. Numerical study and validation against experimental data
Authors: Rocca A , Troyer S , Casetta A 
Published: June 2021

Abstract
When numerically simulating the performance of a complete Francis turbine, it is common practice to omit the seals to save computing power. Volumetric and friction losses are usually taken into account using empirical values. There is abundant literature on the topic, but all analytic formulations rely on widely variable empirical coefficients. To overcome the uncertainty in determining volumetric losses, a detailed analysis of the sealing is necessary. Focusing on straight seals and configurations with cavities, in-house experimental data and numerical simulations have been used to show that few geometric parameters play a fundamental role in defining the flow patterns inside the clearance and even more so inside and between cavities. As is to be expected, the seals effectiveness is heavily influenced by these flow structures. It is also shown that certain methods of dealing with near-wall flow structures are better suited than others for the estimation of the discharge behaviour when compared to experimental results. Even though in the framework of the RANS equations CFD has proven to be a reliable tool for a wide range of geometries, further investigations are necessary on deep cavities. For aspect ratios above 0.75, the flow patterns inside the cavity change drastically, leading to bad convergence rates of the solver and, more important, to a considerable misalignment between numerical and experimental results. Lid-driven cavity flow is known to be a complex problem in 2D domain, and in this case, the flow becomes three-dimensional due to the tangential velocity induced by rotation. However, the reasons behind the problems in CFD analysis are not entirely clear. Given the observed variations of the flow structures inside sealings with different geometric parameters, it becomes clear why a simplified, generic formulation is very difficult to obtain, if not by adopting empirically defined coefficients which are needed to tune the analytical model.
Numerical simulations of Pelton turbine flow to predict large head variation influence
Authors: Alimirzazadeh S , Decaix J , Avellan F , Crettenand S. , Münch-Alligné C. 
Published: June 2021

Abstract
In the framework of the new feed-in-tariff system in Switzerland for Small Hydropower Plants (SHP), the aim of the SmallFLEX project, led by HES-SO Valais and performed in collaboration with EPFL, WSL, EAWAG, PVE, and FMV, is to show how SHP can provide winter peak energy and ancillary services, whilst remaining eco-compatible. The pilot and demonstrator site selected is the new small hydropower plant of Gletsch-Oberwald (KWGO) owned by FMV and commissioned end of 2017. This run-of-river power plant is equipped with two six-jet Pelton turbine units featuring a maximum power of 7 MW each.
The addition of flexibility can be reached by using existing volumes of the power plant: the settling basin, the forebay chamber as well as part of the headrace tunnel. By consequence, the turbine head will undergo variations. To ensure that these variations will not cause any damages to the Pelton runner, the influence of the available head is investigated by numerical simulations. The simulations are carried out using two different software. OpenFOAM, which is based on a Finite Volume Method (FVM), is used for computing the flow inside the distributor until the jet. GPU-SPHEROS, which is based on Arbitrary Lagrangian-Eulerian (ALE) Finite Volume Particle Method (FVPM) is utilized to compute the interaction between the jet and Pelton buckets.
Mixing the two aforementioned approaches, i.e. mesh-based FVM and particle-based FVPM, the overall torque T of the present six-jet Pelton runner can be reconstructed for different rated heads and discharges. The predicted torque fluctuations can then be considered for an estimation of the structural fatigue damage of the runner.
Application of particle-based numerical analysis to the practical design of Pelton turbine
Authors: Kumashiro Takashi , Alimirzazadeh Siamak , Avellan François , Tani Kiyohito 
Published: June 2021

Abstract
For the design optimization of the Pelton turbine, it is highly demanded to investigate the flow inside the turbine casing, which includes the water jet from the nozzles, the interaction between the jet and rotating runner, and the flow ejected from the bucket outlet, in various operating ranges. The behavior of the flow, however, is very complicated due to its unsteadiness and free surface. Further, the experimental observation in the model test is challenging because of the high time resolution requirement and the obstruction by the splashing water inside the turbine housing. In this regard, the numerical analysis is considered as a powerful method to approach the flow behavior in the Pelton turbine. Conventionally, the grid-based numerical analysis is applied to the calculation of the flow for its practical design. However, with the gird-based methods, a huge amount of fine elements is required to capture the unsteady behavior of the water free surface and the tiny splashing water particles. Increasing the number of elements directly results in higher computational costs, which makes it difficult to consider the splashing water in the process of practical design. From this point of view, the GPU-accelerated finite volume particle method is applied to the investigation of the flow in this research. It is firstly confirmed that the particle-based numerical result has a good agreement with the experimental result by the comparison of the turbine characteristics. Furthermore, several evaluations of the flow based on the analysis for the practical design are introduced in the paper.
Research of Turbine Efficiency Test by Current-Meter Method in Circular Pipe
Authors: Zhou Ye , Cao D F , Ge X F , Tan L J 
Published: June 2021

Abstract
For absolute discharge and efficiency measurement of turbine with medium and low water head, the current-meter method has high precision, good reliability, and wide application range. For rectangle flow channel, it is easy to lift down a gate frame with current meters to measure the flow velocity, but for circular pipe, due to the high stress, possible deformation, and strict safety requirement, the design, installation, and implementation of the support bracket is the key to the measurement by current-meter method. In this paper, we made the research of key technology for current-meter method in circular pipe. By building a numerical model for circular pressure pipe and flow measuring bracket, we analysed the influence of meters arrangement, the force and deformation of support pole with CFD, and fluid-solid coupling method, Finally, an optimized reinforcement bracket is proposed, with combined smooth and stress calculation, the measuring bracket is verified it can withstand the flow stress and has good safety characteristics, which can provide a reference for other similar turbine efficiency tests.
Modal testing of the Francis-99 runner
Authors: Solemslie Bjørn W , Dahlhaug Ole Gunnar , Sigurdsson Bjarki , Tengs Erik O 
Published: June 2021

Abstract
The Francis-99 low specific speed Francis runner has undergone much study in the years since it was first made available to the public. The High Head Francis(HiFrancis) project, hosted by the Waterpower Laboratory at NTNU, have conducted multiple experimental campaigns to supply validation data for numerical simulations of the RSI phenomenon for the runner. Due to the amount of instrumentation on board the runner an asymmetry exists in the runner structure that naturally affects the structural response of the runner. From numerical analysis the runner has been found to exhibit multiple natural modes of vibration, within narrow frequency bands. In order to validate the identified natural frequencies, with their corresponding mode of vibration and the amplitude, an experiment has been conducted. The experiment utilises piezo electric patches mounted on the runner hub to excite the runner in a defined mode of vibration and the response at the trailing edge of all blades is measured with a 1D Laser Doppler Vibrometry scanner. Preliminary results are shown that demonstrate the possibilities with the presented experimental method.
Experimental study and parametric analysis for primary frequency regulation of hydropower unit
Authors: Wang Cong , Wang De-kuan , Zhang Jian-ming 
Published: June 2021

Abstract
With the integration of new large-scale energy sources into grids, power system stability is facing huge challenges. The primary frequency regulation of hydropower generators is an important regulation method for grid frequency stability and power balance. It can effectively suppress the grid frequency fluctuations caused by the high proportion of new energy sources, and it plays a very important role in maintaining the stability of the power system. The regulation parameters of the primary frequency regulation of a hydropower unit have a significant impact on its regulation capabilities and performance indices. The experimental analysis of the effects of the regulation parameters is crucial for the safe and stable operation of a hydropower unit. A frequency regulation parameter test on a hydropower station was conducted in this study to determine the effects of the regulation parameters on the performance of the primary frequency regulation. This provides a reference for the selection of the regulation parameters of a hydropower unit.
Experimental influence of a splitter vane on the flow fields in a wide-angled diffuser
Authors: Guo Miao , Meng Xv , Zuo Zhigang , Liu Shuhong 
Published: June 2021

Abstract
Based on PIV and high-speed photography technology, the lengths and area ratios of flow separation zone under different Reynolds numbers Re in a diffuser with a fixed angle (28º), with and without a splitter vane were obtained. The flow field, vorticity and the flow distribution (hydrogen bubble tracing) at the downstream vicinity of the outlet of the diffuser under three representative conditions (Re = 1000, 6000 and 12000) were given. The experimental results show that with increasing Re, the area proportion of the separation zone decreases, but the length proportion of the separation zone increases, because the thickness of the separation zone along the vertical flow direction is reduced. Due to the existence of vane, the area of the corresponding separation zone is always smaller than that without the vane.
Numerical prediction of slurry erosion and its influence on prevailing flow conditions using a dynamic mesh method
Authors: Hankeln F , Kirschner O , Riedelbauch S 
Published: June 2021

Abstract
With the help of Computational Fluid Dynamics (CFD), the amount and location of slurry erosion can be predicted using renowned models. However, all common models do not change the hydraulic contour of the system and can therefore be interpreted as a CFD-post-processing step. Thus, the influence of slurry erosion on the fluid flow is currently not considered and the effects of changing flow conditions on the system performance or perhaps energy efficiency are not predictable. Building upon this state of the art, a numerical method based on the idea of a dynamic mesh procedure is developed. The method uses the predicted erosion to locally deform the mesh during simulation. The method contains the generation of an array-based mesh structure, the precise movement of affected boundary nodes including the tracking of inner nodes as well as a reconstructing procedure to improve mesh quality after deformation. The whole method is implemented in a commercial CFD-code. The functionality of the method is examined using the example of a standardized water pump. The comparison to corresponding experimental results revealed an accurate prediction of the erosion distribution in the pump’s front casing. Furthermore, the evaluation of the pump’s performance curves indicated an accurate prediction of the changing flow field caused by erosive wear.
Numerical assessment of parameters influencing the modal response of a Kaplan turbine model
Authors: Roig Rafel , De La Torre Oscar , Jou Esteve , Escaler Xavier 
Published: June 2021

Abstract
The present study intends to investigate numerically the impact of: i) the fluid added mass, ii) the turbine rotational speed and iii) the variation of the runner blade bearing stiffness due to the turbine water head on the modal response of a reduced scale Kaplan turbine. The impact of each variable has been quantified by means of a series of numerical modal analyses of the turbine in vacuum and in water, and at rest and rotating. It has been found that the natural frequencies of the Kaplan turbine model are sensitive to all the variables investigated in the present paper, the added mass being the factor which has the greatest impact.
Development of a novel numerical framework in OpenFOAM to simulate Kaplan turbine transients
Authors: Salehi Saeed , Nilsson Håkan , Lillberg Eric , Edh Nicolas 
Published: June 2021

Abstract
A novel numerical framework in OpenFOAM is proposed in this work, to simulate transient operation of Kaplan hydraulic turbines. Such transient operations involve a variation of both runner blade and guide vane angles, which also gives rise to a flow rate variation. A numerical simulation of such a process is very challenging, since it requires a deformation of both guide vane and runner meshes, with mesh slip conditions at arbitrarily shaped surfaces, at the same time that the runner mesh is rotating around the turbine axis. The currently available mesh morphing methodologies in OpenFOAM are not able to properly accomplish this. Thus a novel framework for OpenFOAM, including dynamic mesh solvers and boundary conditions, is developed to tackle this problem.
The new framework is utilized to simulate the flow during transient operation of the U9-400 Kaplan turbine model. The guide vanes and runner blades are rotated individually around their own axes with a constant rotational speed, while the runner is rotating, and the flow rate is linearly changed with the guide vane angle. It is shown that the novel numerical framework can successfully be utilized to simulate the load change of Kaplan turbines.
Numerical Simulation of Hydraulic Turbine During Transient Operation Using OpenFOAM
Authors: Salehi Saeed , Nilsson Håkan , Lillberg Eric , Edh Nicolas 
Published: June 2021

Abstract
Power generation from intermittent renewable energy resources (e.g. wind, solar) requires regulation of the electric grid. Although most hydraulic turbines are designed to work in their best efficiency points, nowadays they are being used more often under varying operating conditions to stabilize the electric grid. Unstable and varying conditions of fluid flow in hydraulic turbines during transient operation cause significant pressure fluctuations and load variations that could negatively affect the turbine lifetime. Therefore, the development of high-fidelity numerical tools for hydraulic turbine flow during transient operation, i.e. changing from one condition to another or during start-up and shut-down, is of great importance for the lifetime prediction of the machines.
In the present work, we are investigating the capabilities of the OpenFOAM open-source CFD tool to predict such phenomena. The transient operation of hydraulic turbines most of the time involves changing the guide vane angles while the runner is rotating, which must thus also be allowed by the employed numerical techniques. The high-head Francis-99 turbine is used as a test case, due to the availability of the geometry and rich experimental data. The turbulence resolving computations are performed using the SAS turbulence model. The numerical results are validated against the experimental data and compared with each other in terms of accuracy and usability. The results are also used for describing the flow behaviors during the shutdown.
Numerical and experimental study of pump as turbine for sediment affected micro hydropower project in Nepal
Authors: Pokharel Nischal , Ghimire Amul , Thapa Bhola , Thapa Biraj Singh , Qian Zhongdong , Guo Zhiwei 
Published: June 2021

AbstractDesigning and manufacturing site-specific turbines for small hydropower is not economical. Using abundantly available Pump, from the market, as Turbine (PAT) instead of designing a completely different turbine can be much more economical for small-scale hydropower. Lot of research have been going throughout the world on this and has already proven its effectiveness. In Nepalese hydropower, including the ones already developed and the ones that will be developed in the future, Francis turbines are supposedly the suitable turbine of choice. However, designing and manufacturing Francis turbine is a tedious task and the local manufacturers, who are expert in manufacturing Cross-flow turbines; do not have the technology and competence to manufacture the modern Francis turbines. Sediment in Himalayan rivers are the major hurdles of operation as they reduce the lifetime of the turbine by a very large factor, shooting up the maintenance cost of the hydropower. The operational region of Francis turbine and PAT overlaps quite a lot, thus indicating that PAT can be used in many of the hydropower in Nepal. The Chinese and Indian pump manufacturers are already renowned in developing a wide range of pumps and supplying them in Nepal. Despite having such great opportunity, pumps have never been used in turbine mode in Nepalese hydropower. In addition to that, no research has been done, in Nepal, regarding the effects of sediment on pumps being operated as pump or turbine. This paper describes performance of pump in erosive environment using Computational Fluid Dynamics (CFD). It also compares the results obtained from the CFD analysis of sediment erosion in pump operated in pump mode as well as turbine mode with other researchers work. Finally, it compares the results obtained from the CFD with the results obtained from the experiment.
A marine propeller as a hydrokinetic turbine – CFD analysis of energy characteristics
Authors: Ristić Bogdan , Božić Ivan , Simić Aleksandar 
Published: June 2021

Abstract
It is sometimes economically unreasonable to develop specific turbines, but rather to use a well-known concept of a pump in the turbine mode – PAT (Pump As Turbine). Inspired by PAT, the scope of this paper covers the assessments of the possibility to use marine propellers as runners for the hydrokinetic turbines. Numerical analyses are conducted for selected propeller geometry with the aim of evaluating its energy characteristics in the turbine regime. The chosen propeller belongs to the conventional, thoroughly experimentally tested, Wageningen B-screw series. The experimental data were used for validation of the numerical results in propeller regimes. Based on the obtained results, the researched non-optimized turbine in its optimum regime achieves a satisfactory power coefficient which is close to the value of other types of contemporary hydrokinetic turbines efficiencies.