bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shear and vortex instabilities at deep part load of hydraulic turbines and their numerical prediction
Authors: Nennemann B , Melot M , Monette C , Gauthier M , Afara S , Chamberland-Lauzon J , Jurvansuu T 
Published: June 2021

Abstract
For all types of turbines, deep part load operation (DPL) poses a challenge. An example of a dynamic phenomenon due to vaneless space vortices occurring at DPL is presented for three turbine types: a diagonal, a propeller and a Francis turbine. The backflow region occurring at DPL is often considered to be a main factor in these phenomena. Our results confirm that these backflow regions play an important role, but other factors also seem to be significant in specific cases. In our example of a diagonal turbine, the intersection of the backflow region with the leading edge of the blades seems to generate particularly high pressure pulsations and vibrations. In the case of the propeller turbine, large vaneless space vortices are found in CFD, but vibrations on the prototype machine are well within acceptable levels. Inspecting the flow at an operating point before large vaneless space vortices occur, shows high shear levels near the inner head cover that generate the high-intensity vortices at an even lower load. In the Francis turbine, half the number of strong vaneless space vortices interact with equally strong inter-blade vortices with vorticity of opposite sign to result in high dynamic blade torque. CFD simulations are well capable of capturing these phenomena, allowing them to be considered in the mechanical design of the turbine components for safe operation.
Test facility for transient operation point changes of hydraulic machinery
Authors: Kirschner O , Junginger J , Riedelbauch S 
Published: June 2021

Abstract
With the increase in fluctuating power generation, hydropower plants have more and more taken on the task of regulating the power frequency control for the electrical grid. Therefore turbines in storage hydro power plants often operate outside their optimum and frequently change their operating points. The question in how far hydro power technology is in a position to allocate large amounts of balancing power very quickly requires research related to the dynamic behaviour of the hydraulic machines. The stability and safety of the operation must be guaranteed for a wide operating range and transient operation. Here, vibrations and oscillations as well as high stresses in the material must be avoided so that no fatigue fractures or high wear occur. A flexible test rig is being constructed in the institute’s laboratory for research work related to these transient operating point changes. In this paper, the structure of the test facility and the various operating modes of the test facility are presented. Furthermore, the transfer of the plant conditions of the prototype to the model machine and the test facility is described. The requirements of the planned experiments on the test equipment are presented and special features of the test equipment for executing tests are derived.
Experimental facility for reduced scale model testing of hydraulic machines hybridized with a battery energy storage system
Authors: Gerini Francesco , Vagnoni Elena , Seydoux Martin , Cherkaoui Rachid , Paolone Mario 
Published: June 2021

Abstract
With a continuously growing share of non-dispatchable renewable energy sources in the power mix, flexibility in hydropower provision is becoming fundamental. The major role played by hydropower in frequency regulation in the last years has underlined the possible drawbacks of fast regulation impacting the hydraulic system health. Two of the most promising solutions to address this problem are the hybridisation of hydropower with battery energy storage systems and the variable speed technology. Batteries have already proved to be able to provide multiple services to the power system, and their coupling with hydropower is a possible interdisciplinary solution to increase flexibility provision in power systems. In this respect, one of the main challenges to address is the control of the hybrid system. While research is heading towards this direction, it becomes necessary to have experiment facilities able to test and validate the upcoming solutions. Testing platforms are nowadays decoupling the hydraulic and the electric components, testing them separately, therefore, they are not suitable for the validation of the control strategy under real grid conditions. The scope of this paper is to present an experimental facility where different joint control techniques can be tested on reduced scale models of hydraulic machines hybridized with a battery energy storage system. The presented test-rig combines all the fundamental components, both on the hydraulic and on the electrical side, within the same testing facility. The platform is an adaptation of the already existing laboratory of hydraulic machines at EPFL in Switzerland.
Influence of operation modes and fish behavior on fish passage through turbines
Authors: Stoltz U , Geiger F , Tuhtan J A 
Published: June 2021

Abstract
The assessment of fish passage through turbines is important to develop cost-efficient environmental solutions and strategies that avoid individual fish injuries and, therefore, enhance the fish population development in a catchment. As part of the FIThydro project, fish passage analysis were performed for the bulb turbine in Bannwil, the S-turbine in Guma and the bulb unit at the test facility in Obernach.
Numerical modelling in principle provides the most comprehensive information on hydrodynamic conditions in the turbine passage. Many details of the main relevant stressors on fishes can be derived. The information of different stressors like pressure, strike, shear and turbulence can be extracted with high accuracy assuming that a fish pathway follows a streamline through the turbine. The accurate prediction of the stressors and the validation with measurements enables the designer to develop a turbine that reduces the stress on the fish and, hence, increase the fish survival rate.
The survival rate also strongly depends on biological aspects of a fish species. Besides the reaction of the fish on the different stressors, complex parameters like swim behavior or preferred swim elevations are of high importance on the survival rate. However, these parameters vary among different fish species.
CFD simulations of different turbines are performed and simulation results were compared to measurements with the Barotrauma Detection System (BDS) sensors at the test cases in Guma and Bannwil, as well as live fish tests at the test facility in Obernach. The fish behavior was modeled in the CFD based evaluation method. Studies related to swimming speed, fish orientation and especially the actual passage location demonstrate the sensitivity of these parameters on the fish survival rate. Another aspect was the influence of operating conditions on fish passage. A wide spectrum of operating conditions was analyzed and fish passage hill-charts for different stressors were generated. This knowledge enables an adapted power plant operation related to migration movements of certain fish species. The CFD based analysis method shows to be a powerful tool to improve fish passage through a turbine by changing hydraulic design and by adapting operational modes. Relative improvements to conventional designs and operation can be quantified.
Experimental investigation to determine equivalent sand grain for very rough hydraulic surfaces
Authors: Nicolle J , Hazel B , Gauthier H 
Published: June 2021

AbstractConsidering the actual roughness shape, distribution and orientation found on hydraulics surfaces, obtaining a sand grain equivalent for loss evaluation remains a challenge. To investigate this problem, a variety of surfaces ranging from hydraulically smooth to a very rough surface representing a heavily rusted penstock were tested on an experimental cylinder rotating in water. The larger-scale roughness was replicated through rapid prototyping. The surface effect on the flow for an increasing Reynolds number was measured and the resulting equivalent sand grain was validated against experimental intake head loss measurements.
Calibration of critical speed predictions using experimental measurements
Authors: Dollon Q. , Monette C. , Gagnon M , Tahan A. , Antoni J. 
Published: June 2021

Abstract
Experimental characterization of structures provides information about the real dynamic behavior of machineries. This results in a better estimation of dynamic stress levels, used to predict lifespan, reliability and optimal operating ranges. Experimental results can also be used to improve and calibrate simulations and calculations. In particular, calculation of shaft bending frequencies is needed to define the critical rotation speed. However, natural frequency computation requires a prior knowledge on many subcomponent properties, that are not precisely known in practice. This leads to a great uncertainty on the predicted critical speed. The purpose of this study is to use experimental in-situ measurements as a means to reduce uncertainties on physical properties of the shaft line and increase confidence in the prediction of natural frequencies and critical speed. This involves ambient modal analysis, calibration techniques and statistical approaches to gain insight on the true shaft physical properties.
New test rig for micro and mini hydraulic axial turbines in Uruguay
Authors: Pienika R , Rovira I , Rodríguez N 
Published: June 2021

Abstract
In Uruguay, the potential for small, mini and micro scale hydropower has not been exploited yet, being the high investment costs the main reason. In order to overcome this issue and enhance the development of mini and micro hydropower in the country, the Hydropower group of Universidad de la República (Uruguay) decided to demonstrate the technical and economic feasibility of designing and manufacturing a propeller turbine with national capacities. Furthermore, it was believed that the existence of a test rig for scale model turbine evaluation in the facilities of a public university would be of great relevance for the enhancement of micro hydropower in the country. The hydraulic, mechanical and electrical installations of the test rig are presented, together with the acquisition system. The limitations of the test rig, owed to the dimensions of the piping and the ranges of the instruments within the acquisition system, are stated. The test rig is complemented with a SLA 3D printer for rapid turbine prototyping. The installation will serve not only for evaluation of the designed turbine within the current project, but also for the evaluation of future designs, teaching and other research activities of the university.
Investigation of dynamic pressure fluctuations in closed hydraulic circuits as a function of centrifugal pump speed gradients
Authors: Büker J , Laß A , Witte M , Wurm F-H 
Published: June 2021

Abstract
Electrical consumers, such as pumps, contribute towards the stable operation of the electrical power grid due to active and reactive power consumption. If the consumers are indirectly connected to the grid via power electronic converters, the positive contribution is reduced or non-existent. Consequently, the ability to compensate imbalances within the power grid is greatly reduced. A research project founded by the European Union is focusing on investigations to utilize power converter technology of pump drives for grid stabilization. But in order to stabilize the fluctuating power grid frequency rapid adjustments of the pump speed are required, which can cause major troubles in the hydraulic system. For instance, rapid changes in pump speed are causing the emission of hydro acoustic pressure waves into the pipe system, which are exciting the structure of the hydraulic system and lead to undesirable vibrations and noise emissions. Most critical is the direct excitation of natural frequencies in the entire piping system based on the inherent pressure fluctuations caused by transient fluid flow and pump speed changes. Converter control for grid-adaptive speed adjustment is only possible as long as there is no significant increase in dynamic pressure fluctuations in the whole hydraulic system. For this purpose, a research pump is operated with different rotational speed gradients in a closed hydraulic circuit. Dynamic pressure sensors were used to record the resulting pressure fluctuations at various locations of the hydraulic system. Additionally, an outlook towards an active reduction of the dynamic pressure fluctuations by means of a specially developed hydrodynamic actuator is given. These results are an initial step but of particular interest towards the knowledge of permissible grid adaptive speed control regimes, which can be applied to a pump in a hydraulic piping system.
Development of Low-Specific Speed New-Type Hydraulic Turbine Equipped with Volute: Numerical Investigation and Performance Prediction
Authors: Irie T , Takahashi W , Miyagawa K , Sugimoto T , Naganuma T , Waku R 
Published: June 2021

Abstract
With the goal of broadening the operation range of hydraulic turbines, we propose a new-type hydraulic turbine in our research. The new turbine has no draft tube, but instead is equipped with a parallel diffuser and a volute, i.e. a radial vaneless diffuser and a spiral discharge collector, respectively. In this research, we carried out a CFD investigation on specific speed 77 [m-kW] prototype turbine to predict its performance. The simulation results showed that under large discharge there is a high risk of cavitation or pressure fluctuation. In this condition, the amplitudes of the pressure fluctuation are 0.6 percent and 1.3 percent of the effective head, on the volute wall and the parallel diffuser wall, respectively. The possibility of flow instabilities such as a vortex rope precession and a rotating stall to occur is small enough to keep operating the turbine at both deep part-load and full load. The final design of the turbine has been decided based on this investigation. The turbine verification tests are going to start in early 2021.
Dynamic evolution of rotating stall in a model pump-turbine during runaway transient scenario: three-dimensional simulation
Authors: Zhang Xiaoxi , Chen Qiuhua 
Published: June 2021

Abstract
Rotating stall, the phenomenon of unevenly distributing stall cells rotating in the runner, is one of the most unfavorable flow patterns in the pump-turbine. It occurs at off-design operating conditions and always induces intensive pressure pulsations and hydraulic vibrations, and may cause structural failures of the pump-turbine. Therefore, the characteristics of the rotating stall should be investigated thoroughly at all possible operating conditions. In this study, the rotating stall phenomenon in a model pump-turbine during the runaway transient scenario was simulated by the three-dimensional numerical model. The entire process of the formation of the rotating stall in this scenario was analyzed by the spatial distributions of channel discharges in the runner and their time-varying features. The results show that the rotating stall evolves dynamically and demonstrates irregular local variations. The runner channel discharges can recognize the rotating stall effectively and describe their characteristics semi-quantitatively. This study presents some understandings about the rotating stall in transient scenarios and may contribute to the reveal of the reasons for the hydraulic instabilities of pump-turbines during these scenarios.
Understanding the coherent structures for different fluctuation frequencies at partial load condition of a Francis turbine
Authors: Sun Guoyong , Jiang Bo , Wang Yuchuan , Liu Demin , Avellan François 
Published: June 2021

Abstract
More and more hydropower plants are operating as regulator of renewable energy such as solar and wind energy resources. Because these renewable energy resources are highly volatile, so hydraulic turbines have to switch working condition in a wide flow range to guarantee the steady output to electric grid. It’s known that there are many fluctuating frequency components in runner passage of hydraulic turbines, especially at part-load conditions, which are induced by unsteady flow phenomena like guide vane wake, flow separation or rotor-stator interaction (RSI) and so on. These fluctuation frequency components are varied with working condition due to different dominant inducing resources. Although we can estimate the frequency component resources according to rotating speed, numbers of blades and guide vanes, we can’t know exactly coherent structure pattern of every frequency component. In present study, firstly, we will compute the internal flow of a Francis turbine at lower discharge, and verify the validation of computational results by experimental data. Secondly, Dynamic Mode Decomposition (DMD) method will be employed to extract the three-dimensional coherent structures in runner passage and draft tube for every frequency component based on computational snapshots. Finally, we will demonstrate the patterns and locations of coherent structures for every frequency component and predict the coherent structure or fluctuation component generation resources.
Three-dimensional coupled design for runner blades and guide vanes of tubular turbine based on bidirectional flow control
Authors: Ji Qingfeng , Liao Weili , Jia XIN , Fan Honggang 
Published: June 2021

Abstract
Tidal energy is one of the renewable energy resources in the ocean. The tide-power station can supply more continuous electricity if it produces electricity in rising tide and receding tide, which is conductive to the stable operation of power grids. So it is important that the tubular turbine can operate in both directions with higher efficiency in tide-power stations. A full three-dimensional coupled design model for tubular runner blades and guide vanes is established to take full account of the mutual influence of flow between the distributor and runner. Since the simultaneous governing equations are solved in the flow domain including both blades, the coupled performance matches further. The weighted design method for reversible runner blade is presented based on the bidirectional flow information. The designed blade is fit to operate in both directions, which combined characteristics of the two blades working nicely in the positive and negative direction respectively. The reasonable control on the comprehensive performance of reversible blades is realized by selecting the weighted coefficient flexibly.
Investigation of the Operating Principle of Diffuser Augmented Hydrokinetic Turbines
Authors: Stadler Christa , Wack Jonas , Riedelbauch Stefan 
Published: June 2021

Abstract
Alternative sustainable technologies for energy production are currently receiving increased attention, one of them being hydrokinetic turbines. For some applications an augmentation of the turbine rotor through a diffuser is a reasonable option offering some advantages. In order to get a better understanding of diffuser augmented turbines an extensive literature study is performed also including relevant publications on ducted wind turbines. The published geometry and performance data are collected and reevaluated applying a new procedure, which references the turbine power on the diffuser outlet area instead of the rotor area. Additionally, geometries are generated, manually optimized and compared to the data gathered in literature. Dominant diffuser attributes are identified independent from the exact diffuser concept such as the shape of the diffuser close to the exit plane and the diffuser area ratio. By using the new evaluation approach a strong correlation between the area ratio and the overall turbine power coefficient is observed. Observations suggest that an increase of the exit area is only reasonable up to a certain limit. To a some extent, this constraint can be overcome through boundary layer control, e.g. by applying multi-stage diffuser concepts. The presented work gives a guide line for effective design of diffusers for hydrokinetic turbines and generally improves the understanding of the operating principle of diffuser augmented turbines.
A predictive governing control method of the pumped-storage unit based on lumped-parameter model equivalence
Authors: Zheng Yang , Chen Qijuan , Liu Wanying , Yan Donglin 
Published: June 2021

Abstract
The speed governor is known as one of the most important control parts in the pumped-storage unit (PSU). When operating in transient processes, the stability of the PSU’s hydraulic and mechanical states maintains by the precise regulation of the speed governor. For the sake of improving the governing control performances, the lumped-parameter equivalent circuit model is first introduced for precise modelling of hydraulic-mechanical characteristics of PSU. Subsequently, a multi-variable generalized predictive control system based on receding horizon technique is applied at every sampling instant to optimize the control trajectory within certain finite time horizon. To validate the effectiveness of the proposed predictive control method, the simulation experiment of governing movements during turbine start-up process is conducted under a nonlinear lumped-parameter numerical simulation platform of PSU by comparative case studies, the overall control performance of the proposed control scheme is evaluated and compared with that of the traditional PID algorithm. Simulation results indicate that the proposed governing control method can achieve stronger frequency fluctuation alleviation and hydraulic oscillation damping performances than traditional PID.
Numerical simulation of hydraulic transients in hydropower station with complicated water conveyance system
Authors: Li Gaohui , Chen Shunyi , Dai Jiang , Zhou Tianchi , Zhang Lin 
Published: June 2021

Abstract
With the construction of Jinping II hydropower station with extra-large diversion tunnel, Baihetan hydropower station with complicated tailwater system, Yangfanggou hydropower station with complicated surge chamber, High requirements are put forward for the calculation and analysis of hydraulic transient process. In the water transmission and power generation system design of these projects, the following technical problems was solved by Power China Huadong Engineering Corporation Limited: simulation of variable impedance coefficient of differential surge chamber, interface tracking analysis of free-surface-pressure flow system, narrow upper chamber open channel effect and simulation of trigeminy surge chamber. The solutions to those technical problems and were summarized, and the hydraulic transients simulation and calculation software of complex waterway system - Hysim was developed. Based on the field test of Jinping II Hydropower Station, Baihetan hydropower station and Yangfanggou hydropower station, the simulation calculations were carried out. The accuracy of the hydraulic transients simulation software is verified by comparing the inversion results with the test values.