bluuebunny/crossref_metadata_2025_split huggingface dataset:
60188 The coupled dynamic analysis of hydroelectric unit and powerhouse considering the bolt connection characteristics
Authors: Ma ZY , Chen H Y , Zhang H Z 
Published: June 2021

Abstract
As the increasing of the capacity and water head of the hydropower stations, the hydroelectric unit’s vibration and its induced powerhouse vibrations become a critical problem. The system of hydraulic-mechanical-electric-structural is coupled and with strong non-linear characteristics. The frame and head cover are all connected with the powerhouse pier via high-strength bolt. The paper is concentrated on the dynamic coupling mechanism and simulation model considering the bolt’s connection and load transmission characteristics. With the theory analysis and numerical simulation, the connection and transmission behaviour of the high-strength bolt would be studied and a more accurate and simple mechanical expression would be derived. The connection sliding law and dynamics modelling method of bolts are discussed. Based on the displacement-load curve of single lap and single bolt analysis it is concluded that the increasing preloading will improve the tangential bearing capacity of the bolted joint connection. Then the FEM coupling model of the lower bracket and powerhouse is established with the virtual medium method. Based on the free-vibration and dynamic response analysis the effects of the loosening of the bolt on the static stiffness of the coupling structure are discussed. The von-Mises stress’s increasing due to some of the bolt’s loosening would result to the material fatigue damage. Finally five preloading schemes of the bolts are discussed and the simulation results show that the preloading force has a greater lateral impact on the structure than on the longitudinal direction. The preloading force improves the coupling structure’s stiffness and reduces the vibration amplitude of the frame. As for the preloading force, when it is small the connection effect is not strong enough and the vibration level may be higher, so the actual preloading state should be exactly simulated. When the bolt preloading reaches 60-70% of the material yield strength, the rigid connection can be directly used in the modelling for the convenience of calculation.
Stereo-PIV study of unsteady flow in a laboratory air hydro turbine model over a wide range of operating regimes
Authors: Litvinov I V , Sharaborin D K , Gorelikov E U , Suslov D A , Shtork S I 
Published: June 2021

Abstract
Swirl flow with the formation of a precessing vortex core (PVC) in a hydro turbine draft tube model was studied using Stereo-PIV and four acoustic sensors. Experiments were performed on an aerodynamic setup in a wide range of operating conditions of the hydro turbine. Using a spatial Fourier decomposition of pressure pulsation data obtained from four acoustic sensors, a PVC was observed for part-load operating regimes (0.3-0.7Qc
). Mean flow features were shown for the range of operating regimes from a deep part-load regime (0.3Qc
) to an overload regime (1.5Qc
). Based on phase-averaged velocity distributions, the PVC spatial structure was identified for maximum pressure pulsations on the cone walls of the draft tube.
Numerical study on Unstable Hydraulic Factors of Kaplan turbine with semi-spiral case at large flow rate conditions
Authors: Zhao Yaping , Li Zhihua , Dang Mengfan , Feng Jianjun 
Published: June 2021

Abstract
The operation of semi-spiral case Kaplan turbines at large flow rate conditions is restricted by factors such as severe cavitation and severe vibration, which limit the maximum output of the unit. In order to explore the main hydraulic factors that cause the poor operating stability of the unit at large flow rate conditions, and provide a reference for the operation and design of the turbine, the numerical simulation method is adopted to conduct the performance study of an semi-spiral case Kaplan turbine at different operating conditions, by comparing and analysing the results at the optimal conditions and large flow rate conditions, the unstable hydraulic factors at large flow rate conditions is obtained. The research results show that: at large flow rate conditions, the uneven flow distribution in the semi-spiral case cause vortices between the guide vanes, lead to the large fluctuations of blade torque, and generate unstable back-flow and vortices in the draft tube. These phenomena combined with the various gap flows in the runner, make the internal flow of the Kaplan turbine at large flow rate conditions deteriorate, cavitation increase, efficiency decrease, and cause severe vibration, thereby limiting the stable operation of Kaplan turbine at large flow rate conditions.
Investigation of water column separation induced by pressure pulsation based on critical cavitation rate model
Authors: Yang J B , Yang J D , Guo W C , Luo J J , Fu G F 
Published: June 2021

Abstract
Significant pressure fluctuation may exists at the inlet of the draft pipe during load shedding of water pump and turbine sets. When the tail-water level is low, the minimum water hammer pressure at the inlet of the draft pipe set is higher than evaporation pressure; however, the overall pressure after superposition with pulsating pressure may reach the evaporation pressure in an instant. In these cases, it is unknown if a cavity is formed or water column separation is induced. It is also unknown how frequency and amplitude of the pulsating pressure affect the formation of cavity or water column separation. However, in terms of the physical formation of water column separation, liquid pressure reaching evaporation pressure is only the necessary condition of water column separation rather than a sufficient condition because the growth and aggregation of cavitations take time. In addition, water column separation could be induced only when the cavitation rate in the water reaches a specific value and gas-liquid relative motion occurs. In this study, based on the uniform cavitation distribution model, the critical of flow velocity gradients are calculated both in front and at the back of the section and are the sufficient condition of water column separation. This study uses the criterion of when the ratio of the vaporous cavitation volume to the volume of the pipe segment with a length of Δx exceeds a critical cavitation rate for classifying water column separation segments and non-water column separation segments. In water column separation segments, a concentrated vaporous cavitation model is used for calculation; however, dynamic meshes should be applied for tracking the change of vaporous cavitations. In the non-water column separation segments, the vaporous cavitation volume can be calculated according to the continuity equation but is converted into a cavitation rate in the pipe segment and substituted into gas-liquid two-phase equation to calculate wave velocity. Next, a case study was performed on a pipe-valve system. By taking into account the pulsating pressures with different frequencies and amplitudes on the downstream side in the valve closing process, water column separation and merging processes were analyzed and the change in flows, cavitation volumes and pressures on various sections and their laws during the transient process were concluded.
Accurate and efficient analysis of dynamic runner stresses considering hydrodynamic damping effects
Authors: Hübner Björn , Koutnik Jiri 
Published: June 2021

Abstract
Safe and reliable dynamic designs of Francis and pump turbine runners require an accurate and efficient prediction of the dynamic response during operation including dynamic stresses. If resonance phenomena cause significant dynamic amplifications, response amplitudes strongly depend on damping effects, and numerical simulations have to include realistic damping behavior. For submerged components like turbine runners, hydrodynamic (flow-induced) damping and hydro-acoustic radiation are much greater than structural or material damping, but cannot be assessed sufficiently accurate by simple assumptions. Therefore, a newly developed fluid-structure interaction (FSI) methodology is presented which offers accurate and efficient harmonic response analyses of submerged structures not only accounting for added-mass effects but also for flow-induced damping and acoustic radiation. The acoustic FSI approach, widely used to consider added-mass effects, is enhanced by convective terms to include fluid forces caused by the deflection of the mean flow due to structural motion. Only a stationary flow solution, obtained from standard computational fluid dynamics analyses, is required as additional input. The linearized second-order system with non-proportional damping matrix is solved in frequency domain using a Krylov subspace based model order reduction technique. The methodology is validated using experimental damping data from an elastic hydrofoil in a cavitation tunnel. A first application to a prototype Francis runner, being excited close to resonance by rotor-stator interaction, reveals a significant influence of the operating condition on hydrodynamic damping and dynamic stresses. The numerical results for both part load and full load agree very well with measured prototype strains. Meanwhile, the automated methodology is applied as a standard tool within the hydro-mechanical runner design process ensuring dynamically safe and reliable runner designs.
Numerical analysis of an initial design of a counter-rotating pump-turbine
Authors: Fahlbeck Jonathan , Nilsson Håkan , Salehi Saeed , Zangeneh Mehrdad , Joseph Melvin 
Published: June 2021

Abstract
Renewable sources of energy are on the rise and will continue to increase the coming decades [1]. A common problem with the renewable energy sources is that they rely on effects which cannot be controlled, for instance the strength of the wind or the intensity of the sunlight. The ALPHEUS Horizon 2020 EU project has the aim to develop a low-head hydraulic pump-turbine which can work as a grid stabilising unit. This work presents numerical results of an initial hub-driven counter-rotating pump-turbine design within ALPHEUS. Computational fluid dynamics simulations are carried out in both prototype and model scale, for pump and turbine modes, and under steady-state and unsteady conditions. The results indicate that the initial design have a hydraulic efficiency of roughly 90 % in both modes and for a wide range of operating conditions. The unsteady simulations reveal a complex flow pattern downstream the two runners and frequency analysis show that the dominating pressure pulsations originates from the rotor dynamics. Given the promising high efficiency, this initial design makes an ideal platform to continue the work to optimise efficiency and transient operations further.
Evaluation of guide vanes effect over runner Francis turbine sediment erosion using a quasi-two dimensional approach
Authors: Quishpe L M , Valencia E A , Hidalgo V H , Zambrano O I , Cando E H 
Published: June 2021

Abstract
Francis turbines are widely used in hydroelectric power plants all over the world, Ecuador is not an exception to this trend. Hence, Francis turbine design and assessment have taken importance in order to provide in-house design methods to enhance their performance in the region. The volcanic nature of the region facilitates sediment formation, which produces drastic erosion problems in many Francis turbines. Since guide vanes set the inlet flow velocity of the runner and erosion is related with the velocity distribution through this latter, this work evaluates guide vane profiles using a quasi-two dimensional approach to assess the impact of guide vane design on erosion rate. For this aim, parametric analysis and a mean line analysis are employed for the conceptual geometrical design, which then is coupled with a panel vortex model to assess the two dimensional hydro profiles for the guide vanes. Thus, the velocity triangles at entry and exit of the guide vane-runner setup can be related to the erosion rate within the runner. At this stage the calculations were carried out at the BEP and for the validation experimental data from the San Francisco hydroelectric power plant was used. The results show how the model developed captures main performance trends and enables the correlation of erosion with the geometrical features of the guide vanes. The method used is accurate enough for preliminary design and its low computational resources with versatility make it suitable for optimization routines for erosion proof designs.
Proper orthogonal decomposition of turbulent swirling flow of a draft tube at part load
Authors: Kumar S , Khullar S , Cervantes M J , Gandhi B K 
Published: June 2021

Abstract
A large scale vortical structure, i.e., rotating vortex rope (RVR), generally forms at part load (PL) operation of a reaction turbine due to the combined effect of swirling flow at the runner outlet and the adverse pressure gradient in the draft tube. Even with the data analysis through advanced measurement techniques like Laser Doppler velocimetry (LDV) and Particle Image Velocimetry (PIV), the information available about the flow instabilities developed due to RVR is still incomplete. This paper presents an application of the proper orthogonal decomposition (POD) method to analyze the flow field inside the draft tube cone at PL operation of a high-head model Francis turbine. The POD analysis is performed on 250 PIV snapshots containing the axial and radial velocities. The results show that the first eight modes contain more than 95% of the total kinetic energy (KE) of the flow field and are associated with the organized motion of the flow. The first mode contains more than 50% of the total energy, and the axial velocity profile reconstructed with the first mode is identical to the mean axial velocity flow field. The maximum dissipation of the turbulent kinetic energy (TKE) occurs through unorganized motion.
Performance analysis of a new type of space guide vane for T-type hydraulic turbine
Authors: Li Yanpin , Jiang Yuxuan , Zhang Zichao , Chen Dexin 
Published: June 2021

Abstract
At present, the flow passage of multistage T-type (designed according to the theory of hydraulic prime mover) hydraulic turbine directly adopts pump type interstage guide vane, which has poor matching degree and low performance. In order to improve the performance of T-type hydraulic turbine, this paper takes a two stage T-type hydraulic turbine as the research object, designs a new type of space guide vane as its interstage guide vane according to the theory of hydraulic prime mover, selects the thickness of the baffle, the diameter of outer edge of guide vane, the outlet angle of positive guide vane, and the number of guide vanes to formulate L9 (34) orthogonal test, and applies CFD numerical calculation to 9 Through the range analysis method, the primary and secondary factors affecting the external characteristics of T-type hydraulic turbine are found out. The results show that the outer diameter of the guide vane has the greatest influence on the performance of the new type of space guide vane. In order to further study the influence of guide vane outer diameter on turbine performance, four different guide vane outer diameter of 700mm, 750mm, 800mm and 850mm are selected to analyze its influence on the outer characteristics and internal flow field of the whole T-type hydraulic turbine. It is found that with the increase of the outer diameter of the guide vane, the efficiency of the hydraulic turbine increases first and then decreases, the head decreases first and then increases, and there is an optimal value of the outer diameter of the guide vane. As the diameter of the outer edge increases, the flow path of the positive guide vane and the negative guide vane becomes longer, the flow velocity decreases, the flow control ability decreases, the turbulent kinetic energy increases, the area of the high pressure area of the negative guide vane decreases, and the flow pattern becomes worse.
Analysis and visualization of progressive erosion in Pelton buckets
Authors: Rai Anant Kumar , Kumar Arun , Yexiang Xiao , Guo Bao , Staubli Thomas , Arora Naman 
Published: June 2021

Abstract
Hydropower plants operating in fragile mountainous regions face severe hydro-abrasive erosion of hydraulic components, which results in drop in efficiency, frequent interruptions in power generation and downtime for repair/replacement. Due to high flow velocity in components like nozzles and buckets, a Pelton turbine is highly susceptible to erosion. The effect of erosion is observed as cumulative loss of material and study of its gradual progress required frequent measurement. In this study, in-situ images of Pelton buckets were captured throughout a sediment period at a hydropower plant located in Himalayan region, India and analysed for characteristics of progressive erosion damages. A multi-layered paint method was used to visualize the initiation of erosion in different parts of bucket. Removal of colours due to erosion provided the information on erosion initiation and various erosion zones in bucket. The erosion of outer side of bucket was analysed with single layer paint removal and images from past records of the plant. Further, the effect of initial condition of a bucket on cumulative erosion after a sediment season is also presented for both coated and uncoated buckets.
The in-situ photographs during the silted water period suggested that the outlet portion inside the bucket faces significant erosion. The technique of image capturing throughout sediment season was successful in obtaining progressive erosion. Such method with a reference scale in the image is an effective method to quantify erosion like width increase of the splitter more frequently. The paint in the buckets was found capable of providing information on erosion initiation and erosion zones inside Pelton buckets. The erosion characteristics of outer side of the bucket confirms the presence of a Coanda effect. This study will facilitate turbine designers and manufacturers in better coating and/or surface treatment to specific zones of bucket to minimize efficiency loss due to distorted profile of the bucket, as more prone surfaces can be coated with thicker coatings to protect it longer from erosion.
Experimental investigation of sediment erosion of turbine steel used in Bhilangana-III power-plant
Authors: Sharma Shubham , Gandhi Bhupendra K 
Published: June 2021

Abstract
Turbines located in the geographical regions of Africa, Himalayan, South-East Europe and South America are subjected to erosion due to sediments flowing with water. The extent of damage due to erosion depends on the material property and the impinging condition of particles. In this work, experiments have been performed in a high speed pot tester on the steel used for Francis turbine of Bhilangana-III power-plant. The erosion rate is determined by mass loss of the specimens rotating inside the pot. The erosive wear behavior of turbine steel is evaluated at high velocities of 27 m/s and 32 m/s by varying the orientation angle from 15 to 90 degrees. The mean particle size and sediment concentration are selected as 300 µm and 3000 ppm, respectively. The erosion rate of turbine steel is increased with impact angle upto 30 degree and then decreased with a further increase in impact angle till 90 degree. The effect of variation of particle impingement velocity on erosion rate behavior of turbine steel is determined for the velocity range of 13-32 m/s. The erosion rate increased with increase in the velocity. Further, the mechanism of erosion with the variation in velocity is analyzed at different impact angles using SEM micrographs of worn out samples.
Comprehensive stay vane vibration analysis by means of numerical and experimental approaches
Authors: Sampaio Ricardo , Neto Alexandre D’Agostini , de Camargo Gissoni Humberto , Filho Rubens Marras , de Araújo Pedro Gayer , da Silva Assi Gustavo Roque , Cicolin Murilo Marangon 
Published: June 2021

Abstract
Vortex-induced vibration is the most common phenomenon associated with the development of cracks in hydraulic turbine stay vanes and although the trailing edge modification is an usual and well-known solution, its empirical application may not lead to the complete elimination of the cracks. During Ilha Solteira hydropower plant history several modifications were implemented, but only the one applied to vane 24 was successful in avoiding cracks recurrence.
To better understand this phenomenon, a 2D transient Computational Fluid Dynamics (CFD) simulation was developed incorporating the fluid-structure interaction effect by allowing the simulated vane to move perpendicularly to the flow. Additionally, field measurements and laboratory experimental results were used to calibrate the numerical model. A comparison of the results obtained by CFD with the ones measured in the laboratory revealed differences smaller than 1% for the peak displacement amplitude.
When applied to the prototype scale, the simulation was able to capture the lock-in effect in a frequency around the one measured at site which corresponds to the first bending mode of the vanes. A geometrical modification was developed, tested numerically and implemented at site. Later strain-gauge measurements confirmed that the modified stay vanes were no longer being excited in their first mode, resulting in a 90% reduction of the oscillating stress amplitude.
On the Comparison of Hydroelectric Runner Fatigue Failure Risk Based on Site Measurements
Authors: Morin Olivier , Thibault Denis , Gagnon Martin 
Published: June 2021

Abstract
The fatigue reliability of a turbine runner is closely related to its dynamic behavior. Over the past few years, Hydro-Québec has performed measurement campaigns on many of its turbine runners. These measurements led to the evaluation of the fatigue risk level of each runner in various operating conditions, which allows operating conditions with a higher risk of crack propagation to be avoided. This paper presents the results for turbine dynamic behavior assessed in steady-state conditions. Stress levels at strain gauge locations are used to evaluate the risk of fatigue cracking based on the Kitagawa-Takahashi diagram. Results show a good correlation between the calculated risk of cracking and real cases of cracks found in runners. Furthermore, the results comparison highlights a apparent tendency for recent designs to be more prone to cracking at speed-no-load operating condition than older designs. The paper gives an overview of the methodology used and discusses the conclusions derived from the sample of turbine runners available for this study.
A new real time hydraulic test platform dedicated to Ancillary Services
Authors: Mesnage Hugo , Guillaume Renaud , Bacha Seddik , Bayle Simon , Nichele Sylvain 
Published: June 2021

Abstract
Characterization of Hydraulic turbines, storage pumps and pump-turbines is a well-known process formalized in the IEC60193 standard. Test platforms ensure the acceptance of hydraulic design with respect to hydraulic transpositions such as efficiency, range of operation, cavitation, stability etc. These test platforms only focuses on the static operation of a turbine. The HydroPHIL platform - which stands for Power Hardware In the Loop for Hydro-electrical conversion - focuses on studying transients operations of Pump Storage Plants. It includes a fully operational scale model of a hydraulic units from water to wire. The scaled model interacts with a real time grid emulator and a real time penstock emulator. The test platform allows the simulation of technologies in relevant environment related to three main topics of investigation: a) system behavior study, whether it is solicited by the grid (frequency or voltage dips, etc.) or the piping system (water hammer, etc.) b) new conversion technologies with real electrical components (such as variable speed PSP), and c) development of new control strategies to improve provision of ancillary services and other flexibility services. This paper presents the platform architecture and features.