bluuebunny/crossref_metadata_2025 huggingface dataset:
A new method for calculating transition process based on full characteristic modeling of turbine
Authors: Liu Xiao , Jiang Xiaoping , Xiao Yexiang
Published: June 2021

Hydropower units undertake the tasks of frequency modulation and peak load regulation, flood control and discharge in flood season. When the unit working condition changes greatly, the stability of unit output will be affected. Therefore, the study of the transient process is of great significance to maintain the stability of hydropower units. This paper introduces a calculation method of transition process based on comprehensive characteristic curve. Based on the data of the comprehensive characteristic curve of Chaijiaxia hydropower station, the full characteristic surface of the turbine is obtained by BP neural network algorithm. Finally, the differential algebraic equation of the transient process of the turbine is established, and the transient process is solved by combining with the full characteristics of the turbine.
Numerical simulation of air injection in part load operating point
Authors: Shcherbakov P , Chirkov D , Skorospelov V , Turuk P
Published: June 2021

The operation hydro turbines in the off-design operating points is often accompanied by pressure pulsations with a large amplitude. One way to deal with such pulsations is to inject the air into hydro turbine flow passage. The aim of this work is to simulate this process. Previously we carried out calculations in frames of homogeneous incompressible three-phase «liquid – vapor – non-condensable gas» mixture model. The computational domain consisted of wicket gate, runner and draft tube. The wicket gate and runner were considered in the periodic stage approach. The results obtained were in good agreement with experimental data at full load operating point. It was shown that the calculations on the previous model failed to accurately simulate influence of air flow rate on the amplitude and frequency of pressure pulsations in part load. Therefore the part load regime is studied carefully in this work: different computational domains are considered, different solvers are used, including ANSYS CFX and CADRUN, developed at the Institute of Computational Technologies. Different models of «liquid – gas» mixture are used in the calculations, compressibility is also taken into account. The flow rate of the injected air ranged from 0.5 to 2 percent of the water flow rate. The influence of the injected air on the flow pattern, including the vortex rope, is investigated. The results obtained are compared with experimental data.
Velocity profiles in a water jet of a Pelton nozzle: CFD simulations on both 2D and 3D geometries
Authors: Stivala D. , Rossi M. , Renzi M.
Published: June 2021

Hydropower is an important energy sector deployed all over the World with a significant share in the global electricity production. Due to the ongoing climate changes, the lack of water in summer periods compromises the performance of hydraulic machines, whose efficiency quickly decreases when they operate at strong part-load conditions.

Among the most known hydraulic turbines, Pelton is suitable to be used with high geodetic heights and relatively low flow rates. When dealing with flow rates 30% lower than the Best Efficiency Point (BEP), the efficiency drastically decreases mainly due to the non-uniform velocity profiles of the water jets coming out from the nozzles. The quality of the jet is affected by the distributor geometry, bending pipes and spear valves with the respective supports located upstream.

The aim of this work is to investigate different velocity profiles of the water jet coming out from a Pelton nozzle geometry by means of Computational Fluid Dynamics (CFD) simulations performed by ANSYS® Fluent solver. Four different spear valve angles were simulated on a 2D-axisymmetric geometry, starting from a reference case of = 50° with increasing steps of 5°, maintaining a fixed positioning of the spear valve that corresponds to a partial load operation of the machine.

In addition, also a 3D simulation has been carried out and the streamlines along a symmetry plane are shown. The results of the 3D simulations were compared to the 2D-axisymmetric ones taking into account the aforementioned reference case, showing how this last simplification of the computational domain leads to almost the same macroscopic results.
Digitalization in hydropower generation: development and numerical validation of a model-based Smart Power Plant Supervisor
Authors: Vagnoni E , Gerini F , Cherkaoui R , Paolone M
Published: June 2021

The paper presents the development of a model-based Smart Power Plant Supervisor, a digital tool targeting the optimization of the operation and maintenance of hydroelectric units to improve ancillary services provision to the power system. The paper focuses on a control-oriented modelling methodology which allows integrating the operational parameters of the hydroelectric unit in an optimization algorithm steering the advanced control of the units. The technique to develop analytical functions representing the behaviour of the hydropower plant is presented and validated by comparing numerical simulations with measurements of the real time operation of the run-of-river hydropower plant Vogelgrun. The results show a good performance of the modelling technique able to correctly predict the power generation of the power plant over one month of operation.
Multi-objective shape optimization of Francis runner using metamodel assisted genetic algorithm
Authors: Chirkov D , Filatova A , Polokhin S
Published: June 2021

Nowadays evolutionary optimization techniques become an integral part of the design process of hydraulic turbine runners. For optimization the shape of the runner is parameterized by a set of geometrical parameters. The objective functions of each runner geometry, being the efficiency and cavitation performance, are evaluated through CFD analysis of 3D flow-field. As usual, some kind of genetic algorithm is used for searching the Pareto front, due to its inherent possibility of parallel evaluation of different runner variants within one generation. This approach requires extensive CFD computations of hundreds and thousands of runner variants. In order to speed up the optimization process a metamodel (approximate, surrogate model) can be utilized. The metamodel provides an approximation of true dependency of the objective functions on the design parameters. The metamodel is built based on the known objective functions for some initial set of points randomly taken form the design space. Once built, it can be used to replace time consuming CFD computations during the optimization process. In the present paper a metamodel, based on Gaussian processes, is implemented and integrated into a multi-objective genetic algorithm. The obtained algorithm is applied for shape optimization of the Francis turbine runner. The number of the design parameters varied from 4 to 24. The objective functions are multi-point efficiency and cavitation characteristics. True values of the objective functions are evaluated using Reynolds averaged Navier-Stokes computations of the flow field in a reduced turbine domain, including wicket gate, runner and draft tube. These values are used to train the initial metamodel. In order to enhance predictive capabilities of the metamodel, it is retrained periodically during the optimization loop. The results of metamodel-assisted optimization runs are compared to that obtained without metamodel. It is shown that application of metamodel significantly reduces the number of actual CFD computations even for high number of design parameters and thus speeds up the overall optimization process.
Influence of the runner cone design on the pressure fluctuations in the draft tube of a low head Francis turbine
Authors: Khullar Subodh , Kumar Sandeep , Singh Krishna M , Cervantes Michel J , Gandhi Bhupendra K
Published: June 2021

This paper presents a preliminary numerical investigation on the design of the runner cone for a small turbine test rig under development at IIT Roorkee, India. The test rig is designed to study the formation and mitigation of rotating vortex rope (RVR) in the draft tube of a low head Francis turbine. The original runner cone design needs to be modified to include the provision for axial jet injection. Three different configurations, namely, a truncated cone and two original length cones with different nozzle positions, have been compared with the original cone to choose a suitable one for further investigations. The entire three-dimensional flow passage of the turbine unit has been simulated using the shear stress transport turbulence model after carrying out a mesh independence test on the original design. The proposed designs are compared at three different operating points. The amplitude and frequency of the pressure pulsations in the draft tube have been analyzed using the fast Fourier transform (FFT) method.
Stabilisation of the swirl exiting a Francis runner far from the best efficiency point
Authors: Susan-Resiga R F , Muntean S , Bosioc A , Stuparu A
Published: June 2021

The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge, far from the best efficiency point, develops self-induced instabilities featuring a precessing helical vortex (so-called vortex rope) which hinders the stable and safe turbine operation. This is an intrinsic characteristic of the swirl exiting the Francis runner, which at part load has a relatively large residual flux of moment of momentum as well as an imbalanced specific hydraulic energy with an excess near the band. We address in this paper the question of how one should alter this swirling flow in order to mitigate further instabilities in the discharge cone. In doing so, we consider an actuator disk located in the upstream part of the discharge cone that model a runaway runner which alter the hub-to-shroud angular momentum and specific head distributions without altering the turbine operating point. However, such a runaway runner provides a swirl stabilisation further downstream thereby effectively mitigating the vortex rope.
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

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

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

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

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

Considering 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

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

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

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

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

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

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

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

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

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

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.
Simulation of the structural behavior of a Francis runner in Deep Part Load Operation
Authors: von Locquenghien F , Wack J , Conrad P , Jester-Zürker R , Riedelbauch S
Published: June 2021

With the need for flexible operation, Francis runners are exposed to various operating conditions beyond the traditional operating range. These machines have to be designed for long time Part Load Operation in order to meet hydraulic and structural requirements. Deep Part Load Operation (DPL) mainly consists of stochastic loads on the blades. Whereas calculation methods for the dynamic stress at full load operation are well established, calculation of the dynamics during low load operation are in the focus of current research to increase the prediction accuracy. An unsteady flow simulation has been performed for a deep part load operating condition with the goal to derive the time-dependent pressure distribution in the runner. Based on the results, a FEA simulation with a 360° model is performed for multiple time steps to calculate the structural behavior. For a subsequent comparison to a strain gauge measurement, relevant characteristics with regard to material fatigue are identified. In addition, the calculation time in relation to the accuracy of the main characteristics of the flow induced stresses will be discussed.
Vortex rope mitigation with azimuthal perturbations: A numerical study
Authors: Holmström H , Sundström J , Cervantes M J
Published: June 2021

A novel method to mitigate the rotating vortex rope is investigated numerically on a propeller turbine using ANSYS CFX. Pulsating momentum is injected in a horizontal plane in the diffuser cone from four evenly spaced jets. Three mitigation strategies are tested; M1 in which the momentum is injected perpendicular to the axial flow direction, M2, which exhibit a 12 degree angle against the tangential velocity in the diffuser cone, and finally M3, which exhibit the same horizontal angle as M2 but at a 15 % higher flow rate. It is shown that mitigation attempts M1, M2 and M3 decrease the amplitude of the rotating mode by 51%,96% and 97%, respectively. The amplitude of the plunging mode, on the other hand, increase for all mitigation attempts. However, the amplitude of the plunging mode of the unperturbed RVR is an order of magnitude smaller than the rotating mode, and thus, the overall amplitude of the pressure fluctuations in the diffuser decreases significantly. The more efficient mitigation using attempt M2 and M3 are explained using velocity contour in the diffuser cone, which show that the RVR is significantly reduced downstream of the injection plane in between injections, which is not the case for attempt M1.
Dynamics of pressure pulsations in thin annular gap
Authors: Kůrečka Jan , Himr Daniel , Habán Vladimír
Published: June 2021

Fluid pulsations can significantly influence behavior of bearings or sealing parts of hydraulic machines and therefore their operation. In this contribution, an analytical approach to solve pressure pulsations dynamics is compared with a computational solution using acoustic simulation in ANSYS Mechanical FEM package. Studied problem is simplified to an annular gap and the pressure pulsations are excited either from one annulus end or excitation is made by a movement of an inner cylindrical surface perpendicularly to its axis. Excitation on an annulus surface can have angle dependent phase. This geometry allows a linearization of governing equations and so the equations are solvable analytically. Compressibility was incorporated to analytical and computational approach so the eigen frequencies for both methods were evaluated and compared. Also the added fluid effects were studied and evaluated.
Quantifying the Effect of Kaplan-Type Runner Blade Gaps on Fish-related Flow Conditions
Authors: Romero-Gomez Pedro , Colotelo Alison , Weissenberger Simon
Published: June 2021

In double-regulated Kaplan turbines, gaps form between the rotating blade and the hub as well as the discharge ring due to both the local geometry and the operational positioning of the runner blade. It is conventionally assumed that minimizing such gaps may decrease the likelihood of grinding and exposure of fish to high shear flows. Together with blunt leading edges of runner blades, minimum gap runners (MGR) are featured as the most effective measure to ameliorate the risks of mortal injury for fish passing through the turbine. However, the merits of such premise need yet to be quantified and made publicly accessible in the technical literature. This, in turn, will facilitate the evaluation of candidate MGR geometries in future designs.

In this work, we propose a metric to quantify the influence of the gaps features on the mortality risks for fish passing the turbine runner. Two main outcomes derived from the present research: (1) It informs the minimum set of hydraulic variables that may be considered as test conditions for laboratory experimentation on fish subjected to near gap-like flows and (2) it formulates a metric to be integrated into the modelling strategies currently in use for the biological performance assessment of new turbine geometries. This physics-based examination of the flow phenomena was conducted in two Kaplan-type units of very distinct features (one is a very low-head, mid-size unit of 1.8 MW-rating capacity and another is a large-size unit of 90 MW-rating capacity).
Numerical Simulation and Experimental Verification of Downstream Fish migration in a Kaplan turbine
Authors: Benigni H , Schneider J , Reckendorfer W , Jaberg H , Zenz G , Tuhtan J
Published: June 2021

Fish migrating downstream may face an increased risk of injury when passing through hydropower turbines. The overall influence on fish populations remains unknown. Still, it is undoubtedly linked to the damage potential of the turbines, the stage of maturity and the size of the migrating individuals as well as the proportion of migrating fish in relation to the total population. The sources of injury are usually the contact to the turbine blade and the rapid pressure drop in the turbine as well as shear forces, and large-scale turbulence. The authors investigated the conditions experienced by fish migrating through a 5-bladed vertical Kaplan turbine, each of the two units with a nominal power of 45 MW. Therefore, so-called “Barotrauma Detection Sensors (BDS)” were applied to determine the physical parameters during the turbine passages. Additionally, live fish, fitted externally with Barotrauma Detection Sensors, were introduced.
An experimental platform of variable speed pumped storage unit under wave disturbance: introduction and preliminary progress
Authors: Yang Weijia , Yang Jiandong , Zeng Wei , Zhao Zhigao , Zheng Guiqiao , Peng Tao , Huang Yifan , Hu Jinhong , Zeng Zhenyu , Yang Jiebin , Wang Xuewu , Chen Man
Published: June 2021

The importance of pumped storage plants (PSPs) is continuously increasing in power systems with more and more variable renewable energies. For the research and development of PSPs, variable speed technology and sea-water PSP are two important new orientations. In this paper, an experimental platform of variable speed pumped storage unit under wave disturbance is introduced. The purpose of the platform is to study the design and operation mechanism of variable speed PSP based on various common technical problems, especially for the four aspects: transient processes, variable speed unit, coordination control, wave disturbance. The platform adopts a Chinese sea-water PSP in feasibility stage as the prototype, and a model scale of 1:4 is applied. It consists of nine sub-systems, including waterway system, variable speed reversible model unit, circulating water system, speed governor system, AC excitation and electric protection, coordination control, monitoring system, intelligent AC load and measurement system. The model unit contains a reversible pump turbine, a doubly fed induction machine, etc. The speed variation range is ±8%, and the rated power is 78.13 kW. The model runner meets the IEC standard with a reference diameter of 284.3 mm. The upstream water tank is a closed pressure tank that can adjust the pressure and discharge. The downstream water tank is an open water tank that can simulate wave level fluctuation. Regarding the control system, it has four core parts: local control unit, speed governor, converter and coordination controller. The experimental study content contains three key aspects: (1) performance validation for variable speed unit; (2) operating stability under complex disturbances; (3) capability of variable speed PSP during transient processes. The experimental study based on the platform aims for laying a theoretical and technical foundation for the follow-up construction and operation of real sea-water PSPs with variable speed units.
Analysis of dynamic performance in a pump-turbine during the successive load rejection
Authors: Bi Huili , Chen Funan , Wang Chao , Wang Zhengwei , Fan Honggang , Luo Yongyao
Published: June 2021

Successive load rejection is one of the most crucial transient processes for calculating the maximum pressure in spiral case and maximum rotating speed of runner. One-dimensional mathematical models were established for a pump-storage power station and characteristics method was used to study the successive load rejection. The condition in which the maximum pressure occurs was chosen for three-dimensional unsteady calculation. The boundary conditions at spiral-casing inlet and draft tube outlet were determined by using the one-dimensional result. Based on numerical simulation, the axial hydraulic thrust and transient flow characteristic during the successive load rejection process were analysed. The axial hydraulic thrust during the successive load rejection process was mainly caused by the complex flow in the runner. The complex flow was affected both by hydraulic disturbance and the successive load rejection process.
DISMIR:

D

eep learning-based noninvasive cancer detection by

i

ntegrating DNA

s

equence and methylation information of

i

ndividual cell-free DNA

r

eads
Authors: Li Jiaqi , Wei Lei , Zhang Xianglin , Zhang Wei , Wang Haochen , Zhong Bixi , Xie Zhen , Lv Hairong , Wang Xiaowo
Published: June 2021

Detecting cancer signals in cell-free DNA (cfDNA) high-throughput sequencing data is emerging as a novel noninvasive cancer detection method. Due to the high cost of sequencing, it is crucial to make robust and precise predictions with low-depth cfDNA sequencing data. Here we propose a novel approach named DISMIR, which can provide ultrasensitive and robust cancer detection by integrating DNA sequence and methylation information in plasma cfDNA whole-genome bisulfite sequencing (WGBS) data. DISMIR introduces a new feature termed as ‘switching region’ to define cancer-specific differentially methylated regions, which can enrich the cancer-related signal at read-resolution. DISMIR applies a deep learning model to predict the source of every single read based on its DNA sequence and methylation state and then predicts the risk that the plasma donor is suffering from cancer. DISMIR exhibited high accuracy and robustness on hepatocellular carcinoma detection by plasma cfDNA WGBS data even at ultralow sequencing depths. Further analysis showed that DISMIR tends to be insensitive to alterations of single CpG sites’ methylation states, which suggests DISMIR could resist to technical noise of WGBS. All these results showed DISMIR with the potential to be a precise and robust method for low-cost early cancer detection.
Detecting copy number alterations in RNA-Seq using SuperFreq
Authors: Flensburg Christoffer , Oshlack Alicia , Majewski Ian J
Published: June 2021

Motivation

Calling copy number alterations (CNAs) from RNA sequencing (RNA-Seq) is challenging, because of the marked variability in coverage across genes and paucity of single nucleotide polymorphisms (SNPs). We have adapted SuperFreq to call absolute and allele sensitive CNAs from RNA-Seq. SuperFreq uses an error-propagation framework to combine and maximize information from read counts and B-allele frequencies.

Results

We used datasets from The Cancer Genome Atlas (TCGA) to assess the validity of CNA calls from RNA-Seq. When ploidy estimates were consistent, we found agreement with DNA SNP-arrays for over 98% of the genome for acute myeloid leukaemia (TCGA-AML, n = 116) and 87% for colorectal cancer (TCGA-CRC, n = 377). The sensitivity of CNA calling from RNA-Seq was dependent on gene density. Using RNA-Seq, SuperFreq detected 78% of CNA calls covering 100 or more genes with a precision of 94%. Recall dropped for focal events, but this also depended on signal intensity. For example, in the CRC cohort SuperFreq identified all cases (7/7) with high-level amplification of ERBB2, where the copy number was typically >20, but identified only 6% of cases (1/17) with moderate amplification of IGF2, which occurs over a smaller interval. SuperFreq offers an integrated platform for identification of CNAs and point mutations. As evidence of how SuperFreq can be applied, we used it to reproduce the established relationship between somatic mutation load and CNA profile in CRC using RNA-Seq alone.

Availability and implementation

SuperFreq is implemented in R and the code is available through GitHub: https://github.com/ChristofferFlensburg/SuperFreq/. Data and code to reproduce the figures are available at: https://gitlab.wehi.edu.au/flensburg.c/SuperFreq_RNA_paper. Data from TCGA (phs000178) was accessed from GDC following completion of a data access request through the database of Genotypes and Phenotypes (dbGaP). Data from the Leucegene consortium was downloaded from GEO (AML samples: GSE67040; normal CD34+ cells: GSE48846).

Supplementary information

Supplementary data are available at Bioinformatics online.