Francis Turbine Research Articles

Flow Characteristics Analysis of a 1 GW Hydraulic Turbine at Rated Condition and Overload Operation Condition

Flow stability is extremely important for hydraulic turbines, especially for 1 GW hydraulic turbines, and has a strong impact on mesh stability. However, turbines often operate under non-design conditions, and current research on this aspect is still lacking. So a model of the fluid domains of a high-quality installed 1 GW Francis turbine was established to investigate the flow characteristics of the turbine and fluid domains. CFD simulations of a 1 GW Francis turbine under rated load and overload operation conditions were performed. According to simulation results, when the turbine is under the overload operation condition, the internal flow stability of the 1 GW hydraulic turbine can be obviously different from that of the rated load. In the overload condition, the flow field is more turbulent and a large number of vortices are generated in the draft tube, resulting in significant changes in pressure, flow rate, and output. In order to improve calculation accuracy, a pure clearance model containing only clearances and pressure balance pipes was established. The results of the full flow channel and pure clearance were compared. It was found that under the rated operating condition and the overload condition, compared with the pure clearance model, the axial force of the runner calculated by the full flow channel model is approximately 2–7% biased, the radial force is biased by approximately 7–8%, and the leakage flow is smaller.

Unsteady assessment and alleviation of inter-blade vortex in Francis turbine

Inter-blade vortex refers to a specific type vortex cavitation observed in Francis turbines under partial loads and its adverse impact is widely recognized as a crucial factor that limits the safety and stability of hydraulic turbines. The present study endeavors to examine the spatiotemporal evolution attributes of inter-blade vortex and its contribution to the generation of unstable pressure fluctuations. To achieve this, a comprehensive investigation is conducted using a reduced-scale Francis model turbine with low head, combining numerical investigations and visualization experiments. The study demonstrates that the vapor volume associated with the inter-blade vortex experiences periodic pulsation, with a frequency proximate to the rotational frequency of the runner. Within the turbine runner, cavitation exhibits a dynamic cycle of incipience, growth, expansion, and localized collapse. The most remarkable cavitation disintegration occurs at the convergence point of the trailing edge of the runner blade and the band, wherein the most pronounced amplitude of pressure fluctuation is also discerned. In addition, this research establishes a direct correlation between pressure fluctuations and vapor volume, revealing that the acceleration of the vapor volume is accountable for the occurrence of pressure fluctuations with heightened magnitude. Furthermore, an optimization campaign successfully reduces the cavitation volume by 88.58% and 78.99% at two specific points of interest, resulting in the nearly complete elimination of high-amplitude pressure pulsations. Building upon these findings, data mining techniques are implemented to identify that the blade profile at a spanwise height of 0.75 significantly influences the enhancement of turbine hydraulic performance. Additionally, it has been ascertained that the design parameter governing the geometric placement of the blade trailing edge plays a pivotal role in reducing the intensity of the inter-blade vortex. This study yields invaluable insights into the underlying mechanism of unsteady phenomena induced by inter-blade vortex and formulates a hydraulic optimization approach capable of enhancing the operating stability of the Francis turbine.

Combined Weighted Envelope Spectrum: An enhanced demodulation framework for extracting characteristic frequency of rotating machinery

Envelope spectrum plays a pivotal role in the surveillance and diagnostics of rotating machinery. Two prevailing techniques for constructing this spectral quantity are narrowband demodulation and cyclostationary analysis. However, the former is susceptible to failure under low Signal-to-Noise Ratio (SNR) conditions or in the presence of non-Gaussian noise, while the latter exhibits sensitivity to cyclostationary noise, such as electromagnetic interferences. Notably, specific tasks determine the characteristic frequencies expected to be detected. More precisely, the determination of target component and noise interference depends on the mechanical part under scrutiny. Consequently, the envelope spectra provided by classical methods often manifest deficiencies when confronted with intricate monitoring signals from rotating machinery. To address this challenge, this paper proposes an enhanced demodulation framework—Combined Weighted Envelope Spectrum (CWES), tailored for extracting specific characteristic frequencies. First, a cyclostationary model for rotating machinery is presented, demarcating the target component as solely the cyclostationary signal caused by the mechanical element of concern. Second, the weighting functions with/without prior knowledge of characteristic frequency are elaborately designed, and the Adaptive Combined Weighted Envelope Spectrum (ACWES) and the Optimal Combined Weighted Envelope Spectrum (OCWES) are constructed correspondingly. Moreover, the indicator Characteristic peak-to-Noise peak Ratio (CNR) is proposed to evaluate the demodulation performance of different envelope spectra. Ultimately, the effectiveness of ACWES and OCWES is validated by simulation signals and experimental data from rolling bearing, centrifugal pump, and Francis turbine, and the comparison with the state-of-the-art demodulation methods verifies the superiority of the proposed enhanced demodulation framework.

Testing and Numerical Analysis of Abnormal Pressure Pulsations in Francis Turbines

During the flood season, Francis turbines often operate under low-head and full-load conditions, frequently experiencing significant pressure pulsations, posing potential threats to the safe and stable operation of the units. However, the factors contributing to substantial pressure pulsations in Francis turbines are multifaceted. This paper focuses on a mixed-flow hydroelectric generating unit at a specific hydropower station. Field tests were conducted to investigate abnormal vibrations and hydraulic pressure pulsations under low-head and full-load conditions. Utilizing the Navier–Stokes equations and the RNG k-ε turbulence model, the unsteady flow field within the turbine under these conditions was calculated. The results indicate that the abnormal pressure pulsations detected in the bladeless zone between the wicket gates and the turbine inlet are due to operational points deviating from the normal operating range of the turbine. When water flows at a large inflow angle, striking the turbine blade heads, it leads to significant flow separation and vortex formation at the back of the blade inlet edges, causing severe vibrations in the hydroelectric generating unit. These findings provide a basis and assurance for the safe and stable operation of the power station.

A Methodology for Designing a Fish-Friendly Turbine Rotor Applied to High-Power Generation

Most large hydropower facilities employing conventional hydraulic turbines, e.g., Francis, Kaplan, or Bulb turbines, etc., cause significant harm to fish, resulting in high mortality rates, during turbine operation. This results from strong injury-inducing mechanisms at the rotor, including shear stresses, pressure variations, and pressure drop through the rotor. The study outlines a methodology for designing a fish-friendly turbine that is suitable for high-power generation applications. This methodology for a hydraulic channel design within the turbine rotor was derived based on classical fundamental applications of a rotor design, supplemented by subsequent assessments that incorporate fish-friendly design parameters that have been documented in the existing literature. A spiral curve characterized by a linear angle variation between the rotor's inlet and outlet was employed to project the blade geometry. Here, the Göttingen hydrofoil series was used, while a second-order polynomial function guided the hub design. Both of these parametrizations sought to enhance the turbine's hydraulic efficiency. Minimum Absolute Pressure, Strain Rate, and Pressure Variation Rate intervals were established as assessment criteria for fish survival for certain species, as has also been previously explored in the literature. The findings were outlined in terms of hydrodynamic performance and flow behavior within the rotor. An improvement in hydraulic efficiency was observed, transitioning from a Preliminary Turbine geometry design to an Optimized Turbine Geometry design. The turbine rotor was optimized using Computational Fluid Dynamics (CFD) simulations, generated from a Design of Experiments (DOE). Modifications to the hydrofoil type, the sweep angle, and the trailing edge angle of the blades were all made, coupled with integrations of assessments considering fish-friendly parameters.

LES study of the precessing vortex core mitigation by radial injection in a Francis turbine air model

This work is devoted to a numerical study of the precessing vortex core (PVC) mitigation in a Francis turbine air model. The approach utilized to suppress the PVC, injection of radial jets, was based on influencing flow zones that are most susceptible to control. The analysis of the time-averaged velocity fields revealed extending of a recirculation zone. The time-averaged pressure pulsations in the flow decreased significantly, that indicates a mitigation of the PVC dynamics. Spectra of the azimuthally decomposed pressure pulsations signal demonstrated a suppression of the m = 1 mode by 25% and m = 2 by 40%, however, it does not coincide with the control efficiency in experimental work of I. Litvinov et al. In further investigations it is planned to vary the spatial orientation of the injection jets in order to achieve more effective PVC suppression.

Experimental Study on Performance of a Hydraulic Francis Turbine with Variations of Runner Speed

This investigation was carried out to evaluate the characteristics of a Francis water turbine. Several variations of inlet valve openings of the turbine were tested to determine the effects of changes in rotational speed of runner on turbine performance. The method used in this study was experimental measurement using a test rig installation in Diponegoro University. The results found that discharge was not change significantly with increasing speed. The torque decreases as the turbine rotational speed increases. The break horse power (BHP) and efficiency curves are nearly identical. Both BHP and efficiency increase when speed are increased until the maximum condition is reached, then from this maximum condition, as speed increase, the BHP and efficiency gradually decrease.

Characteristics of the runner vane design for a Francis turbine operated in isolated and off designed flow conditions

Characteristics of the runner vane design for a Francis turbine operated in isolated and off designed flow conditions

Study of frequency band in Von Karman excitation of Francis turbine

Study of frequency band in Von Karman excitation of Francis turbine

Features of the precessing vortex control in the Francis turbine model via jet injection

The study elucidates the mechanisms involved in actively controlling vortex phenomena within hydraulic turbines, particularly prevalent during partial load operations, leading to severe pressure fluctuations within the draft tube. Employing laser Doppler anemometry alongside acoustic sensors, the research delves into the flow structure and pulsation characteristics within the conical section of a Francis hydraulic turbine model under the influence of supplementary control jets injected through the runner streamline body. It was observed that orientation of the control jet has a discernible effect on reduction in pressure pulsations emanating from the precessing vortex core (PVC). An optimal injection strategy for diminishing pressure fluctuations while maintaining high turbine efficiency is identified. The findings align with earlier theoretical predictions derived from linear stability analysis of flow perturbations.

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Hydraulic vibrations in Francis turbines caused by cavitation profoundly impact the overall hydraulic performance and operational stability. Therefore, to investigate the influence of cavitation phenomena under high-load conditions, a three-dimensional unsteady numerical simulation is carried out for a Francis turbine with different head operating conditions, which is combined with the SST k-w turbulence model and two-phase flow cavitation model to capture the evolution of cavitation under high-load conditions. Additionally, utilizing entropy production theory, the hydraulic losses of the Francis turbine during cavitation development are assessed. Contrary to the pressure-drop method, the entropy production theory can quantitatively reflect the characteristics of the local hydraulic loss distribution, with a calculated error coefficient τ not exceeding 2%. The specific findings include: the primary sources of energy loss inside the turbine are the airfoil cavitation and cavitation vortex rope, constituting 26% and 71% of the total hydraulic losses, respectively. According to the comparison with model tests, the vapor volume fraction (VVF) inside the draft tube fluctuates periodically under high-load conditions, causing low-frequency pressure pulsation in the turbine’s power, flow rate, and other external characteristic parameters at 0.37 Hz, and the runner radial force fluctuates at a frequency of 1.85 Hz.

Potential for small hydropower development on the Pumpum River of Ghana using Remote Sensing and Soil Water Assessment Tool

This study focused on identifying potential locations for the implementation of Small Hydropower Systems to enhance the existing energy infrastructure in the Pumpum River Basin (PRB). Utilizing remote sensing and the Soil and Water Assessment Tool, basin parameters were generated and simulated for hydropower analysis. The energy potential of suitable sites was assessed through flow duration curves and power duration curves. The findings reveal that the PRB exhibits potential for small hydropower development, identifying nine sites along the river. The results of the model indicate power capacities of 1,521 kW for the Run of River and 2,290 kW for the dam sites respectively. The most promising hydropower sites were identified as dam site 1, river of run site 1, and dam site 6 with corresponding firm power of 2356.2 kW, 1567 kW and 264 kW, resulting in estimated firm energy production of 12.07 GWh, 8.03 GWh, and 1.35 GWh, respectively. Considering the suitable spacing of more than between 12 km among dam site 1, river of run site 1, and dam site 6 and a combined annual energy production of 21.65 GWh, a recommended approach involves establishing a cascade hydropower arrangement at sites dam site 1, river of run site 1, and dam site 6 along the Pumpum River. With a plant capacity of 65% to 90% dependability range, incorporating an installed Francis turbine, the total annual firm energy that can be produced from the nine (9) (Run of river and dam) projected sites ranges between 0.69 and 12.07 GWh.

Analysis on Hydraulic Design of Runner Blades of Francis Turbine

Francis turbine is the most widely used model in hydropower station, and the hydraulic design of runner blades affects the efficiency of the unit. This paper discusses how to complete the hydraulic design of Francis turbine runner blades according to the given parameters. In hydraulic design of Francis turbine runner, firstly, the structural scheme is determined according to the given parameters. On the basis of referring to excellent hydraulic model, a Francis turbine runner blade is designed according to the given head. By analyzing and calculating the data, the geometric parameters and axial projection of the Francis turbine runner flow channel are determined, and the axial flow network is drawn and checked, so as to complete the calculation of axial vortex line and blade drawing. Finally, the airfoil is thickened by a certain thickening principle.

Evaluation of uncertainties in pressure fluctuations measurement on low-head Francis turbine model during part-load operation

The Francis turbines are often operated at the part load (PL) conditions to meet the electricity demand while maintaining system stability. During PL operations, the turbine experiences flow instabilities and vortex formation in the draft tube, leading to potential damage to the turbine. This experimental study focused on measuring pressure fluctuations in a model low-head Francis turbine at PL operation, i.e. 70% of rated load condition. Eight pressure sensors were installed at various locations to measure the pressure fluctuations. In-situ calibrations were performed for various measuring instruments used in testing, such as flow meters, pressure transducers, torque transducers, and speed sensors. The uncertainty evaluation for hydraulic turbine efficiency and pressure fluctuations in the draft tube cone was carried out at the PL operations. Quantifying the uncertainty for both Type A and Type B was conducted. The maximum estimated uncertainty for measuring hydraulic turbine model efficiency is ±0.272% and for pressure fluctuations during PL operation is ±1.358%.

Numerical Simulation and Analysis of Hydraulic Turbines Based on BIM for Sustainable Development

Hydropower is considered to be an important way to achieve the sustainable development goal of human progress. The performance of turbines is very important to the safety and stability of hydropower stations. Most of the hydraulic turbine performance studies only use Computational Fluid Dynamics (CFD) for performance simulation, lacking the integration of Building Information Modeling (BIM) technology and CFD. Therefore, a performance analysis model of a Francis turbine based on BIM was put forward in this paper. The BIM software OpenBuildings Designer CONNECT Edition Update 10 was used to build the hydraulic turbine model, and then the BIM model was transferred to the CFD numerical simulation platform ANSYS through the intermediate format conversion. In the ANSYS environment, the numerical simulation of different working conditions was carried out with the help of Fluent 2021 R1 software. The numerical simulation results show that the fluid velocity gradient in the volute was 2~3 m/s under the three working conditions, which was relatively stable. The water flow could progress the guide vane mechanism at a higher speed, and the drainage effect of the volute was better. There were some negative pressure areas at the back of the runner blades and the inlet of draft tube, and the negative pressure value was as high as −420,000 Pa and −436,842 Pa under maximum head conditions, which were prone to cavitation erosion. It is proven that BIM supported the hydraulic turbine performance analysis and provided a geometric information model for hydraulic turbine CFD numerical simulation, meaning that the performance analysis model based on BIM is feasible. This study can expand the application value of BIM and provide guidance for the study of hydraulic turbine numerical simulation using BIM technology in combination with CFD methods.

Research on the Hydraulic Characteristics of 1000 MW Francis Runner: Influence of Radial Installation Deviations

This paper focuses on a 1000 MW Francis turbine and conducts a numerical analysis of the entire flow passage using computational fluid dynamics (CFD) under steady-state conditions. Building upon prior research, we further investigate the impact of an uneven gap distribution caused by radial co-directional installation deviations of 0.1 mm, 0.3 mm, 0.5 mm, 1.5 mm, and 2.5 mm on the pressures and radial forces at various locations of the turbine, including the upper crown chamber, the vaneless zone, and the bottom ring chamber, all under steady-state rated operating conditions. By examining the maximum and minimum pressure values under different conditions, we determined that different pressure reading methods should be applied to distinct surfaces. Additionally, we derived the patterns illustrating how different components are affected by radial installation deviations. The significance of this study lies in its comprehensive exploration of the influence of radial installation deviations on the performance of a Francis turbine, particularly under steady-state rated conditions. Through numerical analysis, we elucidated the specific effects of various deviation magnitudes on the pressures and radial forces at different turbine locations. These findings provide valuable insights for the optimization of turbine design and operation. The novelty of this work stems from its in-depth investigation of radial co-directional installation deviations and the extensive results obtained through numerical simulations. These results hold significant implications for improving turbine performance and reliability, surpassing previous efforts in the literature.

Comparison of Pressure Pulsation Characteristics of Francis Turbine with Different Draft Tube Arrangement Direction

Hydroelectric power generation is an important clean energy source, and the stability of water turbine operation determines the quality of hydro energy utilization. For hydro turbines, the layout direction of the draft tube is often only considered from a structural perspective, ignoring the hydrodynamic characteristics. This study adopts the computational fluid dynamics method and verifies the effectiveness of numerical simulation with experimental results, analyzing the influence of asymmetric draft tube layout direction on pressure pulsation of mixed flow turbine. The results show that under different working conditions, there is basically no difference in efficiency corresponding to different inclined directions of the draft tube, and the relative difference in performance values is less than 1%. From the perspective of internal flow, the working condition has a greater impact on the flow, and the draft tube tilt has a smaller impact. Under strong swirling flow conditions in the draft tube, the variational mode decomposition of pressure fluctuation is carried out. Research has found 7 characteristic frequency bands including 140 Hz, 80–90 Hz, 40–46 Hz, 5.5–6.5 Hz, 2.5–3 Hz, 1.67 Hz, and <1 Hz. The frequency of the dominant mode corresponding to the left tilt is higher, while the amplitude of the runner frequency is slightly lower. In general, left tilt is not only more suitable for unit layout but also has a better effect on draft tube pressure fluctuation, which is worthy of application in engineering.

Research on the Hydraulic Excitation Characteristics of the Top Cover Caused by the Radial Installation Deviation of the Seal of a 1GW Francis Turbine

The radial installation deviation of the turbine runner will change the gap flow between the upper crown and the lower ring seal, which will affect the radial force of the runner and the hydraulic excitation characteristics of the top cover. This research focuses on the 1GW Francis turbine on the right bank of the Baihetan hydropower station. The pressure distribution along the circumference of the top cover was analyzed, and the effects of deviations on the specific generation of hydraulic excitation forces were studied. This research shows that the increase in radial deviation will slightly reduce the output and efficiency, and the radial force on the runner increases parabolically. When the radial deviation is 1.5 mm, the radial force is 5.9 times higher compared to the case without any deviation, and the radius of the fitting circle of the radial force behavior trajectory increases with the increase in radial deviation. In addition, the radial deviation has little effect on the internal flow of the runner and the pressure distribution in the upper crown chamber. The dominant frequency components at the upstream monitoring points include fn, 15 fn, 24 fn, and 30 fn. The dominant frequency components at the downstream monitoring points include the blade passing frequencies of 15 fn and 30 fn. However, with the increase in radial deviation, the fluctuation amplitudes exhibit an asymmetric distribution, the uniformity of the pressure distribution in the circumferential direction of the labyrinth seal area becomes significantly worse, and the waveform of the downstream monitoring points changes significantly and presents a non-uniform distribution in one rotation cycle.

Numerical flow field investigation around guide vane of a high head Francis turbine

Guide vanes are the most eroded component of the Francis turbine, and flow instabilities around guide vanes influence the flow field at the runner inlet. Guide vane cascade can be considered an alternative method to investigate the flow field, which maintains flow similarity with the prototype turbine. The objective of this paper is to numerically analyze the flow field around the guide vane cascade. A single guide vane cascade numerical model is developed to perform the simulation using commercial software ANSYS 2022. Two turbulence models, shear stress transport k-ω and standard k-ε, perform steady-state simulation at the best efficiency point. The pressure and velocity distribution are obtained at mid-span, and around the pressure and suction sides of the guide vane. Numerical simulation on a scaled prototype full turbine has also been performed to measure the Francis turbine’s torque and efficiency. The modified Bhilangana- III guide vane profile is installed in the B-III hydropower plant in India and taken as a reference Francis turbine. The velocity and pressure distributions obtained around guide vanes of the scaled full turbine are compared with the velocity and pressure distributions of the single guide vane cascade. A difference of 7.25 % in maximum velocity and 9.40 % in maximum pressure at the mid-span of the guide vane is found between the guide vane cascade and scaled full turbine at the best efficiency point. The overall efficiency of the scaled turbine is also measured, and a difference of 0.83 % between the numerical result and scaled hill chart at the best efficiency point was found.

Challenges with onboard strain measurements on a model Francis turbine runner

As the world transitions towards more renewable energy sources, as a step to reduce the emissions of CO2, intermittent and non-dispatchable sources like solar and wind will take up a larger proportion of the energy production. With more unregulated power in the energy mix, a higher demand is put on the rest of the energy production system. Hydropower is in a unique position as it is both renewable and a highly flexible energy source. The increased use of flexible operation of Francis turbines especially, puts a higher dynamic load on the runner components which as a consequence leads to a reduced lifetime. In this paper we present the experimental setup and results from a measurement campaign performed on a model of a low specific speed Francis runner. Onboard measurements with strain gauges at the trailing edge of two runner blades were performed. The experiments were conducted as a part of the HydroFlex project with the goal of validating numerical simulations and to gain a better understanding of the reduction of lifetime on Francis turbines due to higher fatigue loading from more flexible operation. The results shows that there were a significant drift of the mean strain over time during the measurement campaign, and a lower measured strain at BEP than expected when compared to numerical simulations. In this paper, the experimental setup, results and challenges encountered are presented.