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Ole Gunnar Dahlhaug - One of the best experts on this subject based on the ideXlab platform.
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signature investigation of typical faults on Francis Turbines
Journal of Physics: Conference Series, 2020Co-Authors: G K Storen, Ole Gunnar Dahlhaug, Bjorn Winther SolemslieAbstract:Hydropower is facing new operational strategies as the increasingly competitive power market demands for higher flexibility. Consequently, Turbines are forced to handle tougher operation and are prone to more frequent degradation. By implementing a real-time monitoring system, a better understanding of the behavior of components may contribute to detect faults at an earlier stage, reducing potential downtime. This paper will present the work done in the preliminary work of the author's master thesis. The focus has been to characterize the normal behaviour of a Francis turbine through amplitude and frequency analysis. Steady-state measurements of pressure pulsations have been conducted on the Francis test-rig at the Waterpower laboratory at NTNU. Different hydraulic phenomena and respective frequencies were identified. In addition, the results revealed several unexpected frequencies and suspicious observations, and potential sources of these are discussed. Possible fault detection schemes based on peak-peak and frequency analysis are suggested. Alarm should be raised in case of mismatches in sensor relations, magnitude variations or if new harmonics or frequencies appears.
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numerical prediction of hill charts of Francis Turbines
Journal of Physics: Conference Series, 2019Co-Authors: Andreas Nordvik, Chirag Trivedi, Igor Iliev, Ole Gunnar DahlhaugAbstract:This present work compares numerically predicted hill chart to experimental measurements of a Francis turbine. The main objective is to create a model for recreating hill charts using computational fluid dynamics (CFD). Accurate prediction of hill charts are useful in the design stage of production and may result in a more efficient runner. The primary focus is the prediction of efficiency and investigation of possible simplifications without loss in accuracy. By using steady-state simulations, preliminary tests were made on four different meshes, and two different turbulence models, namely the standard k – e model and the shear stress transport model. Simplifications of geometry have been tested to investigate if the simulation time can be reduced without sacrificing accuracy. Numerical simulations of 132 operating points were carried out. The efficiency was predicted with the maximal difference from measured values of 6.93%.
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Variable-speed operation of Francis Turbines: A review of the perspectives and challenges
Renewable & Sustainable Energy Reviews, 2019Co-Authors: Igor Iliev, Chirag Trivedi, Ole Gunnar DahlhaugAbstract:Abstract The paper presents the recent trends and ideas for flexible operation of Francis Turbines using Full-Size Frequency Converter (FSFC) or Doubly-Fed Induction Machine (DFIM) technology for variable-speed operation. This technology allows for the speed of the runner to be adjusted in order to maximize the efficiency and/or reduce dynamic loads of the turbine according to the available head and power generation demands. Continuous speed variation of up to ± 10 % of the design rotational speed can be achieved with the DFIM technology, while for FSFC there is no such limit by the technology itself. For off-design operation of Francis Turbines, depending on the variation of the head and the hydraulic design, the hydraulic efficiency gain from variable-speed operation compared to its synchronous-speed representative can go up to 10 % . In addition, Turbines operated at variable-speed can have significant improvement in the response times for power output variations, being able to utilize the flywheel effect from the rotating masses (also known as synthetic inertia). This review focuses on the investigations and the achievements done so far and does not tend to enter deeply into each multidisciplinary aspect of the technology itself. Possible further development directions are also disclosed, mainly towards the hydraulic design and optimization of variable-speed Francis Turbines.
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investigation of the unsteady pressure pulsations in the prototype Francis Turbines part 1 steady state operating conditions
Mechanical Systems and Signal Processing, 2018Co-Authors: Chirag Trivedi, Peter Joachim Gogstad, Ole Gunnar DahlhaugAbstract:Abstract Hydropower is one of the most reliable renewable sources of electricity generation. With high efficiency and good regulating capacity, hydropower has the ability to meet rapid changes in power demand. Large investments in intermittent renewable energy resources have increased the demand for balancing power. This demand has pushed hydraulic Turbines to generate electricity over the operating range from part load to full load. High-amplitude pressure pulsations are developed at off-design conditions, which cause moderate damage to the turbine components. The pressure pulsations may be either synchronous- (axial)-type, asynchronous- (rotating)-type or both. In this study, pressure measurements on low specific-speed prototype Francis Turbines were performed; one of them was vertical axis and another was horizontal axis type. Four pressure sensors were mounted on the surface of the draft tube cone. Pressure measurements were performed at five operating points. The investigations showed that, in the vertical axis turbine, amplitudes of asynchronous pressure pulsations were 20 times larger than those of the synchronous component; whereas, in the horizontal axis turbine, amplitudes of asynchronous pressure pulsations were two times smaller than those of the synchronous component. For part 2 of the paper, please read Trivedi, C., Gogstad, P. J., and Dahlhaug, O. G., 2017, “Investigation of Unsteady Pressure Pulsations in the Prototype Francis Turbines during Load Variation and Startup,” Journal of Renewable Sustainable Energy, 9(6), p. 064502. https://doi.org/10.1063/1.4994884 .
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performance comparison of optimized designs of Francis Turbines exposed to sediment erosion in various operating conditions
Journal of Physics: Conference Series, 2018Co-Authors: K P Shrestha, Sailesh Chitrakar, Bhola Thapa, Ole Gunnar DahlhaugAbstract:Erosion on hydro turbine mostly depends on impingement velocity, angle of impact, concentration, shape, size and distribution of erodent particle and substrate material. In the case of Francis Turbines, the sediment particles tend to erode more in the off-designed conditions than at the best efficiency point. Previous studies focused on the optimized runner blade design to reduce erosion at the designed flow. However, the effect of the change in the design on other operating conditions was not studied. This paper demonstrates the performance of optimized Francis turbine exposed to sediment erosion in various operating conditions. Comparative study has been carryout among the five different shapes of runner, different set of guide vane and stay vane angles. The effect of erosion is studied in terms of average erosion density rate on optimized design Francis runner with Lagrangian particle tracking method in CFD analysis. The numerical sensitivity of the results are investigated by comparing two turbulence models. Numerical results are validated from the velocity measurements carried out in the actual turbine. Results show that runner blades are susceptible to more erosion at part load conditions compared to BEP, whereas for the case of guide vanes, more erosion occurs at full load conditions. Out of the five shapes compared, Shape 5 provides an optimum combination of efficiency and erosion on the studied operating conditions.
François Avellan - One of the best experts on this subject based on the ideXlab platform.
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Transposition of the mechanical behavior from model to prototype of Francis Turbines
Renewable Energy, 2020Co-Authors: David Valentín, Alexandre Presas, Carme Valero, Mònica Egusquiza, Eduard Egusquiza, J. Gomes, François AvellanAbstract:Abstract Hydropower is nowadays essential for balancing the electrical grid providing flexibility and fast response. The role of hydraulic Turbines has changed from working at their Best Efficiency Point (BEP) to work in the whole operating range when demanded. Francis Turbines working at off-design conditions suffer from dynamic problems that affect the useful life of their components, especially of the runner. Reduced scale physical models of Francis Turbines are widely used to determine their hydraulic behavior. Most of the hydraulic parameters obtained in model tests are transposable to prototype by using the similarity theories as long as they meet similitude requirements. However, from the mechanical behavior point of view, both model and prototype structures are not always similar and the mechanical behavior of the model is often not considered for transposition. In this paper, a transposition method for the mechanical behavior of Francis Turbines models is presented and the results are compared with the real size prototype. The modal behavior of the runner, its stress and fatigue life estimation for different operating conditions are experimentally compared for both model and prototype. Results present the possibilities and limitations of transposing the mechanical parameters from model to prototype.
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origin of the synchronous pressure fluctuations in the draft tube of Francis Turbines operating at part load conditions
Journal of Fluids and Structures, 2019Co-Authors: Simon Pasche, Francois Gallaire, François AvellanAbstract:Abstract The synchronous pressure surge effect is a critical phenomenon occurring in Francis Turbines operating at part load conditions. In this regime, pressure fluctuations are predominantly coming from the temporal rotation of a single helical vortex inside the turbine draft tube, called the part load vortex rope. However the combination of multi-physics interactions, geometry, cavitation, swirling flow and acoustic waves leads to a pressure amplification, called the synchronous pressure surge effect, which is more dangerous than the fluctuations resulting from the precessing vortex rope. While this subsequent amplification mechanism has been unraveled, the physical mechanism originating in the synchronous pressure wave remains poorly understood. We have therefore investigated the birth and the growth of the synchronous pressure wave in Francis Turbines. By energy consideration of an azimuthal–temporal Fourier decomposition of the three dimensional numerical flow solutions in an axisymmetric draft tube geometry that is slightly disturbed at the wall, the source of the synchronous pressure and its amplification region are identified. In addition, the origin of this wave as the interaction of a wall disturbance with the part load vortex rope, is investigated using an asymptotic analysis and brings deeper comprehension of the synchronous wave generation mechanism.
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urans models for the simulation of full load pressure surge in Francis Turbines validated by particle image velocimetry
Journal of Fluids Engineering-transactions of The Asme, 2017Co-Authors: Jean Decaix, François Avellan, Arthur Tristan Favrel, Andres Muller, Cecile MunchAbstract:Due to the penetration of alternative renewable energies, the stabilization of the electrical power network relies on the off-design operation of Turbines and pump-Turbines in hydro-power plants. The occurrence of cavitation is however a common phenomenon at such operating conditions, often leading to critical flow instabilities which undercut the grid stabilizing capacity of the power plant. In order to predict and extend the stable operating range of hydraulic machines, a better understanding of the cavitating flows and mainly of the transition between stable and unstable flow regimes is required. In the case of Francis Turbines operating at full load, an axisymmetric cavitation vortex rope develops at the runner outlet. The cavity may enter self-oscillation, with violent periodic pressure pulsations. The flow fluctuations lead to dangerous electrical power swings and mechanical vibrations, dictating an inconvenient and costly restriction of the operating range. The present paper reports an extensive numerical and experimental investigation on a reduced scale model of a Francis turbine at full load. For a given operating point, three pressure levels in the draft tube are considered, two of them featuring a stable flow configuration and one of them displaying a self-excited oscillation of the cavitation vortex rope. The velocity field is measured by two-dimensional (2D) particle image velocimetry (PIV) and systematically compared to the results of a simulation based on a homogeneous unsteady Reynolds-averaged Navier–Stokes (URANS) model. The validation of the numerical approach enables a first comprehensive analysis of the flow transition as well as an attempt to explain the onset mechanism.
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Experimental evidence of inter-blade cavitation vortex development in Francis Turbines at deep part load condition
Experiments in Fluids, 2017Co-Authors: K Yamamoto, A Muller, A. Favrel, François AvellanAbstract:Francis Turbines are subject to various types of cavitation flow depending on the operating condition. To enable a smooth integration of the renewable energy sources, hydraulic machines are now increasingly required to extend their operating range, especially down to extremely low discharge conditions called deep part load operation. The inter-blade cavitation vortex is a typical cavitation phenomenon observed at deep part load operation. However, its dynamic characteristics are insufficiently understood today. In an objective of revealing its characteristics, the present study introduces a novel visualization technique with instrumented guide vanes embedding the visualization devices, providing unprecedented views on the inter-blade cavitation vortex. The binary image processing technique enables the successful evaluation of the inter-blade cavitation vortex in the images. As a result, it is shown that the probability of the inter-blade cavitation development is significantly high close to the runner hub. Furthermore, the mean vortex line is calculated and the vortex region is estimated in the three-dimensional domain for the comparison with numerical simulation results. In addition, the on-board pressure measurements on a runner blade is conducted, and the influence of the inter-blade vortex on the pressure field is investigated. The analysis suggests that the presence of the inter-blade vortex can magnify the amplitude of pressure fluctuations especially on the blade suction side. Furthermore, the wall pressure difference between pressure and suction sides of the blade features partially low or negative values near the hub at the discharge region where the inter-blade vortex develops. This negative pressure difference on the blade wall suggests the development of a backflow region caused by the flow separation near the hub, which is closely related to the development of the inter-blade vortex. The development of the backflow region is confirmed by the numerical simulation, and the physical mechanisms of the inter-blade vortex development is, furthermore, discussed.
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mechanical impact of dynamic phenomena in Francis Turbines at off design conditions
HYdropower Plants PERformance and FlexiBle Operation Towards Lean Integration of New Renewable Energies Symposium HYPERBOLE 2017, 2017Co-Authors: F Duparchy, J Brammer, M Thibaud, Arthur Tristan Favrel, P Y Lowys, François AvellanAbstract:At partial load and overload conditions, Francis Turbines are subjected to hydraulic instabilities that can potentially result in high dynamic solicitations of the turbine components and significantly reduce their lifetime. This study presents both experimental data and numerical simulations that were used as complementary approaches to study these dynamic solicitations. Measurements performed on a reduced scale physical model, including a special runner instrumented with on-board strain gauges and pressure sensors, were used to investigate the dynamic phenomena experienced by the runner. They were also taken as reference to validate the numerical simulation results. After validation, advantage was taken from the numerical simulations to highlight the mechanical response of the structure to the unsteady hydraulic phenomena, as well as their impact on the fatigue damage of the runner.
Chirag Trivedi - One of the best experts on this subject based on the ideXlab platform.
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numerical prediction of hill charts of Francis Turbines
Journal of Physics: Conference Series, 2019Co-Authors: Andreas Nordvik, Chirag Trivedi, Igor Iliev, Ole Gunnar DahlhaugAbstract:This present work compares numerically predicted hill chart to experimental measurements of a Francis turbine. The main objective is to create a model for recreating hill charts using computational fluid dynamics (CFD). Accurate prediction of hill charts are useful in the design stage of production and may result in a more efficient runner. The primary focus is the prediction of efficiency and investigation of possible simplifications without loss in accuracy. By using steady-state simulations, preliminary tests were made on four different meshes, and two different turbulence models, namely the standard k – e model and the shear stress transport model. Simplifications of geometry have been tested to investigate if the simulation time can be reduced without sacrificing accuracy. Numerical simulations of 132 operating points were carried out. The efficiency was predicted with the maximal difference from measured values of 6.93%.
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Variable-speed operation of Francis Turbines: A review of the perspectives and challenges
Renewable & Sustainable Energy Reviews, 2019Co-Authors: Igor Iliev, Chirag Trivedi, Ole Gunnar DahlhaugAbstract:Abstract The paper presents the recent trends and ideas for flexible operation of Francis Turbines using Full-Size Frequency Converter (FSFC) or Doubly-Fed Induction Machine (DFIM) technology for variable-speed operation. This technology allows for the speed of the runner to be adjusted in order to maximize the efficiency and/or reduce dynamic loads of the turbine according to the available head and power generation demands. Continuous speed variation of up to ± 10 % of the design rotational speed can be achieved with the DFIM technology, while for FSFC there is no such limit by the technology itself. For off-design operation of Francis Turbines, depending on the variation of the head and the hydraulic design, the hydraulic efficiency gain from variable-speed operation compared to its synchronous-speed representative can go up to 10 % . In addition, Turbines operated at variable-speed can have significant improvement in the response times for power output variations, being able to utilize the flywheel effect from the rotating masses (also known as synthetic inertia). This review focuses on the investigations and the achievements done so far and does not tend to enter deeply into each multidisciplinary aspect of the technology itself. Possible further development directions are also disclosed, mainly towards the hydraulic design and optimization of variable-speed Francis Turbines.
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investigation of the unsteady pressure pulsations in the prototype Francis Turbines part 1 steady state operating conditions
Mechanical Systems and Signal Processing, 2018Co-Authors: Chirag Trivedi, Peter Joachim Gogstad, Ole Gunnar DahlhaugAbstract:Abstract Hydropower is one of the most reliable renewable sources of electricity generation. With high efficiency and good regulating capacity, hydropower has the ability to meet rapid changes in power demand. Large investments in intermittent renewable energy resources have increased the demand for balancing power. This demand has pushed hydraulic Turbines to generate electricity over the operating range from part load to full load. High-amplitude pressure pulsations are developed at off-design conditions, which cause moderate damage to the turbine components. The pressure pulsations may be either synchronous- (axial)-type, asynchronous- (rotating)-type or both. In this study, pressure measurements on low specific-speed prototype Francis Turbines were performed; one of them was vertical axis and another was horizontal axis type. Four pressure sensors were mounted on the surface of the draft tube cone. Pressure measurements were performed at five operating points. The investigations showed that, in the vertical axis turbine, amplitudes of asynchronous pressure pulsations were 20 times larger than those of the synchronous component; whereas, in the horizontal axis turbine, amplitudes of asynchronous pressure pulsations were two times smaller than those of the synchronous component. For part 2 of the paper, please read Trivedi, C., Gogstad, P. J., and Dahlhaug, O. G., 2017, “Investigation of Unsteady Pressure Pulsations in the Prototype Francis Turbines during Load Variation and Startup,” Journal of Renewable Sustainable Energy, 9(6), p. 064502. https://doi.org/10.1063/1.4994884 .
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simplified hydrodynamic analysis on the general shape of the hill charts of Francis Turbines using shroud streamline modeling
Journal of Physics: Conference Series, 2018Co-Authors: Igor Iliev, Chirag Trivedi, Ole Gunnar DahlhaugAbstract:The paper presents a simplified one-dimensional calculation of the efficiency hill-chart for Francis Turbines, based on the velocity triangles at the inlet and outlet of the runner's blade. Calculation is done for one streamline, namely the shroud streamline in the meridional section, where an efficiency model is established and iteratively approximated in order to satisfy the Euler equation for turbomachines at a wide operating range around the best efficiency point (BEP). Using the presented method, hill charts are calculated for one splitter-bladed Francis turbine runner and one Reversible Pump-Turbine (RPT) runner operated in the turbine mode. Both Turbines have similar and relatively low specific speeds of nsQ = 23.3 and nsQ = 27, equal inlet and outlet diameters and are designed to fit in the same turbine rig for laboratory measurements (i.e. spiral casing and draft tube are the same). Calculated hill charts are compared against performance data obtained experimentally from model tests according to IEC standards for both Turbines. Good agreement between theoretical and experimental results is observed when comparing the shapes of the efficiency contours in the hill-charts. The simplified analysis identifies the design parameters that defines the general shape and inclination of the turbine's hill charts and, with some additional improvements in the loss models used, it can be used for quick assessment of the performance at off-design conditions during the design process of hydraulic Turbines.
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investigation of the unsteady pressure pulsations in the prototype Francis Turbines during load variation and startup
Journal of Renewable and Sustainable Energy, 2017Co-Authors: Chirag Trivedi, Peter Joachim Gogstad, Ole Gunnar DahlhaugAbstract:This work investigates the unsteady pressure fluctuations in two prototype Francis Turbines during load variation and start-up. Although hydraulic Turbines are expected to experience such events over their lifetime, the resulting pressure amplitudes are so significant that they take a toll on a machine's operating life. The interest of the present study is to experimentally measure and numerically characterize time-dependent pressure pulsations. Specific focus is on (1) how pressure pulsations of both synchronous and asynchronous types in vertical- and horizontal-axis Turbines change when the load of a turbine changes from steady conditions, (2) what the pressure amplitudes during load change are, and (3) how quickly pressure amplitudes vary when a generator is synchronized to the power grid (load) during start-up. To this end, four pressure sensors were integrated in the draft tube cone. The results are quite interesting, especially during transition from the steady state to the transient load change. In...
Hari Prasad Neopane - One of the best experts on this subject based on the ideXlab platform.
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sediment erosion in low specific speed Francis Turbines a case study on effects and causes
Wear, 2020Co-Authors: Biraj Singh Thapa, Hari Prasad Neopane, Sailesh Chitrakar, Saroj Gautam, Nirmal Acharya, Baoshan ZhuAbstract:Abstract Hydraulic Turbines experience severe operational and maintenance challenges when operated in sediment-laden water. The combined effect of erosive and abrasive wear in turbine components deteriorates their life and efficiency. The quantity and pattern of sediment erosion depends on the nature of the flow and the amount of hard minerals contained in water. Localized erosion patterns are observed mostly in guide vanes, runner blades and facing plates of Francis Turbines due to different natures of fluid flow in those regions. Accelerating flow around the guide vanes and its shaft causes abrasive and erosive wear in its surface, which causes increase in the size of the clearance gap between the facing plates and the guide vanes. Flow leaving the clearance gap forms a vortex filament due to the leakage from high pressure side to the low-pressure side of the guide vane, which eventually strikes the rotating runner blades. This paper presents a case study of a power plant in India with low specific speed Francis Turbines, which is severely affected by sediment erosion problems. A numerical analysis of the flow is conducted inside the turbine to study causes of various erosion patterns in the turbine components. The results from CFD are compared with the actual erosion in Turbines. Erosion in guide vanes and runner blades are taken into consideration in this paper, due to the complex flow phenomena around these regions. It is found that the leakage flow through clearance gaps of guide vanes is the primary cause of erosion at the inlet of the runner blades. Furthermore, the effects of size and shape of quartz particles are studied which shows that erosion is directly proportional to these parameters.
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selection of guide vane profile for erosion handling in Francis Turbines
Renewable Energy, 2017Co-Authors: Hari Prasad Neopane, Ravi Koirala, Oblique Shrestha, Baoshan Zhu, Bhola ThapaAbstract:In guide vane cascade of Francis turbine, highest acceleration occurs, which generates equivalent amount of force for work done and erosion due to instantaneous change in flow dynamics. Hence in addition to runner vane, suitable selection of guide vane profile has equal importance. Usually, NACA defined hydrofoils are used for guide vanes. Numerous options are available, but selection of best one for optimum energy harness is important. Primarily, guide vane torque and turbine efficiency is prioritized. For the Turbines operating in sediment laden water, pressure difference between two sides of guide vane and erosion resistivity are additional factors to be considered. This work was performed in the vicinity of guide vane profile selection for Francis Turbines operating in sediment laden water. Computational analysis on turbine flow passage and experimental study with Rotating Disc Apparatus were performed in order to identify suitable profile. Unsymmetrical profiles were found to be better handling erosion maintaining consistency in turbine performance.
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Study of the simultaneous effects of secondary flow and sediment erosion in Francis Turbines
Renewable Energy, 2016Co-Authors: Sailesh Chitrakar, Hari Prasad Neopane, Ole Gunnar DahlhaugAbstract:Sediment erosion of the hydropower turbine components is one of the key challenges due to the constituent of hard particles in the rivers of Himalayas and Andes. In the case of Francis Turbines, previous studies show that the erosion is mostly observed around stay vanes, guide vanes and runner blades. Depending upon the type of flow phenomena in particular regions and operating conditions, the sediment particles having certain geometric and material properties create distinct erosion patterns on those regions. The flow phenomena in Francis Turbines are highly unsteady, especially around guide vanes and runner. The unsteadiness arises in the form of leakage through clearance gap, horseshoe vortex, rotor-stator-interaction and turbulences supported by high velocity and acceleration. The erosion on the other hand deteriorates the surface morphology, aggravating the flow. Based on a thorough literature survey, this paper explains the simultaneous nature of the two effects, which in combined, contributes to more losses, vibrations, fatigue problems and failure of the turbine. It also discusses some of the research endeavors to minimize the combined effect by controlling either the erosion or the secondary flow in the turbine. This review paper emphasizes the need of understanding the relationship between the two phenomena and techniques of how the combined effect can be predicted as well as minimized.
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prediction of sediment erosion in Francis Turbines
4th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, 2011Co-Authors: Mette Eltvik, Ole Gunnar Dahlhaug, Hari Prasad NeopaneAbstract:Sediment erosion is a major challenge for run-of-river power plants, especially during flood periods. Due to the high content of hard minerals such as quartz and feldspar carried in the river, substantial damage is observed on the turbine components. Material is gradually removed, thus the efficiency of the turbine decreases and the operating time of the turbine reduces. Hydro power plants situated in areas with high sediment concentration suffer under hard conditions, where turbine components could be worn out after only a short period of three months. This short life expectation causes trouble for energy production since the replacement of new turbine parts is a time consuming and costly procedure. It is desirable to design a Francis runner which will withstand sediment erosion better than the traditional designs. The literature states that an expression for erosion is velocity to the power of three. By reducing the relative velocities in the runner by 10%, the erosion will decrease almost 30%. The objective is to improve the design of a Francis turbine which operates in rivers with high sediment concentration, by looking at the design parameters in order to reduce erosion wear. A Francis turbine design tool was developed to accomplish the parameter study. In the search for an optimized Francis runner, several design proposals were compared against a reference design by evaluating the turbine’s performance. The hydraulic flow conditions and the prediction of erosion on the turbine components are simulated by analyzing the models with a Computational Fluid Dynamic (CFD) tool. A Fluid Structure Interaction (FSI) analysis ensures that the structural integrity of the design is within a desired value. Results from this research show that it is feasible to design a runner with an extended lifetime, without affecting the main dimensions and hydraulic efficiency.
Sailesh Chitrakar - One of the best experts on this subject based on the ideXlab platform.
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sediment erosion in low specific speed Francis Turbines a case study on effects and causes
Wear, 2020Co-Authors: Biraj Singh Thapa, Hari Prasad Neopane, Sailesh Chitrakar, Saroj Gautam, Nirmal Acharya, Baoshan ZhuAbstract:Abstract Hydraulic Turbines experience severe operational and maintenance challenges when operated in sediment-laden water. The combined effect of erosive and abrasive wear in turbine components deteriorates their life and efficiency. The quantity and pattern of sediment erosion depends on the nature of the flow and the amount of hard minerals contained in water. Localized erosion patterns are observed mostly in guide vanes, runner blades and facing plates of Francis Turbines due to different natures of fluid flow in those regions. Accelerating flow around the guide vanes and its shaft causes abrasive and erosive wear in its surface, which causes increase in the size of the clearance gap between the facing plates and the guide vanes. Flow leaving the clearance gap forms a vortex filament due to the leakage from high pressure side to the low-pressure side of the guide vane, which eventually strikes the rotating runner blades. This paper presents a case study of a power plant in India with low specific speed Francis Turbines, which is severely affected by sediment erosion problems. A numerical analysis of the flow is conducted inside the turbine to study causes of various erosion patterns in the turbine components. The results from CFD are compared with the actual erosion in Turbines. Erosion in guide vanes and runner blades are taken into consideration in this paper, due to the complex flow phenomena around these regions. It is found that the leakage flow through clearance gaps of guide vanes is the primary cause of erosion at the inlet of the runner blades. Furthermore, the effects of size and shape of quartz particles are studied which shows that erosion is directly proportional to these parameters.
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Opportunities and Challenges of introducing Francis Turbine in Nepalese Micro Hydropower Projects
Journal of Physics: Conference Series, 2019Co-Authors: Anish Ghimire, Sailesh Chitrakar, Bhola Thapa, D. R. Dahal, N. Pokharel, Biraj Singh ThapaAbstract:Despite the initiation of the master plan, envisioned by the government of Nepal, complete electrification of rural Nepal still seems over ambitious for quite a long time. Thus Micro Hydropower Plants (MHP) can still be very effective for rural electrification. Decades of manufacturing of same type Turbines have saturated the turbine manufacturing industries of Nepal, which demands for some new innovations and that could be the introduction of Francis turbine in Nepalese MHP. It's undeniable that there are umpteen opportunities for the turbine manufacturers to manufacture and install the Francis Turbines in Nepalese MHP. The feasibility studies performed by different institutions and the government policy strengthen the claim. In addition to that, data received from, NMHDA and a local turbine manufacturing industry suggest that there are abundant sites suitable for installation of Francis turbine. This paper illustrates the need of introducing the Francis turbine in Nepalese MHP and discusses about the opportunities available for the turbine manufacturers to enter into the market of Francis Turbines for micro hydro and subsequently for larger hydropower projects in the near future. The challenges associated with the introduction of Francis turbine in MHP are highlighted.
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performance comparison of optimized designs of Francis Turbines exposed to sediment erosion in various operating conditions
Journal of Physics: Conference Series, 2018Co-Authors: K P Shrestha, Sailesh Chitrakar, Bhola Thapa, Ole Gunnar DahlhaugAbstract:Erosion on hydro turbine mostly depends on impingement velocity, angle of impact, concentration, shape, size and distribution of erodent particle and substrate material. In the case of Francis Turbines, the sediment particles tend to erode more in the off-designed conditions than at the best efficiency point. Previous studies focused on the optimized runner blade design to reduce erosion at the designed flow. However, the effect of the change in the design on other operating conditions was not studied. This paper demonstrates the performance of optimized Francis turbine exposed to sediment erosion in various operating conditions. Comparative study has been carryout among the five different shapes of runner, different set of guide vane and stay vane angles. The effect of erosion is studied in terms of average erosion density rate on optimized design Francis runner with Lagrangian particle tracking method in CFD analysis. The numerical sensitivity of the results are investigated by comparing two turbulence models. Numerical results are validated from the velocity measurements carried out in the actual turbine. Results show that runner blades are susceptible to more erosion at part load conditions compared to BEP, whereas for the case of guide vanes, more erosion occurs at full load conditions. Out of the five shapes compared, Shape 5 provides an optimum combination of efficiency and erosion on the studied operating conditions.
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Study of the simultaneous effects of secondary flow and sediment erosion in Francis Turbines
Renewable Energy, 2016Co-Authors: Sailesh Chitrakar, Hari Prasad Neopane, Ole Gunnar DahlhaugAbstract:Sediment erosion of the hydropower turbine components is one of the key challenges due to the constituent of hard particles in the rivers of Himalayas and Andes. In the case of Francis Turbines, previous studies show that the erosion is mostly observed around stay vanes, guide vanes and runner blades. Depending upon the type of flow phenomena in particular regions and operating conditions, the sediment particles having certain geometric and material properties create distinct erosion patterns on those regions. The flow phenomena in Francis Turbines are highly unsteady, especially around guide vanes and runner. The unsteadiness arises in the form of leakage through clearance gap, horseshoe vortex, rotor-stator-interaction and turbulences supported by high velocity and acceleration. The erosion on the other hand deteriorates the surface morphology, aggravating the flow. Based on a thorough literature survey, this paper explains the simultaneous nature of the two effects, which in combined, contributes to more losses, vibrations, fatigue problems and failure of the turbine. It also discusses some of the research endeavors to minimize the combined effect by controlling either the erosion or the secondary flow in the turbine. This review paper emphasizes the need of understanding the relationship between the two phenomena and techniques of how the combined effect can be predicted as well as minimized.
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Fully coupled FSI analysis of Francis Turbines exposed to sediment erosion
International Journal of Fluid Machinery and Systems, 2014Co-Authors: Sailesh Chitrakar, Michel Cervantes, Biraj Singh ThapaAbstract:Abstract Sediment erosion is one of the key challenges in hydraulic Turbines from a design and maintenance perspective in Himalayas. The present study focuses on choosing the best design in terms of blade angle distribution of a Francis turbine runner which has least erosion effect without influencing the efficiency and the structural integrity. A fully coupled Fluid-Structure-Interaction (FSI) analysis was performed through a multi-field solver, which showed that the maximum stress induced in the optimized design for better sediment handling, is less than that induced in the reference design. Some numerical validation techniques have been shown for both CFD and FSI analysis. Keywords : CFD, FSI, Francis, Sediment, Erosion 1. Introduction The climatic and geographical scenarios of Nepal like tropical climate, immature geology and intense seasonal rainfall account for the degradation of the hydraulic turbine components from erosion and sedimentation. It has been reported that Southeast Asia alone contributes to two thirds of the world's total sediment transport to oceans which makes the problem of erosion and sedimentation even more challenging [1]. The vulnerability of the sediments is usually judged by the quartz content, as these materials have enough hardness to erode the turbine material. Even with well-designed sediment settling and flushing system, power plants have severe erosion problems. In Francis runner Turbines, the most vulnerable regions to sediment erosion are 1) the inlet region due to high pressure difference between the pressure and the suction side of the runner and local erosion due to separation and 2) the outlet region, where the high relative velocity causes more erosion with the particles moving towards the outer diameter [1]. These localized effects are causing a non-uniform loss of the material and are difficult to repair. Hence, sediment erosion not only reduces efficiency in hydro Turbines, but causes also various problems during the operation and maintenance periods. The damage on hydraulic machineries due to sand erosion was initially studied in [2] by looking at various design aspects such as material selection, mechanics of material and hydraulics. The computational analysis of Francis Turbines including the effect of erosion was done in [1], where the erosion rate was predicted for stay vanes, guide vanes and runner blades of a Francis turbine for different shape, size and concentration of the particle and operating conditions of the turbine. Numerical investigations carried out in the following works have shown that the conventional methods of hydraulic design of Francis Turbines can be improved to minimize sediment erosion [3]. The comparison was done through computational fluid dynamics (CFD) approach by taking pre-implemented erosion model in a commercial CFD code; Finnie and Tabakoff and Grant [3]. The modification of the blade angle distribution from inlet to outlet resulted in a significant change in the degree of erosion, without compromising much for the efficiency of the runner. The need of a structural analysis was felt when the material strength of the Francis runners was needed to be analyzed together with the hydraulic efficiency. However, the implementation of the Fluid-Structure-Interaction (FSI) has not been fully established for the case of Francis Turbines, especially when exposed to sediment erosion. A one-way coupling strategy was presented in [4] to compare the structural integrity between the reference and the optimized designs. Such type of coupling is known to be insufficient to determine runner integrity because the flow field is assumed to be unaffected with the deflection of the runner, hence neglecting the two way effect. The importance of a two-way FSI technique has been highlighted and used for some
