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The growing demand for energy resources highlights the need to optimize traditional energy transformation systems. Pelton-type turbines, which are extensively used in micro-generation systems, can be designed using different methodologies, however, no consensus has been reached on which methodology guarantees greater efficiency. This work aims to compare the fluid-dynamic behavior at the first-time instants of Pelton turbines for micro-generation dimensioned by three different methodologies, namely, OLADE, Nechleba, and Thake, evaluating their capacity to overcome the initial torque. The results show that OLADE methodology leads to the best fluid-dynamic performance, whereas Nechleba fails to overcome the prescribed torque. In the Thake methodology, the impact of water on the back face of buckets and the formation of reverse pressure gradients can counter the turbine rotation.

The growing demand for energy resources highlights the need to optimize traditional energy transformation systems. Pelton-type turbines, which are extensively used in micro-generation systems, can be designed using different methodologies, however, no consensus has been reached on which methodology guarantees greater efficiency. This work aims to compare the fluid-dynamic behavior at the first-time instants of Pelton turbines for micro-generation dimensioned by three different methodologies, namely, OLADE, Nechleba, and Thake, evaluating their capacity to overcome the initial torque. The results show that OLADE methodology leads to the best fluid-dynamic performance, whereas Nechleba fails to overcome the prescribed torque. In the Thake methodology, the impact of water on the back face of buckets and the formation of reverse pressure gradients can counter the turbine rotation. [ABSTRACT FROM AUTHOR]

During operation Pelton turbines suffer from erosion and cavitation wear, which decreases the hydraulic efficiency. Welding repair is a cost-effective method for recovering the original bucket geometry but requires templates to ensure proper results. However, those templates may be unavailable for Pelton units with decades of operation. This is the case of one of the 2.8 MW Pelton units at Nima II, a small hydropower plant in Colombia that began operation in 1942. This paper presents the redesign and optimization of the bucket. First, the bucket is rebuilt following both, technical recommendations, and Design of Experiments (DOE) to verify the effects of the basic dimensions on the hydraulic efficiency. Experimental measurements on the eroded turbine validate the two-phase computational fluid dynamics (CFD) modelling to be applied in the optimization process. Second, the best inner surface is found by using a multi-objective optimization based on Artificial Neural Networks trained by the previous DOE and a genetic algorithm. At the end, the CFD results suggest a total hydraulic efficiency recovery of 8 %. Further experimental tests on the optimized runner showed a difference of 0.7 % from the predicted value. [ABSTRACT FROM AUTHOR]

The article informs on the construction and modernization of Pelton turbines by Josef Erlach. It mentions that the new innovative concept allows the use of six nozzles with a horizontal turbine shaft, and on the one hand, the use of six nozzles increases the power density the impeller can be made smaller for the same amount of water, this reduces the costs for the turbine as well as the required space.

The article informs on the construction of hydroelectric power plant by Wien Energie GmbH on the Gulling in Aigen in Upper Styria in the Austrian Ennstal. It mentions that two Francis and one Pelton turbines are used to produce electricity in an architecturally very successful powerhouse that has been adapted to the area.

The difficulty of delivering electrical power to rural areas motivated the researchers to explore more accessible power sources. Hydropower is considered a desirable option due to its sustainability and lower costs. Pelton turbines have been widely used in hydropower plants because of their low installation and maintenance costs. This study provides a computational fluid dynamics (CFD) model for Pelton turbine performance under various flow conditions. The model is based on the conservation of mass principle, Newton's second law, and the first law of thermodynamics. It is used to predict the torque produced by a turbine at different rotational speeds. Previously published experimental results for the same turbine geometry and flow parameters were used to validate the model's predictions. Validation revealed that the model can reproduce the experimental results. This provides the required robustness for its use as a tool for turbine design and modification. [ABSTRACT FROM AUTHOR]

The difficulty of delivering electrical power to rural areas motivated the researchers to explore more accessible power sources. Hydropower is considered a desirable option due to its sustainability and lower costs. Pelton turbines have been widely used in hydropower plants because of their low installation and maintenance costs. This study provides a computational fluid dynamics (CFD) model for Pelton turbine performance under various flow conditions. The model is based on the conservation of mass principle, Newton’s second law, and the first law of thermodynamics. It is used to predict the torque produced by a turbine at different rotational speeds. Previously published experimental results for the same turbine geometry and flow parameters were used to validate the model’s predictions. Validation revealed that the model can reproduce the experimental results. This provides the required robustness for its use as a tool for turbine design and modification.

Worldwide electricity generation is featured by the growth of intermittent renewable energies. In this context, hydropower plays a fundamental role because it provides flexibility to the power grid and ensures its stability. The new grid requirements have led hydropower units to working under a wider range of loads and with more start/stop sequences. Pelton turbines are the most suitable for high heads and have a large regulation capacity. In operation, the runner is impinged by high-speed water jets, and, thus, subjected to strong pulsating forces. As a consequence, the structure presents large deformations and high stresses, especially on the buckets. This situation can be much aggravated if the frequency and shape of the excitation is resonant with those of the structure. Therefore, the modal response of the turbine must be thoroughly studied and the most dangerous frequencies avoided. In this paper, a detailed analysis of the modal behavior of Pelton turbines is presented. Four prototypes have been studied for such purpose. The first one has been modeled numerically and analyzed experimentally. Following a systematic investigation, the effect on the modal shapes and the frequencies of the different parts comprising the turbine has been evaluated. The single bucket and the whole runner have been studied. Finally, another turbine installed in the same power plant has been analyzed to determine the effect of the mechanical design on the frequencies. In addition, two prototypes belonging to other power plants have been studied to see the effects of the hydrodynamic design on the modal behavior. [ABSTRACT FROM AUTHOR]

Erosive wear of hydraulic machines is a common issue, which results in efficiency degradation, the enhancement of cavitation, and the need for expensive maintenance. Although numerical simulations of the erosion process could be very useful, both for understanding and predicting the process, its multiscale nature renders it very difficult to simulate. A previously validated multiscale model of erosion is presented. It consists of two coupled sub-models: On the microscale, the sediment impacts are simulated by means of comprehensive physical models; on the macroscale, the turbulent sediment transport and erosion accumulation are calculated. A multiscale simulation of the erosion of a prototype-scale Pelton bucket impacted by a sediment-laden water jet is presented. The simulation results, namely the erodent flux and the distributions of average impact angle and velocity on the bucket surface, bring insight into the erosion process. Furthermore, the results explain the obtained erosion distribution, which is in very good agreement with the experimental erosion measurements available in the literature for the same test case. [ABSTRACT FROM AUTHOR]

Abstract In Pelton turbine, two-phase homogeneous model is the fundamental base to investigate the flow inside the turbine. Meanwhile, flow pattern in section of the distributor and bifurcation pipe produces the secondary flow which influences the shape of the jet downstream 6 nozzles. This paper numerically investigated the dynamic process using CFX commercial code under different operating conditions. Volume of Fluid(VOF) model was used to capture the air/water interface. This work focuses on the jet bifurcation problem which can seriously influence the Pelton turbine performance and furthermore it is not yet investigated in hydraulic research. Results indicate that the shape of the distributor induces the secondary flow and Dean vortex structure which are symmetric with the central horizontal plane of the pipe and nozzles. On the other hand, this sequence of vortex develops and transits along the flow and finally affects the shape of jet. Effect of secondary flow in the distributor stretches the jet flow in vertical direction and compress it in horizontal direction. Meanwhile, bifurcating phenomenon is observed outside the nozzle which is also obtained in classical experimentations. This study reveals that the secondary flow is important to be taken into consideration to optimize the performance of Pelton turbine. Highlights • Six nozzles of a Pelton turbine are numerically simulated with unsteady two-phase model. • Secondary flow is detected in the flowing parts and Dean vortex are observed clearly. • Jet bifurcation is visualized and quantitatively confirmed by the former experimentation in the literature. [ABSTRACT FROM AUTHOR]

Abstract Numerical simulations were performed to investigate how the design and the operation conditions of a Pelton turbine injector affect its vulnerability to hydro-abrasive erosion, alongside with its flow control capacity. Use was made of a Volume Of Fluid (VOF) model for simulating the free nozzle jet, a Lagrangian particle tracking model for reproducing the trajectories of the solid particles, and two erosion models for estimating the mass removal. The comparison against earlier studies and the experimental evidence, integrated with a careful sensitivity analysis, gave strength to the reliability of the numerical model. Nozzle seat and needle were the injector components most vulnerable to erosion. As the valve was closing, the erosion of the needle strongly increased, whilst that of the nozzle seat remained broadly constant. The influence of the injector design was also explored, suggesting that a reduction of the needle vertex angle is likely to enhance the risk of erosive wear. Finally, it was found that the possibility to condense the effects of the needle stroke and the needle vertex angle in a single parameter (i.e. the effective opening area) is no more allowed when hydro-abrasive erosion is considered, thereby assessing the need for case-specific wear prediction analyses. Highlights • Particle-laden jets generated by Pelton injector nozzles were numerically simulated. • The regulation characteristics of the injectors were estimated. • The injector components most vulnerable to hydro-abrasive erosion were identified. • The extent of erosion was assessed for different operation and design parameters. • A physical interpretation of the obtained results was provided. [ABSTRACT FROM AUTHOR]

Abstract This article presents the experimental results of a novel energy storage system that combines CAES (Compressed Air Energy Storage) with PHES (Pumped Hydro Energy Storage) technologies. As a reference, we called this system PH-CAES. In this alternative solution two storage tanks, the first with compressed air and the second with water, are separated by a valve. When electric power is required, the valve is opened and water flows to a Pelton turbine, which is coupled to an electric generator. Water from the Pelton turbine is discharged into a third tank. To store energy and recover the initial state, water is pumped back. We built a prototype to assess the PH-CAES performance, with focus on the power generation system. Experimental conversion efficiency was 45%, whilst the rational efficiency remained close to 30%. We also presented a discussion based on the second law of thermodynamics to show that there is a compromise between tanks exergies that maximizes the system performance. We also provide an operating map of this PH-CAES system to assist authors on new studies about this novel technology. Highlights • We present a novel energy storage system based on CAES and Pumped-Hydro. • We test the performance of the PH-CAES prototype. • The generation efficiency reached 45%, despite the system reduced scale. • Experiments have shown that the PH-CAES can be competitive. [ABSTRACT FROM AUTHOR]

The role of particle size and solids concentration on the slurry erosion of a stainless steel was studied with base in laboratory tests and data from field inspections of two Pelton turbines. The slurry for the laboratory tests was composed of water and SiO 2 sand particles with mean diameter ranging from 50 to 655 μm and solids concentrations up to 1200 mg l −1 . The wear rate increased linearly with solids concentration within the range studied, while the sensitivity of the surface to changes in erosive particle size decreased with the particle size. A critical particle size range for the moderate-to-severe wear regime transition was found, which is practically unaffected by the variety of solids concentrations considered in this study. [ABSTRACT FROM AUTHOR]

This paper presents entire flow path simulations in a prototype four-nozzle Pelton turbine under three water heads, from pipe flow to nozzle jet water sheet flow on rotating bucket and drop from bucket brim on the air. Different type flows in the Pelton turbine are analyzed by adopting the three-dimensional transient air-water two-phase flow simulation method. Hydraulic performance of stationary parts and rotating runner are evaluated along the entire flow path. Flow analyses indicate that the pressure pulsation is very low and the water flow could be regarded as steady flow in the stationary parts. The hydraulic loss in these parts drops as the water head increases due to a reduction of the frictional loss. Afterwards, the interactions between the jets and buckets in the rotating runner are discussed. The pressure pulse on the bucket surface pulsates with the spreading of the water sheet flow and takes up 10%–25% water energy. The hydraulic performance of the bucket is highest at optimal water head and decreases as the water head varies. Unsteady flow analyses show that there is a potential for interference between the two adjacent jets if the water head or the angle between the two jets decreases. [ABSTRACT FROM AUTHOR]

This study is dedicated to find a cause of a critical flow rate in a Pelton turbine operating with a constant runner speed, below which the efficiency of the turbine decreases significantly. A critical flow rate was initially found in the performance test of the Pelton turbine for extracting energy from a PRO (pressure retarded osmosis) pilot plant. For higher flow rates than a critical value, the efficiency of the Pelton turbine was nearly constant independent of flow rates. For lower flow rates than a critical value, however, the efficiency drops with decreasing flow rates. 3D flow simulations were conducted at three different flow rates to investigate effects of flow rates on the performance of the Pelton turbine. It was found in the numerical results that a large friction loss is generated in an injector if the spear is closed too tightly for a low flow rate below a critical value. Head loss coefficients of the injector for three different spear positions were calculated and it was found that the loss is doubled below a critical flow rate. This implies that it is important to include the geometry of an injector and spear in the numerical simulations for Pelton turbines. [ABSTRACT FROM AUTHOR]

The ability of hydropower to adapt the electricity generation to the demand is necessary to integrate wind and solar energy into the electrical grid. Nowadays, hydropower turbines are required to work under harsher operating conditions and an advanced condition monitoring to detect damage is crucial. In this paper the methodology to improve the condition monitoring of Pelton turbines is presented. First, the field data obtained from the vibration monitoring of 28 different Pelton turbines over 25 years has been studied. The main types of damage found were due to fatigue, cavitation and silt erosion. By analyzing the vibration signatures before and after maintenance tasks, the symptoms of damage detected from the measuring locations were determined for each case. Second, a theoretical model using numerical methods (FEM) was created in order to simulate the dynamic behavior of the turbine. The model was validated with the results obtained from on-site tests that were carried out in an existing turbine. The deformations and the stresses of the runner under different operating conditions could then be computed. The calibrated model was used to analyze in detail the effect of misalignment between nozzle and runner. In historic cases, this abnormal operating condition lead to severe damage in the turbine, due to the effect of fatigue in some locations of the buckets. The model reproduced well the symptoms detected in the field measurements. The stresses could be calculated, which eventually can be used to estimate the remaining useful life of the turbine. [ABSTRACT FROM AUTHOR]

Power production by conversion of salt gradient energy (osmotic power production) has the potential for global commercialization. Research on the net-power output and osmotic power plant configurations could result in viable methods for improvement of plant efficiency. In this paper, a novel equivalent electric-circuit model of the pressure-retarded osmosis (PRO) process is described and is used to develop a power-hardware-in-the-loop (PHIL) emulator to represent the osmotic power plant. The model considers many dynamics involved with PRO including reverse salt leakage, concentration polarization, and the salt storage capacity of water. The proposed model facilitates real-time dynamic simulation and analysis of the PRO power plant, and its interaction with the rest of the PRO power system, namely the impulse turbine and the synchronous generator supplying power to off-grid or isolated loads. The response of the multidomain system including hydraulic, mechanical, and electrical components of the system is observed, given changes in the input parameters such as source flow rate. The proposed PHIL emulator provides insight into the operational dynamics and behavior of the PRO system. The proposed real-time emulator serves as a powerful tool that can advance research and development of PRO power generation systems. Simulation and experimental results are presented in this paper to validate the PRO plant model and the operation of the proposed real-time PHIL PRO emulator. [ABSTRACT FROM PUBLISHER]

In this paper, an uncommon failure of a Pelton turbine has been analyzed. After the monitoring system detected a sudden increase in the vibration levels, the turbine was inspected. The inspection showed that a fragment of one bucket broke off during operation. Moreover there were several buckets with cracks, always located in the same side of the buckets. An analysis of the detached fragment revealed a fatigue problem. After the damage was found, the vibration signatures measured by the monitoring system before damage, with damage and after repair, were analyzed. Before damage occurred, an excessive axial vibration and the excitation of several natural frequencies of the turbine were detected in the measured vibration. In order to identify the origin of the problem the first task was to analyze the dynamic response of the turbine. A numerical model of the runner using the finite element method (FEM) was done. Experimental research using modal analysis techniques (EMA) was also carried out in the turbine runner. The results of the numerical model were compared with the experimental results obtained. With the validated numerical model natural frequencies and mode-shapes were determined and studied. The next step was to determine experimentally the influence of the mounting conditions on the runner dynamics and the transmissibility of the runner vibrations to the machine bearings where the monitoring sensors are located. From the results of this study it was concluded that the natural frequencies excited during machine operation had axial mode shapes indicating that axial forces were applied to the runner. In a Pelton turbine, this can only be produced by a misaligned jet. To determine the influence of a misaligned jet on the bucket stresses, the dynamic behavior of the runner was performed. The dynamic force of the water jet was applied to the runner bucket. The results showed that with a misaligned jet the dynamic stress distribution increases in one side of the bucket with a maximum stress located where the cracks appeared. [ABSTRACT FROM AUTHOR]

This paper addresses the design, modeling, and performance analysis of a Pelton turbine using CFD for one of the selected micro hydro potential sites in Ethiopia to meet the requirements of the energy demands. The site has a net head of 47.5 m and flow rate of 0.14 m3/s. The design process starts with the design of initial dimensions for the runner based on different literatures and directed towards the modeling of bucket using CATIA V5. The performance of the runner has been analyzed in ANSYS CFX (CFD) under given loading conditions of the turbine. Consequently, the present study has also the ambition to reduce the size of the runner to have a cost effective runner design. The case study described in this paper provides an example of how the size of turbine can affect the efficiency of the turbine. These were discussed in detail which helps in understanding of the underlying fluid dynamic design problem as an aid for improving the efficiency and lowering the manufacturing cost for future study. The result showed that the model is highly dependent on the size and this was verified and discussed properly using flow visualization of the computed flow field and published result. [ABSTRACT FROM AUTHOR]

In this study, we develop a theoretical formula for determining the optimum number of buckets required for achieving the maximum possible efficiency of a Pelton turbine. In addition, by deriving an improved formula for determining the speed ratio limit at which a missing jet begins, we obtain a valid condition for the selection of the number of buckets. To validate these formulas, we conduct a performance test on a pico-scale Pelton turbine by using runners with different numbers of buckets. The results of the performance test validate both the formula for bucket selection, by confirming that the calculated number of buckets maximizes the efficiency of the Pelton turbine, and the formula for the speed ratio limit. We conduct an additional performance test on a micro-scale Pelton turbine, the results of which also verify the formula for selecting the number of buckets. This study should help researchers determine the appropriate number of buckets when designing a highly efficient Pelton turbine. [ABSTRACT FROM PUBLISHER]

Hydraulic turbine generator units with long-running operation may cause the values of hydraulic, mechanic or electric parameters changing gradually, which brings a new challenge, namely that whether the operating stability of these units will be changed in the next thirty or forty years. This paper is an attempt to seek a relatively unified model for sensitivity analysis from three aspects: hydraulic parameters (turbine flow and turbine head), mechanic parameters (axis coordinates and axial misalignment) and electric parameters (generator speed and excitation current). First, a novel approach of the Pelton turbine torque is proposed, which can make connections between the hydraulic turbine governing system and the shafting system of the hydro-turbine generator unit. Moreover, the correctness of this approach is verified by comparing with other three models of hydropower stations. Second, this latter is analyzed to obtain the sensitivity of electric parameter (excitation current), the mechanic parameters (axial misalignment, upper guide bearing rigidity, lower guide bearing rigidity, and turbine guide bearing rigidity) on hydraulic parameters on the operating stability of the unit. In addition to this, some critical values and ranges are proposed. Finally, these results can provide some bases for the design and stable operation of Peltonhydropower stations. [ABSTRACT FROM AUTHOR]

Following new and innovative concepts of energy recovery which use micro-hydro impulse turbines in drinking water systems, more sophisticated turbine designs become essential to improve energy recovery efficiency. In the case of implementing a hydraulic impulse turbine with tailwater depression in such systems, one major challenge to optimising overall efficiency is the reduction of the turbine's air demand. Firstly, a lower air demand would reduce the required dimensions of the ventilation system and therefore increase energy efficiency. Secondly, a minimised air demand would considerably reduce negative effects downstream of the turbine casing, such as a reduced transport capacity and corrosion. To achieve a minimised air demand, detailed experimental investigations are conducted, during which different casing inserts are tested in a micro-hydro Pelton machine. A specially constructed turbine test-bed, featuring two separately installed measuring units, allows for the partitioning and measurement of dissolved and undissolved air. In the case of the used Pelton machine, the results clearly identify different air detrainment processes. The undissolved air demand strongly depends on the particular casing insert and can be reduced by 90 % through optimal flow condition using flow straighteners as insert. In contrast, the amount of dissolved air demand cannot be controlled by additional casing inserts. This can be explained due its different entrainment processes. The analysis of the dependency of the measurement results on scale shows that a direct transfer to a prototype application will underestimate the air demand. Nevertheless, the presented research findings show an effective way, also relevant to turbine manufacturers, to reduce air demand and improve overall efficiency of impulse turbines in counter pressure operation. [ABSTRACT FROM AUTHOR]

The present paper aims to find out the influence of operating head on the rotating bucket free surface sheet flow and hydrodynamics performance for a Pelton turbine. Three-dimensional unsteady air-water two-phase flow simulations in the rotating buckets were performed by adopting the shear stress transport curvature correction turbulence model and homogenous model. The sensitivities of the unsteady simulation results to moving mesh resolution and computational fluid dynamics solver time-step have been evaluated to discuss the effect of Courant–Friedrichs–Lewy conditions on the two-phase flow simulation. The accuracy of the numerical predicted flow pattern and the hydrodynamic performance results are reasonable when compared with the experimental data. The simulation results indicate that the remaining kinetic energy carried by the outflow under the nondesigned water head is the main reason for the efficiency loss in the Pelton turbine. Under low water head conditions, jet distortion caused by the Coanda effect and flow interference will lead to more severe efficiency deterioration. [ABSTRACT FROM AUTHOR]

Over 75% of domestic electric power consumption in Colombia is supplied by hydropower. Abrasive wear is degrading turbine components such as Pelton needle valve nozzles. This problem has been studied on the components themselves (in situ). However, it was necessary reproduce the same hydro-abrasive phenomena in a controlled laboratory environment. This study describes the design and construction of a test rig capable of replicating the same wear mechanism present in Pelton needle valve nozzles at Chivor hydroelectric plant. The development of the test rig allowed to conduct empirical testing for the comparison of the plasma nitriding process versus the WC-Co-Cr coat deposited by HVOF to extend the lifetime of the nozzle. Both processes showed significant improvement in hardness and wear resistance compared to the original material specification of the needle valves. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to propose a strategy to optimize the performance of a Pelton runner based on a parametric model of the bucket geometry, massive particle based numerical simulations and advanced optimization strategies to reduce the dimension of the design problem. The parametric model of the Pelton bucket is based on four bicubic Bézier patches and the number of free parameters is reduced to 21. The numerical simulations are performed using the finite volume particle method, which benefits from a conservative, consistent, arbitrary Lagrangian Eulerian formulation. The resulting design problem is of High-dimension with Expensive Black-box (HEB) performance function. In order to tackle the HEB problem, a preliminary exploration is performed using 2'000 sampled runners geometry provided by a Halton sequence. A cubic multivariate adaptive regression spline surrogate model is built according to the simulated performance of these runners. Moreover, an original clustering approach is proposed to decompose the design problem into four sub-problems of smaller dimensions that can be addressed with more conventional optimization techniques. [ABSTRACT FROM AUTHOR]

This paper presents some information regarding the hydraulic turbines respectively the experimental results on cavitation erosion behavior of a 13Cr-4Ni stainless steel used to manufacture the components exposed to water of the Francis, Kaplan and Pelton hydraulic turbines. So, the presented experimental results of this paper highlight the good cavitation erosion resistance of the analyzed 13Cr-4Ni stainless steel. [ABSTRACT FROM AUTHOR]

This work presents an assessment of the potential use of hydrokinetic turbines in the discharge channels of large hydroelectric power plants in Colombia. The assessment is performed at a pre-feasibility stage in order to evaluate the technical and financial potential of using hydrokinetic devices as a way to exploit kinetic energy in such channels. As a case study, two large hydropower plants were selected, one operated by a Francis turbine and the other operated by a Pelton turbine. The analysis assessed the hydraulic characteristics of the channels and the corresponding discharge flows. A prefeasibility financial analysis in an environment of uncertainty was also carried out using Monte Carlo simulation. The results show that the technology is not currently feasible for the Colombian market conditions, but the situation should be monitored in order to identify the right time for its optimal use in the future. The proposed methodology can be applied to research the feasibility of hydrokinetic energy for other kinds of applications. [ABSTRACT FROM AUTHOR]

Pelton turbines are used for energy recovery in pressure-retarded osmosis (PRO) systems. The quality of jet sprays is a significant factor affecting the performance of these turbines. This study examined jet quality characteristics according to the nozzle geometry of Pelton turbines. Jet quality tests were conducted to analyze the degree of similarity between the actual jet flow and the ideal jet flow. Power loss, discharge coefficients, and performance characteristics of Pelton turbines were examined with respect to the nozzle shape through performance tests of the nozzles and turbines. Furthermore, jet flows were numerically analyzed. The test results and analyses confirm that for a given input power, the recirculation region increases and the jet quality decreases with increasing nozzle throat angle. On the basis of the results, the optimum range of nozzle throat angle for Pelton turbines in PRO systems is suggested. [ABSTRACT FROM PUBLISHER]

Hydraulic turbines are designed for the given values of head, discharge and speed but mostly operate at off designed head and discharge values. Due to variation in head, operating parameters like speed and discharge coefficients are changed affecting the flow and efficiency characteristics of turbine. This makes customary to assess the turbine performance at different operating parameters. Pelton turbine is the most commonly used impulse turbine for high head power plants. The computational fluid dynamics is a cost effective tool to assess the turbine performance in terms of local and global design and operating parameter of turbine. In the present work, multiphase flow analysis in Pelton turbine using water and air as working fluid is carried out to estimate the efficiency, blade loading, velocity and water distribution over the bucket at different operating regimes of the turbine. The effect of mesh size, turbulence model and time step is also studied for transient multiphase flow simulation. [ABSTRACT FROM AUTHOR]

During the runaway process of a Pelton turbine, the runner bears huge amounts of water pressure pulsations and centrifugal forces, which is different from the steady-state condition. In this work, a fine 3D CFD simulation of the runaway process of a Pelton turbine is performed. Both the macro-parameter changing patterns of rotational speed, torque and efficiency, and the micro-flow features of pressure pulsations and flow patterns are intensively studied and analyzed. It is found that the maximum runaway speed is 1.78 times of the rated speed, acceleration is the main feature in the early stage of runaway, and the jet fragment breaks away and strikes once again on the lip region and backside of the buckets in the middle and late stages. The multiple strikes make the frequency of pressure pulsations increase, and the cavitation occurs on the backside mold line. This successful 3D simulation shows that it is possible to simulate other transient processes of Pelton turbines and conduct fluid–structure interaction analysis of the runner. [ABSTRACT FROM AUTHOR]

Impulse turbines with tailwater depression are an efficient choice for energy recovery in drinking water systems. To reduce negative effects of detrained air downstream of the turbine casing, such as corrosion and reduced transport capacity, main processes and possible reduction of air detrainment have been investigated in detailed experimental studies on a micro-hydro Pelton machine with tailwater depression. The experimental setup has been designed to distinguish between dissolved and undissolved air detrainment. In case of dissolved air detrainment there is a clear relation between the amount of dissolved air and the counter pressure as well as the flow rate parameter. Experimental results for the amount of undissolved air detrainment show dependencies on geometrical dimensions, velocity coefficient, casing water level and the flow rate of the turbine. To avoid undissolved air detrainment, design equations are deducted for dimensioning the casing height and the casing diameter. Therefore the presented investigations show how air detrainment can be controlled or rather minimized by optimised casing-design of impulse turbines. [ABSTRACT FROM AUTHOR]

The recent development of CFD has allowed the flow modeling in impulse hydro turbines that includes complex phenomena like free surface flow, multifluid interaction, and unsteady, time dependent flow. Some commercial and open-source CFD codes, which implement Eulerian methods, have been validated against experimental results showing satisfactory accuracy. Nevertheless, further improvement of accuracy is still a challenge, while the computational cost is very high and unaffordable for multiparametric design optimization of the turbine’s runner. In the present work a CFD Eulerian approach is applied at first, in order to simulate the flow in the runner of a Pelton turbine model installed at the laboratory. Then, a particulate method, the Fast Lagrangian Simulation (FLS), is used for the same case, which is much faster and hence potentially suitable for numerical design optimization, providing that it can achieve adequate accuracy. The results of both methods for various turbine operation conditions, as also for modified runner and bucket designs, are presented and discussed in the paper. In all examined cases the FLS method shows very good accuracy in predicting the hydraulic efficiency of the runner, although the computed flow evolution and the torque curve exhibit some systematic differences from the Eulerian results. [ABSTRACT FROM AUTHOR]

This paper uses two modern commercial CFD software packages to compare the performance of a standard and improved impulse turbine injector developed in a previous study. The two injector designs are compared by simulating the two-dimensional (2D) axissymmetric cases as well as full three-dimensional (3D) cases including the bend in the branch pipe and the guide vanes. The resulting jet profiles generated by these simulations are used to initialize the inlet conditions for a full Pelton and Turgo runner simulation at different operating conditions in order to assess the impact of the injector design on the performance and efficiency of a real impulse turbine. The results showed that the optimized injector design, with steeper nozzle and spear angles, not only attains higher efficiencies in the 2D and 3D injector simulations but also produces a jet which performs better than the standard design in both the Pelton and the Turgo runner simulations. The results show that the greatest improvement in the hydraulic efficiency occurs within the injector with the improved design, showing an increase in efficiency of 0.76% for the Turgo 3D injector and 0.44% for the Pelton 3D injector. The results also show that in the case of the 3D injector, the improved injector geometry produces a jet profile which induces better overall runner performance, giving a 0.5% increase in total hydraulic efficiency for the Pelton case and 0.7% for the Turgo case. [ABSTRACT FROM AUTHOR]

The paper presents the HydroHillChart software, which is designed to calculate the hill chart for hydraulic turbines (Pelton, Francis and Kaplan) and the operation diagram, based on the energetic primary data that is obtained through turbine model measurements performed on the test rig. The HydroHillChart software is made up of the following four modules: the Pelton, Francis and Kaplan modules - which are used to calculate the turbine model hill chart and the DEX module - which is used to calculate the operation diagram for the industrial turbine prototype. The resu lts of the software consist of graphical curves and numerical results which can be view ed in HydroHillChart and exported as Excel files with a template structure and also as PDF and Word files. The lack of paper space will limit the presentation to the Pelton and Francis modules only. [ABSTRACT FROM AUTHOR]

In this study, a new approach that is closer to the real turbine without abandoning the advantages of nonlinear modeling simplicity compromising the simplicity of the nonlinear model is proposed. The purpose of the study is to contribute to making theoretical studies of microhydroelectric power plants (MHPPs) more realistic. Studies on their control, especially frequency control, have increased with the expansion of grid-connected power plants. However, some problems have occurred when converting simulation studies of the frequency control to practical studies. The reasons for these problems are that the systems cannot be modeled completely. In this study, first, the nonlinear model equations of a Pelton turbine are primarily constituted. The efficiency curve of the turbine is then obtained experimentally and added to the nonlinear model. The simulation results are compared with the data obtained from the prototype MHPP with a Pelton turbine developed in the laboratory. Finally, it is seen that the proposed method is successful. Thus, with the help of the proposed method, theoretical studies that researchers do can be easily converted into practical applications. [ABSTRACT FROM AUTHOR]

Air-entrainment and detrainment processes in tailrace channels downstream of Pelton turbines were investigated in a physical laboratory model of the new hydropower plant Veytaux 2, Switzerland. These processes are mainly influenced by the emergent jet velocity of the Pelton turbine and the resulting air entrainment to the water cushion due to high-speed jet impact. The air demand in the turbine housing, and the air concentration and velocity distributions in the tailrace channel are analyzed. The project-specific results are generalized by additional investigations involving a simplified model geometry. A comparison with previous model and prototype data is presented. The results indicate that the deaeration length relative to the tailwater flow depth depends mainly on the jet Froude number made up by the emergent jet velocity relative to the tailwater propagation velocity, plus the water discharge, the tailwater cross-sectional area, and the presence or absence of a flow straightener at the tailrace-channel entrance. [ABSTRACT FROM AUTHOR]

Turbine material is heavily eroded when operated in sediment-laden rivers. Erosion reduces the efficiency and increases operational risk. Therefore, welding repair is chosen in Nepal due to low cost to build up the eroded surface. Welding repair of hydraulic turbine does not impair the material property but, it can be catastrophic when carried out improperly. Such problem has been observed in Khimti Hydro-Power (KHP) in Nepal. The Pelton runner at KHP had operated without any major defects for 22,000 h before repair. But, root cracks extending up to 110 mm deep was revealed during inspection of welding repaired runner after 11,000 h of operation. Therefore, quality control during repair of runner is essential to achieve the desired properties and avoid catastrophic failures. Various factors like quality of weld deposit, preheating and post weld heat treatment conditions, and design changes during repair cause failure. The paper presents the possible causes of failure of Runner 1, 3 and 4 with reference to the operation and maintenance history, and quality control measures used in repair of Runner 7 of KHP. [ABSTRACT FROM AUTHOR]

The paper presents the HydroHillChart - Pelton module application, used to calculate the hill chart of the Pelton hydraulic turbine models, by processing the data measured on the stand. In addition, the tools offered by the application such as: interface, menu, input data, numerical and graphical results, etc. are described. [ABSTRACT FROM AUTHOR]

The paper presents the Hydro Hill Chart - Francis module application, used to calculate the hill chart of the Pelton, Francis and Kaplan hydraulic turbine models, by processing the data measured on the stand. After describing the interface and menu, the input data is graphically presented and the universal characteristic for measuring scenarios aO=const. and n11=const is calculated. Finally, the two calculated hill charts are compared through a graphical superimposition of the isolines. [ABSTRACT FROM AUTHOR]

The Pelton turbines industrial design is based on the hill chart characteristics obtained by measuring the models. Primary data measurements used to obtain the hill chart can be processed graphically, by hand or by using graphic programs respectively CAD programs; the HydroHillChart - Pelton module software is a specialized tool in achieving the hill chart, using interpolation cubic spline functions. Thereby, based on measurements of several models of Pelton turbines, a computerized library, used to design industrial Pelton turbines can be created. The paper presents the universal characteristics calculated by using the HydroHillChart - Pelton module software for a series of Pelton runners. [ABSTRACT FROM AUTHOR]

This paper presents a technology that can accelerate the development of hydro turbines by fully automating the initial testing process of prototype turbine models and automatically converting the acquired data into efficiency hill charts that allow straight forward comparison of prototypes' performance. The testing procedure of both reaction and impulse turbines is illustrated using models of Francis and Pelton turbines respectively. For the development of an appropriate hill chart containing no less than 780 points the average duration of the fully automated test is 4 h while the acquired data files can be processed into descriptive standard efficiency hill charts within less than a minute. These hill charts can then be used in research and development to quickly evaluate and compare the performance of initial turbine prototype designs before proceeding to much lengthier and more expensive development stage of the chosen design. [ABSTRACT FROM AUTHOR]

Abstract: The integration of wind power in power systems results in a reduction in greenhouse gas emissions. Thus, it has a positive environmental impact. However, the operation of these power systems becomes increasingly complex, owing mainly to random behaviour of the wind. In the case of island power systems, this problem is even more difficult. The traditional solution is to use diesel generators as an alternative power supply. For a wind-only power supply, an energy storage system is required. If the topography of the island makes possible the use of pumped storage hydropower plants, this is, nowadays, the most suitable energy storage system. This paper presents a novel method of Pelton turbine operation with no water flow, as a way to provide fast power injection in the case of an abrupt wind power decrease, or a wind-generator trip. This operation mode allows maximizing wind power penetration in a reliable and efficient way. This method has been validated by computer simulations, and will be tested during the commissioning of a combined wind-pumped storage power plant in an autonomous power system, on a small island. [Copyright &y& Elsevier]

Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, which lead to a decrease of the performance in time and/or in extreme cases to the rotor mechanical failure. These circumstances have negative repercussions on the annual produced power due to the decay of the efficiency, the delivered power, and to the off line periods as result of ordinary and extraordinary hydraulic profiles maintenances. Consistently, the study of this wearing process is an important step to improve the impeller design, and to avoid or minimize the rise of extraordinary maintenance. While mechanical damages are well documented and studied, little information can be found on cavitation in Pelton turbines. In this paper, a CFD model was applied to study the cavitation mechanics on a Pelton turbine. A Pelton runner affected by pitting cavitation was taken as a test case. The bucket geometry was modeled and analyzed using unsteady Reynolds averaged Navier-Stokes (RANS) multiphase analyses. Numerical results allowed us to highlight the different vapor productions during the cut-in water jet processes by the bucket. Furthermore, a simple procedure to identify the locations of higher damage risk was presented and verified in the test case runner. [ABSTRACT FROM AUTHOR]

This paper addresses the dynamic modeling and the energy storage analysis of a wave energy hyperbaric converter, which consists of a set of oscillating bodies (named as pumping modules) linked to hydropneumatic accumulators and an electric generating unit. A mathematical model of the accumulator is presented and a model for the generating unit is proposed, including a nonlinear model of a Pelton turbine. Then, the hydrodynamic, mechanical, and electrical characteristics of the subsystems that compose the converter are discussed. With the proposed model, it is possible to evaluate the dynamic behavior of the entire system. That is, for a given incident ocean wave, it is possible to evaluate all the system state variables and the generated electric power, including the quality (fluctuation, for example) of the generated voltage and frequency for islanded or power-grid-connected operation. Simulation results considering the proposed wave-to-wire model under the action of regular and irregular incident waves are presented to illustrate the performance of the system. [ABSTRACT FROM AUTHOR]

Unlike the reaction turbines, the hydraulic performance of Pelton turbines varies due to the unsteady flow of the rotating buckets in time and space. This study experimentally and numerically investigates the dynamic performance of a Pelton turbine at five different operating conditions. The unsteady numerical simulations were performed with the SST turbulence model. The three-dimensional unsteady free surface sheet flow behavior in the rotating buckets was modeled by the two-phase homogeneous model. The model was used to analyze the dynamic flow patterns and the torque variations as the buckets rotated. The predicted hydraulic performance at different unit discharge rates are compared with the field test while the free surface flow patterns are compared with previous experimental and numerical results. The predicted relative efficiency agrees well with the field test results. The calculations were used to clarify the hydraulic mechanisms with unsteady free surface sheet flow in the rotating bucket. [ABSTRACT FROM PUBLISHER]

The increasing share of hydropower in world electricity production requires the development of standardized and optimized design procedures leading to increasingly higher efficiency values.To date, despite a certain amount of support from computational fluid dynamics, Pelton turbines are still characterized by semiempirical design criteria that do not make it possible to optimize the jet–bucket interaction in order to maximize turbine performance. Based on an analysis of particle flow tracks, this paper presents a hybrid Eulerian–Lagrangian method to investigate the influence of bucket geometry on the Pelton efficiency at two different operating conditions. Jet–bucket interaction was numerically analyzed by means of a traditional mesh-based numerical approach, using a transient multi-phase homogeneous model. Subsequently, the numerical results were integrated using a predictor–corrector algorithm, combining a fourth order Adams-Bashforth method as predictor and a fourth order Adams-Moulton method as corrector, in order to determine the fluid particle trajectories on the rotating buckets. The particle flow tracks were analyzed in detail to evaluate the single-particle performance in terms of discharged kinetic energy, momentum variation, and total energy variation during the jet–bucket interaction. Moreover, on the basis of the particle discharging position, the contribution of the different bucket areas to the total torque of the turbine was investigated to determine the time-depending influence of the bucket geometry on the turbine energy exchange and to suggest possible design solutions for improving bucket performance. [ABSTRACT FROM PUBLISHER]

This paper deals with an alternative approach to calculate the performance of a Pelton turbine. The discussion begins with an overview on the statement of Newton's second law for variable mass systems. Then the integral form of the Navier-Stokes equation is presented as a special case, which is useful to evaluate the force exerted by the water jet on the turbine buckets. Although the traditional approach based on the angular momentum theorem is more straightforward, the proposed method allows evaluation of the different contributions to the motive force by a suitable choice of control volumes. This in turn makes for a better understanding of factors that penalize overall performance when the ideal assumptions, under which the theory is usually developed, are no longer verified. [ABSTRACT FROM AUTHOR]