Pelton Turbine Research Articles

Numerical study on the influence of the bucket offset angle on the flow field of Pelton turbines with six-nozzles

Abstract Pelton turbines are emerging as a primary means for exploiting ultra-high water head resources. The hydraulic performance of a Pelton turbine is determined by the design of its runner/bucket. Among the critical parameters that affect the hydraulic performance of multi-nozzle Pelton turbines is the bucket offset angle (α). To investigate the influence of bucket offset angle on the flow field of Pelton turbines with six nozzles, this study conducted unsteady numerical simulations of gas-liquid two-phase flow for various bucket offset angles, employing the VOF multiphase model combined with the SST k-ω turbulence model. The results reveal that as the bucket offset angle increases, the axial width of the water sheet formed by the current jet progressively widens, with a tendency to catch up with the water film formed by the previous jet during the torque rising stage. Moreover, the increased bucket offset angle causes the water sheet to distribute more closely to the bucket cutout, raising the risk of leakage from the cutout. Notably, at α= 10°, some of the water sheet has already flowed out of the cutout and collided with the subsequent jet.

Investigation on large fluctuation transient process of high head Pelton turbine

Abstract With the development of hydropower in southern western China, the Pelton turbine is the only choice in this ultra-high head condition which is nearly 1000 m. However, the complex coupling structure of the internal and external flow of the Pelton turbine, the change of flow pattern during the transition process, and the fluid-solid interaction of the bucket greatly increases the difficulty of accurate numerical simulation. Therefore, there are relatively few studies and applications on the transition process of the Pelton turbine. In this paper, the theoretical analysis, numerical calculation on the internal complex flow and the external characteristics of the turbine during the large fluctuation transition process are carried out in three aspects. First, the internal flow mechanism under optimized conditions is investigated, such as Dean vortex pairs, secondary flow, etc. And then analyze the influence of the flow state distribution on the jet flow. Secondly, study the instability and flow characteristics in the large fluctuation transition process of the opening and closing process of the nozzle, and predict the mechanism of the jet flow and the impact on the bucket during the dynamic process. Finally, study change of the hydraulic characteristics under the dynamic process which provides a theoretical guarantee for the safe operation of the Pelton turbine.

Effect of the operating head for hydraulic performance and flow of a Pelton turbine

Abstract The unsteady multi-phase flow simulation in rotating buckets of a model Pelton turbine under various operating heads was performed with the SST-CC turbulence model. The hydraulic performance of the turbine and the flow pattern in the rotating bucket under different operating heads were discussed. The results showed that there was an optimal operating head for the Pelton turbine. The waste of the additional kinetic energy carried by the outflow under off-design heads accounted for the decline in the turbine efficiency. Moreover, the temporal and spatial distribution of the outflowing loss varied with operating head. In the case of high operating head, the outflowing loss last only a short period of time after the water sheet flow started to discharge, and the obvious region of loss was near the bucket root. In the case of low operating head, the outflowing loss occurred during the second half of jet-receiving for the bucket, with the position of high outflowing velocity distributed along the entire brim.

Numerical method analysis of the multi-nozzle distributor hydraulic performance for a Pelton turbine

Abstract The distributor hydraulic efficiency is very important for a Pelton turbine. In order to improve the turbine efficiency and the jet flow stability from the injector, it’s necessary to optimize the design of the distributor. In this paper, the flow behaviors and the hydraulic efficiency of a model Pelton turbine distributor with and without six-nozzle domain were conducted numerically. Comparison of numerical simulation results of different cases with different boundary condition settings and domain was analyzed. The predicted results show that the results of the distributor with six-nozzle domain are agree well with the measured results and the hydraulic performances is quite different from other cases.

A review of the experimental techniques research progress of the Pelton turbine

Abstract The Pelton turbine internal flow is by far the most complex of all hydraulic turbo-machinery, which consists of confined flow, free jet flow, free-surface water sheet flow and dispersed flow. The efficiency of Pelton turbine is closely related to these flow phenomena, thus knowing the dynamic behaviour of these flow patterns is of high interest to the optimization of Pelton turbine hydraulic flow parts. The experimental techniques were used to analyse the relationship between the connect of the turbine performance and flow patterns for the earlier researches. The present paper reviewed the development of experimental techniques of Pelton turbines, summarized the emerging test means and discussed the internal flow mechanism.

Design of Pelton Turbine Test Stand in Plateau Environment

Abstract In recent years, with the continuous development of China’s hydropower projects, Pelton turbines are gradually being valued, and the focus of development has shifted from plain areas to plateau areas. Environmental impacts such as high altitude, water temperature, and high sediment content in the plateau area have caused serious interference to equipment that originally worked in a stable environment, for example, the failure of the cooperation between the parts of the turbine and the mutual seizure, the increased wear of the nozzle needle, the decrease of the flow rate and the water outlet speed of the nozzle, and the decrease of the air pressure in the plateau environment lead to the change of the flow state of the nozzle. In view of the above problems, this paper puts forward the design scheme of impulse turbine test-bed, using the method of changing specific speed to determine the basic parameters of impulse turbine unit, so as to eliminate the influence of plateau environment on the normal operation of turbine, obtain the efficiency condition of model experiment under low ambient pressure, and improve the operation efficiency and reliability of turbine unit.

Hydraulic analysis of jet deflection on Pelton turbine deflector based on CFD simulation

Abstract The deflector of the external regulating mechanism of the Pelton turbine can reduce the pressure of the nozzle structure during the emergency load rejection of the unit, and solve the problem that the pressure in the pressure pipe increases too much and the rotate speed of the unit gets too fast. This paper mainly introduces the flow pattern analysis of jet deflection when the Pelton turbine deflector is in working state. The results of calculation and analysis in this paper are based on the Navier-Stokes equations and k-ω SST turbulent model of CFD simulation.

Evaluation of Forces on the Needle for Regulation of Pelton Turbine Injector

Abstract In hydropower plants, the Pelton turbine is a commonly used hydraulic turbine where flow is regulated with a dual mechanism of needle and deflector. The needle is controlled by a servomotor and governor system, where the flow rate varies by adjusting the needle strokes. The needle is operated under the hydraulic force caused by the high-water pressure inside the injector acting on the needle surface. The objective of computing the force balance in a Pelton injector is to determine the force to be supplied by the servomotor. The closing trend is crucial to design the injector for safe operation during an emergency. In this study, the function of the needle and nozzle curve generalizes the variable needle surface area, allowing the geometric properties of the nozzle and needle to be suitable for the needle force evaluation. The single-axis force transducer, which is mounted on the needle rod, has been used in the experimental method for determining the needle forces. The experimental findings are compared to analytical calculations and serve as validation for the accuracy and reliability of the computed results obtained through the analytical approach.

Numerical analysis of the sand hydro-abrasion of a Pelton turbine injector

Abstract Pelton turbines have great application prospects in the exploitation of high-head hydraulic resources. However, sediment abrasion within its components is the major challenge. In this paper, Euler-Lagrangian method is used to simulate the flow process of the sediment particles in Pelton turbines injector numerically. The hydraulic characteristics of the three-phase flow, the behaviour of the sediment particles and the abrasion distribution are also analysed in detail. Calculation result shows that the predicted motion characteristics of the particles are in good agreement with theoretical model, and the predicted abrasion distribution also matches well with the measured results.

Investigation of hydraulic characteristics of Pelton turbine with casing structure using a moving particle simulation method

Abstract This paper reports the initial results of three dimensional simulation of the jet/bucket interactions in the vertical Pelton turbine with different casing structures. The casing is an important part of the Pelton turbine, and a reasonable casing structure can reduce the interaction between the jet and bucket, so as to improve the hydraulic efficiency of the turbine. Previous research has little numerical simulation analysis on the casing. In this paper, a Moving Particle Simulation(MPS) method without grid generation is adopted to compare and analyze the hydraulic characteristics of the runner under the regular hexagonal and circular casing structures. The simulation results show that the hydraulic efficiency of the runner under the hexagonal casing structure is better, and the runner time average torque is improved by 3.09%, which compared with the circular casing. The distribution of free surface flows in the hexagonal casing is analysis, and the obvious interference phenomenon between jets can be observed, which has an important guiding role in the design of the casing structure of Pelton turbine in the future.

Technical investigation of the ternary pumped storage hydro units with ultra-high-water head

Abstract This paper introduces the ternary pumped storage hydro unit technology and its development status, discusses the technical characteristics of the ternary unit, and looks forward to the broad application prospect of the ternary unit technology in the ultra-high head pumped storage power station. The main technical advantage of the ternary pumped storage hydro unit by using the Pelton turbine as the turbine component is that the hydraulic short circuit operation mode of the combined operation of pump and turbine can realize the smooth adjustment of the input power of the unit pumping condition. In addition, the conversion time between working conditions is greatly shortened compared with the conventional reversible pumped storage unit, thus greatly enhancing the power grid’s ability to absorb and adjust new energy.

Dynamic stress analysis of a large capacity Pelton turbine runner

Abstract The dynamic stress characteristics of a Pelton turbine runner is an important index to evaluate the stability of unit. Aiming to analyse the dynamic stress of a large capacity prototype Pelton turbine runner influenced by the unsteady impact load of a high-speed jet, the unsteady flow simulation was firstly taken for the Pelton turbine runner to conclude the hydraulic model of internal flow and the performance parameters. Then, the dynamic stress of the Pelton runner was solved by fluid-structure coupling numerical method. The dynamic stress variation trend of several monitor points distributed on the splitter, brim, bucket root was analysed. It is concluded that the impact load of the jet could lead to the significant change in the dynamic stress on specific location of the bucket surface, and the stress concentration was found at the bucket root.

Numerical simulation study of hydraulic performance of the ball valve implied in ultra-high head Pelton turbine

Abstract This paper is deal with the hydraulic performance of the ball valve served in ultra-high head Pelton turbine systems, the Moving Particle Simulation method is used for numerical simulation uncommonly instead of the Finite Volume method. A valve rotating range of 0 degree to 90 degree is simulated by the software Particleworks, according to the pressure change through the valve, we get the flow resistance coefficient which is consistent with those of other similar literature. The change of the internal flow distribution can be visually observed. At the small rotation degree, the flow velocity entering the ball valve is very high and the disturbance in flow field is large. With the rotation degree increases, the flow in ball valve and the outlet pipe is gradually stabilized, the pressure difference before and after the ball valve is gradually reduced. It brings reference value for the structure and size design of the ball valve in the future.

Investigation on the effect of particle parameters on the erosion and erosion prediction model of the Pelton turbine

The Pelton turbine will play a massive role in China's water conservancy and power generation development process. In practical engineering applications, sediment will erode the components of the Pelton turbine when they come into contact, threatening the safe and stable operation of the unit. Therefore, based on the Eulerian–Lagrangian method, this study analyzes the effects of particle size, concentration, and position angle on the degree and distribution of erosion of each component without considering the cavitation effect of the flow. The results show that the larger the particle size, the more concentrated the distribution, and the more severe the abrasion caused on the spray needle and water bucket. However, the degree of nozzle erosion weakens, and the erosion area increases. It was also found that the higher the concentration, the more severe the abrasion caused to each component. When the jet completely hits the position on the bucket, due to the low impact speed, the impact angle remains almost unchanged, resulting in less erosion. Finally, the classic Finnie model was refined by adjusting the average erosion rate, particle size, concentration, and rotation angle. This modification yielded an enhanced model, mainly showcasing improved performance for moderate particle sizes.

Analysis of Sediment Erosion in Pelton Nozzles and Needles Affected by Particle Size

The sediment erosion of Pelton turbine components is a major challenge in the operation and development of high-head water resources, especially in mountainous areas with high sediment yield. In this paper, a study using numerical simulation was conducted with different sediment particle sizes in the fine sand range. And the erosion mechanism of the Pelton turbine injector was analyzed. The Eulerian Lagrange method was adopted to simulate the gas–liquid–solid flow. The Mansouri’s model was applied to estimate the injector erosion. The predicted erosion results were in accord with field erosion photographs. In particular, the asymmetrical erosion distribution on the needle surface was physically reproduced. With the sediment particle size increasing from 0.05 mm, the needle erosion rate decreased, while the nozzle casing erosion rate increased dramatically. In order to clarify this tendency, the characteristics of the three-phase flow were analyzed. Interestingly, the results show that with the rise in particle size, the separation of particles and water streamlines became more serious in the contraction section of the nozzle mouth. Consequently, it caused the enhancement of erosion of the nozzle surfaces and weakened the erosion of the needle surfaces. Significant engineering insights may be provided for weakening Pelton injector erosion with needle guides in the current study.

Measurements and Modelling of the Discharge Cycle of a Grid-Connected Hydro-Pneumatic Energy Storage System

Hydro-pneumatic energy storage is a form of compressed-air energy storage that can provide the long-duration storage required for integrating intermittent renewable energies into electrical power grids. This paper presents results based on numerical modelling and laboratory tests for a kilowatt-scale HPES system tested at the University of Malta. This paper presents measurements of the discharge cycle, in which energy stored in compressed air within a pressure vessel is hydro-pneumatically converted back into electricity via a Pelton turbine and fed into the national electricity grid. The tests were conducted using a hydraulic turbine operated under different fixed-turbine rotational speed settings, with the pressure being allowed to decrease gradually during the HPES system’s discharge cycle. The system’s overall efficiency accounted for flow losses, turbine inefficiencies, and electrical losses. The tests showed that this efficiency was practically independent of the compressed-air pressure of specific water turbine runner speeds, despite the water turbine operating at fixed speeds. A numerical model developed in MATLAB Simulink (R2022a) was also presented for use simulating the hydraulic performance of the system during the discharge cycle. The model used secondary loss coefficients for the hydraulic circuit and derived velocity coefficients from computational fluid dynamics (CFD) for the Pelton turbine nozzle. We achieved very good agreement between the predictions based on numerical modelling and the measurements taken during laboratory testing.

Hybrid hydropeaking mitigation at storage hydropower plants combining compensation basins with battery energy storage systems (BESS)

Storage hydropower has the ability of flexibly generating electricity to match fluctuating power demand. However, rapid changes of water discharge in river reaches downstream of storage hydropower plants, referred to as hydropeaking, result from this intermittent production mode and may have potentially damaging effects on a river’s ecosystem. The construction of compensation basins usually embedded along the waterway between the powerhouse and the receiving water represents the state-of-the-art for hydropeaking mitigation. In recent studies, the application of battery energy storage systems (BESS) as an alternative mitigation option has been proposed. Instead of buffering the turbine discharge in a basin, electrical energy is stored in and retrieved from a BESS to meet short-term demand requirements, while the hydraulic machinery is ramping up and down according to environmental discharge constraints. The technical and economic feasibility of BESS compared to compensation basins is evaluated based on a newly introduced first-order assessment approach. If environmental discharge constraints are to be strictly followed, the exclusive application of BESS is deemed not feasible, due to the limited operation range of Francis and – to a lesser extent – Pelton turbines, especially for low partial loads. Therefore, hybrid systems combining a BESS with a smaller compensation basin are investigated as existing research focused either on a basin- or a BESS-only approach. Based on production time series of three case study hydropower plants, the sizes of basins and BESS are estimated. Basin sizes can be reduced with a hybrid system by 51% to 96% compared to a basin-only approach, with BESS energy capacities ranging approximately from 10 to 100 MWh. The cost efficiency of hybrid systems is strongly influenced by two factors, namely the future battery costs as well as the overall unit costs for the compensating basin. While the former are subject to considerable uncertainty especially as BESS reach their end-of-life much earlier compared to hydraulic structures and therefore require regular replacements after 10 to 15 years, the latter are highly site-specific as they include land availability and acquisition costs. The case studies show that a hybrid system of basin and BESS may represent a cost-competitive alternative to a basin-only approach when the latter’s investment costs are high or space is limited, even if additional revenue streams including ancillary services and energy arbitrage are not considered.

Effects of sediment characteristics on the erosion of Pelton turbine

As Pelton turbines are increasingly used in high mountain regions because of their unique advantage of high-water head adaptability, the hydraulic characteristics and multi-phase flow behaviour in Pelton turbines have attracted the attention of many scholars. Most notably, the presence of solid particles such as sand exists in natural river systems, which end up in the turbines, causing erosion. This has become an international academic issue which has not been fully developed yet. In this study, three-phase simulations based on Eulerian–Lagrangian methodology are conducted to investigate the erosion phenomenon, especially in the bucket region. Sediment particle characteristics such as size and concentration in both the distribution system and buckets region are analysed. The innovation of this study is that, unlike other erosion investigations, it focuses on the impact angle of the jet flow as this is a unique characteristic of Pelton turbines. Furthermore, the sediment particle's flow characteristics at different bucket rotating angles and how they influence the erosion mechanism are also investigated. Results reveal that larger particles cause greater erosion on the bucket. In small particle and standard diameter conditions, the impact angle is mostly below 5 ∘ . Finally, this study presents the first successful attempt in using rotating angle to describe the erosion in a Pelton turbine. A corrected erosion model adapted to the Pelton turbine is given through regression and proves effective in predicting erosion.

Effect and mechanism of erosion in Pelton turbine and case studies—A review

Pelton turbines are widely used in hydropower stations located in mountainous regions, especially with water head drop of more than 2000 m. Due to the complex structure and working principle of the turbine, the flow is more complicated than reaction turbines, making the numerical simulation more difficult. The impulse action causes the occurrence of erosion phenomena in Pelton turbines, which will directly decrease the hydraulic efficiency and reduce the turbine's life. For investigating the erosion characteristics, computational fluid dynamics is widely used on variegated platforms according to their unique advantage. Thus, different platforms are introduced and compared in solving the multi-phase flow using a discrete element method or the other meshless methods. In addition, the erosion mechanism is studied and classified in different aspects such as impact angle and impact velocity. However, unlike the feasibility of numerical simulations, experimental work on the erosion mechanism is still challenging to reproduce. Furthermore, the state of experimental research is discussed by listing the various major facilities in operation and comparing their methods of experimental analysis. Case studies all over the world provide a very rich database of erosion patterns which would be highly useful in validation and verification of simulation and experimental results. Studies have shown that particle parameters, such as size, concentration, shape, velocity, and the interaction between particles and material surfaces, significantly impact the erosion of Pelton turbines. In response to this erosion, upgrading materials and implementing geometric optimization have proven to be effective strategies.

Effect of inflow disturbances in Pelton turbine distributor lines on the water jet quality

The proper design of the manifold, distributing the flow to the individual nozzles, is crucial for the Pelton turbine performance. The generation of both energy losses and secondary flows must be reduced to a minimum to provide optimal water jet quality and, hence, efficiency. However, the inflow state due to the penstock is commonly disregarded at the design stage. By numerical flow simulation, we show how such penstock perturbations affect the water jet cross-section and axis deviation by considering different pipe bends upstream of the manifold. The two-phase flows resulting in a typical Pelton turbine manifold are predicted using the Volume-Of-Fluid (VOF) approach in conjunction with the k−ω SST turbulence closure model. Pipe bends are attached five manifold inlet diameters upstream of the manifold itself. The consequences on the secondary flows in the nozzles and the free water jet quality are reported quantitatively. The analysis shows that even small inflow perturbations into the manifold due to penstock piping significantly affect the water jet quality. A yet unreported mechanism is revealed, where the secondary flows mitigate the impact of the flow rate imbalance across the nozzle on the water jet deviation.