Computational Fluid Dynamics Analysis of Integrated Needle-Nozzle Dynamics in Pelton Turbines: Insights from Cañón del Pato Hydroelectric Plant, Peru

As the world strives towards its goal of net zero carbon emissions, it is vital that renewable energy sources be optimized to their full potential. A key source of renewable energy is hydropower, more specifically, the Pelton turbine—a highly efficient, widely used, and well-researched piece of turbomachinery. This review proposes a methodology that will aid future research on Pelton turbines and compares relevant literature to assess effective ways to improve upon the Pelton design. The methodology evaluates how both experimental and computational analysis can be utilized in parallel to accelerate the progress of research, giving an example of the adopted workflow presented in a case study. The literature study in this paper focuses on how a variety of bucket parameters can be optimized to improve the efficiency of a Pelton turbine and analyses the accuracy of CFD compared to experimental data from previous research involving Pelton and Turgo turbines. The findings revealed that a water exit angle of 169°–170° proved to be optimal, while modifications to the depth and internal geometry of the bucket seemed to have the greatest impact on the efficiency of Pelton turbines. A short discussion on the potential for utilizing the strengths of both Pelton and Turgo turbines is included to highlight the need for further research in this field. A combination of both simulation and experimental results running in parallel with each other during optimization is found to be beneficial due to advancements in rapid prototyping. By comparing experimental data with simulated data throughout the optimization process, mistakes can be realized early on in the process, reducing time in later stages. Having experimental data throughout the turbine’s development aids the computational process by highlighting issues that may have been missed when only using CFD.

Fossil fuels are energy sources that supply a large part of the world's energy generation. However, they produce greenhouse gases such as carbon dioxide (CO2), nitrogen oxide (NOx) and particulates that increase global warming. For this reason, other forms of renewable energy such as hydropower have begun to be implemented through turbomachinery such as Pelton turbines, which significantly reduce these emissions since they are highly efficient turbines based on the use of natural resources (water). Pelton turbines are based mainly on three components for their operation, which are the Pelton injector, the bucket and the wheel. The injector is an important component in the energy transformation of Pelton turbines. Although to analyze its behavior, it is possible to use fluid dynamics (CFD) software to predict the trajectory of the flow through a solid or free surface. The objective of this work is to analyze by means of computational fluid dynamics (CFD) the incidence of the length and the needle tip angle of a Pelton turbine injector on the generated power. For this, an ANSYS 2020R2 computational fluid analysis software was used to study how the variation of the injector needle tip angle influences through the volume of fluid (VOF) method, starting from the generation of a commercial model with a tip angle of 60° and two (2) geometries of 55° and 75° respectively. Numerical results show a better performance for the 75° angle of 96 % and lower for the 55° and 60° with 94.1 % and 95.5 % respectively, whereby steeper angles achieve higher performances. In summary, the present study pretends to increase the power generation, in the face of phenomena occurred in the energy transfer. Although the performance of the injector in each angle configuration must be tested in practice

Many consider the Pelton turbine a mature technology, nevertheless the advent of Computational Fluid Dynamics (CFD) in recent decades has been a key driver in the continued design development. Impulse turbine casings play a very important role and experience dictates that the efficiency of a Pelton turbine is closely dependent on the success of keeping vagrant spray water away from the turbine runner and the water jet. Despite this overarching purpose, there is no standard design guidelines and casing styles vary from manufacturer to manufacturer, often incorporating a considerable number of shrouds and baffles to direct the flow of water into the tailrace with minimal interference with the aforementioned. The present work incorporates the Reynolds-averaged Navier Stokes (RANS) k-ɛ turbulence model and a two-phase Volume of Fluid (VOF) model, using the ANSYS® FLUENT® code to simulate the casing flow in a 2-jet horizontal axis Pelton turbine. The results of the simulation of two casing configurations are compared against flow visualisations and measurements obtained from a model established at the National Technical University of Athens. Further investigations were carried out in order to compare the absolute difference between the numerical runner efficiency and the experimental efficiency. In doing so, the various losses that occur during operation of the turbine can be appraised and a prediction of casing losses can be made. Firstly, the mechanical losses of the test rig are estimated to determine the experimental hydraulic efficiency. Following this, the numerical efficiency of the runner can then be ascertained by considering the upstream pipework losses and the aforementioned runner simulations, which are combined with previously published results of the 3D velocity profiles obtained from simulating the injectors. The results indicate that out of all of the experimental cases tested, in the best case scenario the casing losses can be approximated to be negligible and in the worst case scenario ≈3%.

The application of computational fluid dynamics (CFD) in the design of water turbines and pumps started about 30 years ago. This paper reviews the main steps and breakthroughs in the methods that were made during this period, through the eyes of one particular water turbine company which spear-headed some of the first developments for practical applications. Practical examples are used to illustrate the developments of the tools from 1978 to 2008 and to give an overview of the complete revolution in hydraulic turbine design that has occurred over this time. Several periods with distinct levels of complexity, and hence accuracy of the physical models and of the simulation methods can be distinguished. The first steps coincided with the introduction of the Finite Element Method into CFD, and were characterized by simplified Quasi-3D Euler solutions and Fully 3D potential flow solutions. Over the years the complexity continuously increased in stages: via 3D Euler solutions, to steady RANS simulations of single blade passages using finite volume methods, extending to steady simulations of whole machines, until today unsteady RANS equations are solved with advanced turbulence models. The most active areas of research and development are now concerned with including the effects of 2-phase flows (free surface flow in Pelton turbines and cavitation) and fluid–structure interaction.

The design of Pelton turbines has always been more difficult than that of reaction turbines, and their performances lower. Indeed, the Pelton turbines combine 4 types of flows: (i) confined, steady-state flow in the piping systems and injector, (ii) free water jets, (iii) 3D unsteady free surface flows in the buckets, and (iv) dispersed 2-phase flows in the casing. The flow in Pelton turbines has not been analyzed so far with such detail as the flow in the reaction turbines, thus the understanding of the physics of key phenomena, i.e. the initial jet/bucket interaction or the jet cut process, is weak. Moreover, some machines present erosion damages that have not been satisfactorily explained so far. In the framework of this study, the flow in the buckets is investigated with 4 experimental and numerical approaches: (i) Unsteady onboard wall pressure measurements. 43 piezo-resistive pressure sensors are distributed on the bucket inner surface, backside and sides. (ii) High-speed flow visualizations (onboard and external). Small rigid endoscopes are fitted either in a bucket, to observe the relative flow, or in the casing to observe the jet/bucket interaction. (iii) Onboard water film thickness measurements. (iv) CFD simulations. The 2-Phase Homogeneous Model and the 2-Fluid Models are compared with the experimental data. The 2-Fluid Model appears to be more accurate, while the 2-Phase Homogeneous Model is too diffusive. The initial jet/bucket interaction evidences the probable occurrence of compressible effects, generating an outburst of the jet and leading to erosion damages. When the jet impacts the bucket inner surface, a high-pressure pulse, which amplitude is larger than the equivalent stagnation pressure, is generated, caused by compressible effects. The jet appears to remain attached to the backside of the buckets far in the duty cycle, and the separation to be dependent on the test head. The bucket backside acts as the suction side of a hydrofoil undergoing the Coanda effect, generating a depression, and in turn a lift force contributing positively to the bucket and runner torques. The depression nevertheless onsets cavitation, causing erosion damages. The main bucket flow is independent on the test heads. Mixing losses are put into evidence, either due to the crossing of streamlines or due to flow interferences. An analysis of the bucket power budget highlights the important contribution of the central area in terms of power transferred from the fluid to the bucket. The power signal of the whole runner shows important fluctuations that are modulated by the operating conditions. From the Momentum conservation equation, the respective influences of the different forces acting on the flow are evidenced. Even if the inertia forces, i.e. the deviation, Coriolis and centrifugal forces, globally dominate, the viscous and surface-tension forces outweigh the formers at the end of the evacuation process and in the jet separation process. Obtaining significant improvements of the performances of Pelton turbines requires to adequately take into account the secondary forces, i.e. surface tension and viscosity, for the bucket flow and to improve the design of the backside in order to maximize the torque while promoting a neat separation.

Analysis of water quality of Himalayan originated rivers reveals the heavy sediment loading with a major portion of the sediment being hard mineral, quartz. Despite the incorporation of desanders to reduce the sediment content passing through hydro mechanical parts, significant wear is being reported in south-Asian hydroelectric projects. Repeated impact of such solid particles which are harder than the material of mechanical parts (mostly steel) is known to cause the erosion. Flow parameters, impact angle, mechanical properties of wall and particle, particle shape and size are commonly explored variables that affect the erosion of solid by the sediment-laden flow. In order to predict such erosion, starting with Finnie erosion model, several other erosion models considering aforementioned variables are proposed but are mostly case dependent. Application of numerical methods to understand flow problems constitutes the field of Computational Fluid Dynamics (CFD). Due to enclosed flow, reactions turbines took accelerated development in the investigations by CFD modeling. However, free surface jet and complex flow mechanism in buckets have been a major barrier to the application of CFD in case of Pelton turbines. Recent advancements in computational techniques, technological advancements have enabled to investigate flow in Pelton turbine by CFD. However, it is least understood which among the proposed erosion models will predict erosion occurring in Pelton turbine and assembly. This article explores about erosion in Pelton turbine, various erosion models and state of the art in modeling erosion of Pelton turbine injector. It is discussed which among the erosion models shall best predict the erosion occurring in the Pelton turbine injector. A short list of erosion models is then given which can be applied for the case of erosion in Pelton turbine injectors.

The Pelton turbine has been widely regarded as the most efficient hydro turbine for high-head applications. However, the Pelton turbine buckets, especially the area commonly referred to as the ‘splitter’, are highly susceptible to erosion, drastically reducing efficiency over prolonged periods of time. This paper demonstrates a novel turbine idea that has been validated through both computational and experimental methods. This turbine addresses the issues associated with the erosion of the splitter through a redesign of the Pelton turbine to remove the need for a splitter and therefore potentially reducing downtime due to maintenance. The computational fluid dynamics (CFD) simulation results show that the turbine is capable of efficiencies greater than 82% with room for further improvement. The practical experimental results also show efficiencies within 6% of an optimized Pelton turbine. The results from this study indicate that through further optimization this turbine design could provide a means to produce power outputs similar to conventional Pelton turbines, with the added benefit of lower maintenance costs.

Novel trends in modelling techniques of Pelton Turbine bucket for increased renewable energy production

The Pelton turbine is a type of water turbine that is often used in hydroelectric power plants. This Pelton turbine is generally used for locations with a head height of more than 30 meters. The water in the Pelton turbine moves fast, and it extracts energy from the water by slowing down the water, making it an impulse turbine. This study aimed to determine the optimal efficiency of the Pelton turbine by analyzing the blade design using variations in the deflection angle. The fluid flow velocity from the bucket with variable deflection angles of 15°, 17°, and 19° was analyzed using the Computational Fluid Dynamics (CFD) method with SolidWorks simulation software. The simulation data were then analyzed and described using the velocity triangle method. From the simulation, the largest value of turbine power is 329,54kW, and efficiency is 95.98% at an angle of 15° with a discharge of 0.35 m3/s.

Numerical investigation of the unsteady flow patterns around the bucket can be helpful to improve the Pelton turbine efficiency. In fact, by studying the loss mechanisms in the flow, one can optimize the bucket design. For this purpose, an accurate investigation of the water jet is also necessary as an inlet condition for the bucket flow. The water jet ejected from the nozzle is actually non-uniform, due to the upstream turbulence and secondary flow in the distributor, bending pipes, needle and supports. This non-uniformity causes a deviation of the water jet from the ideal jet center, which is tangent to the jet circle, and it directly affects the flow patterns around the bucket. Whereas water splashing makes experimental observations very challenging, a numerical approach is effective and convenient to study the unsteady flow pattern in a Pelton turbine. In the present research, numerical analysis of the two-phase flow through the distributor, bending pipe and nozzle, has been performed. The jet velocity profile has been verified with experimental results, which are measured in the model test equipment, and good agreement is obtained for both velocity profile and jet deviation. In addition, the analysis of the bucket unsteady flow is performed using the aforementioned non-uniform jet velocity profile and the calculated flow pattern around the bucket is compared to the previous calculation using a uniform velocity profile at the inlet boundary. The difference between the two cases is discussed based on the quantitative and qualitative evaluation from the numerical analysis.

The size distribution of oil droplets formed in subsea oil and gas blowouts is known to have strong impact on their subsequent fate in the environment. Fine droplets are frequently neutrally buoyant and within the full body of water they are available for biodegradation. Subsea Dispersion Injection (SSDI) is an integral part of achieving this goal, lowering the interfacial tension between the oil and water. However, despite their many advantages, the use of SSDI are limited both by the logistical constraints of deployment and legislative restrictions over its use. Adding to the toolkit of methods that achieve subsea dispersion without the use of chemicals would therefore enhance oil spill response capability. There are other ways of reducing the effects of interfacial tension within the oil such as increasing the interfacial shear by introducing more turbulence within the rising oil plume. Using a combination of laboratory experimentation and computational fluid dynamics (CFD) we have explored the potential of three mechanisms – 1) a rotating bladed shearing mixer, 2) ultrasonic cavitation and 3) high pressure water jetting. Physical experiments were conducted at the SINTEF Tower Basin facility in Norway. A scaled-down oil plume of Oserberg blend (1 L/min) was subjected to shear using commercially available rotating and ultrasonic devices both normally supplied for industrial mixing applications and adapted for operation within the tank. Results were compared to chemically dispersed oil under the same conditions. CFD modelling of water jetting was conducted using the BP High Performance Computer facility adopting a Volume of Fluid (VOF) multiphase model with advanced turbulence modelling and automated mesh refinement. Boundary conditions were set to replicate, as close as practical, the dimensions and physical properties used in the tank experiments. Results indicate that all three modes of increasing interfacial shear could be effective in dispersing oil. The ultrasonic device created a broad distribution of oil droplet sizes, spanning 10-100 μm in diameter whilst the mechanical shearing technique dispersed oil droplets into a narrower size distribution, centred on 16 μm. These values fall close to the droplet size of the same oil dispersed using chemicals of 70μm. Estimation of droplet sizes in the water jetting scenarios yielded values <50 μm. These tank scale experiments indicate that a new class of oil spill response technology may be possible using a mechanical device – Subsea Mechanical Dispersion (SSMD). The varieties of techniques that have been shown so far to be effective indicate that a range of devices may be designed and scaled to suit different oil spill scenarios and become a valuable addition to this class of response strategy.

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.

Advanced computational fluid dynamics (CFD) models of gas release and dispersion (GRAD) have been developed, tested, validated and applied to the modeling of various industrial real-life indoor and outdoor flammable gas (hydrogen, methane, etc.) release scenarios with complex geometries. The user-friendly GRAD CFD modeling tool has been designed as a customized module based on the commercial general-purpose CFD software, PHOENICS. Advanced CFD models available include the following: the dynamic boundary conditions, describing the transient gas release from a pressurized vessel, the calibrated outlet boundary conditions, the advanced turbulence models, the real gas law properties applied at high-pressure releases, the special output features and the adaptive grid refinement tools. One of the advanced turbulent models is the multi-fluid model (MFM) of turbulence, which enables to predict the stochastic properties of flammable gas clouds. The predictions of transient 3D distributions of flammable gas concentrations have been validated using the comparisons with available experimental data. The validation matrix contains the enclosed and non-enclosed geometries, the subsonic and sonic release flow rates and the releases of various gases, e.g. hydrogen, helium, etc. GRAD CFD software is recommended for safety and environmental protection analyses. For example, it was applied to the hydrogen safety assessments including the analyses of hydrogen releases from pressure ______ *To whom correspondence should be addressed. Vladimir Agranat, 6591 Spinnaker Circle, Mississauga, Ontario, L5W 1R2, Canada; e-mail: info@tchouvelev.org and acfda@sympatico.ca CFD MODELING OF GAS RELEASE AND DISPERSION 2 relief devices and the determination of clearance distances for venting of hydrogen storages. In particular, the dynamic behaviors of flammable gas clouds (with the gas concentrations between the lower flammability level (LFL) and the upper flammability level (UFL)) can be accurately predicted with the GRAD CFD modeling tool. Some examples of hydrogen cloud predictions are presented in the paper. CFD modeling of flammable gas clouds could be considered as a cost effective and reliable tool for environmental assessments and design optimizations of combustion devices. The paper details the model features and provides currently available testing, validation and application cases relevant to the predictions of flammable gas dispersion scenarios. The significance of the results is discussed together with further steps required to extend and improve the models.

The use of Computational Fluid Dynamics (CFD) for predicting the flow behaviour in Pelton turbines is limited by the complex nature of the flow, interaction between the jets and interference of the water after the impact on the buckets. Besides, validation of the numerical results in such turbines is usually challenging due to the unsteadiness of the flow properties. Hence, time-dependent analysis with multi-phase models is required for obtaining such solutions. This paper conducts a CFD analysis on a Pelton turbine using RANS based Eulerian scheme. The fluid domain consists of three successive buckets placed in their corresponding circumferential locations, along with a spear valve, which is adjusted for various operating conditions. Such a domain assumes that the interaction of the jet on the buckets takes place for a maximum of three buckets at any particular time. The results of the CFD analysis are compared with the experimental results for all the studied opening conditions. The objective of this work is to build a suitable numerical model that can be applied to any Pelton turbines, such that a complete performance curve of the turbine can be generated. The flow pattern between entry and exit of the bucket obtained from CFD is compared with images taken from a high speed camera in rotating frame of reference. The results of the numerical analysis are found to be in a good agreement with the experimental data.

This paper presents the transient performance analysis of a micro-hydro Pelton turbine for the osmotic power generation using the commercially available computational fluid dynamics (CFD) code, ANSYS CFX. The detailed flow field in the micro Pelton turbine with a single-jet is investigated by the CFD code adopted in the present study. Predicted characteristic curves agree fairly well with measured data for a prototype Pelton turbine over the normal operating conditions. The computational analysis method presented herein can be effectively applied to the hydraulic design optimization process of general purpose Pelton turbine runners.