Turbine Runner Research Articles

On the Comparison of Hydroelectric Runner Fatigue Failure Risk Based on Site Measurements

The fatigue reliability of a turbine runner is closely related to its dynamic behavior. Over the past few years, Hydro-Québec has performed measurement campaigns on many of its turbine runners. These measurements led to the evaluation of the fatigue risk level of each runner in various operating conditions, which allows operating conditions with a higher risk of crack propagation to be avoided. This paper presents the results for turbine dynamic behavior assessed in steady-state conditions. Stress levels at strain gauge locations are used to evaluate the risk of fatigue cracking based on the Kitagawa-Takahashi diagram. Results show a good correlation between the calculated risk of cracking and real cases of cracks found in runners. Furthermore, the results comparison highlights a apparent tendency for recent designs to be more prone to cracking at speed-no-load operating condition than older designs. The paper gives an overview of the methodology used and discusses the conclusions derived from the sample of turbine runners available for this study.

Multi-objective shape optimization of Francis runner using metamodel assisted genetic algorithm

Nowadays evolutionary optimization techniques become an integral part of the design process of hydraulic turbine runners. For optimization the shape of the runner is parameterized by a set of geometrical parameters. The objective functions of each runner geometry, being the efficiency and cavitation performance, are evaluated through CFD analysis of 3D flow-field. As usual, some kind of genetic algorithm is used for searching the Pareto front, due to its inherent possibility of parallel evaluation of different runner variants within one generation. This approach requires extensive CFD computations of hundreds and thousands of runner variants. In order to speed up the optimization process a metamodel (approximate, surrogate model) can be utilized. The metamodel provides an approximation of true dependency of the objective functions on the design parameters. The metamodel is built based on the known objective functions for some initial set of points randomly taken form the design space. Once built, it can be used to replace time consuming CFD computations during the optimization process. In the present paper a metamodel, based on Gaussian processes, is implemented and integrated into a multi-objective genetic algorithm. The obtained algorithm is applied for shape optimization of the Francis turbine runner. The number of the design parameters varied from 4 to 24. The objective functions are multi-point efficiency and cavitation characteristics. True values of the objective functions are evaluated using Reynolds averaged Navier-Stokes computations of the flow field in a reduced turbine domain, including wicket gate, runner and draft tube. These values are used to train the initial metamodel. In order to enhance predictive capabilities of the metamodel, it is retrained periodically during the optimization loop. The results of metamodel-assisted optimization runs are compared to that obtained without metamodel. It is shown that application of metamodel significantly reduces the number of actual CFD computations even for high number of design parameters and thus speeds up the overall optimization process.

Accurate and efficient analysis of dynamic runner stresses considering hydrodynamic damping effects

Safe and reliable dynamic designs of Francis and pump turbine runners require an accurate and efficient prediction of the dynamic response during operation including dynamic stresses. If resonance phenomena cause significant dynamic amplifications, response amplitudes strongly depend on damping effects, and numerical simulations have to include realistic damping behavior. For submerged components like turbine runners, hydrodynamic (flow-induced) damping and hydro-acoustic radiation are much greater than structural or material damping, but cannot be assessed sufficiently accurate by simple assumptions. Therefore, a newly developed fluid-structure interaction (FSI) methodology is presented which offers accurate and efficient harmonic response analyses of submerged structures not only accounting for added-mass effects but also for flow-induced damping and acoustic radiation. The acoustic FSI approach, widely used to consider added-mass effects, is enhanced by convective terms to include fluid forces caused by the deflection of the mean flow due to structural motion. Only a stationary flow solution, obtained from standard computational fluid dynamics analyses, is required as additional input. The linearized second-order system with non-proportional damping matrix is solved in frequency domain using a Krylov subspace based model order reduction technique. The methodology is validated using experimental damping data from an elastic hydrofoil in a cavitation tunnel. A first application to a prototype Francis runner, being excited close to resonance by rotor-stator interaction, reveals a significant influence of the operating condition on hydrodynamic damping and dynamic stresses. The numerical results for both part load and full load agree very well with measured prototype strains. Meanwhile, the automated methodology is applied as a standard tool within the hydro-mechanical runner design process ensuring dynamically safe and reliable runner designs.

Advanced Optimization Tools for Hydro Turbine Runner Design

The objective of this work is to show how advanced optimization tools can be used for hydraulic turbine design, taking the example of a Francis runner design (new or refurbishment project). The public test case considered corresponds to a R&D turbine model of specific speed Ns = 0.5, originally developed at the Hydraulic Machinery Laboratory (LMH) of École Polytechnique Fédérale de Lausanne (EPFL). Firstly, a standard Computational Fluid Dynamics (CFD) process is used to predict performances, in the form of efficiency and cavitation behaviour. It features structured mesh for distributor (stay vane and guide vane), runner and draft tube. Automatic scripts are created to run computations for several guide vane openings and rotation speeds, covering the whole range of operating conditions, and allowing to obtain numerical hill charts of efficiency and minimum pressure to predict the occurrence of cavitation. Secondly, some operating points are purposefully selected for the optimization and objectives are defined to maximize efficiency while constraints are set for preventing cavitation. To continue with, a parametric blade model is defined: 3D blade shape is obtained from blade to blade sections and a stacking law. Sections are defined by camber and thickness. Finally, a Surrogate Based Optimization (SBO) with Evolutionary Algorithm (EA) is used for searching a global optimum. Design of Experiment (DOE) techniques are employed to efficiently define a database. Dynamic monitoring, data-mining and visualization tools are used; including Leave-One-Out (LOO), Analysis of Variance (ANOVA) and Self-Organizing Maps (SOM), with the objective of facilitating surrogate reliability assessment and a comprehensive understanding of key factors of the problem studied. This methodology is tested iteratively with the Francis Runner Hydraulic design: a first optimization is run, analysed and used to define a second optimization that shows increased benefits in particular for Best Efficiency Point. The results are analysed from a hydraulic point of view to identify the benefits and effects of the last optimization.

Analysis of hydro-abrasive erosion and efficiency changes measured on the coated Pelton turbines of HPP Fieschertal

Geometrical changes and material loss of Pelton turbine runners as well as changes in turbine efficiency have been measured at HPP Fieschertal in Valais, Switzerland since 2012. The HPP is equipped with two horizontal axis Pelton units, with each 32 MW nominal power, 7.5 m3/s design discharge, 515 m head and two injectors. The nozzles and the buckets are hard-coated. Due to the relatively high hydro-abrasive erosion during the summer (sediment transport season), the splitters and cut-outs of the runner buckets are grinded and re-coated on-site usually every winter.Turbine erosion was quantified based on repeated measurements on two runner buckets using 3d-scanning and a coating thickness meter. The detailed geometrical models showed amongst others that the splitter width distributions are similar for buckets of one runner, but differ considerably between runners. Changes in turbine efficiency were measured by the sliding needle procedure and continuously monitored based on operating data. From the efficiency monitoring over eight years of both turbines, efficiency differences were evaluated for each sediment season and for various refurbishment or replacement actions. The mean efficiency reduction was 0.4 % per sediment season. The on-site refurbishment works partly compensate the efficiency reductions due to erosion, leading to an efficiency drop of e.g. 2 % over six years, after which the runners are usually overhauled in the factory.

Quantifying the Effect of Kaplan-Type Runner Blade Gaps on Fish-related Flow Conditions

In double-regulated Kaplan turbines, gaps form between the rotating blade and the hub as well as the discharge ring due to both the local geometry and the operational positioning of the runner blade. It is conventionally assumed that minimizing such gaps may decrease the likelihood of grinding and exposure of fish to high shear flows. Together with blunt leading edges of runner blades, minimum gap runners (MGR) are featured as the most effective measure to ameliorate the risks of mortal injury for fish passing through the turbine. However, the merits of such premise need yet to be quantified and made publicly accessible in the technical literature. This, in turn, will facilitate the evaluation of candidate MGR geometries in future designs.In this work, we propose a metric to quantify the influence of the gaps features on the mortality risks for fish passing the turbine runner. Two main outcomes derived from the present research: (1) It informs the minimum set of hydraulic variables that may be considered as test conditions for laboratory experimentation on fish subjected to near gap-like flows and (2) it formulates a metric to be integrated into the modelling strategies currently in use for the biological performance assessment of new turbine geometries. This physics-based examination of the flow phenomena was conducted in two Kaplan-type units of very distinct features (one is a very low-head, mid-size unit of 1.8 MW-rating capacity and another is a large-size unit of 90 MW-rating capacity).

Strain prediction in Francis runners by means of stationary sensors

The assessment of the remaining useful life due to fatigue in Francis turbine runners implies complex measurements with strain gauges that have to be installed in a submerged and rotating structure, which is excited with high pressure pulsations and strong turbulent flows. Furthermore, the conditioning, storage and transmission of these signals to the stationary frame involves complicated technical solutions. In order to avoid such complex and expensive measurements, in this paper we explore the feasibility of obtaining the strain on the runner with stationary sensors, which can be easily installed and used for a continuous monitoring of the machine. Based on the experimental strain tests performed in a Francis turbine unit, strain on the runner blade is correlated with relevant indicators obtained with stationary sensors. The correlation within indicators is obtained considering linear regression models and improved with artificial intelligence techniques.

Parametric Design Tool for Development of a Radial Guide Vane Cascade for a Variable Speed Francis Turbine

Hydropower as a part of the family of renewable energy sources represents an engineering and scientific field which inspires researchers to work on development of the systems and sub-systems in a way of optimizing the whole energy transformation process to obtain more efficient, flexible and reliable hydropower operation with the best possible water to energy ratio. This research is part of a Horizon 2020 HydroFlex project by the Norwegian University of Science and Technology (NTNU), where the main goal is development of a flexible hydropower generation. The guide vane cascade is one of the most crucial stationary sub-systems of the hydraulic turbine and is a subject of this study. Its re-design for obtaining a quality “flow-feeding” of a variable speed high head Francis turbine is developed. Having this goal in mind, a MATLAB code was generated, based on several key parameters, such as initial energy conditions as net head and turbine discharge at best efficiency point (BEP). Turbine runner geometrical constraints are taken into account during this process, while using recommendations for some initial guide vane calculations such as their number, inlet and outlet diameter, guide vane axis diameter, delivery angles etc. Using an inverse Euler turbine equation, the operating range of the turbine was calculated for a variable speed and discharge conditions, keeping the shock-free flow for all states at the runner’s inlet, as it is the most favourable inflow condition. For those operating points, the flow streamlines angles were obtained at the guide vanes leading and trailing edges. With an interpolating mathematical functions between the angles of the leading and trailing edges, the camber lines of the hydrofoils were obtained for further guide vane cascade geometry development. This algorithm can be implemented on any given runner geometry. The guide vane design is then exported into ANSYS Workbench for further numerical tests, such as CFD simulations for verifying the hydrodynamic characteristics and FEM analysis for verifying the structural integrity of this sub-system for variable speed operating conditions.

Capability of Advanced Ultrasonic Inspection Technologies for Hydraulic Turbine Runners

This paper presents the results of a project aimed at evaluating the performance of ultrasonic techniques for detecting flaws in Francis turbine runners. This work is the first phase of a more ambitious program aimed at improving the reliability of inspection of critical areas in turbine runners. Francis runners may be utilized to supply power during peak periods, which means that they experience additional load stress associated with start and stop sequences. Inspection during manufacturing is then of paramount importance to remove as much as feasible all flaw initiation sites before the heat treatment. This phase one objective is to collect initial data on a simplified mock-up and then to compare the experimental ultrasonic data with the results of simulations performed by CIVA, a computer simulation package. The area of interest is the region with the highest stress between the blade and the web. A welded T-joint coupon made of UNS S41500 was manufactured to represent this high-stress area. During the FCAW welding process, ceramic beads were embedded in the weld to create discontinuities whose size is in the critical range to initiate a crack. Inspection of the material was carried out by various nondestructive testing (NDT) methods namely conventional pulse-echo, phased array, total focusing method (TFM). With these results, detection rates were obtained in order to compare the effectiveness of each method.

A novel energy losses dependence on integral swirl flow parameters in an elbow draft tube of a Kaplan turbine

Energy losses in the region between the runner and outlet section of a conventional hydraulic turbine have been the subject of investigation for a long time. In this paper as well, elbow draft tube losses are determined for the relevant wide range on-cam operating modes of the Kaplan turbine using a contemporary approach. The research considers the impact of swirl flow parameters, defined for the referent inlet of the draft tube, on the hydraulic losses. According to the methodology and obtained numerical results, a new formula for the calculation of draft tube losses is proposed. In the process of a hydropower plant refurbishment, the presented approach may enable more efficient and economically justified consideration of the performance improvement of the entire double regulated hydraulic turbine, especially in the case of keeping the existing elbow draft tube.

Flow behaviors in a Kaplan turbine runner with different tip clearances

Tip clearance between the runner blade tip and shroud in a Kaplan turbine is inevitable, and the tip leakage flow (TLF) and tip leakage vortex (TLV) induced by the tip clearance have a considerable effect on the flow behaviors. To reveal the effect of the tip clearance on the flow characteristics, based on the Reynolds time-averaged Navier-Stokes (N-S) equation and the shear stress transfer (SST) k-ω turbulence model, the three-dimensional turbulence flow in a Kaplan turbine is simulated using ANSYS CFX. Meanwhile, the flow laws in the tip clearance are emphatically analyzed and summarized. Results show with the increase of the tip clearance, the negative pressure region in the blade suction side (SS) middle, the SS near the blade tip and the blade tip becomes more and more obvious. In the meantime, the flow behaviors on the blade pressure side (PS) are relatively stable, and the flow separation on the SS near blade tip merges. The larger the tip clearance is, the more obvious the flow separation phenomenon displays. In addition, the TLV is a spatial three-dimensional spiral structure formed by the entrainment effect of the TLF and main flow, and as the tip clearance increases, the TLV becomes more obvious.

Optimization procedure to design a Francis turbine runner using 2D Through-flow analysis

Due to increasing usage of Feed-in Tariff (FIT), which is a subsidy system to encourage expansion of renewable energy and to reduce costs associated with introduction of renewable energy, demand for hydraulic turbine designers has increased solely for the purpose of improving turbine performance. With these requirements, CFD simulation is a powerful tool for designers to improve the internal flow and pressure distribution in turbines. Traditionally, most designers use a trial-and-error process based on previous experience to design new turbines. Usually, achieving the goal is a lengthy and painstaking process. This paper proposes a novel method which combines both CFD and optimization methods to automatically optimize a Francis turbine. This procedure includes four components: a design program, a CFD solver, a scheduler, and an optimization algorithm. This paper describes an attempt to automatically optimize a Francis turbine runner by using ANSYS Vista TF as the 2D CFD solver based on through-flow theory, and ANSYS CFX 19.1 as the 3D CFD solver based on Finite Volume Method (FVM). The runner geometry is parameterized by Bezier curves in the design program. CFD analysis is performed to assess the efficiency of the runner, and also the output power is calculated by runner torque. These two parameters are used as the objective function of the optimization algorithm. This method is used to optimize the runner geometry, which consists of two parts: the meridional plane and profile camber lines. We confirmed that the new turbine, which was optimized by the above-mentioned method, has better efficiency than the existing one.

Effect of Boundary Conditions on Fluid–Structure Coupled Modal Analysis of Runners

To predict the resonance characteristics of hydraulic machinery, it is necessary to accurately calculate the natural modes of the runners in the operating environment. However, in the existing research, the boundary conditions of the numerical modal analysis of the runner were not unified. In this paper, numerical modal analysis of a prototype Francis pump turbine runner was carried out using the acoustic–structure coupling method. The results of three different constraints were compared. The influence of the energy loss on the chamber wall on the natural modes of the runner was studied by the absorption boundary. The results show that the constraint condition (especially the rotating shaft) has significant impacts on the torsional mode, the radial mode, the 1 nodal-diameter mode, and the 0 nodal-circle mode, and the maximum differences in the natural frequencies under different conditions are 69.3%, 56.4%, 35.1%, and 9.4%, respectively. The change of the natural frequencies is closely related to the modal shapes. On the other hand, the energy loss on the wall mainly affects the nodal-circle modes, and the influence on other modes is negligible. The results can provide references for the design and resonance characteristics analysis of hydraulic machinery runners.

Modeling cavitation erosion using non-homogeneous gamma process

Although hydroelectric generating units are highly reliable, being able to accurately model their degradation level represents a real asset in industrial and financial risk management. This paper presents and models a common degradation phenomenon observed on hydraulic Francis turbine runners: erosive cavitation. It gives an application of stochastic processes for degradation modeling framework in presence of real laboratory experimental data. For degradation modeling, a non homogeneous gamma process is proposed. The model calibration is explained and asymptotic confidence intervals for the model estimate are assessed. Because of the limited size of available dataset, bootstrap techniques are also used to evaluate statistical estimation uncertainties on the model parameters. These uncertainties on the degradation model are then propagated in order to analyze how they impact the distribution of the system lifetime, characterized by the hitting time for a given degradation threshold.

Design and Development of a Mini Steam Turbine for Domestic Electric-Powered Application

This work focuses on the design and development of a single stage De Laval impulse type of steam turbine connected to an AC generator for the purpose of generating electricity for domestic use. The system possesses several components such as turbine runner and blades, turbine casing, steam inlet nozzle and AC generator. The system is designed to work with a steam generator (boiler) fired by biogas, which is connected to the rotary (turbine blade) system via a nozzle. Factors such as steam pressure, temperature, velocity and mass flow rate of steam and nozzle angle are the key input variables that help in the development, construction and fabrication of the turbine wheel (blades and rotor). The developed mini steam turbine was simulated using solid works software and the von mises result obtained for maximum and minimum stresses of the turbine frame and stand unit were 2.725 × 105N/m2 and 4.447 × 101N/m2, respectively with yield strength of 2.5 × 108N/m2. Also, the von mises maximum and minimum stresses of the turbine blade were 3.522 × 107N/m2 and 7.064 × 104N/m2, respectively with a yield strength of 2.413 × 108N/m2. The developed mini-turbine is designed to withstand the working conditions based on the static simulation and analysis of results obtained.

Master equation, design equations and runaway speed of the Kaplan turbine

To make the Kaplan turbine technology comparable to both the Pelton and the Francis turbine, the master equation for the Kaplan turbine has been established by analyses similar to that-for the Francis turbine. The analysis begins with the descriptions of free vortex flows at the runner inlet and the swirl flow at the impeller exit. By considering the Euler equation for specific work and by further evaluating the most significant shock and swirling losses, the first and the second energy equations in the form of hydraulic efficiency were formulated. The master equation is then established by combining both energy equations. In addition, three design equations and a new design parameter are presented. The master equation relates the turbine hydromechanics to the geometrical design of both the runner and the guide-vane parameters. It enables the complete hydraulic characteristics of a given Kaplan turbine to be analytically and simply computed. A computation example demonstrates the functionality and applicability of the method. With the reconstructed master equation, the runaway speed of the Kaplan turbine and its dependence on the guide-vane setting can be easily and precisely computed. For bulb turbines with guide vanes directly ahead of the turbine runner in the same tube, all computations are also applicable using another equivalent control parameter.

Feasibility Study of PVC Pipes as Vertical Axis Wind Turbines Type Savonius Bucket for Remote Areas Application

Independent power plant based on renewable energy is a good solution to solve electricity crisis in remote areas. Wind is a source of energy that has every country in the world. A study of the utilization of PVC pipes as a material for Savonius turbine buckets has been carried out in order to reduce the investment costs of wind turbines. The feasibility test has been carried out in four runners: the 2-bucket without and with overlap and the 3-bucket without and with overlap. All the runners are made using PVC pipes. Based on results, the 2-bucket with overlap is the right solution for remote areas because it has a higher coefficient of performance of 8.39%, and the range of tip speed ratio is wider between 0.57-0.65 compared to others. Compared to aluminum bucket material, the PVC pipes are more profitable because they are easy to make, cheap and good performance. Furthermore, the investment cost of a Savonius turbine bucket made from PVC pipe (USD 37.34) is cheaper than the pico hydro type Turgo (USD 48). Thus, the PVC pipes as materials for making Savonius turbine runner are recommended for remote areas application because the materials are cheap and easy to access (widely available in the market).

Effect of outer edge modification on dynamic characteristics of pump turbine runner

It is currently in the period of high-speed construction of pumped storage projects. However, the problems caused by vibration of pump turbine units, especially the runners, are very serious. It is of great significance to study the dynamic characteristics of pump turbine runner for the safety and stability of power station. In this paper, the natural modes of a pump turbine runner in the air and in the flow channels are calculated by numerical method. The influence and mechanism of the outer edge modification on the natural frequencies of the runner are studied. The results show that, for the object studied in this paper, the frequency of most modes will be decreased by thickening the outer edge. The frequency change can be attributed to two aspects, one is the change of the mass and the stiffness of the runner, and the other is the change of added mass of the water. Furthermore, the main mechanism of outer edge modification affecting the added mass coefficient is that the height of the radial clearance is changed.

Toughening Mechanism of Thermal Barrier Coatings

Thermal barrier coatings are applied to the protection of metal components in aircraft thrusters, power generation and ship gas turbine engines, which can make the gas turbine run for a long time in a high-temperature environment. The fracture toughness of the coating characterizes the ability of the material to prevent crack propagation and is one of the most important factors to be taken into consideration to prolong the life of the thermal barrier coating. The current research is mainly through dispersion toughening, the phase transformation toughening, whisker toughening, ferroelastic toughening, and other methods to improve the fracture toughness of ceramic coatings. In this paper, the use of different toughening mechanisms and the addition of unique materials to improve the fracture toughness of thermal barrier coatings are introduced, and the future research direction is put forward.

Rainflow-counting matrix interpolation over different operating conditions for hydroelectric turbine fatigue assessment

The measurement of stress/strain on blade plays an essential role in the fatigue assessment of the hydroelectric turbine runner. However, a typical measurement campaign does not cover all the possible operating conditions due to the field measurement requirements and limitations, which leads to fatigue evaluation missing for unmeasured conditions. In this paper, kriging interpolation method is used to estimate the missing fatigue information based on the available measured operating conditions of the turbine. The rainflow counting matrix, which contains the fatigue cycles of strain signal, is considered as the input of the interpolation process. For validation, the fatigue cycles are randomly generated, using bivariate Gaussian distributions, from the interpolated matrix for comparison with the experimental values under similar operating conditions. The developed approach will help plan experimental campaign and might contribute to decreasing the measurement requirements for runner fatigue assessment.