Academic literature on the topic 'Francis-Turbine'

Sediment erosion in Francis turbines is a big problem in hydropower plants in and around the Himalayas. The sediment composition in the rivers contains high levels of the hard mineral quarts. When the sediments enter the turbine they cause erosive damage to exposed parts such as covers, guide vanes and runner. The sediment concentration is at its highest during the monsoon period. During this period some turbines are stopped when the sediment consentration reaches certain levels to reduce the damage. Jhimruk power plant in the mid-western part of Nepal is a good example of how the sediment erosion affects the operation of a power plant. During the monsoon period the turbines can be eroded to an almost unrepairable state. The turbines have to go through substantial annually maintenance. A result of this is reduced power output and high maintenance costs. It is therefore of interest to design a new Francis turbine that can better withstand the sediment erosion. A cooperation project between Kathmandu University and The Norwegian University of Science and Technology was started as a part of the RenewableNepal project which aims to develop and start manufacturing of erosion resistant Francis turbines.A parameter study of different blade designs have been performed to find a more erosion resistant design. In this thesis FSI analyses have been performed on three different designs to verify their structural integrity. The designs transfers the hydraulic energy from the water to the blade in different sections. The results showed a stress distribution which coincided with the energy transfer along the blade. The reference design was analyzed with two different blade thickness. For all the designs the stress was relatively low compared to the criteria for hydraulic turbines.

Devant le nombre de degré de liberté disponible dans le choix d'une nouvelle conception d'une turbomachine ou dans l'amélioration d'une machine existante. Il est aujourd'hui nécessaire de développer des techniques de conception et d'optimisation à base d'outils mathématiques permettant l'intégration efficace des méthodes et outils développées dans le dimensionnement et l'analyse des écoulements internes. Ces techniques permettent alors la recherche des meilleurs compromis conduisant à une conception optimisée. Mon travail recherche m'a permis de mettre au point une technique de tracé et d'optimisation de la géométrie des turbines FRANCIS. Cette technique est basée sur une paramétrisation géométrique de tous les éléments de la turbine (bâche avant-distributeur, directrices, roue et aspirateur). L'écoulement est ensuite estimé avec des logiciels de CFD et une fonction objectif définie à partir des performances recherchée pour la machine est évaluée à partir de l'écoulement calculé. Cette fonction objectif est donc une fonction non linéaire des paramètres qui ont servis à paramétriser la géométrie. Son optimisation est alors possible en utilisant, par exemple des algorithmes génétiques. Pour mettre en œuvre une telle optimisation, il est nécessaire d'automatiser l'ensemble du processus grâce à des scripts informatiques, pour construire la géométrie de la turbine à partir des paramètres, puis un maillage robuste des domaines de calcul. Le calcul CFD, avec le post-processing qui permet d'estimer la fonction objectif, sont ensuite exécutés automatiquement pour compléter un cycle de calcul. J'ai mis au point une telle technique d'optimisation pour toute la partie "haute pression" de la turbine. Pour la roue, une technique "manuelle" d'optimisation, beaucoup plus rapide que l'automatique, a été utilisée (5 à 10 itérations à comparer avec 150 à 200 calculs pour la méthode automatique)<br>Because of the higher number of parameters available in the choice of a new design of a turbomachinery or in the improvement of an existing machine. It is today necessary to develop techniques of design and optimization based on mathematical tools allowing the effective integration of the methods and tools developed in dimensioning and in the analysis of the internal flows. These techniques then allow the research of the best compromises leading to an optimized design. My research work enabled me to develop a technique of design and optimization of FRANCIS turbines. This technique is based on a geometry parameterization of ail the elements of the turbine (Spiral-Casing, distributor, runner and draft tube). The flow is then estimated with software of CFD and a function objective defined starting from the performances sought for the machine is evaluated starting from the calculated flow. This function objective is thus a nonlinear function of the parameters which were used for geometry parametrization. Its optimization is then possible while using, for example genetic algorithms. To make an optimization, it is necessary to automate the whole of the process thanks to data-processing scripts, to build the geometry of the turbine starting from the parameters, with a robust grid for the domain calculations, Then Calculation CFD, with the postprocessing which makes it possible to estimate the function objective, are then carried out automatically to supplement a cycle of calculation. I developed such a technique of optimization for ail the part "high pressure" of the turbine. For the runner, a "manual" technique of optimization, much faster than the automatic, was used (5 to 10 iterations to be compared with 150 to 200 calculations for the automatic method). This technique was tested successfully for two examples of turbine Francis, one at slow specific speed (nq=48), the other rapid (nq=81)

Sediment erosion is a large problem for turbines operated in sand laden water, especially in the Himalayas and the Andes Mountains, where the contents of hard minerals in the rivers are high. A program called &lt;i&gt;RenewableNepal&lt;/i&gt; supports the development of a new design philosophy for hydraulic turbines. NTNU and Kathmandu University cooperate within this program, and this master thesis is part of that cooperation.The objective of this thesis is to carry out the hydraulic design of a Francis turbine with reduced velocities. As part of that, a design software has been developed, using Matlab as programming tool. This software has been used to generate a reference design with the same physical dimensions as for the existing runners at Jhimruk Hydrorelectric Centre in Nepal. CFD analysis has been performed to verify the design software output, showing good results. Analysis of erosion from CFD were not successful as mesh independency for the analysis could not be established. Hence results for erosion prediction from CFD studies has not been presented in this thesis.A parametric study has been carried out, varying either the outlet diameter, the number of pole pairs, the inlet velocity, the acceleration of the flow through the runner, the height of the shroud or the blade angle distribution. An erosion model was implemented in the design software, and used as a control variable for the parametric study. CFD analyses using Ansys CFX were performed for selected designs with lower erosion than the reference design. The largest reduction of erosion was obtained when increasing the number of pole pairs, which implies that the rotational speed of the turbine is decreased. This does however increase the size of both the turbine and the generator, which cause increased investment costs as well. CFD analysis shows that the hydraulic efficiency for this design is higher than for the reference design. It was also discovered that by changing the blade angle distribution, and consequently also the energy distribution, a substantial reduction of erosion was possible without changing the physical dimensions or the rotational speed of the turbine. The efficiency for this design is also higher than for the reference design. The most promising design was found as a combination of these two effects, giving a reduction of the erosion of 50 percent compared to the reference design. CFD analysis for this design show a good efficiency and acceptable flow conditions in the runner. This and other designs with the modified blade angle distribution will have an unconventional energy conversion through the runner, leading to larger hydraulic forces on the trailing edge of the blades. Strength analyses of the blade would be beneficial, but have not been performed.The main focus in this thesis has been on developing the design software and developing runner designs for reducing sediment erosion. There have been no attempts for optimizing the designs of the guide vanes and stay vanes due to time constraints.

High concentrations of sediments is a serious problem for hydropower stations in the Himalayas and the Andes Mountains. For run-of-river power plants sediment causes heavy erosion even with settling basins. This leads to reduced operating hours and high maintenance cost. In addition, the original design experienced problem with heavy cavitation.The objective of this master thesis is to carry out new hydraulic design of the runner and guide vanes of the existing Francis turbines in La Higuera Power Plant with reduced velocity components. To achieve this the cause of the heavy cavitation, which made the turbine fail, has to be established.Results from numerical simulations indicates a low pressure zone causing heavy leading edge cavitation is the reason for the turbine failure. The off-design operation has made the cavitation even worse.To carry out a new design, the in-house design software Khoj was used. Some new parameters, like blade leaning, were included in the program. Blade leaning is an important tool for pressure balancing the runner blade. Further, a parameter study was carried out to investigate the effect of blade leaning, blade angle distribution and blade length. The numerical simulation indicates proper pressure balancing could have avoided the cavitation problems and a new design should have an X-blade shape. Because the power plant is already built, the number of variables is limited. The rotational speed, inlet and outlet diameter remained constant. This made it impossible to significantly reduce the relative velocities. Therefore, coating of all wet surfaces is proposed to reduce the effect of erosion.The main objective for this thesis has been to identify the cause of the turbine failure and develop a new design to fit in the existing power plant. Complete 3D-drawings of the design, including runner and guide vanes, has not been made due to lack of time.

Sediment erosion is one of the key challenges in hydraulic turbines from a design and maintenanceperspective in Himalayas and Andes. Past research works have shown that the optimization of theFrancis turbine runner blade shapes can decrease erosion by a signicant amount. This study conductedas a Master's Thesis has taken the proposed designs from past works and conducted a CFDanalysis on a single passage of a Francis runner blade to choose an optimized design in terms of erosionand eciency. Structural analyses have been performed on the selected design through one-way andtwo-way FSI to compare the structural integrity of the designs.Two types of cases have been considered in this thesis work to dene the boundary condition of thestructural model. In the rst case, a runner blade is considered to have no in uence of the joint andother stier components. In the second case, a sector of the whole runner has been modeled withnecessary boundary conditions. Both one-way and two-way FSI have been performed on the casesfor the designs. Mesh independent studies have been performed for the designs, but only for the rstcase, whereas in the second case, a ne mesh has been used to make the analysis appropriate.The loads have been imported into the structural domain from the uid on the interfaces for one-wayFSI. In the case of two-way FSI, the Multi-Field Solver (MFX) supported by ANSYS has been usedto solve the coupled eld analysis. A fully coupled FSI in ANSYS works by writing an input le inthe structural solver containing the information about the interfaces in the structural domain, whichis imported in the uid solver. The interaction between the two domains is dened in ANSYS-CFX,including the mesh deformation and solver setups. The results have been post-processed in CFX-Post,where the results from both the elds are included. It has been found that the structural integrity ofthe optimized design is better than the reference design in terms of the maximum stress induced inthe runner. The two-way FSI analysis has been found as an inevitable part of the numerical analysis.However, with the advancement of the computational capability in the future, there could be a greatscope in the research eld to carry out a fully-coupled transient simulation for the whole runner toget a more accurate solution.

Francis type turbines are commonly used in hydropower generation. Main components of the turbine are spiral case, stay vanes, guide vanes, turbine runner and the draft tube. The dimensions of these parts are dependent mainly on the design discharge, head and the speed of the rotor of the generators. In this study, a methodology is developed for parametric optimization by incorporating Matlab codes developed and commercial Computational Fluid Dynamics (CFD) codes into the design process. The design process starts with the selection of initial dimensions from experience curves, iterates to improve the overall hydraulic efficiency and obtain the detailed description of the final geometry for manufacturing with complete visualization of the computed flow field. A Francis turbine designed by the procedure developed has been manufactured and installed for energy production.

Start and stop procedures affect pressure oscillations throughout a hydropower plant. A desire to study how pressure oscillations behave during these dynamic conditions was the basis of this report. Instrumentation, experimentation and measurement analysis was conducted on a Francis model turbine in the Waterpower Laboratory at NTNU. Eight pressure transducers were calibrated and used during the experiments. Two transducers were installed in the draft tube below the turbine. One was placed in the vaneless space between the guide vanes and the impeller vanes. Three pressure transducers on an impeller vane and two transducers located at the inlet were also included in the experiments. Frequency analysis (PSD) was carried out for all the measurements to explore various pressure oscillations. Except for the low frequent oscillations (&lt; 30 Hz), definite frequencies repeatedly dominated the frequency domain during start/stop as well as for steady state operation. The impeller vane oscillation showed an increase in pressure amplitude during guide vane closing. A bigger amplitude increase was registered for BEP than for part load and full load operation. The guide vane frequency was located in and only in the runner. The amplitude of the guide vane frequency was significant and was located for all studied operational points. The power of this oscillation decreased during guide vane closing. One specific frequency arose the question of an overtone phenomenon for the water hammer oscillation, a phenomenon, were the fundamental frequency is three times higher than the customary water hammer frequency.

<p>This Master Thesis is about the sand erosion challenges with the Francis turbines. The background for studying this subject is the fact that the sand erosion problem is a very negative factor for the development of new hydro electric power plants in many developing countries. The target with this Master Thesis has been to develop a new design, a revised version of the Francis turbine, reducing the sand erosion by 30- 50 per cent compared with today´s version of turbines. The present version of Francis turbines is consisting of three different vane cascades, The stay, guide and runner cascade. The sand erosion is in proportion with the relative speed between the sand particles and the steel cubed. This challenge has thus been analyzed and solved by reducing this speed through the turbine. Regarding the stay vanes, a new design has been proposed where the stay vanes are pressing the spiral casing from outside and not from the inside. This will result in the fact that the whole sand erosion problem has been removed. It has been proposed to remove the the guide vane cascade. This will consequently remove the sand erosion problem here as well. A favourable solution is to increase the reaction degree. For the runner a study of four different parameters has been carried out. These parameters were the number of pole pair in the generator, outlet angle, reaction degree and UCu distribution. The analysis shows that a reduction of sand erosion at the runner outlet was possible by selecting a higher number of pole pair along with a higher outlet angle than what is standard practice today. This result is of high significant importance since the sand erosion is biggest at the runner outlet. A change in the reaction degree may enable the erosion at the inlet of the runner, whereas a change in the UcU will change the erosion between the inlet and outlet. By selecting favourable parameter values, a substantial reduction of sand erosion in a Francis turbine will be possible. The turbines in this Master thesis have been designed in the computer program Matlab. A proposal for new design based upon the results of the parameter study has been analyzed in a CDF analysis. This analysis has been made in Ansys CFX.</p>