Recherche

Decaix Jean

Adjoint-e scientifique HES A

Compétences principales

Modélisation de réseau hydraulique

Adjoint-e scientifique HES A

Téléphone: +41 58 606 86 44

Bureau: ENP.23.N113

HES-SO Valais-Wallis - Haute Ecole d'Ingénierie
Rue de l'Industrie 23, 1950 Sion, CH

Domaine
Technique et IT

Filière principale
Energie et techniques environnementales

Jean Decaix a obtenu son diplôme d’ingénieur en Energie et Production de l’Ecole Grenoble INP en 2009. En 2012, il a obtenu le titre de docteur en Mécaniques des Fluides, Procédés et Energétiques de l’Université de Grenoble suite à la réalisation d’une thèse en simulation numérique de la cavitation au sein du Laboratoire des Ecoulements Géophysique et Industriels. En 2012, il rejoint comme post-doctorant à la Haute Ecole Spécialisé de Suisse Occidentale (HES-SO) Valais-Wallis avec pour activité principale la simulation numérique dans les turbines hydrauliques. Depuis 2016, il occupe le poste d'adjoint scientifique avec comme activité principale la simulation numériques des fluides appliquée des écoulements dans les centrales hydroélectriques. Il participe également à l'enseignement du module méthodes numériques au niveau bachelor.

BSc HES-SO en Energie et techniques environnementales - HES-SO Valais-Wallis - Haute Ecole d'Ingénierie

méthodes numériques

Terminés

SCCER 4 WP 3.2.0 2017-2020 - Supply of Electricity - Contrat CTI 1155002546

AGP

Rôle: Collaborateur/trice

Financement: HES-SO Rectorat; VS - Institut Systèmes industriels; CTI

Description du projet : The Swiss Competence Center on Supply of Electricity (SCCER-SoE) has been established in November 2013 to develop fundamental research and innovative solutions in the domains of GeoEnergies (Deep Geothermal Energy and CO2 sequestration) and HydroPower. In its first two years of implementation, SCCER-SoE has built a true national competence center, with research and cooperation partners from the ETH schools and research centers, six Universities, three UAS, key industry partners, federal offices and services. The SCCER-SoE focus has been on sustainable competence expansion, by establishing new professorships and research positions, on international cooperation, on building new technology platforms, laboratories and testing facilities, on working with industry to design 10-year roadmaps for Deep-Geothermal Energy, Carbon Capture and Sequestration and Hydro-power, aiming at delivering substantial progress towards meeting the challenges of the Energy Strategy 2050. In Phase II, 2017-2020, the SCCER-SoE will continue with the implementation of the innovation roadmaps, the development of integrative solutions, testing and installation of innovative technologies, technology assessment and scenario modelling. It will expand the focus on pilot and demonstration projects, conducted with industry partners, to validate the technologies and proposed solutions; seven pilot and demonstration projects will be pursued in Phase II, covering the whole portfolio of technologies and energy sources of SCCER-SoE.

, , , , , , , , , , , , , , , , , , , , , Equipe de recherche au sein de la HES-SO: Steiner Amandus Walpen Olivier Vaccari Aldo Münch-Alligné Cécile Gallay Steve Gaspoz Anthony Roger Francis Biner Daniel Hasmatuchi Vlad Constantin Decaix Jean Cachelin Christian Pierre Berthouzoz David Chiarelli Maxime Schmid Jérémy Pettinaroli Damien Rapillard Laurent Grand Pascal Pedroni François Luginbühl Flavio Pacot Olivier Clivaz Cédric Mabillard Eric Pignat Marc

Durée du projet: 01.01.2017 - 31.12.2020

Montant global du projet: 1'104'000 CHF

Statut: Terminé

SOLUTION DE TRANSFERT D'ENERGIE PAR POMPAGE-TURBINAGE A PETITE ECHELLE

AGP

Rôle: Collaborateur/trice

Requérant(e)s: VS - Institut Systèmes industriels

Financement: SIG - Services industriels de Genève

Description du projet : Actuellement, les projets de pompage-turbinage concernent principalement des aménagements à l'échelle nationale, voire internationale. Ces dernières années, des études ont par ailleurs été lancées sur des installations à caractère plus régional avec toutefois un positionnement économique sur un marché national, voire international. La présente proposition permet d'aborder l'échelon local. En effet, le projet proposé prévoit d'évaluer le potentiel technique et économique du pompage-turbinage de petite puissance (de l'ordre de 1MW) au niveau du réseau moyenne et basse tension en Suisse. L'objectif de ce projet est de répondre aux questions suivantes: ' Quel est le potentiel hydraulique Suisse pour l'installation d'un système de pompage-turbinage à petite échelle ? ' Quel modèle économique faut-il développer pour valoriser ce potentiel ? ' Quel type de technologie est approprié pour valoriser ce potentiel ? Les principaux résultats attendus sont : ' Développer et mettre à disposition un outil méthodologique d'analyse du potentiel technique et économique d'un site en Suisse basé sur des cas d'études. ' Valider le fonctionnement réversible d'une turbine Diagonale à double réglage.

Equipe de recherche au sein de la HES-SO: Martignoni Shadya , Münch-Alligné Cécile , Decaix Jean , Grand Pascal

Partenaires académiques: VS - Institut Systèmes industriels; Mhylab

Durée du projet: 01.07.2015 - 30.06.2017

Montant global du projet: 150'000 CHF

Statut: Terminé

2023

Quels défis pour les turbines Pelton ? :

Article professionnel ArODES

prédire leur comportement face à la demande accrue de flexibilité

Mathieu Mettille, Maxime Chiarelli, Jean Decaix, Samuel Rey-Mermet, Cécile Münch-Alligné

bulletin.ch = Fachzeitschrift und Verbandsinformationen von Electrosuisse und VSE = Bulletin SEV/AES : revue spécialisée et informations des associations Electrosuisse et AES,

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Résumé:

En Suisse, plus de 65 % des centrales haute chute sont équipées de turbines Pelton. Plusieurs projets de recherche en cours évaluent des méthodes de prédiction et de surveillance de leur comportement grâce aux simulations numériques ainsi qu’aux essais sur site et en laboratoire.

2022

Geometry, mesh and numerical scheme influencing the simulation of a Pelton jet with the OpenFOAM toolbox

Article scientifique ArODES

Jean Decaix, Cécile Münch-Alligné

Energies,

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Résumé:

Hydropower is a key source of electricity production for allowing the integration of intermittent renewable energy resources. Among the various hydraulic power plants around the world, the ones equipped with Pelton turbines already provide large flexibility that is still enhanced with the development, for instance, of the hydraulic short circuit operating mode. However, the knowledge of the flow inside Pelton turbines is still a challenging task, both numerically and experimentally, despite progress in the last two decades. One key feature of the Pelton efficiency is the jet quality, i.e., the jet velocity needs to be uniform, not perturbed by secondary flows and compact. The compactness of the jet is mainly dependent o nthe location of the jet detachment at the nozzle outlet, which is challenging for computational fluid dynamics simulations mainly due to numerical diffusion. Even if this point has already been mentioned in previous papers, the present paper focuses on all the parameters that can influence the jet detachment: the nozzle geometry, the mesh and the numerical scheme used to discretize the convective fluxes. The simulations of an existing Pelton injector are performed using the OpenFOAM toolbox. It is noticed that, in addition to the nozzle geometry and the mesh resolution at the nozzle outlet, the choice of the numerical schemes influences the jet detachment and, consequently, the jet diameter and discharge. The use of an anti-diffusive scheme such as the “SUPERBEE” limiter improves the prediction of the jet in accordance with the on-site measurements.

Dénoyer une galerie en charge pour améliorer la flexibilité d’une centrale hydroélectrique

Article scientifique ArODES

Jean Decaix, Anthony Gaspoz, Vlad Hasmatuchi, Matthieu Dreyer, Christophe Nicolet, Steve Crettenand, Cécile Münch-Alligné

LHB, 2022

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Résumé:

Le développement des nouvelles sources d’énergie renouvelable de nature intermittente nécessite de disposer de sources d’énergie flexibles également d’origine renouvelable afin de garantir la stabilité du réseau électrique et les engagements environnementaux. Dans le cadre du projet pilote et démonstrateur « SmallFlex », l’augmentation de la flexibilité d’une petite centrale hydroélectrique au fil de l’eau, équipée de deux turbines Pelton, a été étudiée. La particularité de cette centrale haute chute d’une puissance installée de 14 MW est l’absence d’une retenue d’eau en amont réduisant la capacité de réglage qui se limite à la prédiction du débit d’apport. Pour accroître la flexibilité de cette centrale un volume de stockage comprenant le dessableur, la chambre de mise en charge et la partie supérieure de la galerie a été identifié. La présente étude se concentre sur la possibilité technique d’utiliser ce volume à l’aide d’études analytiques, d’essais sur modèle réduit et de mesures sur site. En complément, des simulations numériques 1D ont permis de définir la plage de réglage primaire envisageable en considérant ce volume supplémentaire. Enfin, l’analyse économique montre la possibilité d’augmenter la production hivernale et de proposer un service de réglage primaire toute l’année grâce à ce volume de stockage supplémentaire.

Plus de flexibilité grâce aux simulations :

Article professionnel ArODES

évaluations du court-circuit hydraulique et de la vitesse variable

Daniel Biner, Olivier Pacot, Jean Decaix, Cécile Münch-Alligné

bulletin.ch = Fachzeitschrift und Verbandsinformationen von Electrosuisse und VSE = Bulletin SEV/AES : revue spécialisée et informations des associations Electrosuisse et AES, 2022, vol. 2, pp. 68-72

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Résumé:

Pour garantir la stabilité du futur réseau électrique, les centrales hydroélectriques devront être très flexibles. À l'aide de simulations numériques, le projet Xflex Hydro évalue le fonctionnement de centrales de pompage-turbinage en court-circuit hydraulique ainsi que l'utilisation des turbines à vitesse variable avant démonstration sur site.

2021

Development of a freely distributable CFD tool for approximate and detailed simulations of the flow around a complex of buildings

Article scientifique ArODES

Jean Decaix, Pierre Jaboyedoff, Gregory Duthé, Elisa El Sergany, Loris Aiulfi

Journal of Physics: Conference Series, 2021, vol. 2042, article no. 012069

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Résumé:

Indo-Swiss Building Energy Efficiency Project (BEEP) is a cooperation project between the Ministry of Power, Government of India, and the Federal Department of Foreign Affairs of the Swiss Confederation. Started in 2011, the project's central focus is to help India mainstream Energy-Efficient and Thermally Comfortable (EETC) Building Design. BEEP works with building industry, policy makers, and building owners to catalyse adoption of EETC building design and technologies. India wants to avoid or reduce the use of air conditioning by improving natural ventilation at night, which requires numerical simulations to compute the flow around the buildings. However, the simulations of fluid flows are time consuming and are not used at the beginning of a project when the locations of the buildings are set. To improve the situation, a freely distributable environment based on the OpenFOAM toolbox has been developed providing two levels of resolution: an approximate level computing the flow in few minutes and a RANS level of simulation. The user inputs are limited to the geometry and the velocity direction and magnitude. The mesh and the numerical set up are automated. The accuracy of the two levels of resolution have been checked by computing test cases from the CEDVAL database.

Augmenter la flexibilité de l’hydroélectricité :

Article professionnel ArODES

diagnostic de la fatigue prématurée des turbines

Vlad Hasmatuchi, Jean Decaix, Maximilian Titzschkau, Cécile Münch-Alligné

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Résumé:

Dans le contexte récent d’exploitation des réseaux électriques, la nécessité d’augmenter la flexibilité des centrales hydroélectriques peut induire une fatigue prématurée sur certains composants. Une étude menée sur une turbine Francis de 100 MW a permis d’élaborer un protocole de diagnostic grâce à des mesures sur site et des simulations numériques.

Investigation of the time resolution set up used to compute the full load vortex rope in a Francis turbine

Article scientifique ArODES

Jean Decaix, Andreas Müller, Arthur Favrel, François Avellan, Cécile Münch-Alligné

Applied Sciences, 2021, vol. 11, no. 3, article no. 1168

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Résumé:

The flow in a Francis turbine at full load is characterised by the development of an axial vortex rope in the draft tube. The vortex rope often promotes cavitation if the turbine is operated at a sufficiently low Thoma number. Furthermore, the vortex rope can evolve from a stable to an unstable behaviour. For CFD, such a flow is a challenge since it requires solving an unsteady cavitating flow including rotor/stator interfaces. Usually, the numerical investigations focus on the cavitation model or the turbulence model. In the present works, attention is paid to the strategy used for the time integration. The vortex rope considered is an unstable cavitating one that develops downstream the runner. The vortex rope shows a periodic behaviour characterized by the development of the vortex rope followed by a strong collapse leading to the shedding of bubbles from the runner area. Three unsteady RANS simulations are performed using the ANSYS CFX 17.2 software. The turbulence and cavitation models are, respectively, the SST and Zwart models. Regarding the time integration, a second order backward scheme is used excepted for the transport equation for the liquid volume fraction, for which a first order backward scheme is used. The simulations differ by the time step and the number of internal loops per time step. One simulation is carried out with a time step equal to one degree of revolution per time step and five internal loops. A second simulation used the same time step but 15 internal loops. The third simulations used three internal loops and an adaptive time step computed based on a maximum CFL lower than 2. The results show an influence of the time integration strategy on the cavitation volume time history both in the runner and in the draft tube with a risk of divergence of the solution if a standard set up is used.

Production flexibility of small run-of-river power plants: KWGO smart-storage case study

Article scientifique

Münch-Alligné Cécile, Decaix Jean, Gaspoz Anthony Roger Francis, Hasmatuchi Vlad Constantin, Matthieu Dreyer, Christophe Nicolet, Alimirzazadeh Siamak, Jessica Zordan, Pedro Manso, Steve Crettenand

IOP Conference Series: Earth and Environmental Science, 2021 , vol. 774, no 1

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Numerical simulations of Pelton turbine flow to predict large head variation influence

Article scientifique

Alimirzazadeh Siamak, Decaix Jean, François Avellan, Steve Crettenand, Münch-Alligné Cécile

IOP Conference Series: Earth and Environmental Science, 2021 , vol. 774, no 1

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CFD simulations of a Y-junction for the implementation of hydraulic short-circuit operating mode

Article scientifique

Decaix Jean, Biner Daniel, Jean-Louis Drommi, François Avellan, Münch-Alligné Cécile

IOP Conference Series: Earth and Environmental Science, 2021 , vol. 774, no 1

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Identification of 1-D cavitation model parameters by means of computational fluid dynamics

Article scientifique

Decaix Jean, Sébastien Alligné, Andrés Mueller, Christophe Nicolet, Münch-Alligné Cécile, François Avellan

Journal of Hydraulic Research, 2021 , pp. 1-12

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Enhanced Operational Flexibility of a Small Run-of-River Hydropower Plant

Article scientifique

Decaix Jean, Gaspoz Anthony Roger Francis, Hasmatuchi Vlad Constantin, Matthieu Dreyer, Christophe Nicolet, Steve Crettenand, Münch-Alligné Cécile

Water, 2021 , vol. 13, no 14, pp. 1897-1897

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Development of a freely distributable CFD tool for approximate and detailed simulations of the flow around a complex of buildings

Article scientifique

Decaix Jean, Pierre Jaboyedoff, Grégory Duthé, Elisa El Sergany, Loris Aiulfi

Journal of Physics: Conference Series, 2021 , vol. 2042, no 1

Lien vers la publication

Résumé:

Indo-Swiss Building Energy Efficiency Project (BEEP) is a cooperation project
between the Ministry of Power, Government of India, and the Federal Department of Foreign
Affairs of the Swiss Confederation. Started in 2011, the project’s central focus is to help India
mainstream Energy-Efficient and Thermally Comfortable (EETC) Building Design. BEEP
works with building industry, policy makers, and building owners to catalyse adoption of EETC
building design and technologies. India wants to avoid or reduce the use of air conditioning by
improving natural ventilation at night, which requires numerical simulations to compute the flow
around the buildings. However, the simulations of fluid flows are time consuming and are not
used at the beginning of a project when the locations of the buildings are set. To improve the
situation, a freely distributable environment based on the OpenFOAM toolbox has been
developed providing two levels of resolution: an approximate level computing the flow in few
minutes and a RANS level of simulation. The user inputs are limited to the geometry and the
velocity direction and magnitude. The mesh and the numerical set up are automated. The
accuracy of the two levels of resolution have been checked by computing test cases from the
CEDVAL database.

2019

Hydro-structural stability investigation of a 100 MW Francis turbine based on experimental tests and numerical simulations

Article scientifique ArODES

Jean Decaix, Vlad Hasmatuchi, Maximilian Titzschkau, Laurent Rapillard, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science, 2019, vol. 405, article no. 012006

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Résumé:

This work focuses on a 100 MW Francis turbine prototype, part of one of the four horizontal ternary groups of Grimsel 2 PSPP, in Switzerland. Due to the massive integration of new renewable energy, the number of daily starts/stops of the machines has increased. Consequently, cracks on the runner blades of the Francis turbines have been noticed, without a clear explanation regarding the phenomenon responsible for their onset. To identify the main stress-full operating condition causing these cracks, the full turbine hill chart has been covered during the in situ measurement campaign including start-up, speed no-load, deep part load, best efficiency, full load and shut-down operating conditions. Then hydro-structural stability diagnosis diagrams of the prototype have been established for the whole operating range of the turbine. In addition, CFD numerical simulations for different operating conditions, along with FEM structural and modal analysis of the runner, have been carried out. The onboard measurements evidenced the highest mechanical stresses on the runner blades at speed no-load operating condition. This conclusion is supported by CFD and FEM analysis, which put in evidence the possible excitation of one of the runner's eigen frequency by the fluctuations of the pressure field.

Numerical investigation of solutions to suppress the inlet vortex of an existing booster pump

Article scientifique ArODES

Jean Decaix, Anthony Gaspoz, D. Fischer, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science, 2019, vol. 405, article no. 012036

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Résumé:

The study focuses on a booster pump used to feed the main pump of one unit of the FMHL hydropower plant (Veytaux I). From the beginning of the operation of the power plant, vibrations have been observed on this booster pump with sometimes the presence of cavitation erosion. The visualisations carried out show that a cavitating vortex develops at the suction side of the booster pump runner and causes the measured vibrations. The booster pump is running without any modification since the beginning of the operation of the power plant, however future mechanical failures cannot be excluded, since in these harsh conditions, the permissible mechanical strain shall be exceeded. Flow numerical investigations have been carried out using OpenFOAM and shown the presence of vortices below the bell of the booster pump. The main vortex observed is assumed to be responsible for the vibrations due to its interaction with the runner blades and to promote the inception of cavitation, which could explain the cavitation erosion observed. Several modifications of the chamber have been considered by simulation. Two of them provide a solution to suppress or at least to damp the vibrations due to the presence of vortices in the bell inlet.

On-board measurements at a 100 MW high-head Francis turbine

Article scientifique ArODES

Maximilian Ttizschkau, Vlad Hasmatuchi, Jean Decaix, Cécile Münch-Alligné

Wasserwirtschaft, 2019, no. 1

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Résumé:

Modern sources of energy, like solar and wind, force hydropower machines to change their operational behaviour. Rapid changes in the availability of renewable energies lead to instabilities in the grid, which need to be stabilized by flexible machine operation (Lowys et al. [1]). This leads to a significant change in hydropower operations, e.g. to an increasing number of start-stop events (Seidel et al. [2], Robert et al. [3], Coutu and Chamberland-Lauzon [4]). The four ternary machine groups at the Grimsel 2 power plant have been designed under completely different circumstances in the late 1970's and are suffering from this change in operation. After only 35'000 hrs of operation all runners show fatigue cracks at the trailing edges close to the hub which needed to be repaired effortful. As a part of these repairs, the chamfer between the blade and the hub was increased from about 5 mm to 12 mm with local welding and heat treatment to reduce stresses. Apparently, this seems to work out fine but, since the source of the damage was not detected, this situation was not satisfying for the plant owner. The turbines were running at smooth conditions most of the time. Since deep part load could be eliminated as a source of those cracks, it was assumed that either start-up, shutdown or some unknown phenomena lead to the cracks. From recent literature (Gagnon et al. [5] & [6]), it is assumed that the start-up process can be responsible for the observed kind of cracks. To get more information, extensive measurements have been performed on the Group 2 of the power plant. The overall goal of this research is to advice the plant owner concerning the operation of the machines to increase the lifetime of the existing runners.

Cost-effective CFD simulation to predict the performance of a hydrokinetic turbine farm

Article scientifique

Pacot Olivier, Decaix Jean, Münch-Alligné Cécile, Pettinaroli Damien

IOP Conference Series: Earth and Environmental Science, 2019 , vol. 405

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Résumé:

After the performance assessment of a new hydrokinetic turbine prototype in the tailrace channel of a run-of-river power plant (Lavey, CH), the possibility to install a farm of such hydrokinetic turbines on this pilot site is investigated. In order to identify the optimal number and size of the machines as well as their location on this site, numerical simulations are carried out. Such a process requires to simulate a set of several free surface flow computations including different configurations of the farm in order to maximize the energy tapped by the machines. However, free surface flow computations are time and resources consuming. To allow such flow investigations, a different approach has been selected. In the present study, the turbines were replaced by a model mimicking the resistance effect of the machines. This model consists in a pressure drop applied at the turbine location to emulate the disturbance effect on the flow, especially the wake effect that will modify the available kinetic energy for the neighboring machines. Finally, it results that such a low CPU approach allows us to estimate the best location of the hydrokinetic turbines maximizing the energy harvested.

2018

CFD Investigation of a high head Francis turbine at speed no-load using advanced URANS models

Article scientifique ArODES

Jean Decaix, Vlad Hasmatuchi, Maximilian Titzschkau, Cécile Münch-Alligné

Applied Sciences, 2018, vol. 8, no. 12, article no 2505

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Résumé:

Due to the integration of new renewable energies, the electrical grid undergoes instabilities. Hydroelectric power plants are key players for grid control thanks to pumped storage power plants. However, this objective requires extending the operating range of the machines and increasing the number of start-up, stand-by, and shut-down procedures, which reduces the lifespan of the machines. CFD based on standard URANS turbulence modeling is currently able to predict accurately the performances of the hydraulic turbines for operating points close to the Best Efficiency Point (BEP). However, far from the BEP, the standard URANS approach is less efficient to capture the dynamics of 3D flows. The current study focuses on a hydraulic turbine, which has been investigated at the BEP and at the Speed-No-Load (SNL) operating conditions. Several “advanced” URANS models such as the Scale-Adaptive Simulation (SAS) SST k − ω and the BSL- EARSM have been considered and compared with the SST k − ω model. The main conclusion of this study is that, at the SNL operating condition, the prediction of the topology and the dynamics of the flow on the suction side of the runner blade channels close to the trailing edge are influenced by the turbulence model.

RANS computations of a confined cavitating tip-leakage vortex

Article scientifique ArODES

Jean Decaix, Matthieu Dreyer, Guillaume Balarac, Mohamed Frahat, Cécile Münch

European Journal of Mechanics / B Fluids, 2018, 67, pp. 198-210

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Résumé:

Cavitating tip-leakage vortices appear in several hydrodynamic flows such as marine propellers or Kaplan turbines. Cavitating computations are a challenging topic since several keys issues are an ongoing work such as the definition of a universal mass source term. The present study focuses on the computations of the tip-leakage vortex including the gap between the blade tip and the side wall. Two computations are performed, one without cavitation and a second one with cavitation. In both cases, the results are compared with experimental data. The cavitation influence is investigated by comparing the cavitating and the non-cavitating cases. A particular attention is focused on the vortex core trajectory, the vorticity field and the vortex core identification. It is shown that, compared to the non-cavitating case, cavitation leads to a vortex trajectory closer to the suction side and the side wall, which can be of importance regarding the cavitation erosion. Furthermore, cavitation modified the vorticity field in the vortex core region. The main feature is a misalignment between the high vorticity region and the cavitating region, which opens a discussion regarding the definition of the vortex core.

Numerical study of 3D turbulent cavitating flows

Chapitre de livre ArODES

Eric Goncalves, Jean Decaix, B. Charriere

Dans Hoarau, Yannick, Peng, Shia-Hui, Revell, Alistair, Schwamborn, Dieter, Proceedings of Symposium on Hybrid RANS-LES Methods HRLM 2016: Progress in Hybrid RANS-LES Modelling, 26-28 September 2016, Strasbourg, France (pp. 455-464). 2018, Cham : Springer

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Résumé:

A numerical investigation of the behaviour of a 3D cavitation sheet developing along a Venturi geometry has been performed using both a compressible one-fluid RANS solver and a pressure-based solver. The interplay between turbulence and cavitation regarding the unsteadiness and the structure of the flow is complex and not well understood. This constitutes a determinant point to accurately simulate the dynamic of sheet cavities. The mass transfer between phases is driven by a void ratio transport equation model. Turbulence is taken into account using Scale-Adaptive models (SAS). 3D simulations are compared with the experimental data.

2017

URANS models for the simulation of full load pressure surge in Francis turbines validated by particle image velocimetry

Article scientifique ArODES

Jean Decaix, A. Müller, A. Favrel, François Avellan, Cécile Münch-Alligné

Journal of Fluids Engineering, 2017, vol. 139, no. 12, article no. 121103

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Résumé:

Due to the penetration of alternative renewable energies, the stabilization of the electrical power network relies on the off-design operation of turbines and pump-turbines in hydro-power plants. The occurrence of cavitation is however a common phenomenon at such operating conditions, often leading to critical flow instabilities which undercut the grid stabilizing capacity of the power plant. In order to predict and extend the stable operating range of hydraulic machines, a better understanding of the cavitating flows and mainly of the transition between stable and unstable flow regimes is required. In the case of Francis turbines operating at full load, an axisymmetric cavitation vortex rope develops at the runner outlet. The cavity may enter self-oscillation, with violent periodic pressure pulsations. The flow fluctuations lead to dangerous electrical power swings and mechanical vibrations, dictating an inconvenient and costly restriction of the operating range. The present paper reports an extensive numerical and experimental investigation on a reduced scale model of a Francis turbine at full load. For a given operating point, three pressure levels in the draft tube are considered, two of them featuring a stable flow configuration and one of them displaying a self-excited oscillation of the cavitation vortex rope. The velocity field is measured by two-dimensional (2D) particle image velocimetry (PIV) and systematically compared to the results of a simulation based on a homogeneous unsteady Reynolds-averaged Navier–Stokes (URANS) model. The validation of the numerical approach enables a first comprehensive analysis of the flow transition as well as an attempt to explain the onset mechanism.

RANS computations for identification of 1-D cavitation model parameters :

Article scientifique ArODES

application to full load cavitation vortex rope

S. Alligné, Jean Decaix, A. Müller, C. Nicolet, François Avellan, Cécile Münch-Alligné

Journal of Physics: Conference Series, 2017, vol. 813, article no. 012032

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Résumé:

2016

RANS computations for identification of 1-D cavitation model parameters :

Article scientifique ArODES

application to full load cavitation vortex rope

Sébastien Alligné, Jean Decaix, Andrei Müller, Christophe Nicolet, François Avellan, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science, 2016, vol. 49, article no. 082014

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Résumé:

Due to the massive penetration of alternative renewable energies, hydropower is a key energy conversion technology for stabilizing the electrical power network by using hydraulic machines at off design operating conditions. At full load, the axisymmetric cavitation vortex rope developing in Francis turbines acts as an internal source of energy, leading to an instability commonly referred to as selfexcited surge. 1-D models are developed to predict this phenomenon and to define the range of safe operating points for a hydropower plant. These models involve several parameters that have to be calibrated using experimental and numerical data. The present work aims to identify these parameters with URANS computations with a particular focus on the fluid damping rising when the cavitation volume oscillates. Two test cases have been investigated: a cavitation flow in a Venturi geometry without inlet swirl and a reduced scale model of a Francis turbine operating at full load conditions. The cavitation volume oscillation is forced by imposing an unsteady outlet pressure conditions. By varying the frequency of the outlet pressure, the resonance frequency is determined. Then, the pressure amplitude and the resonance frequency are used as two objectives functions for the optimization process aiming to derive the 1-D model parameters.

Computational fluid dynamics as a tool to predict the air pollution dispersion in a neighborhood :

Article scientifique ArODES

a research project to improve the quality of life in cities

Gilles Triscone, Nabil Abdennadher, Christophe Balistreri, Olivier Donzé, D. Greco, Patrick Haas, H. Haas-Pekoz, T. Mohamed-Nour, Pierre Munier, Piero Pontelandolfo, Roberto Putzu, Jacques Richard, H. Sthioul, Nicolas Delley, D. Choffat, Elena-Lavinia Niederhäuser, Roger Schaer, Henning Müller, Jean Decaix, Sylvain Richard, Cécile Münch-Alligné, P. Kunz, F. Despot

International Journal of Sustainable Development and Planning, 2016, vol. 11, no. 4, pp. 546-557

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Résumé:

In large cities, pollution composed of many different chemical components and small particles is an important public health problem that affects especially children and people presenting breathing difficulties. One challenge for public authorities is to respect the norms given by the central state, but how? Today, concrete methods for reducing pollution are perceived by the majority of citizens as constraints. However, the authorities have the possibility of modifying the wind’s action by imposing architectural constraints, such as building emplacement and roof structure. This is the main objective of the Geneva ‘Clean City’ project financed by the University of Applied Sciences Western Switzerland. ‘Clean City’ focuses its research on one of Geneva’s polluted neighborhood called Pâquis, which is situated directly on the Geneva lake front. The project attempts to understand the dispersion of pollution from an experimental and a numerical point of view. After validation of the technique for a simple case, we compare environmental measurements on a 1/500 3D scale model of the Pâquis installed in an instrumented wind tunnel with Computational Fluid Dynamics (CFD) simulation obtained with the help of cloud computing.

2015

RANS computations of tip vortex cavitation

Article scientifique ArODES

Jean Decaix, Guillaume Balarac, Matthieu Dreyer, Mohamed Farhat, Cécile Münch-Alligné

Journal of Physics: Conference Series, 2015, vol. 656, article no. 012183

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Résumé:

The present study is related to the development of the tip vortex cavitation in Kaplan turbines. The investigation is carried out on a simplified test case consisting of a NACA0009 blade with a gap between the blade tip and the side wall. Computations with and without cavitation are performed using a R ANS modelling and a transport equation for the liquid volume fraction. Compared with experimental data, the R ANS computations turn out to be able to capture accurately the development of the tip vortex. The simulations have also highlighted the influence of cavitation on the tip vortex trajectory.

Rans computations of a cavitating tip vortex

Chapitre de livre ArODES

Jean Decaix, Guillaume Balarac, Cécile Münch-Alligné

Dans Caignaert, Guy, Cunge, Jean A., Gourbesville, Philippe, Advances in Hydroinformatics (pp. 519-529). 2015, Singapore : Springer

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Résumé:

The Swiss national research project Hydronet 2 gathers a consortium of industrial and academic partners supported by the Competence Center of Energy and Mobility (CCEM) and Swiss Electric Research (SER) in order to improve the hydropower plants. One of the research topic focuses on the cavitating tip vortex. Such a vortex takes place in axial turbines as Kaplan turbines used for producing hydroelectricity. This phenomenon drives a lot of drawbacks such as erosion, unsteady flow rate and a decrease of the turbine efficiency. To better understand the behaviour of the tip vortex, computations of a simple test case are performed. The test case consists in a NACA profile mounted in a channel with a gap between the NACA tip and the lateral wall. The computations are carried out with the OpenFOAM solver both in one-phase and two-phase flows. The turbulent motion is modelled with a RANS approach. For the two-phase flow computations, the phase change between liquid and vapour is achieved with the model proposed by Kunz. The results will be compared in cavitating and non-cavitating cases with the experimental data provided by the EPFL Laboratory for Hydraulic Machines. The comparisons deal with global picture of the flow, the trajectory of the tip vortex and the velocity field downstream the NACA profile.

A comparative study of cavitation models in a Venturi flow

Article scientifique ArODES

Boris Charrière, Jean Decaix, Eric Goncalvès

European Journal of Mechanics - B/Fluids, 2015, vol. 49, part A, pp. 287-297

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Résumé:

This paper presents a numerical study of an aperiodic cavitation pocket developing in a Venturi flow. The mass transfer between phases is driven by a void ratio transport equation model. A new free-parameter closure relation is proposed and compared with other formulations. The re-entrant jet development, void ratio profiles and pressure fluctuations are analysed to discern results accuracy. Comparisons with available experimental data are done and good agreement is achieved.

2014

Mind the gap :

Article scientifique ArODES

a new insight into the tip leakage vortex using stereo-PIV

Matthieu Dreyer, Jean Decaix, Cécile Münch-Alligné, Mohamed Farhat

Experiments in Fluids, 2014, vol. 55, article no. 1849

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Résumé:

The tip leakage vortex (TLV), which develops in the clearance between the rotor and the stator of axial hydro turbines, has been studied for decades. Yet, many associated phenomena are still not understood. For instance, it remains unclear how the clearance size is related to the occurrence of cavitation in the vortex, which can lead to severe erosion. Experiments are here carried out on the influence of the clearance size on the tip vortex structure in a simplified case study. A NACA0009 hydrofoil is used as a generic blade in a water tunnel while the clearance between the blade tip and the wall is varied. The 3D velocity fields are measured using Stereo Particle Image Velocimetry (SPIV) in three planes located downstream of the hydrofoil for different values of the upstream velocity, the incidence angle and a large number of tip clearances. The influence of the flow conditions on the structure of the TLV is described through changes in the vortex intensity, core axial flow, vortex center position and wandering motion amplitude. Moreover, high-speed visualizations are used to highlight the vortex core trajectory and clearance flow alteration, turning into a wall jet as the tip clearance is reduced. The measurements clearly reveal the existence of a specific tip clearance for which the vortex strength is maximum and most prone to generating cavitation.

RANS and LES computations of the tip-leakage vortex for different gap widths

Article scientifique ArODES

Jean Decaix, Guillaume Balarac, Matthieu Dreyer, Mohamed Farhat, Cécile Münch-Alligné

Journal of Turbulence, 2015, vol. 16, no. 4, pp. 309-341

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Résumé:

In hydraulic turbines, the tip-leakage vortex is responsible for flow instabilities and for promoting erosion due to cavitation. To better understand the tip vortex flow, Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) computations are carried out to simulate the flow around a NACA0009 blade including the gap between the tip and the wall. The main focus of the study is to understand the influence of the gap width on the development of the tip vortex, as for instance its trajectory. The RANS computations are performed using the open source solver OpenFOAM 2.1.0, two incidences and five gaps are considered. The LESs are achieved using the YALES2 solver for one incidence and two gaps. The validation of the results is performed by comparisons with experimental data available downstream the trailing edge. The position of the vortex core, the mean velocity and the mean axial vorticity fields are compared at three different downstream locations. The results show that the mean behaviour of the tip vortex is well captured by the RANS and LES computations compared to the experiment. The LES results are also analysed to bring out the influence of the gap width on the development of the tip-leakage vortex. Finally, a law that matches the vortex trajectory from the leading edge to the mid-chord is proposed. Such a law can be helpful to determine, in case of cavitation, if the tip vortex will interact with the walls and cause erosion.

2022

On-site measurements of the dynamic behaviour of Pelton turbines in the context of predictive maintenance

Conférence ArODES

Maxime Chiarelli, Vlad Hasmatuchi, Ali Amini, Jean Decaix, David Florian Vetsch, Robert M. Boes, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science ; Proceedings of the 31st IAHR Symposium on Hydraulic Machinery and Systems, 26 June-1st July 2022, Trondheim, Norway

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Résumé:

The operating modes of pumped storage power plants, such as that of the Forces Motrices Hongrin-Léman (FMHL) in Switzerland, have drastically changed over the past decades due to the emergence of new renewable energies. The number of starts and stops experienced by machines increased significantly leading to broader fatigue cycles on the different parts of the machine. Therefore, the development of predictive maintenance tools is paramount to increase the availability and reinforce operational safety of the power plant. In this context, vibration measurements were performed on a 60 MW Pelton turbine of one of the ternary units of the FMHL power plant during dynamic and steady state operations. Non intrusive instrumentation has been deployed including accelerometers on the bearing. Comparing the ramp-up and ramp-down of the Pelton turbine, a hysteresis of the vibration level for a similar power has been observed. A reduction of the vibration levels when an additional injector is engaged during the ramp-up is observed. This reduction correlates strongly with the load reduction on the buckets when the total flow rate is distributed over more injectors, leading to a smaller flow rate per injector.

CFD simulations of hydraulic short-circuits in junctions, application to the Grand’Maison power plant

Conférence ArODES

Jean Decaix, Jean-Louis Drommi, François Avellan, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science ; Proceedings of the 31st IAHR Symposium on Hydraulic Machinery and Systems, 26 June-1st July 2022, Trondheim, Norway

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Résumé:

In the framework of the XFLEX HYDRO H2020 European Project, the pumped storage power plant of Grand’Maison (France), owned by Electricit´e De France, focuses on the implementation of the hydraulic short-circuit (HSC) operating mode. This mode increases the flexibility in pumping mode, which helps the integration of intermittent energies. Grand’Maison is divided into two power houses: the first features four Pelton turbine units and the second eight reversible pump-turbines units. A trifurcation splits the flow into three penstocks, each is then split into two branches that feed each power house. The HSC operating mode, which consists in operating the pumps and the Pelton turbines simultaneously, changes the flow paths in the junctions compared to the pump mode. The power plant was not designed to operate in HSC mode over a long duration, therefore an assessment of its feasibility is necessary. 151 computational fluid dynamic simulations are carried out for two bifurcations and one trifurcation. The numerical simulation results show that the local head losses in HSC mode represent less than 1% of the gross head. No flow instabilities are observed at the bifurcations contrary to the trifurcation. Additional analyses are required to better understand the flow in the trifurcation.

2021

Numerical simulations for multipurpose reservoirs for alpine irrigation

Conférence ArODES

Théo Gonin, Jean Decaix, Jérémy Schmid, Alexandre Gillioz, Damien Pettinaroli, Cécile Münch-Alligné

Proceedings of SimHydro 2021: Models for complex and global water issues - practices and expectations, 16-18 June 2021, Sophia Antipolis, France

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Résumé:

In most of the Swiss Alpine regions, the availability of water resources for irrigation is usually adequate, even in period of drought, as evidenced by the summers of 2003 and 2018. Indeed, important natural stocks are for the moment available in the form of snow and ice, but the situation is likely to change in the future considering global and regional climate change. The municipality of Val de Bagnes located in the canton of Valais, Switzerland, is a region where water is a very important economic factor used for hydropower, winter and summer tourism and agriculture. The study will make it possible to apprehend the needs and future availabilities for irrigation water, by 2050 and 2085, and to plan as soon as possible the modifications required to the water supply or distribution networks. This article focuses on the modeling and simulation of future scenarios of the water network. The results are based on the principle of deficit on the water demand compared to the available water in the adduction network. To illustrate the influence of the climate change on these deficits, simulations based on RCP scenarios have been run for years 2050 and 2085. The current network configuration seems to be suitable for the demand and the variability of the input until 2050. Nevertheless, for the 2085 forecasts, the existing network would not be able to match the demand. This study shows that a regional interdisciplinary approach between the technical, agricultural and social fields is necessary to manage water resources in the future even in Alpine regions where no extreme water stress is observed today.

Numerical simulation of the interaction between the jet and a pelton runner under low head

Conférence ArODES

Jean Decaix, Anthony Gaspoz, Steve Crettenand, Cécile Münch-Alligné

Proceedings of SimHydro 2021: Models for complex and global water issues - practices and expectations, 16-18 June 2021, Sophia Antipolis, France

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Résumé:

In Switzerland, during the last decade, the development of the new renewable energies (small hydro, solar, wind…) has been promoted by a specific feed-in tariff. However, the regulator schedules to remove this specific measure to force the producers to match the demand. Regarding the small hydropower plants, this change requires to increase the flexibility of the power plants. The present work focuses on the hydro power plant of Gletsch-Oberwald (KWGO, Valais, Switzerland), a run-of-river power plant equipped with two six-jet Pelton turbines. An extension of the flexibility of the power plant is investigated in the framework of the SmallFlex project by using one-third of the headrace tunnel as a storage volume. The use of this new storage capacity would require emptying the headrace tunnel and to operate the Pelton turbines at a lower head than the one for which they have been designed. By lowering the head, the efficiency of the Pelton turbines will decrease abruptly if the Pelton turbines make faces to the so-called “falaise” effect. Before performing on-site measurements, unsteady two-phase flow simulations of the interaction between the jet and the Pelton runner have been carried out for four different heads with the Ansys CFX software. At the best efficiency point, the efficiency is well predicted by the simulation. For lower heads, the interaction between two consecutive jets is observed but the decrease in efficiency is underestimated compared to the on-site measurements.

Production flexibility of small run-of-river power plants :

Conférence ArODES

KWGO smart-storage case study

Cécile Münch-Alligné, Jean Decaix, Anthony Gaspoz, Vlad Hasmatuchi, Matthieu Dreyer, Christophe Nicolet, Siamak Alimirzazadeh, Jessica Zordan, Pedro Manso, S. Crettenand

IOP Conference Series: Earth and Environmental Science ; Proceedings of 30th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2020) 21-26 March 2021, Lausanne, Switzerland

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Résumé:

In the framework of the new Swiss feed-in-tariff system for Small Hydropower Plants (SHP), the aim of the SmallFLEX project, led by HES-SO Valais and performed in collaboration with EPFL, WSL, EAWAG, PVE and FMV, is to show how SHP can provide winter peak energy and ancillary services, whilst remaining eco-compatible. The pilot and demonstrator site selected is the new SHP of Gletsch-Oberwald (KWGO) owned by FMV and commissioned end of 2017. This run-of-river power plant is equipped with two six-jets Pelton turbine units featuring a maximum power of 7.5 MW each while the average annual power is lower than 5 MW, with a maximum of production during the summer. The capacity of infrastructure, equipment, and other adaptation measures to produce in a flexible way is being assessed while measuring the impact of this new operation on the environment, production and revenues. The paper focuses on the two experimental campaigns and the numerical simulations carried out to assess the flexibility of the power plant by means of smart use of existing infrastructure as additional storage volumes: the settling basin, the forebay and the upper part of the headrace tunnel.

Numerical simulations of Pelton turbine flow to predict large head variation influence

Conférence ArODES

Siamak Alimirzazadeh, Jean Decaix, François Avellan, S. Crettenand, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science ; Proceedings of 30th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2020), 21-26 March 2021, Lausanne, Switzerland

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Résumé:

In the framework of the new feed-in-tariff system in Switzerland for Small Hydropower Plants (SHP), the aim of the SmallFLEX project, led by HES-SO Valais and performed in collaboration with EPFL, WSL, EAWAG, PVE, and FMV, is to show how SHP can provide winter peak energy and ancillary services, whilst remaining eco-compatible. The pilot and demonstrator site selected is the new small hydropower plant of Gletsch-Oberwald (KWGO) owned by FMV and commissioned end of 2017. This run-of-river power plant is equipped with two six-jet Pelton turbine units featuring a maximum power of 7 MW each. The addition of flexibility can be reached by using existing volumes of the power plant: the settling basin, the forebay chamber as well as part of the headrace tunnel. By consequence, the turbine head will undergo variations. To ensure that these variations will not cause any damages to the Pelton runner, the influence of the available head is investigated by numerical simulations. The simulations are carried out using two different software. OpenFOAM, which is based on a Finite Volume Method (FVM), is used for computing the flow inside the distributor until the jet. GPU-SPHEROS, which is based on Arbitrary Lagrangian-Eulerian (ALE) Finite Volume Particle Method (FVPM) is utilized to compute the interaction between the jet and Pelton buckets. Mixing the two aforementioned approaches, i.e. mesh-based FVM and particle-based FVPM, the overall torque T of the present six-jet Pelton runner can be reconstructed for different rated heads and discharges. The predicted torque fluctuations can then be considered for an estimation of the structural fatigue damage of the runner.

CFD simulations of a Y-junction for the implementation of hydraulic short-circuit operating mode

Conférence ArODES

Jean Decaix, Daniel Biner, J.-L. Drommi, François Avellan, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science ; Proceedings of 30th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2020), 21-26 March 2021, Lausanne, Switzerland

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Résumé:

In the framework of the XFLEX HYDRO H2020 European Project, one of the demonstrators focuses on the implementation of the hydraulic short-circuit on the pump storage power plant of Grand-Maison owned by Electricité De France (EDF). The Grand-Maison power plant is a two-level plant production with one plant located above the downstream reservoir and equipped with four Pelton turbines; a second plant located downstream the reservoir and equipped with eight reversible pump-turbines. Hydraulic short circuit consists in running pumps and turbines in the meantime to balance the energy consumption of the pumps compared to the grid. Such an operating mode allows increasing the flexibility of the power plant and targeting the requirement of balancing the intermittent production due to the growing of new renewable energies such as wind and solar power plants. The hydraulic short-circuit operating mode leads to a change in the flow paths in the penstocks and junctions compared to the normal turbine or pump modes. Indeed, compared to the pump mode, this mode will lead to a flow derivation at the junction between the penstocks directed to the Pelton units and the penstocks directed to the upper reservoir. As this mode have not been scheduled at the beginning of the power plant construction, it is necessary to quantitatively assess the singular head losses generated at the junction to be able to simulate the complete behaviour of the power plant by means of a 1D model. CFD simulations are carried out with the Fluent software for several configurations of hydraulic short-circuit defined by the ratio of flow rate deviated to the Pelton turbines.

2020

Production flexibility of small run-off river power plants: KWGO case study

Conférence

Gaspoz Anthony Roger Francis, Decaix Jean, Hasmatuchi Vlad Constantin, Matthieu Dreyer, Christophe Nicolet, Steve Crettenand

Hydro2020, 26.10.2020 - 28.10.2020, Strasbourg

Towards the non-intrusive detection and monitoring of cavitation in hydraulic machines

Conférence

Hasmatuchi Vlad Constantin, Pedroni François, Biner Daniel, Decaix Jean, Gino Blommaert, Münch-Alligné Cécile

Hydro2020, 26.10.2020 - 28.10.2020, Strasbourg

2019

Cost-effective CFD simulation to predict the performance of a hydrokinetic turbine farm

Conférence ArODES

Oliver Pacot, Damien Pettinaroli, Jean Decaix, Cécile Münch-Alligné

IOP Conference Series: Earth and Environmental Science ; Proceedings of IAHR International Workshop on Cavitation and Dynamics Problems in Hydraulic Machinery and Systems, 9-11 October 2019, Stuttgart, Germany

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Résumé:

Leak detection using random forest and pressure simulation

Conférence ArODES

Lucien Aymon, Jean Decaix, Francesco Carrino, Pierre-André Mudry, Elena Mugellini, Omar Abou Khaled, Richard Baltensperger

Proceedings of 2019 6th Swiss Conference on Data Science (SDS), 14 June 2019, Bern, Switzerland

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Résumé:

Water is a scarce resource which is becoming increasingly inaccessible. It is therefore necessary, in most parts of the world, to capture, transport and allocate it efficiently and thoughtfully. The implementation of monitored water distribution networks is often expensive. The purpose of this project is therefore to monitor leakage and consumption in a non-pressurized agricultural irrigation system using only inexpensive and easily installed pressure sensors. We modeled the water network to automatically simulate a leak randomly through the network. These simulated pressures serve as a dataset to train, test and validate a Random Forest algorithm that detects the leaks. Through pressure measures, the model can locate the junction closest to the leak with an accuracy of 96.24%. This approach therefore allows leaks detection in a water distribution system without the use of expensive flow sensors.

2018

On-board measurements at a 100MW high-head Francis turbine

Conférence ArODES

Maximilian Titzschkau, Vlad Hasmatuchi, Jean Decaix, Cécile Münch-Alligné

Proceedings of 20th International Seminar on Hydropower Plants, 14 - 16 November 2018, Vienna, Austria

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Résumé:

The Francis turbine runners of the four ternary groups of Grimsel 2 power plant in Switzerland showed fatigue cracks at the runner blades much earlier than expected. To find the source of these cracks, strain gauges and accelerometers were used to get information about the harmful stresses on the runner during operation. It is observed that the speed no-load operation during the start-up and the shutdown processes of the turbine impose large stresses on the runner blades.

Experimental and numerical investigations of high-head pumped-storage power plant at speed no-load

Conférence ArODES

Jean Decaix, Vlad Hasmatuchi, Maximilian Titzschkau, Laurent Rapillard, Pedro Manso, François Avellan, Cécile Münch-Alligné

Proceedings of 29th IAHR Symposium on Hydraulic Machinery and Systems, 16-21 September 2018, Kyoto, Japan

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Résumé:

Due to the increasing integration of new renewable energies, the electrical grid undergoes more frequent instabilities. Hydroelectric power plants, particularly pumped storage plants, are well suited for grid control. However, this objective requires extending the operating range of the machines and increasing the number of start-up, stand-by and shut-down procedures, which reduces the lifespan of the machines due to high mechanical stresses. The current study focuses on a pumped-storage power plant equipped with ternary groups. Recently, cracks on the runner blades of the Francis turbine have been observed without finding a clear explanation for their onset. During this period, the number of starts and stops per day has strongly increased. In order to better understand the origin of the fatigue of the turbine runner, external and on-board measurements along with CFD and FEM investigations have been performed. The on-board measurements provide evidence high mechanical stresses on the runner blades during the synchronization of the machine at speed no-load (SNL) operating condition. The frequency spectrum observed on the various signals suggests that the high stresses are linked to the excitation of one of the runner modes by some flow instabilities, which is supported by the CFD and FEM analyses.

U-RANS simulations and PIV mesurements of a self-excited cavitation vortex rope in a Francis Turbine

Conférence ArODES

Jean Decaix, Andreas Müller, Arthur Favrel, François Avellan, Cécile Münch

Proceedings of Advances in Hydroinformatics - SimHydro 2017: Choosing the right model in applied hydraulics, 14-16 June 2017, Sophia Antipolis

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Résumé:

In the course of the massive penetration of alternative renewable energies, the stabilization of the electrical power network significantly relies on the off-design operation of turbines and pump-turbines in hydropower plants. The occurrence of cavitation is, however, a common phenomenon at such operating conditions, often leading to critical flow instabilities, which undercut the grid stabilizing capacity of the power plant. In order to predict and extend the stable operating range of hydraulic machines, a better understanding of the cavitating flows and mainly of the transition between stable and unstable flow regimes is required. In the case of Francis turbines operating at full load, an axisymmetric cavitating vortex rope develops at the outlet runner in the draft tube. The cavity may enter self-oscillation, with violent periodic pressure pulsations propagating throughout the entire hydraulic system. The flow fluctuations lead to dangerous electrical power swings and mechanical vibrations through a fluid-structure coupling across the runner, imposing an inconvenient and costly restriction of the operating range. The paper deals with a numerical and experimental investigation of the transition from a stable to an unstable operating point on a reduced scale model of a Francis turbine at full load. Unsteady homogeneous two-phase RANS simulations are carried out using the ANSYS CFX solver. Cavitation is modelled using the Zwart’s model that required solving an additional transport equation for the void fraction. Turbulence is solved using the SST k-ω model. Simulations are compared with the experimental measurements and some insights are provided for a first comprehensive analysis of the transition between the stable and unstable states.

2015

Identification of the wave speed and the second viscosity of cavitation flows with 2D RANS computations - Part I

Conférence ArODES

Jean Decaix, S. Alligné, Christophe Nicolet, François Avellan, Cécile Münch-Alligné

Proceedings of 9th International Symposium on Cavitation (CAV2015), 6–10 December 2015, Lausanne, Switzerland ; Journal of Physics: Conference Series

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Résumé:

1D hydro-electric models are useful to predict dynamic behaviour of hydro-power plants. Regarding vortex rope and cavitation surge in Francis turbines, the 1D models require some inputs that can be provided by numerical simulations. In this paper, a 2D cavitating Venturi is considered. URANS computations are performed to investigate the dynamic behaviour of the cavitation sheet depending on the frequency variation of the outlet pressure. The results are used to calibrate and to assess the reliability of the 1D models.

Identification of the wave speed and the second viscosity in cavitating flow with 2D RANS computations - Part II

Conférence ArODES

Sébastien Alligné, Jean Decaix, Christophe Nicolet, François Avellan, Cécile Münch-Alligné

Proceedings of Journal of the 9th International Symposium on Cavitation (CAV2015), 6–10 December 2015, Lausanne, Switzerland ; Physics: Conference Series

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Résumé:

The 1D modelling of cavitation vortex rope dynamics in Francis turbine draft tube is decisive for prediction of pressure fluctuations in the system. However, models are defined with parameters which values must be quantified either experimentally or numerically. In this paper a methodology based on CFD simulations is setup to identify these parameters by exciting the flow through outlet boundary condition. A simplified test case is considered to assess if 1D cavitation model parameters can be identified from CFD simulations. It is shown that a low wave speed and a second viscosity due to the cavitating flow can be identified.

2014

Computational fluid dynamics as a tool to predict the air pollution dispersio in a neighborhood :

Conférence ArODES

a research project to improve the quality of life in cities

Gilles Triscone, Nabil Abdennadher, Christophe Balistreri, Olivier Donzé, Davide Greco, Patrick Haas, Hasret Haas-Peköz, Tamer Mohamed-Nour, Pierre Munier, Piero Pontelandolfo, Roberto Putzu, Hervé Sthioul, Nicolas Delley, David Choffat, Elena-Lavinia Niederhäuser, Roger Schaer, Henning Müller, Jean Decaix, Sylvain Richard, Cécile Münch-Alligné, Pierre Kunz, Fabienne Despot

Proceedings of Smart city expo world congress 2014

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Résumé:

In large cities, pollution composed of many different chemical components and small particles is an important public health problem that affects especially children and people presenting breathing difficulties. One challenge for public authorities is to respect the norms given by the central state, but how? Today, concrete methods for reducing pollution are perceived by the majority of citizens as constraints. However, the authorities have the possibility of modifying the wind's action by imposing architectural constraints, such as building emplacement and roof structure. This is the main objective of the Geneva "Clean City" project financed by the University of Applied Sciences Western Switzerland. "Clean City" focuses its research on one of Geneva’s polluted neighborhoods called Pâquis which is situated directly on the Geneva lake front. The project attempts to understand the dispersion of pollution from an experimental and a numerical point of view. After validation of the technique for a simple case, we compare environmental measurements on a 1/500 3D scale model of the Pâquis installed in an instrumented wind tunnel with Computational Fluid Dynamics (CFD) simulation obtained with the help of cloud computing. In Barcelona, we will show the first experimental measurements and simulated “Clean City” results.

RANS computations of a cavitating tip vortex

Conférence ArODES

Jean Decaix, Guillaume Balarac, Cécile Münch-Alligné

Proceedings of SimHydro 2014: Modelling of rapid transitory flows, 11-13 June 2014, Sophia Antipolis, France

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Résumé:

The Swiss national research project Hydronet 2 gathers a consortium of industrial and academic partners supported by the Competence Center of Energy and Mobility (CCEM) and Swiss Electric Research (SER) in order to improve the hydropower plants. One of the research topic focuses on the cavitating tip vortex. Such a vortex takes place in axial turbines as Kaplan turbines used for producing hydroelectricity. This phenomenon drives a lot of drawbacks such as erosion, unsteady flow rate and a decrease of the turbine efficiency. To better understand the behaviour of the tip vortex, computations of a simple test case are performed. The test case consists in a NACA profile mounted in a channel with a gap between the NACA tip and the lateral wall. The computations are carried out with the OpenFOAM solver both in one-phase and two-phase flow. The turbulent motion is modelled with a RANS approach. For the twophase flows computations, the phase change between liquid and vapour is achieved with the model proposed by Kunz. The results will be compared in cavitating and non cavitating cases with the experimental data provided by the EPFL Laboratory for Hydraulic Machines. The comparisons deal with global picture of the flow, the trajectory of the tip vortex and the velocity field downstream the NACA profile.

Réalisations

Recherche

Decaix Jean

Adjoint-e scientifique HES A

Compétences principales

Simulation CFD

Turbine hydrauliques

Modélisation de réseau hydraulique

Cavitation

OpenFOAM

Ansys CFX Fluent

Gmsh, ICEM

Adjoint-e scientifique HES A