Jean Decaix

HES-SO Valais-Wallis (Sion) · Hydroelectricity group

Since 1970s, several experimental works revealed that the cavitation sheet inception does not occur at the minimum pressure location but further downstream at the location of a laminar/turbulent transition. Most of the cavitation models use the saturation vapour pressure as a threshold to initiate the production of vapour and therefore, are not abl...

Simulation of the flow in a Pelton turbine is a challenging task for mesh based methods due tothe air/water mixture and the rotation of the runner. Meshless based methods are better suitedfor such flows and take advantage of the graphical power unit to speed up the calculation. Sim-ulations of a Pelton turbine are carried out using the software Par...

Due to the penetration of stochastic low-carbon sources of production, requirements for flexible generation increase. The flexibility of pumped storage hydropower plants in pump mode can be improved by implementing hydraulic short circuit modes, which consists in operating the turbine(s) and the pump(s) in parallel. This new operating mode can be i...

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...

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...

Since the 1970s, several experimental works revealed that the cavitation sheet inception does not occur at the minimum pressure location but further downstream at the location of a laminar/turbulent transition. Most of the cavitation models use the saturation vapour pressure as a threshold to initiate the production of vapour, which imposes the occ...

The computation of the flow in Pelton turbines remains a challenge mainly due to the two-phase flow in the bucket and in the casing. The present study focuses on simulations of two Pelton turbines, applying the finite volume method with the ANSYS ® CFX ® software and is divided into two parts: first, the degradation turbine efficiency due to jet in...

The flexibility of the FMHL+ pumped storage power plants can be improved by extending the hydraulic short-circuit operating mode. CFD simulations of the flow in three bifurcations are performed to calculate the head losses and to investigate the flow topology in the pipes. A specific attention is paid to the influence of the curvature correction th...

Since 1970s, several experimental works revealed that the cavitation sheet inception does not occur at the minimum pressure location but further downstream at the location of a laminar/turbulent transition. Most of the cavitation models used the saturation vapour pressure as a threshold to initiate the production of vapour and therefore, are not ab...

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 op...

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 fle...

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 re...

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...

In the framework of the XFLEX HYDRO H2020 European Project, the pumped-storage power plant of Grand’Maison (France), owned by Electricité 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’Maiso...

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...

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 w...

Hydropower is a key energy conversion technology for stabilizing electrical power. When running at full load, a 3-D cavitation vortex rope develops in Francis turbines that acts as an internal source of energy and instability. 1-D models allow this phenomenon to be predicted and the range of safe operating points to be defined. These models involve...

Over the last two decades, the public policies for promoting new renewable energies allowed the growth of such energies around the world. Due to their success, the policies are changing, forcing the producers to adapt their strategy. For instance, in Switzerland, the feed-in tariff system has been modified in 2018 to promote an electricity producti...

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...

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 sit...

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 demons...

Diagnostic de la fatigue prématurée des turbines I 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...

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 i...

The development of cavitation sheets over an hydrofoil is driven both by the gas content of the liquid and the nature of the boundary layer that develops along the hydrofoil. For a deaerated water and a flow at high Reynolds number and/or high angle of attack, the boundary layer is fully turbulent and the cavitation sheet develops from the leading...

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 th...

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, wit...

In the framework of the FlexStor project, an in-situ experimental investigation has been conducted on a 100 MW Francis turbine prototype following the identification of signs of fatigue on the runner blades, possibly correlated with the drastic increase of the number of daily starts/stops in the recent years. To this end, two synchronised sets of m...

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, numer...

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...

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 s...

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, wh...

The study is motivated by the fact that cracks on the runner blades of a 100 MW Francis turbine prototype have been noticed. The possible origin: a drastic increase of the number of daily starts/stops in the recent years. To this end, an in-situ experimental investigation using two synchronised sets of measurements has been conducted: the first one...

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 cons...

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...

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, lea...

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, lea...

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 poll...

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 poll...

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...

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 beh...

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 paramet...

Due to the massive penetration of alternative renewable energies, hydraulic power plants are key energy conversion technologies to stabilize the electrical power network using hydraulic machines at off design operating conditions. At full load, the axisymmetric cavitation vortex rope, developing in Francis turbine acts as an internal source of ener...

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...

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 fluctuatio...

The tendency of designing large Kaplan turbines with a continuous increase of output power is bringing to the front the cavitation erosion issue. Due to the flow in the gap between the runner and the discharge ring, axial turbine blades may develop the so called tip leakage vortex (TLV) cavitation with negative consequences. Such vortices may inter...

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 eros...

This numerical work investigates the mesh influence in the near-wall area when a partial cavity develops and interacts with the turbulent boundary layer. Different meshes varying by the first cell size are compared, and unsteady simulations are performed with a two-phase one-fluid RANS solver. Numerical results are given for two Venturi geometries...

A numerical investigation of the behaviour of a cavitation pocket developing along a Venturi geometry has been performed using a compressible one-fluid hybrid RANS/LES solver. The interplay between turbulence and cavitation regarding the unsteadiness and structure of the flow is complex and not well understood. This constitutes a determinant point...

A compressible, multiphase, one-fluid RANS solver has been developed to study turbulent cavitating flows. The interplay between turbulence and cavitation regarding the unsteadiness and structure of the flow is complex and not well understood. This constitutes a determinant point to accurately simulate the dynamic behavior of sheet cavities. In the...

The computation of cavitating flows is a challenging issue due to the characteristics of these flows : phase transition, large density gradient, Mach number variation, interaction between phases and turbulent flow, unsteadiness. In the present study, we performed a derivation of the one-fluid compressible homogenous model coupled with a RANS approa...

A compressible, multiphase, one-fluid RANS solver was developed to study cavitating flows. The interaction between turbulence and two-phase structures is complex and not well known. Particularly, compressible effects on turbulence in the mixture due to the presence of the two phases are generally not taken into account. In the framework of averaged...

A compressible, multiphase, one-fluid Euler solver has been developed to study one-dimensional rarefaction problems with cavitation. Two closure relations for the mass transfer between phases are compared. Numerical results are validated with reference solutions computed with the two-fluid models.

SUMMARYA compressible, multiphase, one-fluid Reynolds-averaged Navier–Stokes solver has been developed to study turbulent cavitating flows. The interplay between turbulence and cavitation regarding the unsteadiness and structure of the flow is complex and not well understood. This constitutes a critical point to accurately simulate the dynamic beha...

Résumé : La présente étude concerne la simulation d'un écoulement cavitant, réalisée avec un code diphasique, compres-sible RANS 1-fluide. De précédents travaux ont montré l'incapacité des modèles standards de turbulence à repro-duire les instationnarités d'un écoulement cavitant. En effet, seul l'ajout d'une correction de la viscosité turbulente c...

A compressible, multiphase, one-fluid RANS solver was developed to study turbulent cavitating flows. The interaction between turbulence and two-phase structures is complex and not well known. This constitutes a critical point to accurately simulate unsteady behaviours of cavity sheets. In the present study, different turbulence transport-equation m...

A compressible, multiphase, one‐fluid RANS solver was developed to study cavitating flows. The interaction between turbulence and two‐phase structures is complex and not well known. This constitutes a critical point to accurately simulate unsteady behaviours of cavity sheets. In the present study, different transport‐equation turbulence models are...