Publications de François Avellan

Chattez avec Graph Search

Posez n’importe quelle question sur les cours, conférences, exercices, recherches, actualités, etc. de l’EPFL ou essayez les exemples de questions ci-dessous.

AVERTISSEMENT : Le chatbot Graph n'est pas programmé pour fournir des réponses explicites ou catégoriques à vos questions. Il transforme plutôt vos questions en demandes API qui sont distribuées aux différents services informatiques officiellement administrés par l'EPFL. Son but est uniquement de collecter et de recommander des références pertinentes à des contenus que vous pouvez explorer pour vous aider à répondre à vos questions.

The necessity of controling the nuclei content of the circuit water while conducting cavitation tests on mode! hydraulic machines is considered to be indispensable. We are presenting a description of our cavitation nuclei producing device, the so-called nuclei injector, which is based on the principle of rapid expansion of air-saturated water. An experimental study has been carried out on a transparent mode! injector which has permitted to realize the visualization of the process in the form of photographs

A one-dimensional hydroacoustic model is set up to perform the numerical simulation of the rotor-stator interaction of a Francis pump-turbine scaled model. The numerical results enable to identify both rotating diametrical modes in the vaneless gap between ...

In centrifugal pumps, the interaction between the rotating impeller and the stationary diffuser generates specific pressure fluctuation patterns. When the pump is operated at off design conditions, these pressure fluctuations increase. The resulting rise o ...

In the frame of a joint research program between EDF, Hydro Québec and IMHEF, different methods are investigated to predict cavitation erosion on Francis turbines from model. They are based on measurement of pitting, pressure fluctuations and acceleration. The measurement techniques have been detailed in Part I and Part 2. The present article describes essentially the theoretical and practical aspects of the methods and discusses the results obtained until now from the mode! and prototype tests. The first a

Islanded power networks comprising a small number of large power plants are subject to perturbations leading to important transients, and, hence need high performance governors. The design of these governors requires a detailed model of the system. This is ...

The shedding process of the Kármán vortices at the trailing edge of a 2D hydrofoil at high Reynolds numbers is investigated. The focus is put on the effect of the cavitation on the vortex street morphology. A direct insight is also provided on the role of ...

One-dimensional stability analysis of a hydraulic system composed of a penstock, a runner, and a draft tube was carried out to determine the cause of the full load draft tube surge. It is assumed that the cavity volume at the runner exit is a function of t ...

It is well known that hydraulic machines experience various types of flow instabilities causing a negative influence on the system under off-design operations. The transfer matrix method correlating the flow properties in upstream and downstream of hydraul ...

This paper presents a validation of numerical simulations in case of a forced oscillating hydrofoil. As a representative case study for vibrating blade in hydraulics machines, a 2D NACA 0009 oscillating hydrofoil is considered. Pressure coefficients from e ...

The paper presents the modelling, simulation and analysis of the transient behaviour of a 340 MW pump-turbine in case of emergency shutdown in generation mode with particular attention to the possible draft tube water column separation. First, the model of ...

Francis turbines are designed for a specific set of operating conditions that is particular to each hydropower plant site. It allows this type of turbine to extract as much hydraulic power as possible, as long as they are operating in the right conditions. ...

Anewcavitation erosion testing procedure in high-speed cavitation tunnel is presented. The method is based on surface-mounted obstacles on a plane-convex hydrofoil leading edge. This experimental set-up is able to accelerate the accumulation of damage on specimens located behind the obstacles and presents several advantages. Measurable cavitation erosion damage has been obtained for a thermal spray coating and a stainless steel 13.4 after 75 h of operation. The hydrodynamic operating conditions have been an

Flow visualizations using endoscopes in a 21-bucket single-injector reduced scale Pelton turbine are performed for 2 operating points. 2 types of visualizations are performed with a CMOS high-speed camera: (i) an onboard visualization of the flow in the bu ...

In a hydraulic power plant, it is essential to provide a reliable, sustainable and flexible energy supply. In recent years, in order to cover the variations of the renewable electricity production, hydraulic power plants are demanded to operate with more e ...

The growing development of renewable energies combined with the process of privatization, lead to a change of economical energy market strategies. nstantaneous pricings of electricity as a function of demand or predictions, induces profitable peak producti ...

The operation of Francis turbines at off-design conditions may cause the development of a cavitation vortex rope in the draft tube cone, acting as a pressure excitation source. The interactions between this excitation source and the hydraulic system at the ...

This paper deals with flow investigations using endoscopes in a single-injector reduced scale Pelton turbine performed with a CMOS high-speed camera. Both onboard and external visualizations techniques of the flow in a bucket are presented. The flow observ ...

The work presented in this paper is part of a comprehensive research effort aimed at understanding the influence of flow unsteadiness on leading edge cavitation. Pressure measurements are made on the suction side of an oscillating hydrofoil in the High-Speed Cavitation Tunnel. Leading edge roughness effects are investigated for both cases of fixed and oscillating hydrofoils. The cavity that detaches on the rough leading edge is thicker while its length is approximately the same as for the smooth configurati

In the process of turbine modernizations, the investigation of the influences of water passage roughness on radial flow machine performance is crucial and validates the efficiency step up between reduced scale model and prototype. This study presents the s ...

In real systems, the phenomena, such as pipe-wall viscoelasticity, unsteady friction or fluid structure interaction induce additional damping and dispersion of transient pressure waves than that defined by classical waterhammer. In this paper, unsteady fri ...

François Avellan

Chattez avec Graph Search

The IMHEF system for cavitation nuclei injection

One-Dimensional Modeling of Rotor Stator Interaction in Francis Pump-Turbine

Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage

Cavitation Erosion Prediction on Francis Turbines Part 3 : Methodologies of Prediction

On the Hydroelectric Stability of an Islanded Power Network

Cavitation in Kármán Vortices and Flow Induced Vibrations

One-Dimensional Analysis of Full Load Draft Tube Surge

Evaluation of a Dynamic Transfer Matrix for a Hydraulic Turbine

2D Oscillating Hydrofoil

Parametric study of water column separation in Francis pump-turbine draft tube

Monitoring a Francis Turbine Operating Conditions

Cavitation Erosion Tests on a 2D Hydrofoil using surface-mounted Obstacles

Onboard Flow Visualization in a Pelton Turbine Bucket

Pressure measurements and high speed visualizations of the cavitation phenomena at deep part load condition in a Francis turbine

Prediction of a Francis turbine prototype full load instability from investigations on the reduced scale model

Local wave speed and bulk flow viscosity in Francis turbines at part load operation

High Speed Flow Visualisation of an Impinging Jet on a Pelton Turbine Bucket

Physical Investigation of the Cavitation Phenomenon

Surface Roughness Impact on Francis Turbine Performances and Prediction of Efficiency Step Up

Modeling of Unsteady Friction and Viscoelastic Damping in Piping Systems