Publications de François Avellan

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The paper presents the modelling, simulation and analysis of the transient behaviour of a 340 MW pump-turbine in case of emergency shutdown in turbine mode with focus on possible draft tube water column separation. The model of a pumped storage power plant ...

The present article describes an ambitious research project being conducted jointly by EDF, HQ and EPFL, with the aim of developing a method suitable for industrial use for predicting cavitation in Francis turbines on the basis of scale model testing. Results concerning the notion of erosion aggressiveness, methods to measure it -accelerometer, pressure fluctuations and pitting measurements -, the correlation between measurements on models and erosion on prototypes, and validation testing done on an actual

Hydraulic machines play an increasingly important role in providing a secondary energy reserve for the integration of renewable energy sources in the existing power grid. This requires a significant extension of their usual operating range, involving the presence of cavitating flow regimes in the draft tube. At overload conditions, the self-sustained oscillation of a large cavity at the runner outlet, called vortex rope, generates violent periodic pressure pulsations. In an effort to better understand the n

The aim of this paper is to apply a surface parameterization to a blade. This geometric representation should be used as a practical tool in the process of design optimization. Most parameterizations are based on blade section approaches. The parameters ar ...

Partial flow rate operation of hydroturbines with constant pitch blades causes complex unstable cavitating flow in the diffuser cone. A particle image velocimetry (PIV) system allows investigating the flow velocity field in the case of a developing cavitat ...

The cavitation which causes severe erosion of hydraulic machine runners is produced by the development of fixed cavities attached at the leading edge of the blades. It is clearly shown, from a comparison between the observations of cavity patterns during model tests and the damage found in the prototype, that the damaged areas of the blades extend in the wak:e of the fixed cavities. In this paper we give experimental evidence that this damage is due to the collapse of transient cavities in the fixed cavity

Acoustic resonances in Francis turbines often define undesirable limitations to their operating ranges at high load. The knowledge of the mechanisms governing the onset and the sustenance of these instabilities in the swirling flow leaving the runner is es ...

For Francis turbines, outlet cavitation is a major critical phenomenon in determining the prototype setting level. To predict the full-scale cavitation characteristics, it is technically interesting to provide reliable model cavitation tests. This can be done by a similar cavitation development on the model and on the prototype. In this paper, previous results obtained during systematic cavitation tests using nuclei injection and counting techniques are recalled. An alternative procedure to nuclei injection

Francis turbines with medium or high specific speeds may experience a particular type of instability in the upper part load in which the precessing vortex has an elliptical shape. The occurrence of the upper part-load instability (UPLI) is accompanied by l ...

The Pelton turbine is an impulse turbine typically installed for high head hydroelectric power plants. For a site with a rated head H and discharge Q, a higher specific speed turbine results in a more compact generating unit with reduced manufacturing cost ...

In this paper, we present a 3-D FVPM which features rectangular top-hat kernels. With this method, interaction vectors are computed exactly and efficiently. We introduce a new method to enforce the no-slip boundary condition. With this boundary enforcement ...

Francis turbines operating in full load conditions feature an axisymmetric vortex rotating in the opposite direction of the turbine runner. In low-pressure conditions, the resulting cavitation vortex may enter in an unstable self-exciting process, leading ...

Hydropower is nowadays essential for balancing the electrical grid providing flexibility and fast response. The role of hydraulic turbines has changed from working at their Best Efficiency Point (BEP) to work in the whole operating range when demanded. Fra ...

In the present study, the fluid-structure coupling is investigated in the guide vanes of a pump-turbine scale model placed in one of the test rigs of the Laboratory for Hydraulic Machines (EPFL) in Lausanne. The paper focuses on the advanced instrumentatio ...

In centrifugal pumps, the interaction between the rotating impeller blades and the stationary diffuser vanes generates specific pressure fluctuation patterns. At off design operation, high incidence and large local pressure gradients can lead to flow separ ...

Different measurement techniques have been used to detect cavitation on a Francis turbine model. The results are compared to those obtained on the prototype and presented in the first of this series of articles. The runner mode! used for that study is built on the basis of a geometrical recovery of one of most eroded blade of the prototype. The results of the different measurements are presented and commented by comparison with prototype measurements. This comparison leads to a proposal of the physics which

This paper presents investigations of unsteady flow conditions influence over cavitation dynamics. Measurements of wall pressure fluctuations in a model turbine are first introduced. It is shown that the wake of the spiral casing tongue modulates cavity dynamics near the trailing edge of runner blades. A new device, which permits a 2D hydrofoil to oscillate around its mean incidence angle, is used in order to recreate flow conditions similar to those of blade row wakes experienced in industrial flows. This

Experimental studies have shown that outlet cavitation of a Francis turbine is influenced by the active nuclei content of the test loop water, up to a limit curve called the saturation characteristic. To determine the importance of this influence in operating conditions, tests are performed for a nu= 0.38 Francis mode!, for many operating points. Moreover, based on the resolution of the Rayleigh-Plesset equation, it can be shown that, even with a low nuclei content of the plant water, the cavitation charact

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 ...

Design, operation and refurbishment of hydraulic turbines, pumps or pump-turbine are strongly related to cavitation flow phenomena, which may occur in either the rotating runner-impeller or the stationary parts of the machine. The paper presents the cavitation phenomena featured by fluid machinery including type of cavity development related to the specific speed of machines in both pump and turbine mode, the influence of the operating conditions, such as load, head and submergence. Therefore, for each type

François Avellan

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Simulation of water column separation in Francis pump-turbine draft tube

Predicting Cavitation in Francis Turbines on the Basis of Scale Model Testing

Draft tube discharge fluctuation during self-sustained pressure surge: fluorescent particle image velocimetry in two-phase flow

Surface Parametrization of a Francis Runner Turbine for Optimum Design

Analysis of the Cavitating Draft Tube Vortex in a Francis Turbine Using Particle Image Velocimetry Measurements in Two-Phase Flow

Cavitation erosion of the hydraulic machines : generation and dynamics of erosive cavities

Interaction of a pulsating vortex rope with the local velocity field in a Francis turbine draft tube

Guidelines for performing cavitation tests

Upper part-load instability in a reduced-scale Francis turbine: an experimental study

GPU-accelerated numerical analysis of jet interference in a six-jet Pelton turbine using Finite Volume Particle Method

Silt motion simulation using finite volume particle method

Prediction of unstable full load conditions in a Francis turbine prototype

Transposition of the mechanical behavior from model to prototype of Francis turbines

Advanced Instrumentation for Measuring Fluid-Structure Coupling Phenomena in the Guide Vanes Cascade of a Pump-Turbine Scale Model

Experimental Investigation of Pressure Fluctuations in a High-Energy Centrifugal Pump Stage at Off-Design Conditions

Cavitation Erosion Prediction on Francis Turbines Part 2 : Model Tests and Flow Analysis

The influence of flow unsteadiness on erosive cavity dynamics

Francis cavitation tests with nuclei injection : a new test procedure

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

Introduction to Cavitation in Hydraulic Machinery