Publications de François Avellan

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Hydropower plants play an important regulatory role in the large scale integration of volatile renewable energy sources into the existing power grid. This duty however requires a continuous extension of their operating range, provoking the emergence of com ...

The cross-flow turbine is an attractive technology for small-scale hydropower generation thanks to its low capital cost and relatively high efficiency even under partial discharge operating conditions. It has been proposed that this kind of turbine can be ...

An experimental investigation on Francis turbines suffering from inlet cavitation erosion on the runner blades has permitted to assess several aspects of the actual cavitation erosion detection and prediction methods based on vibrations. Detection tests in three prototypes have consisted in the measurement of vibrations in turbine guide bearing, guide vanes and draft tube during operation. Discussion about RMS levels, auto power spectra and amplitude demodulation results is provided. A dynamic calibration h

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 numeri ...

The setting level of a hydraulic machine, specially for low head machines, is decided with respect to the possible alteration of the efficiency due to the cavity development. This alteration can easily be noticed by following the evolution of the efficiency 'eta' as a function of the Thoma number 'sigma' leading to the so-called 'eta'-'sigma' cavitation curves. Observation of the cavity extent in the flow passage of the runner allows to associate the drop of efficiency with a particular type of cavity devel

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 ...

Francis turbines are subject to various types of cavitation flow depending on the operating condition. To enable a smooth integration of the renewable energy sources, hydraulic machines are now increasingly required to extend their operating range, especia ...

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 exten ...

The eigenvalues analysis method is generally applied to synchronous machines by using d,q-components. This paper presents the application of this method on an equivalent model for the synchronous machine based on phase variables a,b,c instead of d,q-components. The advantages of this approach, essential for programs using phase variables as state variables, are presented. The application of this method to a complete hydroelectric production site including hydraulic components (pump-turbine, penstock, galler

Flow instabilities in hydraulic machines often feature oscillating cavitation volumes, which locally introduce compliance and mass flow gain effects. These unsteady characteristics play a crucial role in one-dimensional stability models and can be determin ...

This paper presents preliminary results of an experimental study on the occurrence and development of the upper part-load instability in a reduced-scale Francis turbine. The study includes draft tube pressure measurements, high-speed flow visualization, an ...

We have recently developed a conservative ﬁnite volume particle method (FVPM) that can efﬁciently model 2-D and 3-D ﬂuid ﬂow with free-surfaces and complex geometries. Tn this paper we present an extension of the method to ﬂuid-structure interaction. A new ...

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 ...

Geometry recovery of a turbine runner can be of prime importance in at least two cases: upgrading of an old power plant and field repair of a runner. Considering the importance of the field geometry recovery, we have decided to compare three methods of measurement, on a Francis runner with a 4.4 m outlet outer diameter. The first method of geometry measurements is the classical template technique, consisting in drafting both horizontal and slanted sections of the runner blade-to-blade passage. The instrumen

The Cavitation Erosion Power based on the assumption that severe erosion is often due to the repeated collapse of the traveling vortex generated by a leading edge cavity has been formerly introduced. We have shown that cavitation erosion intensity may be scaled by a simple set of flow parameters depending on the mean upstream velocity U, the Strouhal number St corresponding to the main cavity fluctuations, the cavity length I and the pressure in the cavity closure. Further tests have been done to validate t

This paper presents an investigation of the hydro elastic behavior of vibrating blades in hydraulic machines, which is of strong interest for turbo machinery applications. As a representative case study for vibrating blade in hydraulic machines, a NACA 000 ...

The experimental investigation of the hydrodynamics of a reversible pump-turbine reduced scale model in off-design operating conditions is presented. The onset and development of flow instabilities outside the “normal” operating range, in generating mode, involving runaway and “S-shape”, are described. Wall pressure measurements, in the stator, are performed with the help of miniature piezoresistive sensors synchronized with high speed flow visualizations in the vaneless gap between the impeller and the gui

A previous report by the present authors [1] clarified the diffuser effect of the draft tube and the effects of swirl in the runner downstream on the hydraulic instabilities in power generation plants. The present study was intended to study the effect of ...

Numerical investigation of the unsteady flow patterns around the bucket can be helpful to improve the Pelton turbine efficiency. In fact, by studying the loss mechanisms in the flow, one can optimize the bucket design. For this purpose, an accurate investi ...

A machine learning meshing scheme for the generation of 2-D simplicial meshes is proposed based on the predictions of neural networks. The data extracted from meshed contours are utilized to train neural networks which are used to approximate the number of ...

François Avellan

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Fluid-structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load

Computational parametric analysis of the design of cross-flow turbines under constraints

Field Assessment of Cavitation Detection Methods in Hydropower Plants

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

Efficiency Alteration of Francis Turbines by travelling Bubble Cavitation

URANS Models for the Simulation of Full Load Pressure Surge in Francis Turbines Validated by Particle Image Velocimetry

Experimental evidence of inter-blade cavitation vortex development in Francis turbines at deep part load condition

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

Stability Study of a Complete Hydroelectric Production Site by Eigenvalues Analysis Method Based on Phase Variables

Measurement of the Self-Oscillating Vortex Rope Dynamics for Hydroacoustic Stability Analysis

An experimental study on the upper part-load elliptical vortex instability in a Francis turbine

Finite Volume Particle Method for Fluid-Structure Interaction

Hydroacoustic Modeling of Rotor Stator Interaction in Francis Pump-Turbine

Geometry Recovery of a Francis Runner Prototype at Site

Cavitation erosion power as a scaling factor for cavitation erosion of hydraulic machines

Numerical investigations of fluid structure coupling: oscillating hydrofoil

Hydrodynamics of a Pump-Turbine under Off-Design Operating Conditions in Generating Mode

One-dimensional analysis of full load draft tube surge

Numerical investigation of the jet velocity profile and its influence on the Pelton turbine performance

How to teach neural networks to mesh: Application on 2-D simplicial contours