Publications by François Avellan

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The growth and collapse of laser-induced vapor cavities inside axisymmetric free-falling liquid water jets have been studied. Bubbles of different size are generated at various distances from the jet axis and the effects on the jet interface are recorded b ...

We investigate the Rotor-Stator Interaction in a pump-turbine reduced scale model by considering fluid-structure coupling. The pressure fluctuations amplitude in the rotor-stator vaneless gap has generally been shown to increase linearly with the operating ...

The flow in a Francis turbine runner (GAMM Turbine) is analysed numerically. Different operating points are calculated using two industrial software packages based respectively on a finite element method (N3S) and a finite volume method (TASCflow®) and compared to experimental results. The numerical results allow to observe physical phenomena in the runner that are important in the process of hydraulic turbomachinery design. Values of Cu and Cm velocity components, blade pressure distribution and recirculat

Cavitation tests using models are essential to determine the full-scale machine cavitation behaviour. As erosion prediction is still very empirical, in practice a "safe" machine shows no visible cavitation on a model at sigma plant. However, this way of defining the setting level can lead to errors due, among other things, to the nuclei transit time in the runner low pressure zone. It is shown in this paper that the absence of visible cavitation on a model does not correspond to absence of cavitation on the

Low frequency fluctuations often occur in hydraulic installations equipped with fixed bladed turbines or pumps operating under off design conditions. Passive measures, such as air ad- mission or minor design modifications, are commonly taken as a last resort to try to reduce these phenomena. This article describes an active control approach to the problem, which is based upon a rotating valve exciter. The idea is to create an external excitation with the hydraulic exciter to diminish an undesired frequency

In order to investigate the dynamics of the vortex cavitation, which is found to be responsible of the cavitation erosion in hydraulic machinery, a cavitation vortex generator (CVG) is used. By producing the cyclic growth and collapse of cavitation vortex, this device provides a good simulation of the realistic hydrodynamics situation corresponding to the travelling cavities downstream a fixed leading-edge cavity. The simultaneous use of the shock and the pressure time-history recordings and the high speed

Regions of positive slope in the pressure-discharge characteristics are one of the major concerns in design and operation of centrifugal pumps, as they are limiting the admissible operating range to values above the critical discharge. The industrial pump ...

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. In the case of traveling bubble cavitation, corresponding to the outlet cavitation at the nominal head, the physical phenomenon underlying such an efficiency alteration is not very clear, even though a strong dependence of this drop with the volume of cavities have been noticed. The aim of this paper is to present the results of an exp

Since many years the EPFL Laboratory of Electrical Machines develops SIMSEN, a numerical software package for the simulation of electrical power systems and adjustable speed drives, in transient and steady-state conditions, having an arbitrary topology. SI ...

More and more hydropower plants are operating as regulator of renewable energy such as solar and wind energy resources. Because these renewable energy resources are highly volatile, so hydraulic turbines have to switch working condition in a wide flow rang ...

In this first part of a 2 papers series, we present the experimental procedure for onboard measurement of pressure and strain fluctuation in a model of low head Francis turbine. 28 miniature pressure sensors are fitted in the pressure and suction sides of two consecutive blades. A specific technique for sensors mounting has been developed allowing a direct manufacturing of the pressure sensors in the runner blades. This prevents from any geometry alteration of the hydraulic profile. Furthermore, miniature p

To identify the distinctive vibratory characteristics of erosive cavitation an investigation program was conducted in the IMHEF High Speed Cavitation Tunnel on a NACA 009 stainlcs~: steel profile equipped with 7 DECER electrochemical cavitation erosion detcctors and high frequency vibration sensors. Forces acting on the profile were inferred from a measured transmissibility function. Above a low threshold value a linear relationship was found between the measured mean square value of acceleration and the av

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 ...

An experimental work has been carried out to investigate the dynamic behavior and the intensity of erosive partial cavitation on a 2-D hydrofoil. Both sheet (stable) and cloud (unstable) cavitation have been tested in a cavitation tunnel for various free s ...

Renewable energy sources (RES) have reached 23.7% of the worldwide electrical generation production in 2015. The hydraulic energy contribution amounts to 16.6% and comes mainly form large-scale hydropower plants, where Francis turbines represents 60% of th ...

Experiments on vortex shedding from a blunt trailing edge symmetric hydrofoil operating at zero angle of attack in a uniform high speed flow, Re-h = 16.1 . 10(3) - 96.6 . 10(3), where the reference length h is the trailing edge thickness, are reported. The ...

The required operating range for hydraulic machines is continually extended in an effort to integrate renewable energy sources with unsteady power outputs into the existing electrical grid. The off-design operation however brings forth unfavorable flow pat ...

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 plotting the evolution of the efficiency 'eta' as a function of the Thoma number 'sigma' leading to the so-called 'eta'-'sigma' cavitation curves. ln order to protect the efficiency at the best operating point against the travelling bubbles effects, the IEC norms suggest some measures relating t

Francis turbines operating in part load conditions experience a swirling flow at the runner outlet leading to the development of a precessing cavitation vortex rope in the draft tube. This cavitation vortex rope changes drastically the velocity of pressure ...

The present paper reports the development of Finite Particle Method (FPM) in the framework of a high-speed water jet simulation. The FPM kernel is used to improve the consistency of standard SPH for non-uniform particle distribution. The time integration is performed with a modified Verlet scheme. At the end of each time step, a particle shifting method is applied to mitigate the particle clustering issue by restoring a uniform particle spacing. The influence of particle spacing and maximum CFL number are i

François Avellan

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Cavitation bubble behavior inside a liquid jet

Influence of the Pump-Turbine Guide Vanes Vibrations on the Pressure Fluctuations in the Rotor-Stator Vaneless Gap

Numerical Flow Analysis of the GAMM Turbine at nominal and off-design Operating Conditions

Similarity of cavitation inception in Francis turbines

Active control of Francis turbine operation stability

Dynamics of vortex cavitation involved in the erosion of hydraulic machines

Numerical Analysis of Flow Phenomena Related to the Unstable Energy-Discharge Characteristic of a Pump-Turbine in Pump Mode

Mechanism of the Efficiency Drop due to traveling Bubble Cavitation

Simulation tool linking hydroelectric production sites and electrical networks

Understanding the coherent structures for different fluctuation frequencies at partial load condition of a Francis turbine

Onboard Measurements of Pressure and Strain Fluctuations in a Model of low Head Francis Turbine. Part 1 : Instrumentation

Vibratory characteristics of erosive cavitation vortices downstream of a fixed leading edge cavity

Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine

Dynamics and Intensity of Erosive Partial Cavitation

Part Load Vortex Rope as a Global Unstable Mode

The Effects of a Tripped Turbulent Boundary Layer on Vortex Shedding from a Blunt Trailing Edge Hydrofoil

On the physical mechanisms governing self-excited pressure surge in Francis turbines

Prediction of Francis Turbines Efficiency Alteration by travelling Bubble Cavitation

Transposition of Francis turbine cavitation compliance at partial load to different operating conditions

FPM SIMULATIONS OF A HIGH SPEED WATER JET VALIDATION WITH CFD AND EXPERIMENTAL RESULTS