Publications by François Avellan

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Flow in a elbow draft tube is a turbulent complex unsteady flow caused by its rotating nature and the draft tube's geometry. The understanding of the main phenomena that could appear near the BEP and at off-design conditions is important to master the instability of the machine. The results shown in this work are a summary of a very large experimental database. The aim of this investigation work is to analyze the steady and unsteady pressure fields at the wall of the draft tube through extensive pressure me

In this paper, a numerical simulation to analyze the influence of the surrounding water in a turbine runner has been carried out using finite element method (FEM). First, the sensitivity of the FEM model on the element shape and mesh density has been analy ...

At part load operation of Francis turbine, the swirl in the draft tube leads to flow instability known as vortex breakdown. This flow instability can interact with the rest of the hydraulic circuit through axially propagating plane-waves. Moreover, at low cavitation index , the gaseous rope is suspected to modify locally the propagation velocity. Acoustic models have been commonly used to tackle this problematic. In order to validate the parameters of those models, an experiment with equivalent phenomenolog

In a centrifugal pump the interaction between the rotating impeller pressure field and the stationary diffuser pressure field yields pressure fluctuations as the result of a modulation process. These fluctuations may induce hydroacoustic pressure fluctuati ...

The mitigation of the precessing vortex core developing in the draft tube of Francis turbines operating under part load conditions is crucial to increase the operation flexibility of these hydraulic machines to balance the massive power production of inter ...

A transport-equation-based homogeneous cavitation model previously assessed and validated against experimental data is used to investigate and explain the efficiency alteration mechanisms in Kaplan turbines. On the one hand, it is shown that the efficiency ...

The flow hydrodynamics in a low specific speed radial pump-turbine reduced scale model is experimentally investigated under off-design operating conditions in generating mode. Wall pressure measurements, in the stator, synchronized with high-speed flow vis ...

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 this second part of a 2 papers series, we present the analysis of “onboard” measurements on the runner of a Low Head Francis model and comparison with the same type of measurements on a similar prototype, as well as a comparison with numerical calculations. The details of the experimental procedures for onboard measurement of pressure and strain fluctuation in the model runner are presented in the first part (Ref. 1). Load fluctuations on the blade of a Francis runner depend largely on the different hydr

In the present paper, we compare two different computation methods for the simulation of leading edge cavitation. In the first one, known as interface tracking method, the cavity interface is taken as a free surface boundary in the computation domain and the calculation is performed in a single phase flow. The cavity shape is then determined apart from the flow calculation using an iterative procedure. We have used the Neptune code which derive the initial cavity shape from the envelope of a travelling bubb

Hydroelectric units can be operated in synchronous condenser mode to provide reactive power to the electrical power system (EPS) for voltage regulation. In this operating mode, the hydraulic turbine consumes active power and in case of hydroelectric units ...

To enhance the sustainability of water supply systems, the development of new technologies for micro scale hydropower remains an active field of research. The present paper deals with the implementation of a new micro-hydroelectric system for drinking wate ...

Regions of positive slope in the pressure-discharge characteristics can result in a reduction or even lack of damping of system instabilities. They are therefore one of the major concerns in design and operation of centrifugal pumps as they are limiting th ...

This paper introduces an experimental method for the evaluation of dynamic transfer matrices using only pressure transducers. The discharge fluctuations are evaluated from the fluctuation of the pressure difference at different streamwise locations. The tr ...

Model testing of hydraulic turbines, storage pumps and pump-turbines is of great importance especially for large units involved in power generation. Among all the aspects of machine operation, cavitation plays a fundamental role with respect to the possible alteration of the efficiency and to the erosion risk. This paper describes the procedures of cavitation tests and the related instrumentation, depending both on the type of hydraulic machine and its operation range. Discussion is mainly directed toward t

The work presented in this paper details the methodology applied to inventory and estimate the power losses in a micro-turbine with counter-rotating runners. The separation between the impact of design parameters and operational parameters on each identifi ...

An experimental investigation has been carried out to quantify the effects of surrounding fluid on the modal behavior of a reduced scale pump-turbine impeller. The modal properties of the fluid-structure system have been obtained by Experimental Modal Anal ...

Francis turbines can experience critical instabilities at high load operating points, limiting their maximum power output. The swirling flow developed in the draft tube produces a cavitating axisymmetric volume, acting as an internal energy source leading to a self-excited surge phenomenon. The pulsation of the vortex rope corresponds to one of the eigenfrequencies of the hydraulic system. Efforts to accurately characterize, simulate and predict this phenomenon have been undertaken by several researchers, u

Models of hydraulic components based on impedance method have been implemented in a software called “SIMSEN”. This tool allows the simultaneous solution of the electrical, hydraulic, mechanic and control equations ensuring a proper interaction between the four parts of a system. In this paper the interaction between hydraulic and electric part of 2 Francis turbines power plant is investigated by comparing the simulation results obtained with and without coupling hydraulic and electric phenomena. Using hydra

Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow lea ...

François Avellan

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Pressure Wall Measurements in the whole Draft Tube : Steady and Unsteady Analysis

Numerical simulation of fluid added mass effect on a francis turbine runner

ACOUSTIC RESONNANCE IN CAVITATION FREE AND CAVITATING FLOWS

Rotor-Stator Interaction Induced Pressure Fluctuations: CFD and Hydroacoustic Simulations in the Stationary Components of a Multistage Centrifugal Pump

Optimal Control of Part Load Vortex Rope in Francis Turbines

On the Efficiency Alteration Mechanisms Due to Cavitation in Kaplan Turbines

High-speed flow visualization in a pump-turbine under off-design operating conditions

SURFACE ROUGHNESS IMPACT ON FRANCIS TURBINE PERFORMANCES AND PREDICTION OF EFFICIENCY STEP UP

Onboard Measurements of Pressure and Strain Fluctuations in a Model of low Head Francis Turbine. Part 2 : Measurements and Preliminary Analysis Results

Numerical Simulation of Leading Edge Cavitation over 2D Hydrofoil

Dynamic behaviour of a Francis turbine during voltage regulation in the electrical power system

DuoTurbo: Implementation of a Counter-Rotating Hydroturbine for Energy Recovery in Drinking Water Networks

Unsteady Numerical Simulations of the Flow Related to the Unstable Energy-Discharge Characteristic of a Medium Specific Speed Double Suction Pump

Experimental method for the evaluation of the dynamic transfer matrix using pressure transducers

Cavitation test of hydraulic machines : procedure and instrumentation

Comprehensive power loss modelling to improve the performance of an Energy Recovery Station for water utility networks

Modal behavior of a reduced scale pump-turbine impeller. Part 1: Experiments

Determination of Hydroacoustic Draft Tube Parameters by High Speed Visualization during Model Testing of a Francis Turbine

Simulation of Transient Phenomena in Francis Turbine Power Plants : Hydroelectric Interaction

Influence of the Francis turbine location under vortex rope excitation on the hydraulic system stability