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Mind the gap: a new insight into the tip leakage vortex using stereo-PIV

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Swirl number based transposition of flow-induced mechanical stresses from reduced scale to full-size Francis turbine runners

François Avellan, Arthur Tristan Favrel, Christian Landry, Joao Gomes Pereira Junior, Keita Yamamoto

At part load conditions, Francis turbines are subject to the emergence of a hydrodynamic instability in their draft tube, referred to as precessing vortex rope. It induces pressure pulsations in the water passages at the precession frequency of the vortex, ...

2020

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

François Avellan, Joao Gomes Pereira Junior

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 ...

Pergamon-Elsevier Science Ltd2020

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

François Avellan, Ebrahim Jahanbakhsh, Audrey Paulette Solange Maertens, Sebastián Camilo Leguizamón Sarmiento, Siamak Alimirzazadeh

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 ...

IOP Publishing2019

LES investigation of the influence of cavitation on flow patterns in a confined tip-leakage flow

Mohamed Farhat

In the present paper, Large Eddy Simulations combined with the Zwart-Gerber-Belamri cavitation model are conducted to study the flow characteristics in a tip-leakage flow. A reasonable agreement is obtained between the numerical and experimental data. With ...

PERGAMON-ELSEVIER SCIENCE LTD2019

Vortex siphon - from 1:1 scale physical model to SPH simulation and prototype

Giovanni De Cesare

The rail link between Geneva Cornavin Station, Eaux-Vives Station and Annemasse (CEVA) is currently under construction including a cut-and-cover tunnel built by slurry walls located in the alluvium of the Foron River. The covered trench cuts the groundwate ...

2019

Physical Mechanism of Interblade Vortex Development at Deep Part Load Operation of a Francis Turbine

François Avellan, Arthur Tristan Favrel, Keita Yamamoto

For seamless integration of growing electricity production from intermittent renewable energy sources, Francis turbines are under increasing demand to extend their operating range. This requires Francis turbines to operate under off-design conditions, wher ...

ASME2019

Mitigating tip vortex cavitation by a flexible trailing thread

Mohamed Farhat, Ali Amini

Tip Vortex Cavitation (TVC) is a major issue in design and operation of axial hydraulic machines. We investigate the capacity of a flexible trailing thread in alleviating TVC by analyzing the flow-induced motion. For this purpose, a nylon thread with three ...

AMER INST PHYSICS2019

Procedure for predicting part load resonance in Francis turbine hydropower units based on swirl number and local cavitation coefficient similitude

François Avellan, Christophe Nicolet, Sébastien Alligné, Christian Landry, Loïc Andolfatto, Arthur Tristan Favrel

Francis turbines operating at part load conditions develop a cavitation precessing vortex known as a vortex rope in the draft tube cone below the runner outlet. At part load conditions, this vortex precession acts as an excitation source inducing pressure ...

ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD2019

On the hysteresis of cavitation incipience and desinence in hydraulic machines

Mohamed Farhat, Ali Amini, Martino Reclari

The omnipresent vortical structures in hydraulic machines are extremely prone to the occurrence of cavitation. It is well known that besides the flow parameters, the incipience, development, and disappearance of cavitation within a vortex is very sensitive ...

IOP Publishing2019

Coherent Structure Interaction During Unsteady Separation

Karen Ann J Mulleners

Unsteady flow separation in rotationally augmented flow fields plays a significant role in the aerodynamic performance of industrial rotors, including wind turbines. Current computational models underestimate the aerodynamic loads due to the inaccurate pre ...

2019

Roll-up region of tip vortex: numerical investigation

Mohamed Farhat, Azin Amini, Matthieu Dreyer, Ali Amini, Martino Reclari

The appearance of gas-filled vortices at the tip of hydraulic machines blades is usually associated with increase of losses, vibrations, noise and erosion risk. The understanding of the roll-up region, where the boundary layer on the pressure side crosses ...

IOP Publishing2019

Dynamic modal analysis during reduced scale model tests of hydraulic turbines for hydro-acoustic characterization of cavitation flows

François Avellan, Arthur Tristan Favrel, Christian Landry, Joao Gomes Pereira Junior

Francis turbines operating at off-design conditions experience the development of unfavourable cavitation flows in the draft tube at the runner outlet, which induce pressure pulsations and hydro-acoustic resonances in the worst cases. The assessment of hyd ...

2019

On the physical mechanism of tip vortex cavitation hysteresis

Mohamed Farhat, Matthieu Dreyer, Ali Amini, Martino Reclari

Inception and desinence thresholds of tip vortex cavitation (TVC), generated by an elliptical NACA 16-020 hydrofoil, are measured at different flow conditions for various gas contents. It is observed that TVC often disappears at cavitation indices signific ...

SPRINGER2019