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

Enhancing Wind Farm Performance through Axial Induction and Tilt Control: Insights from Wind Tunnel Experiments

Fernando Porté Agel, Guillem Armengol Barcos

Static axial induction control and tilt control are two strategies that have the potential to increase power production in wind farms, mitigating wake effects and increasing the available power for downstream turbines. In this study, wind tunnel experiment ...

MDPI2024

Numerical study on the scale effect of tip vortex cavitation induced by incoming velocities and scale ratios

Mohamed Farhat, Huaiyu Cheng, Mohan Xu

Large eddy simulations of tip vortex cavitation (TVC) around an elliptical hydrofoil is performed to study its scale effect. A satisfying agreement is obtained between the numerical and experimental data. It indicates that the scale effect of TVC is remark ...

PERGAMON-ELSEVIER SCIENCE LTD2023

The effects of kinematics, flexibility, and planform on the vortex formation and aerodynamic performance of flapping wing flight

Alexander Gehrke

In this thesis, the aerodynamic challenges in flapping wing flight are addressed. In particular, the effects of different wing kinematics, flexibilities, and planforms on the the leading edge vortex development and aerodynamic performance are investigated. ...

EPFL2023

The effects of a spur dike location in a 90° sharp channel bend on flow field: Focus on anisotropy degree and anisotropy nature

Anton Schleiss

In this research, the flow features around a spur dike located in a 90˚ sharp channel bend have been studied experimentally in detail. Results showed that the effects of the spur dike on upstream sections increased by increasing α (spur dike location from ...

2023

Dynamic stall characterisation and control for vertical-axis wind turbines

Sébastien Le Fouest

According to the International Energy Agency, the global net-zero emissions objective requires the installed wind power capacity to increase 11-fold between 2020 and 2050. The scientific community has recently voiced concerns about the logistic feasibility ...

EPFL2023

Strength and timing of primary and secondary vortices generated by a rotating plate

Karen Ann J Mulleners, Diego Francescangeli

Accurate predictions of how vortices grow, evolve, and separate from aerodynamic objects are desirable for various applications ranging from autonomous aerial vehicles to wind turbines. Here, we present an experimental characterisation of the formation pro ...

2023

Growth, timing, & trajectory of vortices behind a rotating plate

Diego Francescangeli

The presence of aerodynamic vortices is widespread in nature. They can be found at small scales near the wing tip of flying insects or at bigger scale in the form of hurricanes, cyclones or even galaxies. They are identified as coherent regions of high vor ...

EPFL2022

Lagrangian analysis of bio-inspired vortex ring formation

Karen Ann J Mulleners, Mrudhula Baskaran

Pulsatile jet propulsion is a highly energy-efficient swimming mode used by various species of aquatic animals that continues to inspire engineers of underwater vehicles. Here, we present a bio-inspired jet propulsor that combines the flexible hull of a je ...

2022

Estimating the non-dimensional energy of vortex rings by modelling their roll-up

Karen Ann J Mulleners, Guillaume de Guyon-Crozier

The non-dimensional energy of starting vortex rings typically converges to values around 0.33 when they are created by a piston-cylinder or a bluff body translating at a constant speed. To explore the limits of the universality of this value and to analyse ...

Cambridge University Press2022

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

François Avellan, Andres Müller, Arthur Tristan Favrel, Elena Vagnoni, Ali Amini

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 ...

IOP PUBLISHING LTD2021

Evolution of the vorticity distribution in vortex rings

Guillaume de Guyon-Crozier

Vortex rings are very efficient at transporting fluid on long distances and can generate large forces, either thrust or drag. These abilities are influenced by the vorticity distribution within the vortex. Previous work on vortices produced by piston-cylin ...

EPFL2021

Effects of leading-edge separation on the vortex-induced vibration of an elongated bluff body

Hongyu Li, Guiyue Duan

Wind-tunnel experiments were conducted to investigate the effects of leading-edge separation on the vortex-induced vibration (VIV) of an elastically-supported elongated bluff body. Solid wind barriers of various heights were fixed in the leading edge to ad ...

ELSEVIER2021

Scaling of the translational velocity of vortex rings behind conical objects

Karen Ann J Mulleners, Guillaume de Guyon-Crozier

Ring vortices are efficient at transporting fluid across long distances. They can be found in nature in various ways: they propel squids, inject blood in the heart, and entertain dolphins. These vortices are generally produced by ejecting a volume of fluid ...

2021

A new Euler-Lagrangian cavitation model for tip-vortex cavitation with the effect of non-condensable gas

Mohamed Farhat, Huaiyu Cheng

Numerical simulation of tip vortex cavitation (TVC) remains a challenging task in a variety of applica-tions, such as axial turbines and pumps as well as marine propellers. Although it is well known that TVC is highly sensitive to gas content, be it dissol ...

PERGAMON-ELSEVIER SCIENCE LTD2021

Phenomenology and scaling of optimal flapping wing kinematics

Karen Ann J Mulleners, Alexander Gehrke

Biological flapping wing fliers operate efficiently and robustly in a wide range of flight conditions and are a great source of inspiration to engineers. The unsteady aerodynamics of flapping wing flight are dominated by large-scale vortical structures tha ...

IOP PUBLISHING LTD2021

On the numerical simulation of a confined cavitating tip leakage vortex under geometrical and operational uncertainties

Mohamed Farhat

The effects of operational and geometrical uncertainties on Tip Leakage Vortex (TLV) characteristics are investigated in the current research. Geometrical uncertainties are comprised of manufacturing tolerances or gradual geometry degradation over the time ...

PERGAMON-ELSEVIER SCIENCE LTD2021

Physical Mechanism and Flow Control of Tip Vortex Cavitation

Ali Amini

Occurrence of cavitation in hydraulic machines is a challenging issue because it is often accompanied with loss of efficiency, noise emissions, vibrations, and erosion damages. Tip vortices, in particular, are an ideal site for the development of cavitatio ...

EPFL2020

Large eddy simulation of the tip-leakage cavitating flow with an insight on how cavitation influences vorticity and turbulence

Mohamed Farhat, Huaiyu Cheng

Cavitation within a tip leakage flow remains a challenging issue in a variety of axial hydraulic machines. It is still not possible nowadays to predict cavitation occurrence in such a flow with acceptable accuracy. In the present study, we have carried out ...

ELSEVIER SCIENCE INC2020

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

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

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

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

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 PUBLISHING LTD2019