Transitions to tubulence in shear flows

Collaborators : J. E. Wesfreid (DR Emérite CNRS), Grégoire Lemoult (PhD student from 2010 to 2013), Tristan Cambonie (PhD student from 2008 to 2011), Thomas Duriez (PhD student from 2005 to 2009).

Hydrodynamic instabilities

Instabilities of a Jet-In-Crossflow (JICF) in collaboration with T. Cambonie

When a vertical jet interacts with an incoming boundary layer, the jet will undergo various transitions depending on the value of velocity ratio between the jet velocity and the freestream velocity of the boundary layer. A nice example is shown below with the creation of a serie of hairpin vortices :

Interaction between a round jet and an incoming boundary layer leading to the creation of hairpin vortices. These are instantaneous Volumetric Velocimetry measurements made during Tristan Cambonie’s PhD thesis.

Transition to turbulence in shear flows

Subcritical transition to turbulence in a Plane Poiseuille Flow (PPF), with G. Lemoult and J. E. Wesfreid

Visualization of a the structure of a turbulent spot growing in the subcritical régime :


Visualisation of the nucleation of a turbulent spot growing in the PPF after an initial pulse in the middle of the channel :

 Self-Sustained Process (SSP) in boundary layer with T. Duriez and J. E. Wesfreid.

We have shown experimentally that the SSP is indeed a key mechanism in the transition to turbulence of wall-bounded shear flows. It was achieved using small cylinders to force the transition of a subcritical boundary layer :


Creation of streaks of high and low streamwise velocity downstream the cylinders.