Instability, Transition, Turbulence and Control

Y. Duguet, F. Lusseyran, L. Martin-Witkowski, S. Pellerin

Fluid flows can be classified into several regimes such as laminar, transitional or turbulent, with huge important differences from an energetic point of view. The dynamic processes allowing to transition from one regime to another, or to stabilise one of them, are as of today still not well understood. The instability of a given laminar flow with respect to arbitrary perturbations, either infinitesimal or finite-amplitude, gives rise to interesting mathematical and numerical developments. Transitions between different regimes, often of a hysteretic nature, can be found even within turbulent flows themselves. An effort is dedicated to the analysis of spatial symmetries and their breaking by instability mechanisms. They are described qualitatively and quantified using novel and efficient algorithms in the frame of unsteady three-dimensional simulations necessating important ressources and method specific to large data-sets. An experimental lab allows for visualising and quantifying these same flow set-ups complementarily to numerical studies. Finally, some deeper understanding and modelling of the underlying hydrodynamical mechanisms leads to new experimental/numerical ways of controlling these flows towards the desired working point. The flow configurations investigated in this team are academical yet inspired by industrial cases stemming from ground aerodynamics (vehicle wakes and open cavities) or aeronautics (boundary layers flows). Collaborations at local, national or international level as well as student training are at the core of our methodology. Current topics of investigation include in a non-exhaustive way:

  • Experimental/numerical study of the effect of ambiant pollution on the stability of rotating flows with rigid or deformable free surface.
  • Numerical simulation, modelling and control of the symmetry breaking of a turbulent wake
  • Simulation of subcritical laminar-turbulent transition in wall-bounded shear flows, from both a nonlinear (state space analysis) and a spatiotemporal point of view (intermittent regimes)
  • Experimental/numerical application of closed-loop control in open shear flows.

 

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