Transition to turbulence in fluids remains one of the unsolved problems of modern mechanics, despite its importance in various fields of engineering ranging from aerodynamics to oil transport. An especially challenging topic is the question of "subcritical" transition in wall-bounded flows, i.e. when the base flow is linearly stable and classical stability analysis fails at explaining the coherent structures commonly observed in experiments and in simulations. This concerns most flows in simple geometries such as pipes, ducts, channel and also boundary layer flows. This special problem lies at the crossroad between hydrodynamics, chaos theory and statistical physics. Specific cutting-edge experimental and/or numerical strategies have been been developed in the last decade. New questions arise as to how this problem extends to non-Newtonian rheologies, or how to control or delay this transition in realistic situations.
The colloquium will feature individual contributions, poster sessions and round tables for discussions.

Non-exhaustive list of topics :

• Spatiotemporal aspects of subcritical transition: large-scale pattern formation, intermittency, lifetimes measurements, experimental techniques
• Dynamical systems approach to transitional flows: exact coherent structures, unstable periodic orbits, edge states, chaotic saddles, related numerical methods
• Localised states in fluids
• Low-dimensional modelling strategies
• Non-Newtonian rheologies
• Nonlinear control strategies
•  Cross-disciplinary analogies