The wakes formed downstream fixed or moving bodies submitted to unsteady detachment are still a fascinating research topic, both fundamentally and industrially. With respect to fundamental aspects, state-of-the-art research focuses on stability analysis and the different steps that a wake-like flow goes through when the Reynolds number increases, on its way to turbulence. Theories of chaos, attractors and the laminar-turbulent transition are of great interest.
The physical mechanisms associated with these successive stages are still barely known. In particular, taking into account the non-linearity in the transfer mechanisms between the shear zones downstream of the detachment and the vortex formation regions according to different types of instabilities opens up important research perspectives for physical comprehension, in order to better model these mechanisms later. The interaction between different types of vortices is also a fascinating research topic, which allows for the analysis and explanation of the birth and development of turbulence around and in the wake of a body, from moderate Reynolds numbers to high Reynolds numbers.
The birth of three-dimensionality in particular is connected to the aspects of secondary instability and the birth of more complex vortex structures, characterized by dislocations, by "horse-shoe" or "hair-pin" vortices. The spatio-temporal analysis of these structures is directly associated with the unsteady evolution of drag and lift forces around a body (cylinder, aircraft wing, submarine, helicopter blade, blade, etc). The dynamics of the wakes and their fluid instabilities interact with the mobile and / or deformable modes of the structure and lead to fluid-structure couplings that are associated with induced vibration and floating phenomena, beyond the critical numbers characterizing the fluid-structure interaction.
The study of all these mechanisms that govern wakes is essential to model these flows and their interaction with the solid structure at high Reynolds numbers, interesting industrial applications where the approaches of the type "Direct Numerical Simulation" are not applicable, as well as to develop approaches to control instabilities and harmful vortices, also used by the downstream sector. The wakes thus represent an important and fascinating area of Fluid Mechanics and are present in everyday life, visible (streams, boat wakes, ...) and less visible (wakes of planes when the weather conditions erase their trace), among others. What would be life without wakes?
