Sophie Goujon-Durand

The wake of a cylinder performing rotary oscillations

We study the wake of a cylinder performing rotary oscillations around its axis at moderate Reynolds number. We observe that the structure of the vortex shedding is strongly affected by the forcing parameters. The forced wake is characterized by a lock-in region where the vortices are shed at the forcing frequency and a region where the vortices can be reorganized to give a second frequency close to those observed for the unforced wake. We show that these modifications of the wake structure change the dynamic of the fluctuations downstream from the cylinder. We vary the amplitude and the frequency of the oscillations and study the consequences of these modifications on the mean flow and the global drag applied on the cylinder. We then discuss the mechanism responsible for the modification of the fluctuations and the modification of the drag coefficient.

The wake behind a rotating sphere

The wake behind an axisymmetric body rotating about an axis aligned with the streamwise direction has been experimentally investigated in a low-velocity water channel for the intermediate Reynolds number. The measurements focused on the evolution of the flow regime with two counter rotating vorticies, as a function of two control parameters, namely the Reynolds number and the dimensionless rotation rate Ω.

Spatial Inhomogeneities of Hydrodynamic Instabilities

We describe the spatial inhomogeneities in hydrodynamic patterns, in the cases of confined systems such as the Rayleigh-Benard convection and open systems such as as the Benard-von Karman instability of vortex shedding. From experimental results, we define the typical correlation lengths and their scaling law in each situation.