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 increasing amount of information available, makes
filters crucial tools.
Filtering algorithm used nowadays in the World Wide Web will be introduced.
A version based on the detection and use of especially well informed
individuals in a evaluator population will be presented.