Abstract

Experimental results on the temporal evolution of the wake of a flat plate submitted to an external harmonic mechanical forcing are presented. The system consists of a horizontally fixed flat plate with a small flap at the trailing edge, which performs small oscillations when forced by an external shaker. At low Reynolds number, and working with weak forcing amplitudes, frequency response results show strong evidence of a spatio-temporal resonance of the near wake. Harmonic content of the wake is found to be related to interfaces of organized flow structures under resonant conditions. Near the resonant forcing frequencies, drag reduction is observed. In addition, the wake flow was tested as a wave propagating media, where arbitrary signals, like discrete number of bursts, were successfully propagated. Hot wire measurements and flow imaging through light scattering from smoke particles using a rapid ccd camera, allowed to record the inner and outer structures of the forced wake. © Europhysics Letters Association.