Delaying transition to turbulence by a passive mechanism

Authors: Fransson, J. H. M., Talamelli, A., Brandt, L.B., Cossu, C.
Document Type: Article
Pubstate: Published
Journal: Physical Review Letters
Volume: 96   064501
Year: 2006


Reducing skin friction is important in nature and in many technological applications. This reduction may be achieved by reducing stresses in turbulent boundary layers, for instance tailoring biomimetic rough skins. Here we take a second approach consisting in keeping the boundary layer laminar as long as possible by forcing small optimal perturbations. Due to the highly non-normal nature of the underlying linearized operator, these perturbations are highly amplified and able to modify the mean velocity profiles at leading order. We report results of wind-tunnel experiments in which we implement this concept by using suitably designed roughness elements placed on the skin to enforce nearly optimal perturbations. We show that using this passive control technique it is possible to sensibly delay transition to turbulence.