Transition to turbulence delay by means of a passive mechanism

Authors: Fransson, J. H. M., Talamelli, A., Brandt, L.B., Cossu, C.
Document Type: Conference
Pubstate: Published
Journal: CEAS/KATnet II Conference on Key Aerodynamic Technologies, 12-15 May 2009, Bremen
Volume: 1  
Year: 2009


An experimental activity aimed at the development of a passive method for delaying the laminar-turbulent transition of the boundary layer on an aerodynamic body is presented. The research is motivated by a simplified linearized theoretical analysis where it was demonstrated that stable streaks in a boundary layer are capable to stabilize the growth of Tollmien-Schlichting waves. In this paper the results of a series of experiments, performed on a flat plate, aimed at proving the feasibility of this concept are presented. Firstly, it is shown that by means of suitable roughness elements it is possible to generate stable steady streaks of amplitudes up to 12% of the free stream velocity. Secondly, it is demonstrated that the generated streaks are really effective in reducing the growth of the Tollmien-Schlichting waves as predicted by the theory. Finally, it is shown that using this passive control technique it is possible to sensibly delay transition to turbulence.