Experimental analysis of transition delay by means of roughness elements

Authors: Fransson, J. H. M., Brandt, L.B., Talamelli, A., Cossu, C.
Document Type: Conference
Pubstate: Published
Journal: AIAA-06-3528, 36th AIAA Fluid Dynamics Conference and Exhibit, June 5-8, San Francisco
Year: 2006


An experimental activity aimed at the development of a passive method for viscous drag reduction in an aerodynamic body is presented. The reduction is achieved by delaying the laminar-turbulent transition of the boundary layer. The research is motivated by previous theoretical analysis where it was demonstrated that optimal stable streaks in a boundary layer are capable to stabilize low amplitude Tollmien-Schlichting waves. In this paper the results of a series of experiments on a flat plate are presented. First, it is shown that by means of suitable roughness elements it is possible to generate stable steady streaks of sufficient amplitude. Then, it is be 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.