In this paper the results of a large experimental activity aimed at the development of a passive method for delaying the laminar-turbulent transition of the boundary layer on an aerodynamic body are presented. The research was at the beginning motivated by a simplified linearized theoretical analysis where it was demonstrated that the presence of stable streaks in a zero pressure gradient boundary layer are capable to stabilize the growth of Tollmien-Schlichting waves. To prove the feasibility of the concept the following activities are presented. First of all it will be shown that by means of cylindrical roughness elements it is possible to generate stable steady streaks of amplitudes up to 12% of the free stream velocity. In a second part it will 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. A further possible development will be presented in the conclusions.

Roughness: a new passive mechanism to delay transition to turbulence on boundary layers

TALAMELLI, ALESSANDRO;
2009

Abstract

In this paper the results of a large experimental activity aimed at the development of a passive method for delaying the laminar-turbulent transition of the boundary layer on an aerodynamic body are presented. The research was at the beginning motivated by a simplified linearized theoretical analysis where it was demonstrated that the presence of stable streaks in a zero pressure gradient boundary layer are capable to stabilize the growth of Tollmien-Schlichting waves. To prove the feasibility of the concept the following activities are presented. First of all it will be shown that by means of cylindrical roughness elements it is possible to generate stable steady streaks of amplitudes up to 12% of the free stream velocity. In a second part it will 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. A further possible development will be presented in the conclusions.
Proceedings of the Annual International Meeting of the Japan Society of Fluid Mechanics
1
9
A. Talamelli; J.H. Fransson; L. Brandt; C. Cossu
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/83701
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