Adding streamwise streaks in the plane Poiseuille flow

In recent investigations, finite amplitude streamwise streaks, venerated with roughness elements, have been used to delay transition to turbulence. The maximum height of these roughness elements is limited by the appearance of instabilities in their near wake, therefore putting a limit on the maximum streak amplitude they can produce. Here we prove that large amplitude streaks can be generated by 'adding' lower amplitude streaks with Multiple arrays of toughness elements. To cite this article: M. Hollands, C. Cossu, C. R. Mecanique 337 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.