Interaction of noise disturbances and streamwise streaks

The evolution of disturbances in boundary layers modified through span-wise periodic, steady streamwise streaks is studied via numerical simulations The disturbances are introduced via random two- and three-dimensional noise of various amplitudes close to the inlet (Re-iota approximate to 60000) The aim of the present work is to determine the impact of the interaction of streaks and noise on the arising Bow structures and, eventually, on the location and details of the breakdown to turbulence. It is shown that large-scale 2D noise can be controlled via streaks, whereas the more general 3D noise configuration is prone to premature transition due to increased instability of the introduced streaks It is interesting to note that the latter transition scenario closely resembles the flow structures found in bypass transition. Transition in true bypass transtion forced by ambient free-stream turbulence is also promoted by the addition of streamwise streaks in the laminar part of the boundary layer