Experiments on stream-wise streaky structures in a laminar separation bubble

Wind-tunnel data on stationary streaky structures developing in a laminar flow behind backward-facing step on a flat plate are reported. The streaks are generated in a controlled manner by three-dimensional surface humps placed periodically close to the separation line and spaced in the span-wise direction. The mean flow distortions of the separation region created in this way are investigated through hot-wire measurements. As a result, details on evolution of the stationary perturbations in the separation region are elucidated as well as their effects upon the separated flow which are of interest due to elaboration of perspective methods for control of low-speed aerodynamics.