Control of a laminar separating boundary layer by induced stationary perturbations

Wind-tunnel data on stationary streaky structures developing in a laminar flow behind a backward-facing step on a flat plate are presented. The streaks were generated in a controlled manner by a row of three-dimensional surface humps placed periodically in the span-wise direction close to the separation line. The mean flow distortion of the separation region created in this way was documented by hot-wire measurements. Details of the evolution of the stationary perturbations in the separation region as well as their effect upon the oscillatory flow component, which are of interest due to elaboration of prospective methods for control of low-speed aerodynamics, are elucidated.