RÉSUMÉ

A free stream vortical disturbance generated by a single axial vortex of controlled strength and position was used to investigate vortical receptivity of flat plate and swept wing boundary layers. In both cases, the boundary-layer response was dominated by streamwise velocity perturbations, that grew downstream essentially linearly over the flat plate and quasi-exponentially over the swept-wing model. It was shown that the disturbance characteristics in the flat plate boundary layer are in agreement with data of previous experiments performed under natural and control conditions concerning 'by-pass' transition initiated at high free stream disturbance level. It was proved that the role of the leading edge in the process of streak formation and growth in this case is not dominant. In contrast, the disturbance transformation on the swept wing occurs close to the leading edge followed by formation of a wave packet dominated by waves which are specific for cross-flow instability. Meanwhile, disturbances, which can be attributed to the effect found at the flat plate were also identified.