A flow surface (16), e.g. on a swept aircraft wing, has a three-dimensional boundary-layer flow. The surface is defined by a spanwise direction (z) and a chordwise direction (x). In or on the flow surface excitation locations (22) are arranged, exciting primary disturbances. The disclosure is characterized in that the excitation locations (22) are arranged such that benign steady primary disturbances are excited and maintained on a sufficiently-high amplitude level as longitudinal vortices respectively crossflow vortices, suppressing naturally growing nocent primary disturbances by a non-linear physical mechanism. The benign primary disturbances preserve a laminar flow, such that unsteady secondary disturbances, which may initiate turbulence and which, otherwise, are excited in streamwise direction by nocent primary vortices, are suppressed or at least stabilized.