Abstract
Disturbances in turbulence are cause and effect of non-linear interactions, so that turbulence itself is known as a non-linear phenomenon. Recently, it was surprisingly found that there exists a linear disturbance excited by a periodic vibration in a two-dimensional turbulent jet. Amplitude of the disturbance normalized by that of the initial disturbance is constant when the initial disturbance amplitude is not considerably strong. In this study, artificial periodical disturbance from a wall surface is introduced to a flat-plate turbulent boundary layer, and development of the disturbance is investigated using a hot wire anemometry. The periodical component, extracted from the streamwise velocity signals with ensemble-average technique, indicates that the existence of a linear disturbance in a turbulent boundary layer, where strong non-linear interaction among turbulent disturbances occurs. It is worth noting that the excited disturbance structure is similar to a hairpin vortex that is generally observed in turbulent shear flows, suggesting that the point-like initial disturbance generates an artificial hairpin vortex.
