Experiments on the receptivity of a boundary layer to a localized free stream disturbance

摘要

The receptivity of the boundary layer on a straight-wing model to controlled free stream disturbances is studied. The disturbances are generated by a special source located upstream of the leading edge of the model. The measurements show that perturbations with a streamwise-extended structure arise in the boundary layer. This structure consists of regions with excess nd defect velocity relative to the local mean velocity, and these regions alternate in the spanwise direction. These "streaky" structures arise in boundary layers under the action of intense external turbulence. An important role of the mean flow characteristics near the leading edge of the model in the process of transformation of external localized disturbances to boundary layer disturbances is shown. A weak effect of pressure gradients on the basic characteristics of disturbance evolution is found.