Artificial Control of the Three-Dimensionalization Process of T-S Waves in Boundary-Layer Transition

Abstract

An attempt to control the three-dimensionalization process of T-S waves by utilizing the receptivity of a three-dimensional roughness element on a flat-plate boundary layer to outer acoustic disturbances is carried out by wind-tunnel experiments. The term "receptivity"⁽¹⁾describes the process through which external distur-bances are transformed into instability waves in a boundary layer. It is known that several types of oblique waves can be found in the three-dimensionalization process in the later stages of the boundary-layer transition. In the present experiment, we artificially introduce oblique waves in the boundary layer in order to control the boundary-layer transition. It is shown that an oblique wave can be generated in a flat-plate boundary layer with a roughness element attached to the plate inclined and an acoustic forcing. An attempt to induce three-dimensionalization modes that are observed in the later stages of boundary-layer transition is also carried out. However, the natural three-dimensional mode flow structures could not be generated by our method.