Attempt to induce the three-dimensionalization process of T-S waves in boundary-layer transition

The receptivity of a three-dimensional roughness element on a flat-plate boundary layer to outer acoustic disturbances is investigated by wind-tunnel experiments. The term `receptivity' describes the process through which external disturbances are transformed into instability waves in a boundary-layer. It is known that several types of oblique waves can be found in a three-dimensionalization process in the later stages of boundary-layer transition. In the present experiment, we investigate the behavior of oblique waves and try to control boundary-layer transition by utilizing receptivity. It is shown that oblique waves can be generated on a flat-plate boundary layer with an inclined roughness element under acoustic forcing. An attempt to induce three-dimensionalization modes which are shown in the later stages of boundary-layer transition is carried out. However, flow structure generated by our method did not match the natural three-dimensional modes.