ARTIFICIAL CONTROL OF THE 3-DIMENSIONALIZATION PROCESS OF T-S WAVES IN BOUNDARY-LAYER-TRANSITION

An attempt to control the three-dimensionalization process of T-S wave s by utilizing the receptivity of a three-dimensional roughness elemen t on a flat-plate boundary layer to outer acoustic disturbances is car ried out by wind-tunnel experiments. The term ''receptivity''((1)) des cribes 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 the three-dimensionalization pr ocess in the later stages of the boundary-layer transition. In the pre sent experiment, we artificially introduce oblique waves in the bounda ry layer in order to control the boundary-layer transition. It is show n that an oblique wave call be generated in a flat-plate boundary laye r with a roughness element attached to the plate inclined and an acous tic 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 structur es could not be generated by our method.