Active control of boundary-layer transition using a thin actuator

An experimental study to generate T-S (Tollmien-Schlichting) waves and obli que waves in a flat plate boundary layer is carried out. This is considered to be the first step towards controlling boundary-layer transition. In ord er to generate T-S waves and oblique waves, an array of piezoelectrically d riven actuator pieces attached to a flat plate surface was used. The actuat or pieces were sufficiently thin to keep the boundary layer in the laminar state. In order to generate various oblique waves, ten actuator pieces were aligned in the spanwise direction, each of which could be controlled separ ately. It is shown that both two-dimensional T-S wave and oblique waves of various angles could be generated using this device. It is also shown that when a flow pattern similar to the Craik-type three-dimensionalization mode was excited, the onset of turbulence took place early and locally at a cer tain spanwise location.