Active control of the boundary-layer transition using a thin actuator

Experimental study to generate T-S waves and oblique waves in a flat plate boundary layer is carried out. It is regarded as the first step towards controlling the boundary-layer transition. In order to generate T-S waves and oblique waves, an array of piezoelectrically driven actuator pieces attached to the flat plate surface is used. The actuator is thin enough to keep the boundary layer in the laminar-state. In order to generate various oblique waves, the actuator consists of an array of 10 small pieces aligned in the spanwise direction. Each piece can be controlled separately. It is shown that various oblique waves can be successfully generated using this actuator. It is also shown that when the three-dimensionalization mode is induced, the onset of turbulence takes place locally at a certain spanwise location.