Active Control of TS-Instabilities on an Unswept Wing

The laminar-turbulent transition of a boundary layer can be delayed by active and passive methods. Active control methods are directly reducing the instability waves, so called Tollmien Schlichting waves (TS-waves) of the laminar boundary layer, by wave superposition, whereas passive methods stabilize the mean velocity profile. Active control requires much less energy compared to passive control and could be used complementary or alternatively to passive methods such as distributed suction. Active control of TS-waves could be performed with an active skin consisting of sensors, actuators and controllers. The application of an active skin may be useful for TS-waves in the early linear stage up to the weak nonlinear stage, especially if they are dominated by two-dimensional TS-modes. Such a TS-scenario may also be found on a swept wing in the mid-chord region, especially if crossflow instabilities were previously suppressed by suction in the leading edge region.