ACTIVE CANCELLATION OF TOLLMIEN–SCHLICHTING INSTABILITIES ON AN UNSWEPT WING USING MULTI–CHANNEL SENSOR ACTUATOR SYSTEMS

The paper reports on multiple control systems cancelling Tollmien-Schlichting (TS) instabilities on an unswept wing with a modified NACA 0008 profile. TS disturbances are canceled in their linear stage of development by superimposition with artificially generated counter waves. This method requires a considerably lower energy input than the stabilization by manipulation of the local mean velocity profile (e.g. boundary layer suction). The emphasis of the present investigation is on multiple control of TS waves. A fast digital signal processor (DSP) is employed to achieve an optimum wave superimposition. A reference sensor upstream of the actuator detects the traveling TS disturbances. The reference sensor signal is used to calculate a corresponding actuator signal by convolution with a linear transfer function. The transfer function is continuously adapted to minimize the error signal measured downstream of the actuator. This paper deals with the multiple application of this method to attenuate three-dimensional TS waves and the implementation of streamwise repeated disturbance damping to obtain a maximum delay of laminar-turbulent transition.