Active Control of Tollmien-Schlichting Instabilities by Multi-Channel Sensor Actuator Systems

This work describes experimental investigations intended to actively attenuate TollmienSchlichting(TS) instabilities on an airfoil. It is possible to superimpose harmonic TS-waves in the early linear stage with artificial damping waves in order to minimize these disturbances. Sensors and actuators integrated in the wing surface controlled by a fast signal processor are required to enable an optimum active wave control (AWC). High attenuation rates have already been achieved with a single sensor actuator system for a 2D–dominated TS–perturbation. Linear 3D–instabilities were successfully cancelled in recent experiments by a spanwise arrangement of sensors and actuators. The sensors feed a controller which drives the actuators by performing the simultaneous adaptation of the corresponding transfer functions. Further experiments have demonstrated the additional delay of transition due to the repeated use of sensor actuator systems in streamwise direction. Actuator tests were carried out on a 2D sensor actuator system in parallel with experiments on multiple systems. Slot actuators are preferably used, mainly due to their easy application in basic experiments. First tests with membrane actuators have shown a better local receptivity, especially at high amplitudes of the TS-disturbances.