Tollmien-Schlichting Wave Control on an Airfoil Using Dynamic Surface Modification

The present study demonstrates experimental mitigation of Tollmien-Schlichting waves on an unswept natural laminar flow airfoil at a chord-based Reynolds number of 9.90x105. This was facilitated by dynamic surface modifications using piezoelectrically driven oscillating surface actuators. The actuators were located at three streamwise locations on the airfoil's suction side. The upstream actuator introduced a disturbance to the flow, which phase locked the Tollmien-Schlichting waves. The downstream actuators were used to mitigate the induced Tollmien-Schlichting waves by introducing an antiphase disturbance with the proper amplitude. The disturbances included either a single-frequency or multiple-frequency input signals. The Tollmien-Schlichting waves were mitigated in both open- and closed-loop control schemes. In open-loop control, the results demonstrated that dynamic surface modification can be used to mitigate the waves, even in the presence of a large adverse gradient for varying frequency bandwidths. In addition, the closed-loop scheme, using an iterative learning control algorithm, succeeded in reducing the induced disturbance amplitudes to 11%. In addition, the experiments demonstrated the ability to not only mitigate the wave but also amplify it if transition to turbulence is desired.