Feasibility of using dynamically oscillating surfaces to control Tollmien-Schlichting waves

Abstract

This work characterizes and controls Tollmien-Schlichting (T-S) waves by means of Piezoelectrically-Driven Oscillating Surface (PDOS) actuators, using Particle Image Velocimetry (PIV). A parametric study of PDOS actuator design parameters was conducted and a 0.79 mm thick rubber surface with a 12.7 mm diameter circular dimple, a cavity height of 2 mm, and a neck height of 2 mm was selected for implementation in T-S wave control over a flat plate. Two circular PDOS actuators were used to excite and control the most amplified frequency of the T-S wave on a flat plate. The actuators were placed at the mid-span of a flat plate at two streamwise locations of x/L = 0.18 and x/L = 0.28 downstream from the leading edge, where the free-stream velocity was U = 16 m/s. The upstream actuator was used to excite and phase-lock the T-S waves at an excitation frequency of fact = 250 Hz (corresponding to the most amplified frequency of the T-S wave, based on linear stability analysis), and the downstream PDOS was used to mitigate the T-S wave by driving it at an anti-phase with the appropriate amplitude. Time- and phase-averaged flow fields were acquired at two downstream interrogation domains. The first window of data, taken in between the two PDOS actuators, explored the effect of the excitation amplitude on the magnitude of the excited T-S waves. At the second window, located downstream of both PDOS actuators, the simultaneous activation of both actuators at an appropriate phase shift and amplitudes resulted in a significant reduction or augmentation of the T-S waves, depending on the phase shift between the two actuators.