Cancellation of Tollmien-Schlichting Waves in Direct Vicinity of a Plasma Actuator

The active cancellation of Tollmien-Schlichting waves is a promising and energy-efficient laminar flow control technology with the goal of drag reduction by delaying laminar-turbulent transition. This paper analyzes, for the first time, the control mechanism in the direct vicinity of the actuator using particle image velocimetry. Artificial Tollmien-Schlichting waves are generated at a frequency of f(TS) = 250 Hz in a two-dimensional zero-pressure-gradient flat-plate boundary layer (U-infinity = 15 m/s). The Tollmien-Schlichting waves travel downstream and are attenuated with an unsteady dielectric-barrier-discharge plasma actuator force. Phase-locked particle image velocimetry measurements at an acquisition rate of f(acq) = 800 Hz in double-frame mode are conducted in the direct vicinity of the plasma actuator, resolving 16 phase angles of the wave cycle. The use of two cameras allows measurement of two full wavelengths of the Tollmien-Schlichting waves and a detailed analysis of the cancellation process. The phase-averaged velocity fields of the artificially generated Tollmien-Schlichting waves are validated with a linear stability theory. The wavelength, amplification, and shape of the Tollmien-Schlichting wave disturbances and the counterwaves generated by the plasma actuator are analyzed.