Delay of Boundary-Layer Transition Using Plasma Actuators

Abstract

In the present work two different methods are presented to attenuate artificially excited perturbations in a laminar boundary layer using plasma actuators resulting in a delay of transition. In both cases Tollmien-Schlichting waves are artificially excited by a vibrating surface driven by an electromagnetic actuator flush mounted in a flat plate. The waves were amplified by an adverse pressure gradient induced by an insert on the upper wall of the test section. One or two control plasma actuators are positioned downstream of the excitation actuator to attenuate the waves by imparting a steady force or an unsteady force into the boundary layer. The steadily operated actuators change the boundary-layer profile locally resulting in a damping of the oscillations in the boundary layer. If the control actuator is operated in pulsed mode it depends on the phase shift between the oscillations and the actuator if the oscillations are amplified or cancelled. Operated in pulsed mode with correct frequency, phase shift and amplitude the energy consumption necessary to achieve the same attenuation as achieved with the steadily operated actuator is only 12 percent of the steady actuator.