A. Kurz

Characterization of Tollmien-Schlichting Wave Damping by DBD Plasma Actuators Using Phase-Locked PIV

A phase averaged optical measurement technique is used for characterization of externally excited boundary-layer disturbances. Two-dimensional velocity fields of flat-plate boundary-layer flow are recorded via Particle Image Velocimetry to resolve the effect of Dielectric Barrier Discharge plasma actuators on Tollmien-Schlichting waves. These are artificially excited by a vibrating disturbance source flush-mounted with the surface of the flat plate. A delay-generator is used to trigger the image acquisition on predetermined phase angles of the excitation frequency. Phase averaging unveils the temporal and spatial evolution of the boundary-layer disturbances. Characteristics of the excited waves are quantified and compared to linear stability theory. The phase-locked technique allows the evaluation of plasma actuation on the excited waves. A reduction of the wave amplitude by 26% was recorded for a continuously operated, single Dielectric Barrier Discharge actuator. A comprehensive investigation of the actuator effect under variable flow velocities and pressure gradients is presented in this manuscript.

Development of Active Wave Cancellation using DBD Plasma Actuators for In-flight Transition Control

Dielectric Barrier Discharge (DBD) Plasma actuators have proven to be an effective means for the cancellation of Tollmien-Schlichting waves in laminar boundary layers. Previous studies have demonstrated their capability to cancel such disturbances, to be integrated into closed-loop control circuits and even to be operated in unmanned aerial vehicles. This manuscript focuses on the development of a more sophisticated in-flight setup for active wave cancellation experiments on the wing of a full-sized glider plane. Several new technologies have been developed or implemented for this purpose, such as compact and lightweight high-voltage power supplies, sensors and control algorithms. First successful wave-cancellation and transition-delay experiments conducted with this setup in a wind tunnel are presented.

Influence of air flow on the performance of DBD Plasma Actuators

In the present work the effect of the airflow on the performance of dielectric-barrier discharge (DBD) plasma-actuators is investigated experimentally at low and moderate velocities. This velocity range appears relevant for take-off and approach scenarios of many aerodynamic lifting surfaces, but is also essential for plasma-assisted control of unmanned aerial vehicles or internal flows. In order to analyze the actuator performance, luminosity measurements have been carried out simultaneous with the recording of the relevant electrical parameters. A performance drop of about 10% is identified for the entire measured parameter range at a flow speed of M = 0.15 (U1 = 50m/s). This insight is of particular importance, since the plasma-actuator control authority is reduced even at this modest speed level. From the combined analysis the conclusion is drawn that the decreased electrical performance PA correlates with a decreasing peak intensity b G for increasing airflow velocities. Two non-dimensional scaling numbers , i.e. �PA and K, are proposed to characterize and quantify the air flow influence. It is demonstrated that these numbers span a universal performance drop diagram for the entire range of investigated operating parameters.