Interaction between a surface dielectric barrier discharge and transonic airflows

The use of plasmas in aerodynamics has become a recent topic of interest. The potentialities of different types of plasmas are being investigated for low velocity and high velocity flow control, as well as for plasma-assisted combustion. Dielectric barrier discharges (DBDs) are good candidates since the transition of the glow or filamentary discharge to an arc is prevented by the dielectric barrier. Moreover, surface DBDs allow to ionize the gas very close to the dielectric surface and can be used to ionize the boundary layer around an object immersed in a flow. The research in flow control has basically followed two main paths: the study of DBDs in low-speed airflows and the study of volume glow or corona discharges in supersonic airflows. Until today, there has been an important technological barrier in experimental investigations with surface DBDs. Atmospheric pressure surface DBDs in air have been difficult to maintain for long operation times, typically several hours, because reactive species created in the plasma (for example atomic oxygen) generate intensive etching of the electrode and dielectric materials. Oxidation of the electrodes or reduction of the dielectric thickness will eventually lead to plasma extinction or arcing respectively. This important issue has prevented detailed studies of DBDs in extreme environment, namely in high-speed airflows. In the present work, a solution to this technological problem has been found and is presented. Low temperature co-fireable ceramic (LTCC) technology allows, for the first time, to fully encapsulate the electrodes in a ceramic matrix and maximize the lifetime of the DBD system. Encapsulation improves the reproducibility of the experiments. Moreover, the plate can be manufactured in a curved shape. This technological advance permits, in the frame of the research presented here, to carry out a detailed experimental investigation of DBDs in high-speed flows. The goal of this experimental research is to improve the physical understanding of the interaction between a local atmospheric discharge, causing a localized weak ionization of the surrounding airflow, and the shock wave structure in transonic and supersonic flows typical for aeronautic applications. The fundamental nature of the research makes it relevant in a large domain of applications such as sonic boom alleviation, the reduction of aerodynamic losses (drag reduction) or combustion improvement. The surface dielectric barrier discharge is first characterized without airflow in order to understand the influence of the applied electrical conditions and the structure of the DBD plate on the discharge regime its spatial distribution. Current curves and photomultiplier measurements show that the DBD comprises a filamentary and a continuous (glow- or corona-like) component. Increasing the applied voltage ramp (dU2/dt) results in an increase in the filament generation rate and current peak amplitude. The geometry of the electrodes has little e