Flow and Thermal Properties Induced by Electric Arc Plasma Actuators

Recently renewed interest in flow control devices using various forms of plasmas has motivated the design and systematic investigation of a localized arc filament plasma actuator, or LAFPA-type devices. The newly constructed system creates electric arcs by generating electric fields in the range of 20 kV/cm between two pin-type electrodes. The flow actuation then occurs due to volumetric gas (Joule) heating, synthetic jet production, blast wave creation (dilatation effects), and electro-magnetic (electrostatic and Lorentz2 effects. The potential of the actuator to influence surrounding quiescent flow was investigated using emission imaging, schlieren imaging, current and voltage probes, particle image velocimetry (PIV), and emission spectroscopy. The schlieren imaging revealed a potential to cause blast “Mach” waves and a synthetic jet with controllable directionality dependent on cavity orientation. The electric measurements revealed that, in order to increase the power discharged by the plasma, the electrode separation will only aid mildly and that an optimum plasma current exists (between 300-400 mA for the tested parameter space). The PIV data were acquired for various actuation frequencies and showed a negative trend between discharge frequency and maximum induced jet velocity. Finally, the emission spectroscopy data were acquired for four different cases: two electrode separations and two plasma currents. For each of the four conditions tested, the spectrum fit very well to a thermal distribution for early times in the emission. However, at later times in the emission, the spectrum no longer matched that of the second positive system under optically thick conditions for any combination of rotational and vibrational temperatures.