Laxminarayan L. Raja

Experimental Study of a Magnetohydrodynamic Plasma Actuator in Quiescent Atmospheric Air

An experimental study was conducted on a magnetohydrodynamic plasma actuator called the rail plasma actuator (RailPAc). The actuator consists of two parallel, six inch long, copper rails flush mounted on an insulating ceramic plate. When a current pulse (~1kA) at ~100V is supplied, an electrical arc (armature) is generated and driven along the rails by a Lorentz force. The motion of the plasma armature induces flow in the surrounding air through compression and entrainment. Experiments were performed on a prototype RailPAc in quiescent atmospheric air to characterize the plasma armature and the momentum transferred to the surrounding air. Measurements included dynamic force and total impulse generated by the RailPAc, armature voltage and current, as well as temperature and species composition of the plasma armature. The plasma armature shape and transit velocity were determined by high speed imaging. A peak force of 0.6 N imparting an impulse of 0.68 mN-s was measured for a peak current of 1.3 kA. The armature temperature was measured as approximately 10,000 K. The armature was found to comprise of copper, aluminum, hydrogen, nitrogen and oxygen species. These results indicate the feasibility of the RailPAc concept for atmospheric flow control and offer considerable insight into the dynamics of transient arcs.

Arc breakdown in high-pressure large gap sources using surface streamer based initiation

A non-equilibrium atmospheric streamer discharge has been investigated as a means to seed a large gap arc breakdown. The dynamics of a surface streamer discharge has been analyzed with high speed imaging, voltage and current characterization as well as light intensity measurements. The temporal evolution of the discharge has been examined and a mechanism for the formation and propagation of the discharge presented. Thermodynamic properties of the atmospheric streamer discharge were determined from a time and spatially averaged spectra and a collisional-radiative model. The electron temperature and density were measured to be 1.25 eV and 10 m respectively. The velocity of the surface streamer was estimated to be ~110 km/s with a diameter of ~400 μm.

Experimental Characterization of the RailPAc Plasma Flow Actuator

An experimental study is conducted to characterize the development of a novel magnetohydrodynamic plasma actuator for aerodynamic flow control. The actuator is composed of two parallel rail electrodes embedded chord-wise on the surface of an airfoil. Self-induced electromagnetic fields force a low-voltage, high-current, pulsed arc along the length of the electrodes. The repetitive pulsed arc travels at high velocities, transferring momentum to the surrounding air, creating a high-velocity pulsed air wall jet. To quantify the physical characteristics of the plasma flow, the actuator is surface mounted on a flat plate test article and a cambered airfoil to measure the electrical properties, perform highspeed flow visualization, and measure the flow velocity induced by the plasma discharge. The experimental results demonstrate that the plasma arc requires discharge energies on the order of 300 J per pulse to achieve a peak arc velocity of 100 m/s. Wind tunnel tests on a 14.5 inch chord airfoil section, at a Reynolds number of 4.5 x 10 5 show a mean velocity of 20.5 m/s induced by the pulsed arc.