|Ph.D Student||Ronis Anton|
|Subject||Experimental Characterization of the Cathodic Arc Actuator|
for Flow Manipulation
|Department||Department of Aerospace Engineering||Supervisors||Dr. Igal Kronhaus|
|Dr. Ian Jacobi|
|Full Thesis text|
Plasma actuators are devices that manipulate a local flow field with the use of electric
discharge. The type of discharge is determined by input power and can be classified
as non-equilibrium discharges in low power and thermal arc discharge in high power.
A cathodic arc is a special form of arc discharge that is formed in vaporized cathode
material. Cathode spots form at distinct microscopic locations on the cathode, termed
cathode spots, to support the discharge. When operated in atmosphere, the cathodic
arc is known to produce expanding gas plumes normal to the cathode surface termed
a cathodic arc jets (CAJ).
A cathodic arc actuator (CAA) is a device that produces CAJs. A CAA typically
consists of two electrodes and an insulator sandwiched in between. The device is
operated by a pulsed DC power processing unit (PPU). In this work several design
configurations were evaluated for the CAA and its inductive PPU.
The CAJ propagation in air was measured and analyzed using temporal spatially
resolved spectroscopy, and visible photography. The CAJ is shown to have significant
excited metal and ionized hydrogen emission along the jet. The plasma is shown to
concentrate in a localized region in the vicinity of the cathode. The jet pressure front
expands initially at a few km/s and decays to a few m/s after ∼ 1 μs (or ∼ 1 mm).
The CAJ pressure front is shown to follow a Taylor-Sedov blast wave model.
Direct thrust measurement of the CAA were performed in vacuum and atmospheric
pressure. The thrust is shown to be highly dependent on external pressure. For atmospheric pressures, the TSBW model coupled with the Friedlander equation for over
pressure is capable to reproduce the results. In atmospheric pressure the blast wave
thrust is higher than the metal ions thrust but only for short durations. These results were used to determine the optimal duration of actuation in terms of thrust at atmospheric pressure.
To evaluate the influence of the CAJ on the surrounding air, at large time scales,
a particle image velocimetry (PIV) technique was used. The actuator was shown to
produce a train of vortices that resulted in a mean velocity of 0.5 m/s, moving normal
to the cathode surface. The momentum added to the flow was shown to correspond
with the direct thrust measurements of the actuator.
To test the actuator effect on a subsonic flow, a backward facing step experiment
was designed, selecting the experimental parameters according to published data from
flow control experiments. The cathodic arc actuator was shown to produce noticeable
reduction in the reattachment length and to reduce the height of the recirculation
region, with the reattachment length reduced by 35% at CAA pulse repetition rate of
50 Hz and 0.4 W of average arc power.
These findings suggest that the cathodic arc actuator is suitable for subsonic flow