טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRonis Anton
SubjectExperimental Characterization of the Cathodic Arc Actuator
for Flow Manipulation
DepartmentDepartment of Aerospace Engineering
Supervisors Dr. Igal Kronhaus
Dr. Ian Jacobi
Full Thesis textFull thesis text - English Version


Abstract

ABSTRACT:



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

manipulation.