Structure of propagating arc in a magneto-hydrodynamic rail plasma actuator

Experimental and computational studies of a rail plasma actuator (RailPAc) magnetohydrodynamic flow actuator were performed. The actuator functions by inducing flow around a fastmoving gliding arc, with device current ∼ 1000 A, which is generated between flush mounted copper electrodes. Highspeed imaging photometry is used to analyze the composition and internal structure of the arc for flush mounted electrode spacings of 2 mm, 5 mm, and 12.5 mm, as well as freefloating electrodes with 12.5 mm spacing. Results are compared with 2D thermal plasma simulations. The dynamics of the arc movement are found to be dependent on the height of the plasma column above the RailPAc surface and on the presence of prominent anode and cathode jets. Mechanisms are proposed for wallstabilization of the arc and rootjet formation based on agreement between experimental and computational results.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of the dynamic behavior of the rail plasma actuator arc

Gray

Choi

Sirohi

et al. 2018

“…The deflection is a result of flush mounted rails because the ceramic in the gap prevents the arc from forming near the RailPAc surface. The physical mechanism behind the deflection was studied by Gray et al [20]. They proposed that the initial deflection of the arc away from the insulating gap is provided by gas expansion due to ohmic heating.…”

Section: High-speed Imagingmentioning

confidence: 99%

“…As shown in figure 13(b), the arc resistance increases with the electrode spacing. It was expected from the spectroscopy measurements by Gray et al [20] that the arc resistance would be linearly proportional to the arc length because their measurements showed that the arc temperature, and by extension the arc resistivity, does not vary significantly as a function of the arc current. The non-linearity in the plot of arc resistance versus gap distance is due to the fact that the gap distance is not a true measure of the arc length.…”

Section: Rod Electrodesmentioning

confidence: 99%

“…Although the motion of anode root along the electrode can be characterized as discrete jumps, the cathode root moves smoothly along the electrode. This phenomenon was defined by Gray et al [20,21] as the "anchoring" behavior, and Choi et al [19] hypothesized that the actuation authority and efficiency of a RailPAc can be improved by preventing the asymmetric transit of the arc roots. Based on this hypothesis, Gray et al [21] further investigated some mechanisms to suppress anchoring in the arc transit.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of anchoring and arc structure on the control authority of a rail plasma actuator

Choi¹,

Gray²,

Sirohi³

et al. 2017

Self Cite

Experiments were conducted on a rail plasma actuator (RailPAc) with different electrode cross sections (rails or rods) to assess methods to improve the actuation authority, defined as the impulse generated for a given electrical input. The arc was characterized with electrical measurements and high-speed images, while impulse measurements quantified the actuation authority. A RailPAc power supply capable of delivering ∼1 kA of current at ∼100 V was connected to rod electrodes (free-floating with circular cross-section) and rail electrodes (flush-mounted in a flat plate with rectangular cross-section). High-speed images show that the rail electrodes cause the arc to anchor itself to the anode electrode and transit in discrete jumps, while rod electrodes permit the arc to transit smoothly without anchoring. The impulse measurements reveal that the anchoring reduces the actuation authority by ∼21% compared to a smooth transit, and the effect of anchoring can be suppressed by reducing the gap between the rails to 2 mm. The study further demonstrates that if a smooth transit is achieved, the control authority can be increased with a larger gap and larger arc current. In conclusion, the actuation authority of a RailPAc can be maximized by carefully choosing a gap width that prevents anchoring. Further study is warranted to increase the RailPAc actuation authority by introducing multiple turns of wires beneath the RailPAc to augment the induced magnetic field.

Static stall alleviation using a rail plasma actuator

Choi¹,

Gray²,

Sirohi³

et al. 2018

An experimental study was conducted to investigate the ability of a rail plasma actuator (RailPAc) to alleviate static stall on an airfoil. The RailPAc device consists of parallel rails flush mounted on the upper surface of a VR-12 airfoil, with a high-current (∼1.3 kA) arc bridging the gap between the rails. A Lorentz force (∼0.3 N lasting ∼1 ms) generated on the arc propels it along the airfoil chord and transfers momentum to the surrounding flow. Experiments were conducted in a low speed wind tunnel at two different Reynolds numbers ( and ) and various static angles of attack (up to ∼30°). Particle image velocimetry (PIV) was used to measure the flow over the passive and actuated airfoil, while the airfoil lift was measured using a force balance. The experiments showed that the RailPAc promotes flow reattachment and can suppress static stall over a wide range of angles of attack. Operation of a single RailPAc resulted in ∼40 improvement in post-stall lift and ∼4° increase in stall angle compared to a passive airfoil with an unpowered RailPAc. The results provide insight into the actuation mechanism and demonstrate, for the first time, the ability of the RailPAc to alleviate static stall on an airfoil.