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Enhanced Plasma Actuator

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Results of recent experiments showing enhanced plasma actuator control authority using a titania catalyst with an SDBD plasma actuator.

Results of recent experiments showing enhanced plasma actuator control authority using a titania catalyst with an SDBD plasma actuator.

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  • 1. Enhanced Plasma Actuator Forces through Plasma Catalysis Applied Science Products, Inc Neal E. Fine, PhD, ASPI Steven J. Brickner, PhD, Consultant July, 2010 1
  • 2. Enhanced Plasma Actuation through Plasma Catalysis July 2010 THE PLASMA ACTUATOR Exposed Electrode Dielectric Plasma AC Voltage Insulated Electrode Induced Flow 2 of 13
  • 3. Enhanced Plasma Actuation through Plasma Catalysis July 2010 THE PLASMA ACTUATOR… Exposed Electrode • …is an electrical device that induces flow in a background gas (such as air) with no moving Dielectric Plasma parts. • … is favored by aerodynamicists for active flow control because: AC Voltage – it has no moving parts Insulated Electrode Induced Flow – it mounts flush to a surface (no “parasitic” drag) – it consumes very little power See recent review article by Corke, et al: “Dielectric Barrier Discharge Plasma Actuators for Flow Control,” Annual Review of Fluid Mechanics, Vol. 43, pp505-529. 3 of 13
  • 4. Enhanced Plasma Actuation through Plasma Catalysis July 2010 Despite their promise, plasma actuators have limited control authority and researchers are searching for new methods to enhance the force generated by the actuators. One way to improve the control authority may be to apply a catalyst to the surface of the dielectric where the plasma forms. 4 of 13
  • 5. Enhanced Plasma Actuation through Plasma Catalysis July 2010 HYPOTHESIS: Certain heterogeneous in-plasma catalysts may cause more efficient production of reactive species, including ions. Possible catalysts include titania (TiO2), aluminum oxide (Al2O3), zinc oxide (ZnO) and others. The greater number of ions in the plasma could then result in greater momentum transfer from the ions to the neutral air molecules, potentially increasing the actuator control authority. Exposed Electrode Add a thin layer Add a thin layer Dielectric Plasma of catalyst of catalyst AC Voltage Insulated Electrode Induced Flow 5 of 13
  • 6. Enhanced Plasma Actuation through Plasma Catalysis July 2010 THEORY: ρ = charge density r r ε0 r E = electric field f = ρ E = − 2 φE λD φ = electric potential ε0 = permittivity where k = Boltzman constant −1 ε 0k ⎡ 1 1⎤ e = electron charge λ = 2 ⎢ + ⎥ 2 D e n0 ⎣ Ti Te ⎦ Ti = ion temperature Te = electron temperature Increasing the ion density, n0, will result in increased force, f, provided changes in the electric field, E, do not offset the increase. Reference: Enloe et al., “Mechanisms and Responses of a Single Dielectric Barrier Plasma Actuator: Geometric Effects,” AIAA Journal, Vol. 42, No. 3, March 2004. 6 of 13
  • 7. Enhanced Plasma Actuation through Plasma Catalysis July 2010 EXPERIMENT: We measured the force generated by a plasma actuator before and after applying a titania (TiO2) photocatalyst on the dielectric surface above the covered electrode. Dielectric 25 mil Alumina Tape Ceramic Dielectric Thin Layer of Covered Titania Catalyst Electrode OxiTitan® by OxiTitan® by Exposed EcoActive Surfaces, Inc EcoActive Surfaces, Inc Electrode OHAUS A812 Precision scale Induced thrust 7 of 13
  • 8. Enhanced Plasma Actuation through Plasma Catalysis July 2010 Alumina ceramic dielectric (25 mil thickness) Plasma zone OHAUS precision scale 8 of 13
  • 9. Enhanced Plasma Actuation through Plasma Catalysis July 2010 HV Probe PlexiGlas® containment box Power Supply 9 of 13
  • 10. Enhanced Plasma Actuation through Plasma Catalysis July 2010 1.60 RESULTS 1.40 With catalyst 1.20 Without catalyst Force (g/m) The force per meter of actuator Force (g/m) The force per meter of actuator 1.00 generated by a plasma actuator and generated by a plasma actuator and 0.80 0.60 measured with and without the titania measured with and without the titania 0.40 catalyst. catalyst. 0.20 0.00 0 2 4 6 8 10 Voltage (kV) a) Voltage kVrms 1.60 1.40 False catalyst Without catalyst A “false catalyst” (tap water) produces A “false catalyst” (tap water) produces 1.20 Force (g/m) no additional force, indicating that the Force (g/m) no additional force, indicating that the 1.00 force enhancement with the catalyst is 0.80 force enhancement with the catalyst is 0.60 not introduced by the measurement not introduced by the measurement 0.40 procedure. procedure. 0.20 0.00 0 2 4 6 8 10 Voltage (kV) Voltage kVrms b) The error bars show the high and low measurement for each voltage and are a measure of 10 of 13 the variability in the results.
  • 11. Enhanced Plasma Actuation through Plasma Catalysis July 2010 RESULTS 140 120 % Force Increase 100 High 80 60 Average 40 20 Low 0 3 3.5 4 4.5 5 5.5 6 6.5 7 RMS Voltage(kV) RMS Voltage (kV) Composite %-increase of catalyst-enhanced thrust measured in the proof-of-principle experiment (solid line represents the average force increase, the two dashed lines are maximum and minimum force increase). The composite results represent five separate experiments, using five actuators constructed using an identical protocol. While the intent was to create identical test conditions for the five actuators, clearly a variety of factors influenced the variability (such as variations in the electrode length and the overlap or gap between the exposed and covered electrodes). 11 of 13
  • 12. Enhanced Plasma Actuation through Plasma Catalysis July 2010 SUMMARY & CONCLUSIONS • The TiO2 catalyst appears to produce significant (as high as 120%) and repeatable increases in plasma actuation force. • This phenomenon could help to make plasma actuators more effective for active flow control applications. • The proposed mechanism (increased charge density) remains a hypothesis. Further experiments will clarify the phenomenon, including the effects of other catalysts. The following detailed plasma chemistry experiments are planned: ─ Optical Emission Spectroscopic (OES) measurement of the concentration of certain charged species ─ OES measurement of the electron temperature and density ─ Electric field strength measurement ─ Surface voltammetry ─ Power consumption • The results of the proof-of-principle experiment described here were submitted for publication in the AIAA Journal in June, 2010. 12 of 13
  • 13. Enhanced Plasma Actuation through Plasma Catalysis July 2010 NOTES The proof-of-principle experiment was supported in part by funding from Navatek, Ltd. Further experimentation has been proposed in coordination with University of Connecticut Department of Chemistry Chair and Board of Trustees Distinguished Professor Steven L. Suib. A joint proposal has been submitted to the Air Force Office of Scientific Research for review and consideration for FY2011 funding. ASPI owns a license to U.S. Patent No. 6,200,529 (“Paralectric Gas Flow Accelerator”), which appears to be the first to make claims describing what is now commonly referred to as the plasma actuator. 13 of 13