nov. 8, 2006af academy workshop on plasma actuators order of magnitude improvement of sdbd actuator...

Nov. 8, 2006 AF Academy Workshop on Plasma Actuators

Order of Magnitude Improvement of SDBD

Actuator Effect

T. Corke, F. Thomas, D. Orlov, M. Iqbal, A. Kozlov,

H. Othman, D. Shatzman

Center for Flow Physics and ControlAerospace and Mechanical Engineering

University of Notre Dame


Questions: How do we improve the performance of

SDBD plasma actuators?

What are the governing properties?

What is the ultimate performance limit?


Approach: Develop space-time model for ionization in

SDBD operation. Include amplitude and frequency effects. Not including maximum limits. Compare to experiments.

Perform experiments that investigate limiting conditions on SDBD design and operation parameters. Develop a theory to be included in space-time

model.


SDBD Actuators: What we know Three time scales:

Micro discharges (nsec) a.c. period (.1ms) Fluid response (10ms)

Ionization space-time dependent. Static models give wrong results (e.g. fb~V2). Temporal/space-uniform models give correct V-

dependence (fb~V7/2), need spatial weighting Space-time models give correct V, frequency

and space dependence (Orlov, 2006).


Steps to model actuator in flow Space-time electric potential,

Space-time body force

Flow solver with body force added


Space-time model

Physical space over the encapsulated electrode is divided into N parallel networks.

Each parallel network consists of air capacitor, dielectric capacitor, plasma resistive elements and zenor diodes.


Model circuit elements

Voltage on the dielectric surface in the n-th sub-circuit

Plasma current

air capacitor dielectric capacitor


Model Time Series

0.0 0.5 1.0 1.5

-2.0

-1.0

0.0

1.0

2.0

t / Ta.c.

Vo

ltag

e,

kV

Vapp

n=1n=2n=3n=4n=5

0.0 0.5 1.0 1.5-1

0

1

2

3

4

5x 10

-5

t / Ta.c.

Cu

rre

nt,

A

n=1n=2n=3n=4n=5

t/Ta.c. t/Ta.c.

Vn (t) Ipn (t)

1

5

1

5


Model Space-time Characteristics

Model Ip(t)

Experiment Illumination

dxp/dt

(xp)max


Plasma Propagation Characteristics

dxp/dt vs Vapp (xp)max vs Vapp

Effect of Vapp


Plasma Propagation Characteristics

dxp/dt vs fa.c. (xp)max vs fa.c.

Effect of fa.c.


Numerical solution for (x,y,t)

Model provides time-dependent B.C. for


Body Force, fb(x,t)YN

orm

aliz

ed f

b(x

,t)

-5.08 0.0 5.080.0

1.14

x, mm

y,

mm

-5.08 0.0 5.08

0.0

0.5

1.0

x, mm

| f b |

-5.08 0.0 5.080.0

1.14

x, mm

y,

mm

-5.08 0.0 5.08

0.0

0.5

1.0

x, mm

| f b |

t/Ta.c.=0.2

t/Ta.c.=0.7


Frequency Dependence of fb & Wp

Impact: Optimum frequency for body force. Depends on actuator capacitance.


What limits maximum body force? SDBD Plasma actuator is voltage driven,

fb~V7/2. Not current driven like voice-coil type

actuators.

For fixed power (I·V), one needs to limit current to maximize voltage.

What governs maximum achievable voltage for fixed power?


Maximum Voltage Optimization

Investigated different parameters on thrust produced by actuator


Order of Magnitude Improvement

Material Quartz 3.8 Kapton 3.4Teflon 2.0

Imax

Imax

Imax

Imax


Premise The maximum voltage at fixed power is

limited by local electric field exceeding breakdown of air.

Thicker dielectrics and/or lower dielectric constants reduce capacitance of actuator and reduce concentration of electric field lines.

Other parameters?


Effect of frequency on Vmax

0.25in. quartz glass1kHz

2kHz

4kHz

8kHz

Vmax(f)


Effect of dielectric thickness on Vmax

quartz glass; 1,2,4,8kHz

fa.c. ~ (t/)dTmax ~ Vmax


Tmax Efficiency0.25in. quartz glass


Answers to Questions: To improve the performance of SDBD plasma actuators?

Maximize V for fixed power.

Minimize I by preventing formation of strong plasma filaments.

Governing properties?

Dielectric design (t & ) and a.c. frequency.

Ultimate performance limit?

Maximum local E-field for air breakdown?


Further Improvements: Additive Effect

nov. 8, 2006af academy workshop on plasma actuators order of magnitude improvement of sdbd actuator...

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