Center for Flow Physics and Control (FlowPAC)

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PLASMA-ENHANCED AERODYNAMICS A NOVEL APPROACH
AND FUTURE DIRECTIONS FOR ACTIVE FLOW CONTROL
Thomas C. Corke Clark Chair Professor University
of Notre Dame Center for Flow Physics and
Control Aerospace and Mechanical Engineering
Dept. Notre Dame, IN 46556
Ref J. Adv. Aero. Sci., 2007.
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Presentation Outline

• Background SDBD Plasma Actuators
• Physics and Modeling
• Flow Control Simulation
• Comparison to Other FC Actuators
• Example Applications
• LPT Separation Control
• Turbine Tip-gap Flow Control
• Turbulent Separation Control
• Summary

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Single-dielectric barrier discharge (SDBD) Plasma
Actuator

• High voltage AC causes air to ionize
• (plasma).
• Ionized air in presence of electric
• field results in body force that acts
• on neutral air.
• Body force is mechanism of flow
• control.

The SDBD is stable at atmospheric pressure
because it is self-limiting due to charge
accumulation on the dielectric surface.
Ref AIAA J., 42, 3, 2004
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Flow Response Impulsively Started Plasma Actuator
Phase-averaged PIV
Long-time Average
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Example Application Cylinder Wake, ReD30,000
Video
OFF
ON
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Physics of OperationElectrostatic Body Force
D - Electric Induction
(Maxwells equation)
(given by Boltzmann relation)
solution of equation - electric potential ?
Body Force
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Current/Light Emission ?(t)
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Current/Light Emission ?(x,t)
t/T
Voltage
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Electron Transport Key to Efficiency
a
c d
More Optimum Waveform
b
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Steps to model actuator in flow

• Space-time electric potential, ?
• Space-time body force
• Flow solver with body force added

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Space-Time Lumped Element Circuit Model Boundary
Conditions on ?(x,t)
Electric circuit with N-sub-circuits (N100)
Ref AIAA-2006-1206
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Space-time Dependent Lumped Element Circuit Model
(governing equations)
air capacitor
dielectric capacitor
Voltage on the dielectric surface in the n-th
sub-circuit
Plasma current
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Model Space-time Characteristics
Experiment Illumination
Model ?Ip(t)?
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Plasma Propagation Characteristics
Effect of Vapp
dxp/dt vs Vapp
(xp)max vs Vapp
Model
Model
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Plasma Propagation Characteristics
Effect of fa.c.
dxp/dt vs fa.c.
(xp)max vs fa.c.
Model
Model
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Numerical solution for ?(x,y,t)
Model provides time-dependent B.C. for ?
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Body Force, fb(x,t)
?
t/Ta.c.0.2
Normalized fb(x,t)
t/Ta.c.0.7
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Example LE Separation Control
Computed cycle-averaged body force vectors
NACA 0021 Leading Edge
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Example Impulsively Started Actuator
t0.01743 sec
Velocity vectors
?2 -0.001 countours
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Example AoA23 deg.
U8 30 m/s, Rec615K
Steady Actuator
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Comparison to Other FC Actuators?

• Zero-mass Unsteady Blowing
• generally uses voice-coil system.
• Current driven devices, VI.
• Losses result in I2R heating.
• Flow simulations require actuator
• velocity field (flow dependent).

• SDBD plasma actuator is voltage driven,
  ?fb?V7/2.
• For fixed power (IV), limit current to maximize
  voltage.
• Low ohmic losses.
• Flow simulations require body force field (not
  affected by external flow, solve once for given
  geometry).

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Maximizing SDBD Plasma Actuator Body Force At
Fixed Power
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Sample Applications

• LPT Separation Control
• Turbine Tip-Clearance-Flow Control
• Turbulent Flow Separation Control
• A.C. Plasma Anemometer

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LPT Separation Control

• Span 60cm
• C20.5cm

Pak-B Cascade
Flow
Plasma Side
Ref AIAA J. 44, 7, 51-58, 2006 AIAA J.
44, 7, 1477-1487, 2006
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Plasma Actuator x/c0.67, Re50k
Ret.
Actuator Location
Sep.
Steady Actuator
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Plasma Actuator x/c0.67, Re50k
Base Flow
Unsteady Plasma Act.
Deficit Pressure
Loss Coeff. vs Re
200
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Turbine Tip-Clearance-Flow Control
Objective

• Reduce losses associated with
• tip-gap flow

Approach

• Document tip gap flow behavior.
• Investigate strategies to reduce pressure-
• losses due to tip-gap-flow.
• Passive Techniques How do they work?
• Active Techniques Emulate passive effects?

Ref AIAA-2007-0646
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Experimental Setup
Pak-B blades 4.14 axial chord
Flow
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Under-tip Flow Morphology
g/c0.05
Separation line Receptive to active flow
control.
t/g 2.83
t/g 4.30
Tip-flow Plasma Actuator
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Unsteady Excitation Response
Re500k
z/span
Shear Instability 0.01ltFlt0.04, U maximum
shear layer velocity, l momentum
thickness Viscous Jet Core 0.25ltFlt0.5, U
characteristic velocity of jet core, l gap
size, g
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Unsteady Excitation Response Selected F
Cpt/Cptbase0.95
Cpt/Cptbase0.92
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Cpt and Loss Efficiency
g/c t/g F Cpt ??
No Squealer 5 2.83 N/A 0.301 --
Squealer 5 2.83 N/A 0.194 0.7
Winglet 5 4.30 N/A 0.247 0.3
No Actuator 4 3.52 N/A 0.251 --
Actuator 4 3.52 0.07 0.232 0.1
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Turbine Tip-Clearance-Flow Control Future
Directions
Suction-side Blade Squealer Tip
Plasma Squealer
Active Casing Flow Turning
Plasma Roughness Rao et al. ASM GT 2006-91011
Plasma Winglet
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Turbulent Flow Separation Control
Wall-mounted hump model used in NASA 2004 CFD
validation.
Ref AIAA-2007-0935
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Baseline Benchmark Cp and Cf
k-? SST best up to x/c0.9 k-? best for (x/c)ret
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SDBD Plasma Actuator Simulation and Experiment
?Rx/c
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Turbulent Separation Control Future Applications

• Flight control without moving surfaces

Miley 06-13-128 Simulation
AIAA-2006-3495, AIAA-2007-0884
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Plasma Flow Control Summary

• The basis of SDBD plasma actuator flow control
  is the
• generation of a body force vector.
• Our understanding of the process leading to
  improved plasma
• actuator designs resulted in 20x improvement
  in performance.
• With the use of models for ionization, the body
  force effect can
• be efficiently implemented into flow solvers.
• Such codes can then be used as tools for
  aerodynamic designs
• that include flow control from the beginning,
  which holds the
• ultimate potential.

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A.C. Plasma Anemometer
Originally developed for mass-flux measurements
in high Mach number, high enthalpy flows.
Principle of Operation

• Flow transports charge-carrying ions downstream
  from electrodes.
• Loss of ions reduces current flow across gap-
  increases internal resistance increases voltage
  output.
• Mechanism not sensitive on temperature.
• Robust, no moving parts.
• Native frequency response gt 1 MHz.
• Amplitude modulated ac carrier gives excellent
  noise rejection.

Flow
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Plasma Sensor Amplitude Modulated Output
Amplitude Modulated Output
Frequency Domain Output
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Real Time Demodulation
FPGA-based digital acquisition board allows host
based demodulation in real time.
GnuRadio
Modulated signal recovered
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Real-time Measurement of Blade Passing Flow
Video
Jet
f1-2kHz
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Plasma Anemometer Future Applications

• Engine internal flow sensor
• - Surge/stall sensor
• - Casing flow separation sensor
• - Combustion instability sensor