Mixing in Coaxial Jets Using Synthetic Jet Actuators

1
Mixing in Coaxial Jets Using Synthetic Jet
Actuators
38th Aerospace Sciences Meeting

• Brian Ritchie
• Dilip R. Mujumdar
• Jerry Seitzman
• Supported by ARO-MURI

2
Overview

• Goal
• Control of (scalar) mixing rate
• Fuel-air mixing
• Requirements
• Large-scales, stirring/entrainment
• Small-scales, leads to molecular mixing
• Approach
• Synthetic jets

3
Synthetic Jets

• Amplitude and frequency control
• High frequency, small scales
• Low frequency amplitude modulation, large scales
• Need no external fluid

4
Mixture Fraction Measurements

• Measurement technique acetone PLIF
• Acetone PLIF data corrected for
• laser sheet energy distribution
• laser energy absorption
• acetone seeding variation with time
• shot-to-shot laser energy
• Mixture fraction ( f mannulus fluid/mtotal )
• f 1 at annulus exit

5
Facility
Secondary laser sheet
Metalpost
Small acetone jet
3 UV laser sheet
r
Acetone-seeded air
Di 1.59 cm
camera
Do 2.54 cm
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Previous Results - Single Jet
0 on 9 on Pulsing
(modulated)
2.54 cm
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Single Jet Mixing

• Less mixing in pulsing case, lower duty cycle

8
Facility Comparison
Ui/Uo 0.3 0.62 1.4
Mean Velocity (m/s)
15 0
x/Do 0.25
RMS Velocity (m/s)
2 0
-0.5 0 0.5
-0.5 0 0.5
-0.5 0 0.5
r / Do
r / Do
r / Do
mixing facility
velocity facility
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Mixture Fraction Images
0 on
9 on
5 x/Do 0
10
PDF Images
f 1 0
-0.5 0 0.5
r/Do

• Slices acquired every ?x/Do 0.25
• Sets of 300 x 5 rows

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PDF x/Do 0.25
1 0
9 on
1 0 f
0 on
r/Do
-1 0
1
12
PDF x/Do 1.5
1 0
9 on
1 0 f
0 on
r/Do
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PDF x/Do 2.5
1 0
9 on
1 0 f
0 on
r/Do
-1 0
1
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Amplitude Modulation (Pulsing)
F
0? 40? 80?
120? 160? 200?
240? 280? 320?
x/Do
0 1 2 3
f 0
1
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Comparison to Velocity
F
80? 120? 160? 200?
0 U/Um 1 -0.25 V/Um 0.25
0 f 1
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PDF Pulsing
x/Do 2.5 2 1.5 1 0.5 0.25
F 40?
F 80?
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Profiles x/Do 0.25
0 on 9 on 9 pulsing
f '
r/Do
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Profiles x/Do 2
0 on 9 on 9 pulsing
f '
r/Do
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Integrated Data

• Integrate across slices to get single data point
  at each downstream location
• Assume axisymmetric on average

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Integrated Acetone
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Integrated Pure Acetone
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Conclusions

• Velocity and mixing data acquired for similar
  conditions
• Direct small-scale and large-scale excitation
• Control by
• Changing amplitude
• Turning modulation on/off
• Spatial distribution of actuators (causes
  asymmetry seen in current data)

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Conclusions (cont.)

• Near-field mixing enhancement
• Initially on outer mixing layer
• Inner mixing layer more enhanced downstream
• Large-scale structures survive
• Enhanced entrainment outweighs duty cycle loss
  for coaxial jets (unlike single jet case)
• Most effective on outer mixing layer
• Other velocity ratios
• 0.3 case similar to 0.62 1.4 case less response