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Mixing in Coaxial Jets Using Synthetic Jet Actuators

Brian RitchieDilip R. Mujumdar

Jerry Seitzman

Supported by ARO-MURI

38th Aerospace Sciences Meeting

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Overview

• Goal– Control of (scalar) mixing rate

• Fuel-air mixing

• Requirements– Large-scales, stirring/entrainment– Small-scales, leads to molecular mixing

• Approach– Synthetic jets

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Synthetic Jets

• Amplitude and frequency control– High frequency, small scales– Low frequency amplitude

modulation, large scales

• Need no external fluid

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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

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Facility

camera

x

Acetone-seeded air

r

3” UV laser sheet

Secondary laser sheet

Small acetone jet

Metalpost

Di = 1.59 cm

Do = 2.54 cm

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Previous Results - Single Jet

air jet fluid

0 on 9 on Pulsing (modulated)

2.54 cm

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Single Jet Mixing

0

1

2

3

4

50 60 70 80 90 100 110 120Average Pixels of Pure Jet Fluid

x/D

0 on9 on9 pulsing

• Less mixing in pulsing case, lower duty cycle

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Facility Comparison

Ui/Uo = 0.3 0.62 1.4

mixing facility velocity facility

-0.5 0 0.5r / Do

15

0

r / Do r / Do

2

0 -0.5 0 0.5 -0.5 0 0.5

Mea

n V

eloc

ity (m

/s)

RM

S V

eloc

ity (m

/s)

x/Do = 0.25

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Mixture Fraction Images0 on 9 on

5

x/Do

0

0 Probability (%) 10 ... 100

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PDF Imagesf

1

0

• Slices acquired every x/Do= 0.25

• Sets of 300 x 5 rows

-0.5 0 0.5

r/Do

0 Probability (%) 10 ... 100

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PDF: x/Do = 0.25

0 Probability (%) 10 ... 100

-1 0 1r/Do

1

0f

1

0

0 on

9 on

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PDF: x/Do = 1.5

0 Probability (%) 10 ... 100

-1 0 1r/Do

1

0f

1

0

0 on

9 on

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PDF: x/Do = 2.5

0 on

9 on

0 Probability (%) 10 ... 100

-1 0 1r/Do

1

0f

1

0

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Amplitude Modulation (Pulsing)

0

40

80

120

160

200

240

280

320

0 1 2 3 x/Do

f = 0 1

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Comparison to Velocity

0 U/Um 1 -0.25 V/Um 0.25 0 f 1

80

120

160

200

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PDF: Pulsing

x/Do

2.5

2

1.5

1

0.5

0.25

= 40 = 80

0 Probability (%) 10

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Profiles: x/Do = 0.25

f '

f

r/Do

0 on

9 on

9 pulsing

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Profiles: x/Do = 2

f '

f

r/Do

0 on

9 on

9 pulsing

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Integrated Data

dr2I

f

• 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