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Mixing in Coaxial Jets Using Synthetic Jet Actuators

38 th Aerospace Sciences Meeting. Mixing in Coaxial Jets Using Synthetic Jet Actuators. Brian Ritchie Dilip R. Mujumdar Jerry Seitzman Supported by ARO-MURI. Overview. Goal Control of (scalar) mixing rate Fuel-air mixing Requirements Large-scales, stirring/entrainment

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Mixing in Coaxial Jets Using Synthetic Jet Actuators

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

  6. air jet fluid Previous Results - Single Jet 0 on 9 on Pulsing (modulated) 2.54 cm

  7. 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

  9. 0 Probability (%) 10 ... 100 Mixture Fraction Images 0 on 9 on 5 x/Do 0

  10. 0 Probability (%) 10 ... 100 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

  11. 0 Probability (%) 10 ... 100 PDF: x/Do = 0.25 1 0 9 on 1 0 f 0 on r/Do -1 0 1

  12. -1 0 1 0 Probability (%) 10 ... 100 PDF: x/Do = 1.5 1 0 9 on 1 0 f 0 on r/Do

  13. 0 Probability (%) 10 ... 100 PDF: x/Do = 2.5 1 0 9 on 1 0 f 0 on r/Do -1 0 1

  14. Amplitude Modulation (Pulsing) F 0 40 80 120 160 200 240 280 320 x/Do 0 1 2 3 f = 0 1

  15. Comparison to Velocity F 80 120 160 200 0 U/Um 1-0.25 V/Um 0.25 0 f 1

  16. 0 Probability (%) 10 PDF: Pulsing F = 40 x/Do 2.5 2 1.5 1 0.5 0.25 F = 80

  17. f Profiles: x/Do = 0.25 0 on 9 on 9 pulsing f ' r/Do

  18. f Profiles: x/Do = 2 0 on 9 on 9 pulsing f ' r/Do

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

  20. Integrated Acetone

  21. Integrated Pure Acetone

  22. 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)

  23. 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

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