1. MITE Mixing Control of Fuel Jets Using Synthetic Jet Technology: Velocity Field Measurements Staci A. Davis and Ari Glezer Woodruff School of Mechanical Engineering Georgia Tech February 26, 1999 Supported by ARO-MURI DAAH04-96-1-0008

2. MITE Approach Traditional mixing control in free shear flows  Accomplished through manipulation of large- scale vortical structures  Is indirect and relies on energy cascade thus  Mixing at the smallest scales is only weakly coupled to the control input Focus of present work  Direct excitation of small-scales  Simultaneous control of large-scale motions via couplings within the small scales

3. MITE Experimental Facility NOZZLE ACTUATOR HOUSING AIR FILTER SCREEN HONEYCOMB r x D = 2.54 cm U = 11.4 m/s Re = 1.9x10 4

4. MITE Modes of Forcing RadialAxial Synthetic Jet Actuators Synthetic Jet

5. MITE Axial Mode - Streamwise Velocity r /D 0.5 -0.5 9 On

6. MITE Mean Axial Velocity    x / D 0 1 2 3 4 Unforced y 9 On y r /D U / U 0 u’/ U 0

7. MITE Small-Scale: High Frequency Forcing u’ CL /U 0 x /D Power Frequency (Hz) 2 x /D = 1 3 x U/U CL = 0.5 m = -5/3 9 On

8. MITE Amplitude Modulation Modulating Waveform Hot Wire Voltage 40 Hz Modulation100 Hz Modulation x / h = 20

9. MITE Pulsed Modulation: Triple Decomposition 0.1 1.0 10.0 0.1 0.01 fmfm 20 Hz  40 Hz  60 Hz  80 Hz 100 Hz 9 Pulsed u’u’ U0U0 0.1 1.0 10.0 1.0 0.1 x / D U U0U0 0.1 1.0 10.0 1.0 0.1 0.01 0.001 | u | ~ U0U0 m = -1 ff

10. MITE Pulsed Modulation: Phase-Averaged Centerline Velocity A 1.2 0.8 0.4 0.0 / U cl,0 1.2 0.8 0.4 0.0 B / U cl,0  0 2  4  6  10 8 6 4 2 0  A B 0 2  4  6  x / D 10 8 6 4 2 0 x / D 9 On Pulse Modulation 0.3 0.6 0.9 1.2

11. MITE Pulsed Modulation: Phase-Averaged Centerline Velocity  0 2  4  6  x / D 10 8 6 4 2 0 0 2  4  6  9 On, Pulse Modulation 20 Hz40 Hz60 Hz80 Hz100 HzUnforced Modulation Frequency / U cl,0 0.3 0.6 0.9 1.2

12. MITE Pulsed Modulation: Phase-Averaged Centerline RMS Velocity  0 2  4  6  x / D 10 8 6 4 2 0 0 2  4  6  9 On, Pulse Modulation 20 Hz40 Hz60 Hz80 Hz100 HzUnforced Modulation Frequency 0.0 0.05 0.10 0.15 0.20 u ’ / U cl,0

13. MITE Pulsed Modulation: Power Spectra Power Frequency (Hz) 2 x /D = 1 3 x U/U CL = 0.5 m = -5/3 9 Pulsed

14. MITE Pulsed Modulation: Time Averaged Velocity Profiles U / U 0 u’ / U 0    x / D 0 1 2 3 4 y r / D 9 Pulsed

15. MITE Pulsed Modulation: Phase-Averaged Streamwise Velocity 0.3 0.6 0.9 1.20 x / D 0.041234 Unforced r 0 0.5 r / D 6 06 0  9 Pulsed S F

16. MITE x / D 0.041234 r r / D 6 06 0  9 Pulsed Pulsed Modulation: Phase-Averaged Radial Velocity S F 0 0.5 -0.3 0.0 0.3

17. MITE Pulsed Modulation: Phase Averaged Velocity x / D = 3 6 06 0 0 0.5 r / D  0.3 0.6 0.9 1.20 -0.3 0.0 0.3 / U 0 r 9 Pulsed

18. MITE Pulsed Modulation: Volume Flow Rate Unforced 9 On 9 Pulsed x /D Q ^ Q 0 = volume flow rate of unforced flow at x /D = 0.04

19. MITE Spatial Modulation: Time-Averaged Velocity Profiles    x / D 0 1 2 3 4 y 6 Spinning r / D 6 On 3 Off U / U 0 y

20. MITE Spinning Modulation: Decay of Streamwise Velocity 6 Spinning 9 Pulsed Unforced x /D U CL /U 0 m = -1

21. MITE Spinning Modulation: X-Wire Velocity Measurements 6 Spinning 0 2   /U 0 1 0 x /D = 1, r /D = 0.6x /D = 1, r /D = 0.4x /D = 4, r /D = 0.6 u measured with w  u measured with v

22. MITE Spinning Modulation: Phase-Averaged Streamwise Velocity x / D = 1 x / D = 0.04 x / D = 2 x / D = 3 x / D = 4 r

23. MITE Conclusions  Direct excitation of small-scale motions is demonstrated in an axisymmetric jet  Forcing increases turbulence intensity and dissipation in the near field  Natural (K-H) instabilities of the jet shear layer are suppressed  Azimuthally-periodic forcing distorts the jet cross section and appreciably lengthens the jet shear layer  Amplitude modulation of the excitation frequency results in controllable large-scale flow structures and increased entrainment  Spinning mode leads to precession of the primary jet axis with substantial impact on mixing

24. MITE Experimental Facility NOZZLE ACTUATOR HOUSING r x D i = 1.41 cm, D a,i = 1.59 cm, D a,o = 2.54 cm U i /U o = 0.33, 0.67, and 1.5 INNER FLOW PLENUM INNER FLOW CENTER JET SUPPORTS

25. MITE Coaxial Jets Streamwise Velocity U r/D Operating SeparatelyOperating Together

26. MITE Coaxial Jets Streamwise Velocity Unforced Pulsed x/D = 0.25 x/D = 1 Unforced  Forced  Pulsed 80 Hz x / D  0.25 1

27. MITE Future Work  Match mixing facility profiles  Investigate three velocity ratios: U i /U o = 0.33, 0.67, & 1.5  Determine modulation frequency  Compare three forcing conditions: »unforced »steady axisymmetric forcing »amplitude modulated axisymmetric forcing  Analyze velocity data with concentration data