Robert P. Lucht School of Mechanical Engineering , Purdue University, W. Lafayette, IN

1. Development of a High-Spectral-Resolution PLIF Technique for Measurement of Pressure, Temperature, and Velocity in Hypersonic Flows Robert P. Lucht School of Mechanical Engineering , Purdue University, W. Lafayette, IN Presentation at the AFOSR MURI Review College Station, TX October 12, 2007

2. Introduction and Motivation • Characterization of hypersonic turbulent flows in non-thermochemical equilibrium is critical for many DoD missions, including high-speed flight • Optical measurements of instantaneous flow and thermodynamic properties is essential for the development of reliable predictive models • We are pursuing high-spectral-resolution PLIF imaging of NO for P, T, V imaging in high-speed flows, combined with emerging pulse-burst laser technology offers the potential for instantaneous imaging of thes properties

3. Optical Parametric Laser Systems • At Purdue, we have developed tunable, pulsed, injection-seeded optical parametric systems capable of producing very narrow linewidth laser radiation • These OP systems are similar to the more expensive ring dye lasers; all-solid state, rapidly tunable systems are ideal for high-resolution spectroscopy • Underexpanded free jet is produced using a convergent nozzle supplied with 100 ppm NO in buffer N2 at stagnation pressure of about 6 atm • High-spectral resolution PLIF, first demonstrated in the 1980’s with ring dye lasers by Hanson and Miles groups, performed using our OP systems

4. Underexpanded Jet Flowfield

5. Laser System DFB can be current or temperature tuned Spectral linewidth at 452 nm ~ 200 MHz = 0.007 cm-1

6. Flow and Imaging System ~0.5 mJ/pulse

7. Timing Diagram

8. Typical PLIF Image Calibration Cuvette Underexpanded Jet Flowfield Nozzle Exit (D) = 5 mm z

9. Image Processing: Correction Factor NO, P = 1 atm, T = 300 K Region of Interest (ROI)

10. Image Processing: Zero Degree Images near NO Peak (44,097.53 cm-1) Normalized Image Raw Image

11. Image Processing: 45 Degree Images near NO Peak (44,097.53 cm-1) Raw Image Normalized Image Laser Sheet

12. Spatially Resolved Spectra Extracted from Multiple Images

13. Analysis of PLIF Spectra • The PLIF spectrum is dependent on pressure, temperature, and velocity in the underexpanded jet

14. Analysis of PLIF Spectra • Spectral line width determined primarily by the pressure for this underexpanded jet • Temperature profile can then be determined from the relative PLIF intensities at different spatial locations, complicated in this experiment by spatial profile of the laser sheet • Flow velocity can be measured from spectral line shift for velocities in excess of ~ 100 m/s

15. Determination of Pressure from PLIF Spectra z/D = 0.422 P = 1.28 atm z/D = 0.567 P = 0.86 atm

16. Determination of Pressure from PLIF Spectra z/D = 0.778 P = 0.47 atm z/D = 0.995 P = 0.28 atm

17. Determination of Pressure from PLIF Spectra z/D = 1.35 P = 0.12 atm z/D = 1.50 P = 1.27 atm

18. Determination of Pressure from PLIF Spectra

19. LIF Signals Before and After the Normal Shock z/D = 1.35 (Before Normal Shock) z/D = 1.50 (After Normal Shock) Experiment Theory

20. Spectral Line Shapes Just Before Normal Shock Fitting Parameters T = 100 K P = 0.13 atm Dw = 0.05±0.01 cm-1 V = 500 ± 100 m/s

21. Axial Velocity Profile in UE Jet z/D = 0 M = 1 z/D = 1.45 Normal Shock

22. Conclusions • Injection-seeded optical parametric systems are used for high-spectral-resolution PLIF imaging in supersonic underexpanded free jet • PLIF spectra were obtained from different laser pulses, measurements were not instantaneous • Pressure and temperature values compare favorably with previous N2 CARS measurements, measurements in underexpanded jet complicated by large dynamic range of P and T • Measured Doppler shift gives reasonable value of axial velocity profile in the supersonic region before the normal shock, measurement accuracy ~ 100 m/s