SCHOOL OF MECHANICAL ENGINEERING 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

SCHOOL OF MECHANICAL ENGINEERING 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

SCHOOL OF MECHANICAL ENGINEERING 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 N 2 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

SCHOOL OF MECHANICAL ENGINEERING Underexpanded Jet Flowfield

SCHOOL OF MECHANICAL ENGINEERING Laser System DFB can be current or temperature tuned Spectral linewidth at 452 nm ~ 200 MHz = cm -1

SCHOOL OF MECHANICAL ENGINEERING Flow and Imaging System ~0.5 mJ/pulse

SCHOOL OF MECHANICAL ENGINEERING Timing Diagram

SCHOOL OF MECHANICAL ENGINEERING Typical PLIF Image Nozzle Exit (D) = 5 mm Calibration Cuvette Underexpanded Jet Flowfield z

SCHOOL OF MECHANICAL ENGINEERING Image Processing: Correction Factor NO, P = 1 atm, T = 300 K Region of Interest (ROI)

SCHOOL OF MECHANICAL ENGINEERING Image Processing: Zero Degree Raw Image Normalized Image Images near NO Peak (44, cm -1 )

SCHOOL OF MECHANICAL ENGINEERING Image Processing: 45 Degree Normalized Image Images near NO Peak (44, cm -1 ) Laser Sheet Raw Image

SCHOOL OF MECHANICAL ENGINEERING Spatially Resolved Spectra Extracted from Multiple Images

SCHOOL OF MECHANICAL ENGINEERING Analysis of PLIF Spectra The PLIF spectrum is dependent on pressure, temperature, and velocity in the underexpanded jet

SCHOOL OF MECHANICAL ENGINEERING 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

SCHOOL OF MECHANICAL ENGINEERING Determination of Pressure from PLIF Spectra z/D = P = 1.28 atm z/D = P = 0.86 atm

SCHOOL OF MECHANICAL ENGINEERING Determination of Pressure from PLIF Spectra z/D = P = 0.47 atm z/D = P = 0.28 atm

SCHOOL OF MECHANICAL ENGINEERING Determination of Pressure from PLIF Spectra z/D = 1.35 P = 0.12 atm z/D = 1.50 P = 1.27 atm

SCHOOL OF MECHANICAL ENGINEERING Determination of Pressure from PLIF Spectra

SCHOOL OF MECHANICAL ENGINEERING LIF Signals Before and After the Normal Shock z/D = 1.35 (Before Normal Shock) z/D = 1.50 (After Normal Shock) ExperimentTheory

SCHOOL OF MECHANICAL ENGINEERING Spectral Line Shapes Just Before Normal Shock Fitting Parameters T = 100 K P = 0.13 atm  = 0.05±0.01 cm -1 V = 500 ± 100 m/s

SCHOOL OF MECHANICAL ENGINEERING Axial Velocity Profile in UE Jet z/D = 0 M = 1 z/D = 1.45 Normal Shock

SCHOOL OF MECHANICAL ENGINEERING 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 N 2 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