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
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SCHOOL OF MECHANICAL ENGINEERING Development of a High-Spectral- Resolution PLIF Technique for Measurement of Pressure, Temperature, and Velocity in Hypersonic.
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SCHOOL OF MECHANICAL ENGINEERING
Development of a High-Spectral-Resolution PLIF Technique for
Measurement of Pressure, Temperature, and Velocity in
Hypersonic Flows
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 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 SystemsOptical 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
Spatially Resolved Spectra Extracted from Multiple Images
Spatially Resolved Spectra Extracted from Multiple Images
SCHOOL OF MECHANICAL ENGINEERING
Analysis of PLIF SpectraAnalysis of PLIF Spectra
• The PLIF spectrum is dependent on pressure, temperature, and velocity in the underexpanded jet
2
0
1~
21
, ,
, ,
, ,
LIF B NO
aa
a
B B NO NO
a a
AS f N
A Q
f f P T N N P T
Q Q P T P T
P T V
SCHOOL OF MECHANICAL ENGINEERING
Analysis of PLIF SpectraAnalysis 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
Determination of Pressure from PLIF Spectra
Frequency (cm-1)
44096 44097 44098 44099
LIF
Sig
nal
(ar
b. u
nit
s)
0
50
100
150
200
250MeasuredCalculated (X) z/D = 0.422
= 0.4
z/D = 0.422P = 1.28 atm
z/D = 0.567P = 0.86 atm
SCHOOL OF MECHANICAL ENGINEERING
Determination of Pressure from PLIF Spectra
Determination of Pressure from PLIF Spectra
z/D = 0.778P = 0.47 atm
z/D = 0.995P = 0.28 atm
SCHOOL OF MECHANICAL ENGINEERING
Determination of Pressure from PLIF Spectra
Determination of Pressure from PLIF Spectra
z/D = 1.35P = 0.12 atm
z/D = 1.50P = 1.27 atm
SCHOOL OF MECHANICAL ENGINEERING
Determination of Pressure from PLIF Spectra
Determination of Pressure from PLIF Spectra
SCHOOL OF MECHANICAL ENGINEERING
LIF Signals Before and After the Normal Shock
LIF Signals Before and After the Normal Shock
z/D = 1.35 (Before Normal Shock)
z/D = 1.50 (After Normal Shock)
Experiment Theory
SCHOOL OF MECHANICAL ENGINEERING
Spectral Line Shapes Just Before Normal Shock
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 JetAxial Velocity Profile in UE Jet
z/D = 0M = 1
z/D = 1.45Normal Shock
SCHOOL OF MECHANICAL ENGINEERING
ConclusionsConclusions
• 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