Single Shot Temperature Measurements using Coherent Anti-Stokes Raman Scattering in Mach 14 Flow at the Hypervelocity AEDC Tunnel 9

Dogariu, Arthur; Dogariu, Laura; Smith, Michael S.; Lafferty, John; Miles, Richard B.

doi:10.2514/6.2019-1089

Cited by 9 publications

(2 citation statements)

References 13 publications

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“…In May 2017, FLEET was studied in pure nitrogen (≥ 99.995%) over a range of temperatures (72-298 K) and pressures (0.228-101 kPa) using a free jet facility custombuilt for testing laser-based diagnostics at NASA Langley Research Center. These conditions were chosen for general characterization of FLEET in sub-atmospheric environments and applicability to the temperatures and pressures in the Princeton indraft facilities (at Mach 3.5-3.8), the pressures (and nearly the temperatures 6 ) in the AEDC hypervelocity tunnel (at Mach 14 [18]), and the temperatures (but not the pressures to complement previous work in nitrogen at higher pressure [8]) in the NASA cryogenic wind tunnels. Gas cylinders supplied high-pressure (≤1 MPa) flow to an axisymmetric, converging-diverging nozzle to produce a pressure-matched free jet inside a hermetically sealed and continuously evacuated chamber instrumented for optical access (see figure 1).…”

Section: Variable Temperature and Pressure Flow Facilitymentioning

confidence: 99%

Effect of low temperatures and pressures on signal, lifetime, accuracy and precision of femtosecond laser tagging velocimetry

Peters¹,

Burns²,

Miles³

et al. 2020

Meas. Sci. Technol.

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Femtosecond laser electronic excitation tagging velocimetry is experimentally characterized in pure nitrogen at pressures (0.228-101 kPa) and temperatures (72-298 K) relevant to high-speed ground testing. Evaluated metrics of performance include signal intensity/lifetime and velocity accuracy/precision. A fast-framing camera lens-coupled to a bandpass-filtered image intensifier acquired data at six principal time delays (0.1-5.0 µs). Results show signal intensity depends primarily on density and secondarily on temperature. Relative to atmospheric conditions, signal intensity is optimized at reduced densities and cryogenic temperatures. In agreement with previous experiments, the density dependence breaks down at extended time delays. Signal lifetime depends largely on density with a mild to moderate inverse correlation to initial signal strength. In contrast to previous work in pure nitrogen at above atmospheric densities, initial signal and lifetime exhibit different, more complicated trends at sub-atmospheric densities. Although accuracy lacks clear thermodynamic dependencies, precision strongly depends on density and temperature, largely driven by its more fundamental (though inverse) relationship to signal intensity. Precision also inversely depends on the length of the time interval used to determine velocity, in agreement with previous studies. Normalized accuracies and precisions of less than a percent and a few percent, respectively, are obtained in the supersonic free jet.

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Section: Variable Temperature and Pressure Flow Facilitymentioning

confidence: 99%

Effect of low temperatures and pressures on signal, lifetime, accuracy and precision of femtosecond laser tagging velocimetry

Peters¹,

Burns²,

Miles³

et al. 2020

Meas. Sci. Technol.

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show abstract

“…In this regime, optical distortions are produced only by gradients of the density field inside flow structures such as a turbulent boundary layer [5]. By contrast, environments such as hypersonic flight [6][7][8][9], reentry [10], laser gain media [11], and pulsed electrical discharges [12] produce conditions of thermal non-equilibrium that can appreciably alter the mean polarizability [13], leading to a higher refractive index expected based on the translational temperature alone. Neglecting the non-equilibrium effects on polarizability can result in systematic errors in quantitative measurements, for example, by artificially reducing the inferred gas density.…”

Section: Introductionmentioning

confidence: 99%

Measurements of N₂ refractive index and scalar polarizability in a pulsed nanosecond non-equilibrium discharge by Mach–Zehnder interferometry and spontaneous Raman scattering

Wu¹,

Tropina²,

Miles³

et al. 2020

J. Phys. D: Appl. Phys.

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This paper presents quantitative measurements of the N2 Gladstone–Dale constant and scalar polarizability in non-equilibrium conditions, created by a nanosecond pulsed discharge at a pressure of 90 Torr. Optical path differences and spatially varying refractive index profiles are obtained by temporally-resolved Mach–Zehnder interferometry. Spontaneous Raman scattering spectroscopy is used to investigate the highly non-equilibrium vibrational population and to measure the N2() vibrational temperature and rotational temperature in the discharge afterglow region. The local gas density is inferred from the rotational temperature with isobaric conditions at long time delays ranging from 10 to 500 µs after initiating the pulsed discharge. The non-equilibrium effects on the N2 Gladstone–Dale constant and scalar polarizability are reported within a rotational temperature ranging from 300 to 1000 K. To the best of our knowledge, this is the first time the refractivity of gas has been measured under non-equilibrium conditions in a pulsed discharge afterglow.

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Localized time accurate sampling of nonequilibrium and unsteady hypersonic flows: methods and horizons

Miles

Dogariu

Dogariu³

2021

Exp Fluids

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Modern “non-intrusive” optical methods are providing revolutionary capabilities for diagnostics of hypersonic flow fields. They generate accurate information on the performance of ground test facilities and provide local time accurate measurements of near-wall and off-body flow fields surrounding hypersonic test articles. They can follow the true molecular motion of the flow and detect nonequilibrium states and gas mixtures. They can be used to capture a wide range of turbulent scales and can produce highly accurate velocity, temperature and density measurements as well as time-frozen images that provide intuitive understanding of flow phenomena. Recent review articles address many of these methods and their applications. The methods highlighted in this review are those that have been enabled or greatly improved by new, versatile laser systems, particularly including kHz rate femtosecond lasers and MHz rate pulse burst lasers. Although these methods can be applied to combusting environments, the focus of this review is on external high Mach number flows surrounding test articles and wind tunnel core flow properties. The high repetition rates enable rapid time evolving flows to be analyzed and enable the collection of large data sets necessary for statistical analysis. Future capabilities based on the use of atomic vapor filters and on frequency tunable, injection locked MHz rate lasers are promising.

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Single Shot Temperature Measurements using Coherent Anti-Stokes Raman Scattering in Mach 14 Flow at the Hypervelocity AEDC Tunnel 9

Cited by 9 publications

References 13 publications

Effect of low temperatures and pressures on signal, lifetime, accuracy and precision of femtosecond laser tagging velocimetry

Effect of low temperatures and pressures on signal, lifetime, accuracy and precision of femtosecond laser tagging velocimetry

Measurements of N₂ refractive index and scalar polarizability in a pulsed nanosecond non-equilibrium discharge by Mach–Zehnder interferometry and spontaneous Raman scattering

Localized time accurate sampling of nonequilibrium and unsteady hypersonic flows: methods and horizons

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Single Shot Temperature Measurements using Coherent Anti-Stokes Raman Scattering in Mach 14 Flow at the Hypervelocity AEDC Tunnel 9

Cited by 9 publications

References 13 publications

Effect of low temperatures and pressures on signal, lifetime, accuracy and precision of femtosecond laser tagging velocimetry

Effect of low temperatures and pressures on signal, lifetime, accuracy and precision of femtosecond laser tagging velocimetry

Measurements of N2 refractive index and scalar polarizability in a pulsed nanosecond non-equilibrium discharge by Mach–Zehnder interferometry and spontaneous Raman scattering

Localized time accurate sampling of nonequilibrium and unsteady hypersonic flows: methods and horizons

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Measurements of N₂ refractive index and scalar polarizability in a pulsed nanosecond non-equilibrium discharge by Mach–Zehnder interferometry and spontaneous Raman scattering