Nonequilibrium determination of temperature profiles by emission spectroscopy

Labracherie, L.; Billiotte, M.; Houas, L.

doi:10.1016/0022-4073(95)00027-i

Cited by 12 publications

(2 citation statements)

References 3 publications

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“…Sharma and Gillespie [18] completed their measurements using photomultiplier tube radiometers and the second positive system of N 2 . Using the Marseille free-piston shock tube and a shock velocity of 5:8 km=s, Labracherie et al studied the nonequilibrium region downstream of a normal shock wave [22]. Labracherie et al presented the temporal evolution of vibrational and rotational temperatures and did not specifically investigate spatial temperature gradients.…”

Section: Introductionmentioning

confidence: 99%

NO and OH Spectroscopic Vibrational Temperature Measurements in a Post-Shock Relaxation Region

et al. 2010

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In this paper, spatial temperature profiles are examined in the nonequilibrium relaxation region behind a stationary shock wave in a hypervelocity air Mach 7.42 freestream. The normal shock wave is established through a Mach reflection from an opposing wedge arrangement in an expansion tube facility. Schlieren images confirm that the shock configuration is steady and the location is repeatable. Emission spectroscopy is used to identify dissociated species and to make vibrational temperature measurements using both the nitric oxide and the hydroxyl radical A-X band sequences. Temperature measurements are presented at selected locations behind the normal shock. LIFBASE is used as the simulation spectrum software for OH temperature-fitting; however, the need to access higher vibrational and rotational levels for NO leads to the use of an in-house developed algorithm. For NO, results demonstrate the contribution of higher vibrational and rotational levels to the spectra at the conditions of this study. Very good agreement is achieved between the experimentally measured NO vibrational temperatures and calculations performed using an existing state-resolved, three-dimensional forced-harmonic oscillator thermochemical model. The measured NO vibrational temperatures are significantly higher than the OH temperatures.

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Section: Introductionmentioning

confidence: 99%

NO and OH Spectroscopic Vibrational Temperature Measurements in a Post-Shock Relaxation Region

et al. 2010

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“…Using the Marseille free-piston shock tube and a shock velocity of 5.8 km/s, Labracherie et al studied the non-equilibrium region downstream of a normal shock wave. 12 Labracherie et al presented the temporal evolution of vibrational and rotational temperatures and did not specifically investigate spatial temperature gradients. Temperature measurements were made for a methane-nitrogen-argon mixture using the CN B-X electronic transition.…”

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confidence: 99%

Spectroscopic Measurements in the Shock Relaxation Region of a Hypervelocity Mach Reflection

Sharma

Austin

Glumac

et al. 2009

39th AIAA Fluid Dynamics Conference

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We examine the spatial temperature profile in the non-equilibrium relaxation region behind a stationary shock wave. The normal shock wave is established through a Mach reflection configuration from an opposing wedge arrangement for a hypervelocity air Mach 7.42 freestream. Schlieren images confirm that the shock configuration is steady and the location is repeatable. Emission spectroscopy is used to identify dissociated species and to obtain vibrational temperature measurements using the NO and OH A-X band sequences. Temperature measurements are presented at selected locations behind the normal shock. LIFBASE is used as the simulation spectrum software for OH temperature-fitting, however the need to access higher vibrational and rotational levels for NO leads to the use of an in-house developed algorithm. For NO, results demonstrate the contribution of higher vibrational and rotational levels to the spectra at the conditions of this study. Very good agreement is achieved between the experimentally measured NO vibrational temperatures and calculations performed using a state-resolved, one-dimensional forced harmonic oscillator thermochemical model.

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Characterization of non-Boltzmann CN X2Σ+ behind shock waves in CH4–N2 via broadband ultraviolet femtosecond absorption spectroscopy

Radhakrishna

Tancin

Goldenstein

2023

The Journal of Chemical Physics

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This article describes the temporal evolution of rotationally and vibrationally non-Boltzmann CN X2Σ+ formed behind reflected shock waves in N2–CH4 mixtures at conditions relevant to atmospheric entry into Titan. A novel ultrafast (i.e., femtosecond) laser absorption spectroscopy diagnostic was developed to provide broadband (≈400 cm−1) spectrally resolved (0.02 nm resolution) measurements of CN absorbance spectra belonging to its B2Σ+ ← X2Σ+ electronic system and its first four Δv = 0 vibrational bands (v″ = 0, 1, 2, 3). Measurements were acquired behind reflected shock waves in a mixture with 5.65% CH4 and 94.35% N2 at initial chemically and vibrationally frozen temperatures and pressures of 4400–5900 K and 0.55–0.75 bar, respectively. A six-temperature line-by-line absorption spectroscopy model for CN was developed to determine the rotational temperature of CN in v″ = 0, 1, 2, and 3, as well as two vibrational temperatures via least-squares fitting. The measured CN spectra revealed rotationally and vibrationally non-Boltzmann population distributions that strengthened with increasing shock speed and persisted for over 100 µs. The measured vibrational temperatures of CN initially increase in time with the increasing CN mole fraction and eventually exceed the expected post-shock rotational temperature of N2. The results suggest that strong chemical pumping is ultimately responsible for these trends and that, at the conditions studied, CN is primarily formed in high vibrational states within the A2Π or B2Σ+ state at characteristic rates, which are comparable to or exceed those of key vibrational equilibration processes.

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Nonequilibrium determination of temperature profiles by emission spectroscopy

Cited by 12 publications

References 3 publications

NO and OH Spectroscopic Vibrational Temperature Measurements in a Post-Shock Relaxation Region

NO and OH Spectroscopic Vibrational Temperature Measurements in a Post-Shock Relaxation Region

Spectroscopic Measurements in the Shock Relaxation Region of a Hypervelocity Mach Reflection

Characterization of non-Boltzmann CN X2Σ+ behind shock waves in CH4–N2 via broadband ultraviolet femtosecond absorption spectroscopy

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