Spontaneous Raman Scattering Temperature Measurements and Large Eddy Simulations of Vibrational Non-equilibrium in High-Speed Jet Flames

Reising, Heath H.; Haller, Timothy; Clemens, Noel T.; Varghese, Philip L.; Fiévet, Romain; Raman, Venkat

doi:10.2514/6.2016-3550

Cited by 7 publications

(3 citation statements)

References 18 publications

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“…Possibly, one intermediary level could have a relaxation timescale comparable to the mixing timescale. As observed in the experiment of Reising et al, 23 there is an inflection point in the shear layer where the flow switches from under to over-populated vibrational modes. This happens when the mixing and relaxation timescales become similar and no process dominates the other.…”

Section: B Turbulent Planar Jetsupporting

confidence: 58%

Numerical investigation of vibrational relaxation coupling with turbulent mixing

Fiévet

Voelkel

Raman

et al. 2017

55th AIAA Aerospace Sciences Meeting

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In flows where the relaxation rate of vibrational motion of the molecules to equilibrium is comparable to the flow through time scales, the presence of turbulence can alter the mixing and equilibration process. To understand the coupling between mixing and vibrational relaxation, a novel state-specific species model is solved in a background turbulent flow. The method is applied to mixing of two nitrogen streams at different static temperatures. The relaxation rates for each state are computed using quasi-classical trajectory analysis. For the flow conditions considered, the first ten vibrational levels are computed in the flow solver.The direct numerical simulation shows that population in different vibrational levels are significantly affected by turbulence and that the local distribution becomes non-Boltzmann. In certain locations in the jet, the population from the direct calculation can be several orders of magnitude different than the local-temperature based Boltzmann level. Last, while the bulk vibrational energy is inferior to its local equilibrium value throughout the mixing layer, the high energy level populations (levels 3 to 8) are on the opposite always over-populated. As chemical reactions are affected by these high vibrational energy populations, a simple temperature model would underestimate the impact of nonequilibrium on combustion.

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Section: B Turbulent Planar Jetsupporting

confidence: 58%

Numerical investigation of vibrational relaxation coupling with turbulent mixing

Fiévet

Voelkel

Raman

et al. 2017

55th AIAA Aerospace Sciences Meeting

Self Cite

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“…Consequently, it may be suggested that pumping is unimportant for practical intents and purposes, and there is no significant need to have multitemperature models be able to qualitatively recreate this phenomenon. Although the pumping from O2-N2 VVT set B is still a significant contributor to the O2 vibrational energy transfer throughout relaxation in both cases, as shown in Figure 8 (b) and Figure 13 (b), and, consequently, influences the relaxation profile, this is not of significant concern as the numerous rates and parameters in the multi-temperature models can generally be tuned to adequately reproduce the same relaxation profile given the qualitative features can be captured first [69,70].…”

Section: Nonequilibrium Initial Condition (Constant-volume Reactor)mentioning

confidence: 99%

Can vibrational pumping occur via O2–N2 collisions in nonequilibrium vibrationally excited air?

2023

Physics of Fluids

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The occurrence of vibrational pumping in air under nonequilibrium conditions is investigated as this phenomenon is not considered in the design of the current phenomenological models. It is shown that pumping can only happen during de-excitation and when the translational temperature is below around 1000 K. O2 is the molecule that would get pumped, and pumping will not occur when the initial equilibrium temperature is greater than around 1200–1600 K due to the formation of enough O to extinguish pumping via the O2–O vibration–translation reaction. The limiting initial temperature can be increased to around 2000 K if a nonequilibrium initial condition is considered. In cases where pumping does occur, constant–volume reactor simulations showed pumping of ≈5%. Nozzle simulations representative of that in hypersonic wind tunnels are conducted for an equilibrium temperature of 1100 K at the throat; pumping of up to around 10 K (≈1%) can be observed. It can be suggested that constant–volume reactors generally overestimate the manifestation of thermochemical nonequilibrium-associated phenomena and are a better zero-dimensional analogy for the relaxation process in flows with large length scales and no further expansion after an initial rapid expansion. After examination of the uncertainties of the most important rates used in the simulations, one may suggest that the current results correspond to the upper bound for the magnitude of pumping. It may be concluded that pumping is unimportant for practical intents and purposes in nonequilibrium hypersonic flows, and phenomenological models need not be able to recreate this phenomenon.

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“…Vibrational Raman is ineffective in low temperature regimes due to the lack of the anti-Stokes bands; however, pure rotational Raman spectr oscopy, which is not dependent upon anti-Stoke lines, has been used to interrogate expanding supersonic flows of CO 2 for measuring temperature [13]. Vibrational and rotational Raman have also been used together, either separately to measure and contrast temperature in high speed turbulent diffusion flames [14]; or simultaneously in a low resolution, low bandwidth Raman technique yielding a manifold encompassing both rotational and vibrational Raman for extracting temperature in high pressure H 2 /air flames [15]. Transient gradient spectroscopy (TGS), a relatively new diagnostic tool, has also seen recent application to temperature measurement.…”

Section: Introductionmentioning

confidence: 99%

Rotational Raman-based temperature measurements in a high-velocity, turbulent jet

Locke¹,

Wernet

Anderson

2017

Meas. Sci. Technol.

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Spontaneous rotational Raman scattering spectroscopy is used to acquire measurements of the mean and root mean square (rms) temperature fluctuations in turbulent, high-velocity heated jets. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 50 mm diameter nozzle operating from subsonic to supersonic conditions over a wide range of temperatures and Mach numbers, in accordance with the Tanna matrix frequently used in jet noise studies. These data were acquired in the hostile, high noise (115 dB) environment of a large scale open air test facility at NASA Glenn Research Center (GRC). Temperature estimates were determined by performing non-linear least squares fitting of the single shot spectra to the theoretical rotational Stokes spectra of N2 and O2. The laser employed in this study was a high energy, long-pulsed, frequency doubled Nd:YAG laser. One thousand single-shot spectra were acquired at each spatial coordinate. Mean temperature and rms temperature variations were calculated at each measurement location. Excellent agreement between the averaged and single-shot temperatures was observed with an accuracy better than 2.5% for temperature, and rms variations in temperature between ±2.2% at 296 K and ±4.5% at 850 K. The mean and normalized rms temperatures measured here were then compared to NASA’s Consensus data set of PIV velocity and turbulence measurements in similar jet flows. The results of this and planned follow-on studies will support NASA GRC’s development of physics-based jet noise prediction, turbulence modeling and aeroacoustic source modeling codes.

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Spontaneous Raman Scattering Temperature Measurements and Large Eddy Simulations of Vibrational Non-equilibrium in High-Speed Jet Flames

Cited by 7 publications

References 18 publications

Numerical investigation of vibrational relaxation coupling with turbulent mixing

Numerical investigation of vibrational relaxation coupling with turbulent mixing

Can vibrational pumping occur via O2–N2 collisions in nonequilibrium vibrationally excited air?

Rotational Raman-based temperature measurements in a high-velocity, turbulent jet

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