Modeling of nonequilibrium radiation phenomena - An assessment

Sharma, Surendra P.; Whiting, E. E.

doi:10.2514/3.802

Cited by 20 publications

(6 citation statements)

References 14 publications

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“…Comparison of the radiation peak intensity measurements at l ; 391.4 nm, the experimental data presented in Ref. 6 for V s = 10.2 km/s, and our calculation data using the SWR model show good agreement with measured data. The measured data I m lie slightly above the calculated value.…”

Section: Resultssupporting

confidence: 80%

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Experimental and Numerical Study of Nonequilibrium Ultraviolet NO and N Emission in Shock Layer

Gorelov¹,

Gladyshev²,

Kireev³

et al. 1998

Journal of Thermophysics and Heat Transfer

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The results on an investigation of nonequilibrium uv radiation in the systems of molecular bands NO and (12) in a shock layer in air are presented. The studies included the experiments on a measurement + N 2 of the nonequilibrium radiation behind a strong shock wave in an electric arc-driven shock tube within the range of shock-wave velocity change V s = 5 to 10 km/s at the initial air pressure P 1 = 0.1 torr, and numerical simulation of radiation processes behind the shock wave and in a hypersonic viscous shock layer, where the ow was simulated on the basis of Navier -Stokes equations. A numerical model of the radiation behind the strong shock wave has been used to verify a kinetic scheme of radiation processes by comparison with experimental results. Examples of emission calculations in the NO and (12) sys-+ N 2 tems for the conditions of a ight test are presented. Nomenclature B = rotational constant c = speed of light, cm /s D = energy of dissociation, K e = electron H = ight altitude, km h = Planck's constant I = radiation intensity, W /cm 3 sr mm k = rate constant of reaction m = mass, g n = concentration, cm 2 3 P = pressure, torr R = radiance, W /cm 2 sr mm T = temperature, K t = time, s or ms U = rate of electron energy exchange V = ight or shock wave velocity, km /s v = vibrational number x = distance behind shock wave, cm y = stagnation line distance, cm b, g = parameters in vibration -dissociation model l = wavelength, nm or mm u = characteristic vibrational temperature, K n = collision frequency, s 2 1 s = cross section, cm 2 t = time, lifetime, s, ns, or ms v 0 , v 0 x 0 , v 0 y 0 , v 0 z 0 = vibrational constants ai = associative ionization e = electron, electronic el = elastic f = forward m = maximum R = rotational r = reverse s = shock-wave condition v = vibrational 1 = condition ahead of a shock wavè = freestream condition Superscripts 9 = upper excited state 0 = lower excited state

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Section: Resultssupporting

confidence: 80%

“…l about 235.0 nm -system NO, P 1 = 0.1 torr, V s = 5 -10 km /s l about 391.4 nm -system(12), P 1 = 0.1, torr, l = 391.4 nm, the measurements performed in the EAST for V s = 10.1 km /s and P 1 = 0.1 torr were in a good agreement with the data obtained in Ref 6…”

supporting

confidence: 88%

Experimental and Numerical Study of Nonequilibrium Ultraviolet NO and N Emission in Shock Layer

Gorelov¹,

Gladyshev²,

Kireev³

et al. 1998

Journal of Thermophysics and Heat Transfer

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“…Shock-tube measurements of the intensity profile behind a moving shock provide the desired spatially dependent radiation measurement. These have been reported by Allen et al 14 , Sharma 15,16,17 , Donohue et al 18 , Koreeda et al 19 , Morioka et al 20 , Fujita et al 21 , and Matsuda et al 22 . With the exception of Allen et al, these studies do not provide spectrally resolved data in the important 700 -1200 nm range.…”

Section: Introductionsupporting

confidence: 47%

A Comparison of EAST Shock-Tube Radiation Measurements with a New Air Radiation Model

Johnston

2008

46th AIAA Aerospace Sciences Meeting and Exhibit

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This paper presents a comparison between the recent EAST shock tube radiation measurements (Grinstead et al., AIAA 2008-1244) and the HARA radiation model. The equilibrium and nonequilibrium radiation measurements are studied for conditions relevant to lunar-return shock-layers; specifically shock velocities ranging from 9 to 11 km/s at initial pressures of 0.1 and 0.3 Torr. The simulated shock-tube flow is assumed one-dimensional and is calculated using the LAURA code, while a detailed nonequilibrium radiation prediction is obtained in an uncoupled manner from the HARA code. The measured and predicted intensities are separated into several spectral ranges to isolate significant spectral features, mainly strong atomic line multiplets. The equations and physical data required for the prediction of these strong atomic lines are reviewed and their uncertainties identified. The 700 -1020 nm wavelength range, which accounts for roughly 30% of the radiative flux to a peak-heating lunar return shock-layer, is studied in detail and the measurements and predictions are shown to agree within 15% in equilibrium. The ±1.5% uncertainty on the measured shock velocity is shown to cause up to a ±30% difference in the predicted radiation. This band of predictions contains the measured values in almost all cases. For the highly nonequilibrium 0.1 Torr cases, the nonequilibrium radiation peaks are under-predicted by about half. This under-prediction is considered acceptable when compared to the order-of-magnitude over-prediction obtained using a Boltzmann population of electronic states. The reasonable comparison in the nonequilibrium regions provides validation for both the non-Boltzmann modeling in HARA and the thermochemical nonequilibrium modeling in LAURA. The N 2 + (1-) and N 2 (2+) molecular band systems are studied in the 290 -480 nm wavelength range for both equilibrium and nonequilibrium regimes. The nonBoltzmann rate models for these systems, which have significant uncertainties, are tuned to improve the comparison with measurements. Nomenclature B= Blackbody or Planck function written in terms of wavelength (erg/cm 3 /s/sr) c = velocity of light, equal to 2.997925x10 10 cm/s e = electron charge, equal to 4.80298x10 -10 cm 3/2 g 1/2 /s f ij = oscillator strength for the atomic line transition with a lower level i and an upper level j g i = degeneracy for an atomic level i h = Planck's constant, equal to 6.6256x10 -27 erg-s I = wavelength dependent intensity (erg/cm 3 /sr/s) j line = wavelength-integrated emission coefficient over a single atomic line or multiplet (erg/cm 3 /sr/s) j = wavelength dependent emission coefficient (erg/cm 4 /sr/s) J c = wavelength-integrated normalized intensity for a given wavelength range (erg/cm 3 /sr/s), which is often presented in this paper multiplied by 100, as indicated by *100 J line = wavelength-integrated normalized intensity for a single atomic line or multiplet (erg/cm 3 /sr/s) J other = normalized intensity resulting from atomic continuum, molecular bands, and weak atomic lines ...

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“…Comparison of those measurements with modeling also showed the computations to overpredict the data. 5 The disagreement between theory and data for the higher density cases is most likely due to remaining inadequacies in the radiation modeling. Since the boundary layer is optically thick the radiance at the body should be relatively insensitive to uncertainties of the computed flow atomic oxygen concentration and temperature in the shock layer.…”

Section: Calculationsmentioning

confidence: 98%

“…We use an approach that has been followed in earlier work; i.e., we accept approximations to Eqs. (5) and (6) given in Refs. 9 and 11 that give a closed form for p and permit an approximate solution of Eq.…”

Section: Radiation Modelmentioning

confidence: 99%

Comparison of theory with atomic oxygen radiance data from a rocket flight

Levin

Candler

Howlett

et al. 1995

Journal of Thermophysics and Heat Transfer

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Results obtained from a state-of-the-art flow and radiation model are compared with vacuum-ultraviolet radiance data obtained from the recent Bow Shock 2 Flight Experiment. An extensive data set of atomic-oxygen resonance radiance measurements was obtained in flight for a re-entry speed of 5 km/s between the altitudes of approximately 65-85 km. A description of the NO photoionization cell used, the data, and the interpretation of the data will be presented. A new radiation model appropriate to the flight conditions of Bow Shock 2 is proposed. Comparison of theory with the data shows that at high altitudes the flow is optically thin. At altitudes lower than about 75 km the flow is optically thick and the disagreement between theory and experiment is attributed to the inadequate treatment of photon escape mechanisms from the shock layer. Nomenclature A = Einstein spontaneous emission coefficient, s" 1 B -absorption rate, cm 3 /(erg-s 2 ) B' = stimulated emission rate, cm 3 /(erg-s 2 ) h = Planck's constant, erg-s I v = specific intensity, erg/(s-sr-cm 2 -Hz) J v -mean intensity, erg/(s-cm 2 -Hz) k f = forward rate coefficient, cm 3 (/molecule-s) k r = reverse rate coefficient, cm 3 (/molecule-s) k Q = absorption coefficient at the resonance wavelength, cm" 1 M = a neutral species, number/cm 3 n t -total number density in the flow, number/cm 3 <2, = electronic partition function S v -source function, (erg-s/cm 3 ) y = angle between the sensor and the effective stagnation streamline, deg AJC = penetration distance, cm p -escape factor T V -optical depth 4> v = line absorption profile normalized to unit area, ŝ = emission line profile normalized to unit area, s Subscript v -frequency

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Modeling of nonequilibrium radiation phenomena - An assessment

Cited by 20 publications

References 14 publications

Experimental and Numerical Study of Nonequilibrium Ultraviolet NO and N Emission in Shock Layer

Experimental and Numerical Study of Nonequilibrium Ultraviolet NO and N Emission in Shock Layer

A Comparison of EAST Shock-Tube Radiation Measurements with a New Air Radiation Model

Comparison of theory with atomic oxygen radiance data from a rocket flight

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