Electron Diffusion ahead of Shock Waves in Argon

Weymann, Helmut D.

doi:10.1063/1.1706089

Cited by 76 publications

(7 citation statements)

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“…In 1960s, shock tube experiments were conducted using argon as a test gas to clarify the thermochemical nonequilibrium processes behind shock waves (Weymann, 1960, 1969, Holmes and Weymann, 1969. These results showed that precursor electrons were generated ahead of shock waves and had a great influence on the thermochemical nonequilibrium processes behind shock waves.…”

Section: Introductionmentioning

confidence: 99%

Electron density measurements behind a hypersonic shock wave in argon

Yamada

Kawazoe

Obayashi

2016

JFST

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The purpose of the research is to characterize the ionization process behind a shock wave with precursor photoionization in argon. In this study, the H- line is observed by spectroscopic measurements using a hypersonic shock tube and the Stark broadening of the H- line is evaluated to obtain the electron density behind a shock wave. As a result, the electron density is on the order of 10 21 m -3 and tends to decrease with increasing the distance from the shock front. The decrease of the measured electron density is caused by the radiative energy loss from the test gas because the radiative energy loss corresponds to a decrease of the temperature or the density of the test gas, both of which can decrease the electron density. Previous study showed that photoionization occurred ahead of the shock wave, making use of the radiation energy emitted from the region behind the shock wave. The fact might be related to the radiative energy loss obtained in the present study. From the present study, it is found that the radiative energy loss is dominant behind the shock wave under the condition that precursor photoionization occurs ahead of the shock wave. In future, we should investigate the radiative transfer phenomena around the shock wave for further clarification.

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Section: Introductionmentioning

confidence: 99%

Electron density measurements behind a hypersonic shock wave in argon

Yamada

Kawazoe

Obayashi

2016

JFST

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“…Figure 3 shows that the n a2 concentration increases by a factor of 5 for a three-fold increase in pd\ From Eq. (46) we find that n a2 is increased three-fold due to the increase in n a i (1) . The remaining factor of 1.7 is contributed by a larger value of the Planck function resulting from an increased T (2 \ The argon ion concentration, when the dominant production reaction is the photoionization of photoexcited states, is found by inserting (43) into (40), setting ei = 0, and integrating.…”

Section: Some Numerical Resultsmentioning

confidence: 91%

“…In the numerical results that are presented below, the distance between the shock front and the contact surface in the shock tube is given by the following dimensional expression,, L = ^ + L 2 = 4.84 PWR* [1 -(M -ll) /29] (44) where P (1) is in torr, and R and L in cm. Equation (44) is developed from MireFs theory 27 for test time in argon-filled shock tubes where, when PiR < 6 torr-cm, a laminar wall boundary layer persists.…”

Section: Some Numerical Resultsmentioning

confidence: 99%

“…n* = effective principal quantum number Qiz = photoexcitation rate from state 1 to state 2 Qzi = photoionization rate from state 2 to state i p (1) = pressure upstream of shock wave R = shock tube radius R y = Rydberg constant /S (i) = line strength TW = temperature in region i TAO = frozen flow temperature behind the shock wave u (l) = velocity of gas approaching shock wave as measured in coordinates fixed in the wave x = distance from shock front x' = distance from the equilibrium region a (2) = degree of ionization in the equilibrium region (XL = semi-half width due to Lorentz broadening A = frequency interval f = distance measured in ratio x'/R y] = distance measured in ratio x/R 6 = arctangent of R/x f K X = atomic absorption coefficient X = wavelength \2i…”

Section: Nomenclaturementioning

confidence: 99%

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Precursor photoexcitation and photoionization of argon in shock tubes

Dobbins

1970

AIAA Journal

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A chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave in a shock tube is examined on a quantitative basis. The model includes the propagation of resonance radiation far from the shock front in the wings of the resonance absorption line, imprisonment of the absorbed resonance radiation, subsequent photoionization of excited atoms, photoionization of ground state argon, and certain recombination and de-excitation processes. Specific consideration is given to shock tube geometry, the finite extent of the equilibrium region and the (experimentally) known shock tube wall reflectivity. Theoretical predictions of excited atom and argon ion concentrations in the precursor region are presented for typical shock tube operating conditions. The regimes favorable to the production of argon ions by photoionization of ground state argon and by photoionization of photoexcited argon, respectively, are delineated. NomenclatureA 21 = spontaneous emission probability B(i>i2,T ({) ) = Planck function evaluated at temperature Tĉ = speed of light e r i,c r 2 = first and second reflectivity constants e -charge on an electron / = oscillator strength QI = statistical weight of ground state #2 = statistical weight of excited state <7/2(*0 = Gaunt factor for photoionization cross section of excited state g t i = escape probability from radiation imprisonment theory h = Planck's constant 3 = impurity concentration in parts per million I v -specific spectral intensity J v = average spectral intensity KO = absorption coefficient at center frequency of a spectral line k = Boltzmann constant K V W = spectral absorption coefficient L = distance between shock wave pressure discontinuity and contact surface Li = distance between the pressure discontinuity and the equilibrium front L% = distance between equilibrium front and the contact surface M = Mach number of shock wave m e = mass of an electron n a i = number of ground state atoms per unit volume n a z -number of excited state atoms per unit volume n a + = number of argon ions per unit volume Presented as Paper 68-666 at the AIAA Fluid and Plasma effective principal quantum number Qiz = photoexcitation rate from state 1 to state 2 Qzi = photoionization rate from state 2 to state i p (1) = pressure upstream of shock wave R = shock tube radius R y = Rydberg constant /S (i) = line strength TW = temperature in region i TAO = frozen flow temperature behind the shock wave u (l)= velocity of gas approaching shock wave as measured in coordinates fixed in the wave x = distance from shock front x' = distance from the equilibrium region a (2) = degree of ionization in the equilibrium region (XL = semi-half width due to Lorentz broadening A = frequency interval f = distance measured in ratio x'/R y] = distance measured in ratio x/R 6 = arctangent of R/x f K X = atomic absorption coefficient X = wavelength \2i= wavelength corresponding to frequency vzi v = frequency vzi = frequency of radiation accompanying de-excitation from...

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“…25,26) Electrons are also produced by the electron diffusion from the shock front. 27,28) The presence of electrons ahead of shock waves might affect the relaxation process behind the shock front. Radiative processes are important mechanisms for precursor heating.…”

Section: Parametric Studymentioning

confidence: 99%

Numerical Analysis on the Nonequilibrium Phenomena of the Electronic Excitation Process behind Hypersonic Shock Waves

Yamada

Takayanagi

Suzuki

et al. 2013

Trans. Japan Soc. Aero. S Sci.

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In this study, the nonequilibrium phenomena of the electronic excitation process behind hypersonic shock waves have been investigated through numerical analysis. In the analysis, the three-temperature model is employed and temperature profiles are computed along the distance from the shock front. In the three-temperature model, the translationalrotational, vibrational and electron-electronic excitation temperatures are separately described and the relaxation processes for each energy mode are considered. Numerical calculations are conducted under the conditions corresponding to the shock tube experiments conducted in our previous study and the results are compared with the experimental data. It is found that the calculated and measured vibrational temperature profiles are in good agreement. In contrast, the calculated electronic excitation temperature is much lower than the measured one, revealing the discrepancy in the modeling of the electronic excitation temperature. To investigate the effect of electron behavior, parametric studies are conducted using the three-temperature model. The calculated temperatures agree well with the measured temperatures by considering the electrons in the region ahead of the shock wave. This result suggests that the effect of electron behavior is significant for hypersonic shock waves and a detailed model to describe the nonequilibrium phenomena is needed.

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Electron Diffusion ahead of Shock Waves in Argon

Cited by 76 publications

References 3 publications

Electron density measurements behind a hypersonic shock wave in argon

Electron density measurements behind a hypersonic shock wave in argon

Precursor photoexcitation and photoionization of argon in shock tubes

Numerical Analysis on the Nonequilibrium Phenomena of the Electronic Excitation Process behind Hypersonic Shock Waves

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