Titan atmospheric composition by hypervelocity shock-layer analysis

Nelson, H. F.; Park, Chul; Whiting, E. E.

doi:10.2514/3.243

Cited by 65 publications

(15 citation statements)

References 14 publications

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“…A reduced species model was also developed through a sensitivity analysis performed across a range of conditions relevant to Titan entry, as shown in Table 1 [9,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. As this model contains a smaller number of species and reactions, it is better suited to coupling with radiation flow solvers while still providing accurate results [9].…”

Section: A Titan Chemical Reaction Setmentioning

confidence: 99%

Analysis of Nonequilibrium CN Radiation Encountered During Titan Atmospheric Entry

Brandis

Morgan

McIntyre

2011

Journal of Thermophysics and Heat Transfer

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The focus of this paper is to analyze the Titan reaction scheme and determine the mechanisms that control the formation and decay of the radiation emitted by the cyanogen molecule (CN) during entry into Titan's atmosphere. Through a parametric study of important reactions combined with an investigation into reaction pathways, it has been concluded that the coupling between the dissociation of N 2 and the formation of the CN (through the reaction N 2 C $ CN N) controls the radiation decay rate. The reason for the super equilibrium concentrations (approximately 50% higher than equilibrium) was identified to be a result of the N 2 C $ CN N reaction continuing to overproduce the CN after nominal equilibrium values were reached. This is due to the slow buildup of N to drive the reverse reaction. The absolute level of emitted radiation has been shown to be controlled by the lifetime of the CNB state and the excitation of CNX to CNB by heavy particle impact. Thus, it is the conclusion of this paper that CN radiation is primarily controlled by N 2 dissociation.

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Section: A Titan Chemical Reaction Setmentioning

confidence: 99%

Analysis of Nonequilibrium CN Radiation Encountered During Titan Atmospheric Entry

Brandis

Morgan

McIntyre

2011

Journal of Thermophysics and Heat Transfer

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“…The change in emissive power of the test gas over the unsteady expansion was then found by evaluating the differential, @ @u T n 0 , using the coupling between total enthalpy and speed over the unsteady expansion [Eq. (9)] and making the following substitutions and simplifications:…”

Section: A Radiative Heat Transfer Resultsmentioning

confidence: 99%

Radiative and Total Heat Transfer Measurements to a Titan Explorer Model

Capra

Morgan

2012

Journal of Spacecraft and Rockets

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This paper reports on the design and testing of a heat transfer gauge suitable for the spectrum of radiation encountered during entry to the atmosphere of Titan. Experiments were performed on a 70 sphere-cone in the X3 expansion tube at average freestream velocity, pitot pressure, static pressure, and density of 5:83 km=s, 76 kPa, 1.15 kPa, and 2:43 10 3 kg=m 3 , respectively. The radiation gauges used thin-film-sensing elements mounted behind a borosilicate window on the windward surface and were therefore shielded from the convective heat transfer. The assembled gauges are uniformly sensitive for radiation in the wavelength range from 0.347 to 2 m and give an integrated measurement of the total radiant flux in this band. Externally mounted thermocouple gauges were used to measure the total heat transfer and the ratio of radiant to the total heat flux found. The Titan atmosphere was simulated by a mixture of 5% methane (by volume) in nitrogen. Comparative tests using pure nitrogen confirmed that, without the methane content, negligible radiation was produced, which is consistent with cyanogen being the primary radiator. Results from this study demonstrate that the gauges and the superorbital expansion tube facility are useful resources for the study of nonequilibrium radiating flows. Nomenclaturea = speed of sound, m=s d g = distance between thin-film sensors and rear surface of optical window on radiation gauge, mm d! = solid angle, sr E = radiative energy, W F ij = fraction of energy leaving surface i that is incident on surface j (inverse view factor of f v ) f v = radiation gauge view factor H 0 = total enthalpy, J=kg h = enthalpy, J=kg, or distance separating front surface of optical window and thin-film sensors, mm L = characteristic length, m l s = dimensionless length scale, equal to L f =L exp M = Mach number p = pressure, Pa _ q = heating rate, W=cm 2 _ q r surface = surface radiative heating rate to test model R = radius (related to vehicle/model), m or mm r = radius, m or mm S = entropy, kJ=kg K T = temperature, K, or transmission through optical windows U = velocity, m=s U e = equivalent velocity, m=s U1 = primary shock speed, m=s U2 = secondary shock speed, m=s mc = Mach cone angle R = heat flux gauge sensitivity, V=K = Goulard number = ratio of specific heats = shock standoff, cm or mm = density, kg=m 3 v = optical thickness = mole fraction Subscripts c = convective or corner exp = experimental f = flight gw = glass window (for radiation gauge) N = nose p = pitot r = radiative s = static s 0 = postshock tf = thin-film sensing element tot = total 0 = stagnation/total 1 = freestream

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“…In Figures 1 and 2 are plotted the sensitivity coefficients of the temperature and the CN molar fraction for six reactions: the five we want to remove (i.e., nos. 13, 15, 16, 17, and 35) and the reaction (1) which is here for comparison. It is easily noticeable that the five first reactions do not impact on the molar fraction of CN and on the temperature.…”

Section: Sensitivity Analysismentioning

confidence: 99%

“…The main components are N 2 , CH 4 , and Ar. One of the first kinetic models commonly used was proposed by Nelson et al [1] in 1991. However, this first model does not take into account the formation of CN via HCN (as this species is not included).…”

Section: Introductionmentioning

confidence: 99%

Reduced Chemical Kinetic Model for Titan Entries

Savajano

Sobbia

Gaffuri

et al. 2011

International Journal of Chemical Engineering

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A reduced chemical kinetic model for Titan's atmosphere has been developed. This new model with 18 species and 28 reactions includes the mainfeatures of a more complete scheme, respecting the radiative fluxes. It has been verified against three key elements: a sensitivity analysis, the equilibrium chemical composition using shock tube simulations in CHEMKIN, and the results of computational fluid dynamics (CFDs) simulations.

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Titan atmospheric composition by hypervelocity shock-layer analysis

Cited by 65 publications

References 14 publications

Analysis of Nonequilibrium CN Radiation Encountered During Titan Atmospheric Entry

Analysis of Nonequilibrium CN Radiation Encountered During Titan Atmospheric Entry

Radiative and Total Heat Transfer Measurements to a Titan Explorer Model

Reduced Chemical Kinetic Model for Titan Entries

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