Translational nonequilibrium in free jet expansions

Cattolica, Robert J.

doi:10.1063/1.1694620

Cited by 73 publications

(39 citation statements)

References 10 publications

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“…where Q^ and Q^ are the Mie scattering and absorption efficiency, tD^ is the Mie scattering phase function, Bx is the Planck function, xx is given by (15), CI is the elementary solid angle from r to r', and T^ is computed from (10). The implicit assumption of spherical grain shape is consistent with the assumption of sphericity made for computing the hydrodynamic interaction of the grains.…”

Section: Radiative Transfer In the Continuummentioning

confidence: 80%

“…Figure 1 shows some of the results, which reveal the following classical behavior observed in laboratory jets (e.g., [2,10] and Figure 2):…”

Section: The Direct Monte Carlo Simulation Approachmentioning

confidence: 99%

“…https://doi.org/10.1017/S0252921100012781 (K = 1). Based on DMC simulations [33] and comparison between theory and laboratory experiments [8,10,65,79], the situation can be qualified as follows:…”

Section: Legacy and Usefulness Of The Hydrodynamic Approachmentioning

confidence: 99%

“…is no longer Maxwellian, but where the effect of collisions is not negligible. In principle, the collisional Boltzman Equation (CBE) must be used there, but since it is intractable, various approximate simpler forms of the CBE are used [8,10,73,79]. 3.…”

Section: Catastrophic Effectsmentioning

confidence: 99%

“…Accordingly, the various degrees of freedom that describe the jet gradually behave separately from one another. For instance, the velocity and temperature of dust grains with different masses separate from one another and from those of the gas [31,62,66,80], the gas phase chemical composition departs from chemical equilibrium values [35], the vibrational and rotational level population of each molecule deviate from Boltzman equilibrium at the kinetic temperature of the molecule [6,24], and even the thermal velocity distribution of each species ceases to assume a Maxwell-Boltzman form [2,3,8,10,33,73,79]. When complete uncoupling of all degrees of freedom is achieved, one is in the collisionless region of the coma.…”

Section: 1 Local Thermal Equilibrium and Relaxationmentioning

confidence: 99%

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Hydrodynamic Models of the Collisional Coma

Crifo

1991

International Astronomical Union Colloquium

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ABSTRACT. The hydrodynamic approach to the modeling of the coUisional regions of the cometary atmospheres is reviewed. A concise account of the existing Monte Carlo simulations is also incorporated. Emphasis is placed on works stimulated by the Halley flyby missions. The basic physical processes are described, based on the analogy with the physics of underexpanded jets. The general structure of the governing equations is presented and their legacy discussed. A detailed intercomparison is made of the application of these methods to the modeling of the comas. The reliability of the conclusions brought forward by existing models is discussed. . IntroductionIn view of the extreme rarity of past and foreseeable in situ cometary missions, remote sensing of comets has been and will continue to be the essential tool of cometary investigation. Therefore, most properties (and, in particular, the statistical properties) of the solid nucleus of all comets have been and will continue to be inferred from observations of the cometary atmosphere-the coma. With the refinements of the observational techniques, a detailed and reliable understanding of the formation of the coma has emerged as a key objective of cometary physics.The application of gas-dynamic methods to the formation of the coma seems to date only back to the year 1965. Fluid equations were first used in order to account for the acceleration of cometary dust and for the formation of many minor molecules. It is not a simple problem to delineate the precise extent of the collision-dominated part of a coma, i.e., that region where hydrostatic or hydrodynamic methods provide satisfactory results (see Sections 3.3 to 3.5). Primitive considerations, based on evaluations of the ratio of the local collision mean free path (m.f.p.) to the cometocentric distance, suggest that a waterdominated coma has a very small collision zone beyond an heliocentric distance = 3 AU, while that zone covers the whole water survival zone within = 0.5 AU (see, e.g., [13,17]). The essential point, however, is that the distribution of matter in the coma, the dynamical properties of all constituents, and the chemical composition of the gas phase are 937

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Section: Radiative Transfer In the Continuummentioning

confidence: 80%

“…Figure 1 shows some of the results, which reveal the following classical behavior observed in laboratory jets (e.g., [2,10] and Figure 2):…”

Section: The Direct Monte Carlo Simulation Approachmentioning

confidence: 99%