Title

Analysis Of Tangential Momentum Accommodation Coefficient Using Molecular Dynamics Simulation

Abstract

Molecular Dynamics techniques are used to study the impacts of free atoms upon solid surfaces. Such conditions apply to flows with high Knudsen numbers and are similar to those of spacecraft traveling through the rarefied environment of space and also similar to those encountered in mico- and nano-channels. Solid surfaces were modeled with sizes of approximately 3 atoms wide by 3 atoms deep by 40 or more atoms long. These were impacted by individual free gas atoms. The impacts were modeled using Lennard Jones potentials over a combination of geometry and energy ratio variants, then analyzed with respect to conservation of tangential momentum. Results include demonstration of varying tangential momentum transfer at approach angles from 10° to 70°, varying tangential momentum transfer at energy ratios from 70 to 1 and backscattering of gas atoms, which can result in TMAC values greater than 1. Energy Ratio, over the range from 70 to 1 has been shown to be a major determinant in the overall value of TMAC. The ratio of final momentum to initial momentum for a given sequence of gas molecules followed a piecewise continuous curve for most situations evaluated. The effects of nanoscale single atom "bumps" at the upper surface of a solid are analyzed and found to either increase or decrease overall TMAC, depending on their positioning. Checks were performed to assure conservation of total energy and validate the selected cut off radius. Results of the simulation compare favorably with He gas on Cu experimental data.

Publication Date

12-1-2006

Publication Title

Collection of Technical Papers - 44th AIAA Aerospace Sciences Meeting

Volume

22

Number of Pages

17136-17159

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

Socpus ID

34250769073 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/34250769073

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