Application of the Born-Mayer Potential with a Hard-Sphere Scattering Kernel to Rarefied Hyperthermal Gas Flow Modeling (Preprint)
Abstract
Mid ultraviolet Cameron band emission from carbon monoxide is seen in plumes of Space Shuttle Orbiter engine burns in low earth orbit. The observed emission has been attributed to chemiluminescence from two and three step chemistry of a minor amount of methane in the plume with atmospheric atomic oxygen. DSMC modeling has played an important role in determining the mechanism, but standard DSMC methods show significant discrepancies in the size and shape of the radiance. The differences have been traced to a need to extend the validity of scattering treatment to hyperthermal (E(rel) > 1 eV) collision energies. Variable Hard Sphere (VHS) and Variable Soft Sphere (VSS) scattering treatments have been based on inverse-power-law repulsive inter-particle potential energy functions. The legacy of such functionality comes from the ability of the Lenard-Jones formalism to produce a realistic potential well and the convenience in mathematical treatments. It is known, however, that such potentials predict interactions that are too stiff at hyperthermal energies when fit to thermal data. Interaction potentials which have been characterized at hyperthermal energies indicate that a Born-Mayer exponential formalism is generally valid to interaction energies up to about 50 eV. Born-Mayer potential formalism has been introduced into DSMC treatment to extend its validity into the hyperthermal regime to define Extended Variable Hard Sphere (EVHS) and Extended Variable Soft Sphere (EVSS) treatments. The addition can be introduced without computational penalty. Comparisons between VHS and EVHS modeling at thermal energies and EVHS with hyperthermal plume radiance data demonstrate the validity of the modification.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 16, 2008
- Accession Number
- ADA484438
Entities
People
- Ingrid J. Wysong
- Lawrence Bernstein
- Matthew Braunstein
- Sergey F. Gimelshein
- William Dimpfl
Organizations
- Air Force Research Laboratory