Direct Simulation Monte Carlo Modeling of High Energy Chemistry in Molecular Beams: Chemistry Models and Flowfield Effects
Abstract
Underlying the many models for simulating chemistry in rarefied gas flows are the cross sections for fundamental chemical processes occurring at high energy and under non-equilibrium conditions. As a rule, these cross sections are not known and must be extrapolated from thermal equilibrium measurements often beyond their measured energy range and far from thermal equilibrium. Large errors in the derived reaction probability can occur which are reflected in uncertainties in chemically reacting flow results. The problem of extracting cross sections from measured thermal data becomes even more difficult when a detailed quantum state specific cross section description is needed. In this paper, benchmark state-to-state cross sections previously obtained on O+CO - vibrational energy excitation and chemical exchange reaction provide an opportunity to check the validity of widely used models for computing reaction probabilities from measured equilibrium reaction rates. The benchmark cross sections are converted to reactions probabilities based on the variable hard sphere (VHS) model for the total collision cross section and compared to extrapolations based on thermal measurements. To illustrate the impact of the use of the proper state-specific cross section on the results of rarefied gas simulations, the benchmark cross sections are used in the DSMC modeling of a high energy pulsed (non-steady) crossed-molecular beam experiment (MBE). Results from these simulations show how uncertainties in the input reaction cross sections are reflected in the predicted excited state populations and infrared radiation signature of the product molecules. A fully three dimensional DSMC simulation including reactive chemistry, energy exchange and radiative decay processes is described and used in the modeling. In addition, it is shown how these DSMC simulations can be an important diagnostic tool, enabling a more a
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 28, 2000
- Accession Number
- ADA412489
Entities
People
- I. J. Wysong
- M. Braunstein
Organizations
- Air Force Research Laboratory