Nonequilibrium gas flows can be observed in many areas of science and technology including space and atmospheric science, vapor processing of materials, spacecraft propulsion systems, and micro-scale gas flows. There are significant challenges such as modeling inaccuracy, computational inefficiency and robustness that have made existing methods like Computational Fluid Dynamics (CFD) and Burnett equations solution insufficient for the numerical analysis of these flows. As an answer to address these problems, the direct simulation Monte Carlo method (DSMC) has evolved over 40 years into a powerful numerical technique for the computation of complex, nonequilibrium gas flows. However, with limited availability found in NASA, there is a lack of robust and efficient numerical solution scheme in this field. As a result, the need for development of a DMSC software code makes it a promising area of research for analyzing low pressure gas flows.
Researchers at the University of Michigan have developed a numerically efficient implementation of the DSMC method and successfully verified for nonequilibrium flows. The heart of the technique is its detailed treatment of collisional phenomena including momentum exchange, relaxation of internal energy modes, chemistry, radiation, and gas-surface interaction. This allows the method to be effective in simulating high temperature, real gas effects as well as to provide detailed information on the gas flow at the level of particle velocity and energy distributions. As a part of the study of three-dimensional electron beam physical vapor deposition process of yttrium, film deposition thicknesses on the substrate and atomic absorption spectra given by the DSMC method and experiment were in excellent agreement. It was also demonstrated by numerical experiments of hypersonic entry flows that the proposed DSMC technique is able to simulate strong nonequilibrium phenomena generated inside strong shock waves of noble gases more accurately than CFD methods. Written in modular form that allows great flexibility in simulating different gases and different geometries, the DMSC software is strongly capable of meeting the need for performing accurate and efficient computations of nonequilibrium gas flows.
Applications and Advantages
- Analysis of gas flow in MEMS and NEMS technologies
- Analysis of gas flow around spacecraft and small rockets
- Analysis of deposition of materials (i.e. semi-conductors, photovoltaics)
- Flexible, modular software with many options
- More accurate and efficient than CFD methods
- Developed to run on multi-processor architectures