Numerical study of gas-surface interaction models for micro scale rarefied gas flow simulation

Micro scale rarefied gas transport attracts great research interests recently due to the special phenomena arising from small spatial scales, as well as its extensive applications in microelectromechanical systems. Due to the large surface-to-volume ratio at small scale, gas-surface interaction plays an important role in micro scale rarefied gas transport, which is currently described through empirical models and incorporated in various numerical methods for rarefied gas flow simulations. The validity of the empirical gas-surface interaction models needs systematic evaluation and the accommodation coefficients which are the adjustable parameters in the empirical models require to be determined through a feasible approach. These challenges of the existing empirical models form the two objectives of this thesis: 1) to validate the empirical gas-surface interaction models in typical micro scale rarefied gas transport problems based on the resolved macroscopic flow quantities; 2) to develop simple model for estimating accommodation coefficients. First, an efficient hybrid DSMC-MD scheme is developed for the simulation of micro scale gas flows with accurate gas-surface interaction boundary condition. It applies molecular dynamics (MD) method in the thin gas-surface interaction layer and the direct simulation Monte Carlo (DSMC) method in the remaining portion of flow field. The coupling between the two methods is realized by matching the molecular velocity distribution function at the DSMC/MD interface. Further improvement in efficiency is achieved by taking advantage of gas rarefaction inside the gas-surface interaction layer and by employing the “smart-wall model”. The developed hybrid algorithm resolves the accurate macroscopic flow field and measures the accommodation coefficients at the same time. It provides the evaluation criterion for the performance of empirical gas-surface interaction models. Secondly, a systematic study on the performance of two widely-used emp