Study And Application Of Gas-surface Interaction Models Using Molecular Dynamics Simulation

The study of gas-surface interaction is one of the most difficult problems in rarefied gas flow.To intensively study its mechanism is not only of great importance to the fast development of aerospace flights and micro/nano electromechanical systems,but it can also provide theoretical support to numerical solution in rarefied gas flow.In this paper,we use the molecular dynamics method(MD)to build the gas-surface interaction model.By studying the scattering characteristics of gas atoms Ar colliding with solid wall atoms Pt,we find four collision models: colliding once before scattering,colliding many times before scattering,adapted to wall temperature before scattering and adsorption.The incident-reflected velocity nephogram of MD shows wedge shape.Comparing the results with three common gas-surface interaction models: Diffusion model,Maxwell model and Cercignani-Lampis-Lord(CLL)model,we find that incident-reflected velocity nephogram of CLL model shows elliptical shape,which is similar to the wedge shape of MD.Constant accommodation coefficient in CLL model obviously causes the model's failure in matching with MD results.Thus,we study the influence of wall temperature,incident velocity and incident angle on TMAC,and the results shows that wall temperature has little influence on TMAC while TMAC decreases with increasing velocity square,following exponential decay law.Quasi-Newton Method is used to build TMAC model,which is incorporated with CLL model to obtain the revised gas-surface interaction model.Results show that the new model could capture the wedge-shaped characteristic in velocity nephogram.At last,the modified gas-surface interaction model is extended to DSMC to study the heat conduction problem and the results match well with experimens.Couette problem is also studied and the results fit well with MD results.When considering the problem of hypersonic flow around cylinder,we find that the results obtained using modified gas-surface interaction model coincide with results obtained when correct TMAC is used.With all the work above,it is proved that the modified gas-surface interaction model is reliable.