A Study Of Gas-solid Interaction

The study of interaction between gas and solid surface is important in mechanical theory and engineering application. In order to obtain the physical pattern directly, the gas-solid interaction is studied numerically based on the kinetic theory in the present thesis.Firstly, a Molecule Dynamics (MD) code based on GPU (Graphic Processing Unit) with CUDA (Compute Unified Device Architecture) architecture is provided to research the scat-tering properties of gas. Compared with the code based on CPU, the maximum speedup is about89. Then, the MD code is used to simulate the interaction between Ar and Pt. The incident velocity of Ar follows Maxwellian distribution which is in equilibrium. It was found that the reflection velocity distribution could be predicted by the previous scattering model such as Maxwell and CLL model. However, there is obvious difference between the cloud distribution. This suggests that the traditional scattering models where the accommodation coefficients are constant are incapable of expressing the scattering features completely. Then a corrected scattering model based on CLL model is proposed. For axisymmetric stagnation flow, it was shown that the prediction by the corrected CLL model agreed very well with the MD simulation.It is difficult to verify the corrected CLL model directly, so the planar microchannel force-driven Poiseuille flow which is influenced obviously by gas-solid scattering model was analyzed by the Direct Simulation Monte Carlo(DSMC) method. It is shown that the non-monotonic pressure distribution in Knudsen layer can not be captured by Maxwell mod-el which adopts single accommodation coefficient and both Maxwell-Yamamoto and CLL model are able to predict the Knudsen layer effects correctly in qualitative respect if the two accommodation coefficients in these models have the proper value. Unfortunately, it is very difficult to determine the value of accommodation coefficient satisfactorily. By using the cor-rected CLL model, the change of the flow distribution in Knudsen layer is more violent and the result is qualitatively reasonable.At last, the high order continuum model such as Burnett and super Burnett equations and the boundary conditions which come from DSMC simulations are used to study the planar microchannel force-driven Poiseuille flow. To capture the strong non-equilibrium effects near the wall, a correction of Knudsen layer to constitutive relations was proposed. With a perturbation method, the super Burnett equations were linearized and the analytical solutions were obtained. Compared with DSMC simulation, super Burnett model was able to predict the flow correctly in the bulk region. However, near the wall, the correction of Knudsen layer was essential. With the correction, the analytical solutions agreed very well with DSMC simulations when the Knudsen number was up to0.5. Especially, due to the correction of heat2This work is supported by the National Natural Science Foundation of China (Grant No.10976029). flux along the transverse direction, the temperature dip was also captured at larger Knudsen number and it was impossible for original high order continuum model.