Research And Application Of The Algorithm, Sph And Dsmc-based Multi-scale Coupling

A new micro-separation device combined characteristics of gel chromatogram method and technologies of microfluidic chips is developed, in order to produce biochemical drug for resisting new virus and enhancing human immunity consecutively and effectively. In micro-separation device, the separated fluid flows from the input region to the micro-channel for separation, then samples at the output region. In the whole separation process, multiscale flows which go through continuum flow region, rarefied flow region and continuum flow region, will be encountered. So Investigation of the separate characteristic of the complicated micro-channels is the key for the design and development of the new micro-separation device. Numerical simulations have been used extensively for the simulation of multiscale flows based on the rapid development of the computer technology.Simulation of the complete flow path is, however, very complicated. On one hand, the use of continuum theories for the entire device can produce inaccurate results because of the breakdown of the continuum theories in the rarefied region, on the other hand, the simulation of such multiscale problem by molecular methods alone has low computational efficiency. An efficient approach for such multiple length scale problem is to develop a multiscale approach combining continuum theories with molecular approaches. In this paper, we investigate the application of coupling smoothed particle hydrodynamics (SPH) for continuum region with direct simulation Monte Carlo (DSMC) for rarefied region.Firstly, setting buffer cells, a new treatment of flow boundary conditions is proposed in SPH method, and the method based on the assumption of the linear pressure distribution in the cells is used to implement pressure boundary conditions in DSMC method. The validation of the improved SPH method and DSMC method is testified by simulating 2-D channel flow separately.Secondly, issues of the coupled method, such as the matching of parameters, the connect mode and data transfer at the interface, and the choice of the couple time, arepresented. Improvements and solutions of these issues, techniques in couple code were concretely given. Then the coupled method was used to calculate the 2-D channel flow model. The good agreement of the simulation results with the DSMC solution shows the correctness and the efficiency of the coupled SPH/DSMC methodand its code, and the feasibility of the coupled theories is also proved.Finally, the setting of SPH and DSMC parameters and their influence for the coupled algorithmic are respectively discussed. Furthermore, effective measurements are presented, which are available for further research.