@Article{CiCP-14-5,
author = {},
title = {A Unified Gas-Kinetic Scheme for Continuum and Rarefied Flows III: Microflow Simulations},
journal = {Communications in Computational Physics},
year = {2013},
volume = {14},
number = {5},
pages = {1147--1173},
abstract = {<p style="text-align: justify;">Due to the rapid advances in micro-electro-mechanical systems (MEMS), the
study of microflows becomes increasingly important. Currently, the molecular-based
simulation techniques are the most reliable methods for rarefied flow computation,
even though these methods face statistical scattering problem in the low speed limit.
With discretized particle velocity space, a unified gas-kinetic scheme (UGKS) for entire Knudsen number flow has been constructed recently for flow computation. Contrary to the particle-based direct simulation Monte Carlo (DSMC) method, the unified
scheme is a partial differential equation-based modeling method, where the statistical
noise is totally removed. But the common point between the DSMC and UGKS is that
both methods are constructed through direct modeling in the discretized space. Due
to the multiscale modeling in the unified method, i.e., the update of both macroscopic
flow variables and microscopic gas distribution function, the conventional constraint
of time step being less than the particle collision time in many direct Boltzmann solvers
is released here. The numerical tests show that the unified scheme is more efficient
than the particle-based methods in the low speed rarefied flow computation. The main
purpose of the current study is to validate the accuracy of the unified scheme in the
capturing of non-equilibrium flow phenomena. In the continuum and free molecular
limits, the gas distribution function used in the unified scheme for the flux evaluation
at a cell interface goes to the corresponding Navier-Stokes and free molecular solutions. In the transition regime, the DSMC solution will be used for the validation of
UGKS results. This study shows that the unified scheme is indeed a reliable and accurate flow solver for low speed non-equilibrium flows. It not only recovers the DSMC
results whenever available, but also provides high resolution results in cases where
the DSMC can hardly afford the computational cost. In thermal creep flow simulation,
surprising solution, such as the gas flowing from hot to cold regions along the wall&nbsp;surface, is observed for the first time by the unified scheme, which is confirmed later
through intensive DSMC computation.</p>},
issn = {1991-7120},
doi = {https://doi.org/10.4208/cicp.190912.080213a},
url = {https://global-sci.com/article/80594/a-unified-gas-kinetic-scheme-for-continuum-and-rarefied-flows-iii-microflow-simulations}
}