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Two critical issues in Langevin simulation of gas flows
Zhang J(张俊); Fan J(樊菁)
Source PublicationProceedings of 29th International Symposium on Rarefied Gas Dynamics/AIP Conference Proceedings, v.1630
Conference NameThe 29th International Symposium on Rarefied Gas Dynamics
Conference Date2014-07-13
Conference Place中国陕西西安
AbstractA stochastic algorithm based on the Langevin equation has been recently proposed to simulate rarefied gas flows. Compared with the direct simulation Monte Carlo (DSMC) method, the Langevin method is more efficient in simulating small Knudsen number flows. While it is well-known that the cell sizes and time steps should be smaller than the mean free path and the mean collision time, respectively, in DSMC simulations, the Langevin equation uses a drift term and a diffusion term to describe molecule movements, so no direct molecular collisions have to be modeled. This enables the Langevin simulation to proceed with a much larger time step than that in the DSMC method. Two critical issues in Langevin simulation are addressed in this paper. The first issue is how to reproduce the transport properties as that described by kinetic theory. Transport coefficients predicted by Langevin equation are obtained by using Green-Kubo formulae. The second issue is numerical scheme with boundary conditions. We present two schemes corresponding to small time step and large time step, respectively. For small time step, the scheme is similar to DSMC method as the update of positions and velocities are uncoupled; for large time step, we present an analytical solution of the hitting time, which is the crucial factor for accurate simulation. Velocity-Couette flow, thermal-Couette flow, Rayleigh-Benard flow and wall-confined problem are simulated by using these two schemes. Our study shows that Langevin simulation is a promising tool to investigate small Knudsen number flows.
Document Type会议论文
Recommended Citation
GB/T 7714
Zhang J,Fan J. Two critical issues in Langevin simulation of gas flows[C]Proceedings of 29th International Symposium on Rarefied Gas Dynamics/AIP Conference Proceedings, v.1630,2014.
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