Browsing by Author "Shao, YL"

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Parallel DSMC simulation of a single under-expanded free orifice jet from transition to near-continuum regime
(2005-11-01)
Wu, JS
;
Chou, SY
;
Lee, UM
;
Shao, YL
;
Lian, YY
This paper describes the numerical analysis of the flow structure of a single underexpanded argon free jet issuing into a lower-pressure or vacuum environment using the parallel three-dimensional direct simulation Monte Carlo (DSMC) method employing dynamic domain decomposition. Unstructured and tetrahedral solution-based refined mesh depending on the local mean free path is used to improve the resolution of solution. Simulated Knudsen numbers of the stagnation conditions based on orifice diameter, Reynolds numbers based on the conditions at the orifice exit, and stagnation-to-background pressure ratios are in the range of 0.0005-0.1, 7-1472, and 5-infinity, respectively, where "infinity" represents vacuum condition in the background environment. Results shou, that centerline density decays in a rate proportional to the inverse of the square of the axial distance (z(-2)) from the orifice for all ranges of flow in the current stud's The more rarefied the background condition is, the longer the z(-2)-regime is. In addition, a distinct flow structure, including barrel shock, Mach disk and jet boundary, is clearly identified as the Knudsen number reaches as low as 0.001. Predicted location and size of Mach disk in the near-continuun limit (Kn = 0.001, 0.0005) are found to be in reasonable agreement with experimental results in the continuum regime.
Simulation of flow past a square cylinder by parallel lattice Boltzmann method using multi-relaxation-time scheme
(2006-03-01)
Wu, JS
;
Shao, YL
;
機械工程學系
;
Department of Mechanical Engineering
The flows past a square cylinder in a channel are simulated using the multi-relaxation-time (MRT) model in the parallel lattice Boltzmann BGK method (LBGK). Reynolds numbers of the flow are in the range of 100 similar to 1,850 with blockage ratio, 1/6, of cylinder height to channel height, in which the single-relaxation-time (SRT) scheme is not able to converge at higher Reynolds numbers. Computed results are compared with those obtained using the SRT scheme where it can converge. In addition, computed Strouhal numbers compare reasonably well with the numerical results of Davis (1984).
Simulation of lid-driven cavity flows by parallel lattice Boltzmann method using multi-relaxation-time scheme
(2004-11-30)
Wu, JS
;
Shao, YL
;
機械工程學系
;
Department of Mechanical Engineering
Two-dimensional near-incompressible steady lid-driven cavity flows (Re= 100-7,500) are Simulated using multi-relaxation-time (MRT) model in the parallel lattice Boltzmann BGK Bhatnager-GrossKrook method (LBGK). Results are compared with those using single-relaxation-time (SRT) model in the LBGK method and previous simulation data using Navier-Stokes equations for the same flow conditions. Effects of variation of relaxation parameters in the MRT model, effects of number of the lattice points, improved computational convergence and reduced spatial oscillations of solution near Geometrically singular points in the flow field using LBGK method due to MRT model are highlighted in the study. In summary, lattice Boltzmann method using MRT model introduces much less spatial oscillations near geometrical singular points, which is important for the successful simulation of higher Reynolds number flows. Copyright (C) 2004 John Wiley Sons, Ltd.