Browsing by Author "Lee, UM"

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Development of a general parallel three-dimensional Direct Simulation Monte Carlo Code
(2005)
Wu, JS
;
Tseng, KC
;
Lee, UM
;
Lian, YY
;
機械工程學系
Development of a general parallel three-dimensional direct Simulation Monte Carlo Code, termed as PDSC, is reported in this paper. The PDSC is implemented on the memory-distributed parallel machine (e.g., PC-cluster system) using message passing interface (MPI) with several important features, including tetrahedral unstructured mesh, solution-based adaptive mesh refinement, variable time-step method, dynamic load balancing technique, extended conservative weighting scheme for trace species, very low-speed flows, iterative pressure boundary treatment method and hybrid NS-DSMC method. In addition, a graphic user interface (GUI) using VTK (Visualization Toolkit) library and Qt is developed to ease the settings of boundary conditions and domain decomposition for parallel processing and to preserve future possibility of including more features into the code.
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.