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TECHNICAL PAPERS

# Parallel DSMC Simulation of a Single Under-Expanded Free Orifice Jet From Transition to Near-Continuum Regime

[+] Author and Article Information
J.-S. Wu

Department of Mechanical Engineering,  National Chiao-Tung University, Hsinchu 30050, Taiwanchongsin@faculty.nctu.edu.tw

S.-Y. Chou, U.-M. Lee, Y.-L. Shao, Y.-Y. Lian

Department of Mechanical Engineering,  National Chiao-Tung University, Hsinchu 30050, Taiwan

J. Fluids Eng 127(6), 1161-1170 (Jun 26, 2005) (10 pages) doi:10.1115/1.2062807 History: Received March 05, 2004; Revised June 26, 2005

## Abstract

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 $5–∞$, respectively, where “$∞$” represents vacuum condition in the background environment. Results show 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 study. 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-continuum limit $(Kn=0.001,0.0005)$ are found to be in reasonable agreement with experimental results in the continuum regime.

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## Figures

Figure 1

Flow structure of a single under-expanded orifice jet in the continuum regimen (1)

Figure 2

Flow chart of the parallel DSMC method (PDSC) with mesh refinement

Figure 3

Surface mesh and its isodensity distribution on a 1∕16-domain of a single jet (Kn=0.001, PR=150) (initial: 149, 168 cells; level-2: 1,109,411 cells)

Figure 4

Properties distribution at Kn=0.1, PR=50 of underexpanded argon jet (y=0 plane) (a) normalized density; (b) temperature; (c) Mach number; (d) data along centerline

Figure 5

Centerline normalized density, temperature, velocity, and Mach number distributions at different pressure ratios (Kn=0.1)

Figure 6

Properties distribution at Kn=0.001, PR=50 of argon jet (y=0 plane) (a) normalized density; (b) temperature; (c) Mach number; (d) data along centerline

Figure 7

Centerline normalized density, temperature, velocity and Mach number distributions at different pressure ratios (Kn=0.001)

Figure 8

Position and diameter of Mach disk as a function of pressure ratio for a single argon underexpanded jet

Figure 9

Comparison of the radial profiles of normalized density at different positions at (PR=5000)

Figure 10

Flow condition of different ξ

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