DSMC calculation of supersonic expansion at a very large pressure ratio

Supersonic expansion of room temperature argon from a sonic orifice at a very large pressure ratio up to 16000 for different stagnation Knudsen numbers, 2×10−3 and 4×10−4 is simulated by the DSMC method. In order to calculate a large flowfield different sized cells and a different time-step scheme were adopted. It was shown that the effects of rarefaction and background gas to the jet size can be evaluated using a rarefaction parameter or a local Knudsen number. The calculation was also made for the expansion to a vacuum for a wide range of the stagnation Knudsen number, 4×10−4–0.1. The terminal parallel temperature dependence to the stagnation Knudsen number agrees well with the sudden freezing model.