Experimental investigation of a supersonic free jet in vacuum

Recent technological advancements have sparked significant interest in exploring fluid dynamics in vacuum conditions within the semiconductor and aerospace industries. Air jets, in particular, are widely utilized in various processes such as deposition within semiconductor facilities and in controlling the position of satellites. When operating in a vacuum environment, these air jets typically have a complex shock structure. The effect of rarefaction changes the flow characteristics of the jet which makes it challenging to understand the detailed flow physics both in the near-field and far-field zones. Previous studies have primarily concentrated on investigating the shock structure in the near field (i.e. zone of silence). There is a lack of quantitative understanding regarding the fluid dynamics within the supersonic core after shock wave dissipation. Therefore, this study aims to quantitatively visualize the supersonic core of a rarefied supersonic free jet utilizing particle image velocimetry (PIV) with ultra-fine nanometer sized tracer particles, along with acetone molecular tagging velocimetry (MTV). These results are expected to provide fundamental insight that can advance the design of equipment operating in vacuum environments.