Numerical and Experimental Investigation of the Origin of a Rarefied Jet

摘要

We investigate the flow region close to a cylindrical nozzle from which a free rarefied jet is issuing. Analytical, numerical, and experimental procedures are used to completely describe the aerodynamic flow field from the upstream stagnation chamber, through the nozzle, and, finally, to the downstream ambient region. The combined theoretical-experimental investigation addresses the shortage of results in the literature concerning rarefied flow through finite length tubes, particularly in the region close to the jet origin. We also investigate the sensitivity of the jet characteristics to the velocity profile at the nozzle exit. Attention is paid to the physical differences between a continuum flow and a rarefied gas flow operating in the same geometrical conditions. The analytical expressions are derived from free molecular kinetics, the computational code is based on the direct simulation Monte Carlo method, and the experimental investigation uses measurements from a Patterson impact pressure probe. The broader implications of the results are discussed.