Analysis of interacting, underexpanded, rarefied jets

The interaction between rarefied free jets expanding into vacuum has received some attention in recent years because of the relevance to rockets and other space vehicles. Although the flow is sill rarefied and the shock structure is much diffused, the primary and secondary shock-cell structures can still be observed. One should note that the interaction region between the two primary jets is generally referred to as the secondary jet. This is not the case for the primary jets, where the background gas does not significantly affect the expansion core within the zone of silence when Kn is small. The reason may be found in the small density values in the secondary jet, relative to the primary jets. Therefore, the molecules of the background gas can penetrate into the secondary jet flow more easily. The simulations carried out in this Note are the first for interacting rarefied jets expanding into a background with finite pressure.