Analysis of Interacting, Underexpanded, Rarefied Jets

摘要

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 [1-3]. Rapidly expanding plumes at high altitudes involve the entire range of flow regimes, from continuum flows near the nozzle exit to transitional and free molecular flows at large distances from the nozzle. Furthermore, for flight at different altitudes, the plumes from the spacecraft exhaust may be expanded into a background with finite pressure for the flight in the Earth's atmosphere, or into vacuum, for flight in outer space. Therefore, rarefaction effects are expected to play significant roles. Experimental investigations are expensive and encounter practical difficulties, making numerical analysis an attractive option [4]. This Note focuses on the simulation of the interaction of rarefied jets in the presence of background pressure. We are not aware of a previous simulation exercise for this case. It is pointed out that a numerical investigation of the problem is extremely challenging, even for the direct simulation Monte Carlo (DSMC) approach, and the present work represents the first such simulation. Among other things, the simulation in this Note is made possible by the adaption of the particle conservation method [5] for the imple mentation of the pressure boundary conditions in DSMC.