I need some suggestion, please.
 

I am trying to simulate an unsteady gas flow under vacuum conditions with large variance of temperature and density. I read many papers about CFD, and know many schemes, such as artificial compressibility, pseudo-compressibility, and so on. But up to now, I am still not sure which scheme is suitable for solving the continuity, NS and energy equations under vacuum. Most of the articles are for incompressible gas or compressible gas, in which gas is compressed and with high Mach number. Could anybody give me any suggestions and any reference information? Thanks a lot!