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!

Hi,

sorry for the joke at the begining, but you definitely read too much! )).

I think that standart NS equations for compressible flow should be valid even at low pressures. The thing which you should take care is the properties of the gas at those pressures you are in.

not much help, i'm affraid

Matej

Hi Zhihang and matej,

Matej's comments seem about right. The Navier Stokes equations will be OK until their basic assumption that the fluid can be modelled as a continuum breaks down. Of course at these very low pressures you might get some weird fluid properties so be careful with how you model the fluid properties.

The most important parameter to consider when choosing the solution method is the Mach number. CFX 4 and 5 both give you some options here, so you should be able to solve your problem. Or are you writing your own code?

Glenn

A few weeks trail and error calculations with a CFD code can safe you an afternoon reading )

Glenn and Jan, thanks a million! I am going to write my own code. Could you tell me some efficient methods for solving compressible NS coupled with continuity and energy and state equations.

Thanks again!

Hi Zhihang,

This is the CFX forum. We use CFX so we don't have to write our own code! I think you will need to do a lot of reading before proceeding much further. Time to visit the library.

Glenn