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-   -   Incompressible vs compressible solvers (https://www.cfd-online.com/Forums/main/16225-incompressible-vs-compressible-solvers.html)

 James January 18, 2009 14:32

Incompressible vs compressible solvers

Hi,

I have to model an internal flow situation where the Mach number varies from 0.03 to 1.2. I have a compressible flow solver at hand. I'm wondering whether a compressible solver can solve the flow even if I have very low Mach numbers?

I was told that I could re-scale my geometry so that I can have a higher Mach number and the re-scaling would a lower Re.

Cheers

 otd January 18, 2009 17:00

Re: Incompressible vs compressible solvers

Not sure I understand:

If you change the geometry in the compressible solver (CS) in such a way that you change the velocity field, that would change the Mach number field. The Reynolds number has velocity and a geometry dimension in it - so Re might go up or down depending on what was changed in what direction.

It might be more useful to set up the same geometry in both compressible and incompressible codes - if both codes are well-understood and checked out.

Some of the older Los Alamos codes (sola-ice comes to mind) would work at low Mach numbers.

Hope this is of some use to you.

 Harish January 18, 2009 20:39

Re: Incompressible vs compressible solvers

The compressible flow solver would work fine at the lower mach number range if you have preconditioning implemented in the compressible solver. You rescale the wave speeds to achieve this.

 momentum_waves January 19, 2009 00:32

Re: Incompressible vs compressible solvers

What about viscous stresses? If the solver is based on Euler equations & not Navier-Stokes, you're going to be solving for the wrong physics. Surely?

mw...

 James January 19, 2009 06:07

Re: Incompressible vs compressible solvers

Sorry I meant rescaling the geometry and using a higher Mach numbers so that the Reynolds number still remains constant (if that makes sense). Will this be valid?

 Timon January 19, 2009 06:15

Re: Incompressible vs compressible solvers

No. For flows to be dynamically equivalent, both Reynolds and Mach number need to be the same!

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