[gschaider]

@Wladimyrs question concerning the Wiki:

I think, that as long as it is an ongoing discussion, this site is definitly the place for it.

It would be nice if, when the discussion has "converged" to a usable answer, one of the participants could write an article on the Wiki: as the quality of a lot of the contributions here is quite good, in most cases this would just mean copying parts of the contributions, editing them (to make them readable) and extending them a bit if needed.

Right know I'm looking through the old postings on this site and trying to do this with threads where
- I think that the question is of interest (this is of course purly subjective)
- there seems to be a definitve conclusion to that thread
- I understand the answer and think that it is correct (again: the limiting factor is me)

[alberto]

Good idea Bernhard. If you need some help, just tell me (feel free to use my e-mail).

P.S. I did some add at the wiki (solvers list) and started to write my notes in a readable for humans form :-)

Regards,
Alberto

[dbxmcf]

Hi, all:

I am also studying a situation where rho and p relations are not explicity given (unlike ideal gas relation), how should the pressure equation be?

fvScalarMatrix pEqn
(
fvm::ddt(psi, p)
+ fvm::div(phid, p, "div(phid,p)")
- fvm::laplacian(rho*rUA, p)
);

here psi=p/rho, but if my rho does not have such an explicit relationship with p, how should we re-formulate fvm::ddt(psi, p) term?

Or could someone tell is there any reference on how to derive the pressure equation?

Thanks a lot!

[stephan]

hi,

i hope somebody with more experience in the compressible flow area might help me:
i want to calculate a very low mach number problem (ma=0.05) with an compressible solver since i need the small variation in density and temperature without coupling these both to the pressure via ideal gas law. for example a simple flow through a channel with a decent pressure drop (high visc.).

is there any compr. solver which does not use an EOS to couple pressure, density and temperature??
any help would be appreciated!!!!!
thanx
stephan

[dpalko]

Hi Stephan,

Anyone please correct me if i'm wrong. I would just change EOS. You can use perfectGas equation of state as a template, (in src/thermophysicalModels/specie/equationOfState) and define your new equation of state where density is either constant or any function of pressure and temperature. That you can do by changing method rho(scalar p, scalar T). Is this approach acceptable for you? I did something similar for supercritical water.

David

[stephan]

hi,

thanks david! this sounds like introducing an artificial compressibility?!
since you answered this way i guess there is no solver which solves the problem i mentioned without using a different EOS?
thanks again to david!
br
stephan

[lillberg]

Hi Stephan,

Have a look at the boussinesqBuoyantFoam solver in the 1.4.1-dev release. It will probably solve your problem, just set gravity to zero.

Regards

/Eric

[stephan]

hi,

thanks for your ideas eric.
br
stephan

[nishant_hull]

hi Vatant

I am not sure which compressible subsonic solver you are talking about. Could you please tell which one you have used? I am currently working on sonicFoam solver to run a low mach flow. but unfortunately the case is not running quite well for forward step problem. The solution obtained is unrealistic to be honest.The solver seems to be working well for supersonic foam though.

Henry,

In the sonicfoam solver code, i can see a line at the top of the loop:
#include "rhoEqn.h"
which solves the eqn: fvm::ddt(rho) + fvc::div(phi)

i am wondering what this equation is doing here, when PISO is a pressure based eqaution and it does not solve for density in continuity equation. ???

Also the PISO proposed by Issa is taking out the central part AU0 from H(ui), but your code doesnt seems to be taking that in account. however the code seems to be stable but the final result is poor for compressible flow in low mach region of 0.03. (and worst in further low)

I am looking forward to your suggestions and planning to work on the solver to run for low mach flow in the region of 0.001.

regards,

Nishant

[Rickard.Solsjo]

I want it, if you want to send it to me, rickard.solsjo@gmail.com
thx!

[mg.mithun]

Originally Posted by hjasak

I've got an old report on this which contains the derivation of the pressure equation for compressible flow - send me an E-mail if you want it.

Hrv

Hi Hrv, I know this is a very old post.
Can you please send the report with the derivation of compressible pressure correction to my email?
mg.mithun@gmail.com

Myth