Difference between reactingFoam & rhoreactingfoam
 

Hello Friends!

1.) Could any of you know the difference between reactingFoam and rhoreactingFoam as the density is changing in both the cases so why bother to create new solver?
2.) What is the low-mach formulation for a solver? I know that reactingFoam is one low-mach solver. But how can we tell whether a solver is a low mach or not?

Hello Ayush,

I'm wandering the same question.

Could you tell me why do you think that reactingFoam is Low-Mach? I'd like to run a low-mach case using it in OF 4.X, but according to what I read it is compressible by default (and that is why I'm thinking of modifying it).

I hope someone will reply and clarify.

Dear Andrea,
Actually after doing some research. I find out that reactingFoam is not a low Mach solver. Sry for the confusion. But again I am unable to figure out what is difference between reacting and rhoreacting as both solves for compressible flows. Do you have any idea?

Dear Ayush,

The main difference is that reactingFoam is a pressure based solver, while the other one is density based. And yes, they are both compressible, but rhoreactingFoam should be recommended if there is a strong coupling between the variables you are solving for.

Please someone correct me if I'm wrong.

Hi,
I am not actually sure that rhoReactingFoam is a density-based solver. Because if you check the src of rhoReactingFoam you will see that the pressure is updated by pEqu and pcEqu of rhoPimpleFoam which is a pressure-based solver. Therefore, rhoReactingFoam cannot be a density based solver. Correct me please if I am wrong.

Regards,
Ghazal

This thread is kind of old, but I'm wondering the same thing! I do think that reactingFoam and rhoReactingFoam are both pressure-based solvers, because they both solve for the pressure. The main difference, as pointed out in one of the posts, is that they update the density in different ways.

The real question is why? And I feel that the pressure equation may be the key. I can somewhat understand the pressure equation in reacingFoam, what about the pressure equation in rhoReactingFoam? How is it derived?

Hi,
reactingFoam and rhoReactingFoam are both pressure-based solvers.
As far as I know, the only difference is about the thermophysical model (psiReactionThermo for reactingFoam and rhoReactionThermo for rhoReactingFoam). Anyway, I do not know very well the differences between these two thermophysical models, so I am interested in it, too.


Tommy

reactingFoam and rhoReactingFoam both are low mach number solvers as pressure equation solution in terms of pEqn.H. The reason npt to use compressible solver is that density rho is only function of temperature not pressure so dp/drho wont affect much ( A typical ideal gas auumption in open atmosphere).
In reactingFoam psi is taken as comprehensibility or psudo comprehensibility to take advantage in compressible models. while in rho reacting foam thermal libraries are updated on the basis of P=rho*R*T. IdeaL gas equation also holds in psiCombustion models but solution of pressure equation are different due to inclution of psi.

Since they are both low mach number solvers, is the main difference the bouyancy effect??

I noticed that the constant/g (which should be the gravity) don't really bend the flame when the burner is buring horizontally in the reactingFoam.

I haven't tried rhoReatingFoam, maybe I should build a simple geometry to test that! :p