[Dan1788]

Hello foamers,

In the rhoSimpleFoam solver, one of the line in the pEqn.H file reads:

pEqn.setReference(pRefCell, pRefValue);

I would like to know what this means and what happens if I remove this line. Anyone knowing this please help. Thanks

[Cyp]

Hi Daniel,


Actually when solving a Navier-Stokes problem, the pressure field is off by an additive constant. Most of the time, this constant is determined by a fixed value boundary condition. However, in some case (periodic conditions for instance) the boundary conditions are of no use to fix this constant and in order to help the convergence, the trick consists to arbitrarily set a reference value to a cell of the mesh. So usually, the value of p at a refCell is set to pRefValue (usually 0).

This line is only used if there is no fixedValue boundary condition in the domain. You can set up the value of pRefCell and pRefValue in fvSolution.

If you remove this line and the pressure field is no fixed somewhere, then you will face tough convergence problem.

Best,
Cyp

[Dan1788]

Hi Cyprien,

Thanks so much for your reply. I noticed that the statement is present only in steady state solvers like rhoSimpleFoam but not in transient solvers like rhoPimpleFoam. Would you happen to know why that is ?

[Cyp]

What you said is only true for the compressible solver (icoFoam and pisoFoam have this setReference() snippet).

Actually I never noticed that this term was missing in rhoPimpleFoam... I guess it is because of the accumulation term in the pressure equation. I don't have a real explanation, sorry.

Best,
Cyprien