[Arya_the_Rabbit]

Hi,

I have problem to set up a pressure-velocity coupling solver in OpenFoam due to discordant opinion I've found online.

I would like to use a coupled solver for an incompressible steady state case in order to improve the convergence speed and the robustness of the solution.

I've found that for solve together the flow equations I need to set "type coupled" in the U solver in fvsolution, but I haven't found anything about the most appropriate linear solver to use (i.e. GAMG, PCG) and the pressure-based algorithm to use (SIMPLE, SIMPLEC, PISO).

So far I tried using:
- GAMG for pressure
- PCiGC for velocity and turbulence quantities
- SIMPLE
- First order and then switch to second order the div U schemes

but the solution is similar to segregated solver. What I would have expected is an earlier convergence with lower residual and a more stable solution.


- Have someone experience in coupling velocity-pressure in OpenFoam? Could I have some advice about numerical schemes and set up of solver?

- I found that SIMPLEC is faster than SIMPLE. Is it true in a pressure-velocity coupling simulation too?

Thanks for your help.
Arya

[Artur.Ant]

Hello,
In openFoam there is no a coupled pressure-velocity solver.
The coupled solver is only for U, in that case the solver couples the velocity in x,y,z direction and solves it in a single matrix at once.
If you use coupled solver you can gain some stability.
In theory (I verified it in some cases) the converged solution found with a segregated solver is prety close (quasi identical) to the coupled solution and vice versa.
For coupled solution you can use PBiCICG or PBiCCCG linear solvers. The type of solver really depend on the problem.