Poisson equation solution using Code_Saturne solver

[Nicolas]

Good morning,

I am currently trying to solve a Poisson equation based on a scalar field that I define beforehand within NEPTUNE_CFD.

My approach is to reuse the Poisson solver that is originally used for the pressure field in Code_Saturne. However, I noticed that some boundary condition conversions are required between NEPTUNE and Saturne conventions.

At the moment, the solutions I obtain have the correct polynomial order (e.g. quadratic profiles when expected), but they do not match the exact analytical solution. It seems as if the integration constants are not correctly recovered, which makes me suspect an issue related to boundary conditions or their implementation.

I would like to ask:

Are there specific recommendations when reusing the Poisson solver for a custom scalar field?
Are there known pitfalls regarding boundary condition handling between NEPTUNE_CFD and Code_Saturne?
Could this issue be related to how Dirichlet/Neumann conditions are internally treated?

Any advice or feedback would be greatly appreciated.

Best regards,
Nicolas