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Calu February 14, 2014 14:31

Units problem and boundary conditions with potentialFoam
I have a problem that I think involves some mixed up units and/or a problem in the boundary conditions.
I am trying to solve a compressible flow through a nozzle. The geometry and boundary conditions are copied from the tutorial of Ansys Fluent called Unsteady Compressible Flow.
As a first step, I import the fluent mesh to OpenFoam using fluentMeshToFoam. This mesh is written in meters, that is, it's values range in X axis is -.1 to 0.3 m. As such, I import the mesh without specifying scale. Then I run potentialFoam using the boundary conditions specified in the tutorial. My guess (maybe I'm wrong) is that I should obtain a similar velocity distribution to that obtained after using hybrid initialization in fluent. In fluent I get a maximum value of 60 m/s (U magnitude). But, in potentialfoam, although the distributions is quite similar, the maximum value is around 57000 m/s. Comparing both velocities field with contour plots I see that all the values are multiplied by around 1000.

Then, if I import the mesh using the option -scale 1000 (fluentMeshToFoam -scale 1000) the values range in the imported mesh is -100 to 200. With such mesh I run potentialFoam (using the same BCs, i.e. same T, p and U file than before) and I get correct values of velocity (around 57 m/s as maximum value).

I understand that the points file in polyMesh folder is assumed to be in meters. Is it correct? (Maybe I should ask that particular point in the mesh subforum).

Maybe my BCs are wrong. Can potentialFoam be used with my boundary conditions? I prescribe pressure fixed values at inlet and outlet and the velocity is zeroGradient at inlet and outlet.

I uploaded the files here in case anyone is interested. The polyMesh folder contains the mesh imported without scale option, but I include the original fluent mesh so my problem can be fully replicated.

I will appreciate any hint.

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