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Oh I thought I was trying to do something stupidly simple to start with... grrrr

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Old   January 3, 2013, 06:29
Default Oh I thought I was trying to do something stupidly simple to start with... grrrr
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DDB
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ok, this is ridiculously stupid and I am unbelievably frustrated... I am a newbie to foam and I can't see me sticking around for long if this continues!

I have v2.1.1 installed, the official rpm for f17.

I have a channel, 15ftx7.5ftx3ft, a stupidly coarse grid for testing purposes of just over 21k cells. I have modified the file from the lid driven cavity to produce my channel in blockMesh.

I am using simpleFOAM.

I have done loads of tutorials, the problems arise when I try to do my own stuff

I want to have a velocity inlet and a pressure outlet. I want my velocity to be a positive (say 70m/s in x direction).

I have no patience with paraview, it seems totally unintuitive to me, so I am converting to fluent to check things as this works for me.

Why does my velocity inlet read into fluent as a pressure outlet?

Why does my pressure outlet velocity always end up equalling the exact negative of the velocity inlet when I have 'run' the simulation?

I can get things to work perfectly when I create the initial mesh in blockmesh, read into fluent, change the bits that are totally wrong, save as a case, convert back to foam and then run - but what good is that if I want to use free software?????

Please, someone, what is going on here?
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Old   January 3, 2013, 06:51
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I should probably add that I am not new to CFD, just foam.

I am using the following BCs, as in tutorials and this post Boundary conditions 2D Poisseuille flow in a pipe

Inlet: U fixedValue, p zeroGradient
Outlet: U zeroGradient, p fixedValue uniform 0
Walls: U fixedValue uniform (0 0 0), p zeroGradient
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Old   January 3, 2013, 13:12
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The mapping between BCs going from OpenFOAM to Fluent and vice versa is not exact. If you are specifying your boundary conditions as mentioned in your last post, everything should work. Paraview is used mainly for pre-processing internal fields/boundary values and post-processing results; its not as useful for checking your boundary conditions.

Based on these boundary conditions, are you not getting the flow you expect? Could you throw your case up for us to see (only include blockMeshDict in the polyMesh directory)?
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