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Negative values in scalarTransportFoam with upwind discretization

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Old   June 6, 2017, 06:18
Default Negative values in scalarTransportFoam with upwind discretization
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Gerd
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I tried to set up the well known test case for the 1D Advection/Diffusion equation with scalarTransportFoam. With a linear discretization of the advection term the results look as expected. However, also with an upwind discretization the result becomes negative for large Peclet numbers, which should not be the case, right? Is there something wrong with my setup (or my understanding of what should happen) or is this an OpenFOAM problem?
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Old   June 7, 2017, 07:58
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I made the following changes:
  • change the convection scheme to bounded Gauss upwind to remove warnings
  • change the laplacian scheme to orthogonal, since there is no non-orthogonality
  • change the outlet BC of T to inletOutlet
  • change the solver for the linear system to smoothSolver
The last two points are the ones that do the trick.
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Old   June 8, 2017, 05:06
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Hi Gerhard,
thanks for your reply.
With the zeroGradient boundary condition imposed by the inletOutlet setting the solution is no longer negative but T=0 over the whole domain. This is the correct solution for the zero Gradient BC, but unfortunately not the solution for the problem I want to solve (with the boundary condition T(L)=1).

I already had checked and looked at the warning (suggesting the bounded Gauss method) and other solvers, but I think these settings do not cause/solve the problem.
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Old   July 25, 2017, 15:15
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FYI:

I have just noticed that this issue has been reported as a bug here (not by myself):

https://develop.openfoam.com/Develop...lus/issues/545

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Niels
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Old   August 21, 2017, 15:57
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I have the same problem. Does someone have a solution?
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Old   August 25, 2017, 20:33
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Hello, there is no native solution for this problem in FOAM. I commented on the topic in the FOAM+ bugtracker.

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Old   August 30, 2017, 10:46
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Thanks for this hint.
Were the boundary conditions suggested in the earlier discussion (Wrong fvm::div assembling) actually added to -extend?
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Old   August 30, 2017, 12:22
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Another thing:
In the earlier thread only the fixedValue BC was discussed. However, for me the same thing happens with the fixedGradient BC.
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Old   August 30, 2017, 13:24
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With another look I am not quite sure that this is the same problem.
As I understand the earlier discussion, the solution oscillated for the upwind scheme as it did for the linear scheme.
In my case the linear scheme oscillates at high Pe but the Upwind (but also the Gamma-scheme) simply give a negative solution.
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