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[Bruno Chareyre <question640093@xxxxxxxxxxxxxxxxxxxxx>]

Question #640093 on Yade changed:
https://answers.launchpad.net/yade/+question/640093

    Status: Open => Answered

Bruno Chareyre proposed the following answer:
Hi Robert,
Imagine a compressible fluid flowing in a pipe.
The fluid density is not the same at the inlet and outlet due to pressure gradient. Nevertheless you can always define locally, in one point along the pipe, a relation between the local pressure gradient and the local mass flux. In the stokes regime this relation is linear. At this point I did not need to assume incompessibility, parallel plates, circular cross section or anything else. Just local linearity vs. pressure gradient.

What you say (if I understand) leads me to consider that the coefficient
of the linearity itself (conductivity) can be a function of the absolute
pressure. I agree that the change of density may lead to a change of
viscosity, which means a change of conductivity. This is the only way I
see for the compressibility to have an influence on the flow property.

I would thus describe the current model as "approximating the viscosity by a constant value independent of absolute pressure".  
This would certainly not work for gas storage, but I guess it is acceptable for most geomechanical fluids. Else it would need a more sophisticated solver since the problem with non-constant viscosity is non-linear.

Besides, I think it is truly compressible. :)

Bruno

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