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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