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Laminar flow of Carreau fluid with variable density
Posted Mar 13, 2014, 6:07 a.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD), Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3a 2 Replies
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I am using the Laminar flow physics together with the Carreau fluid properties and I was trying to write a formula for the density as a function of pressure 'p'. From my experimental data I have a fitted a curve of density vs pressure and the relation is logarithmic.
Now, I am writing this into the density field: 50*log(p) and I get an error because COMSOL is trying to find the logarithm of a negative number, which is weird since I don't think I have negative pressures. I tried to do something different just to see if I could avoid the error, so I wrote 50*log(abs(p)), but I am still getting the same error.
Does anybody know what might be wrong here?
Thanks in advance,
Daniel
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The pressure you are using in this equation is the gauge pressure which starts at zero and can go negative or positive. What you need is probably the absolute pressure, which you can account for doing something like “log(p+1e5)”.
Nagi Elabbasi
Veryst Engineering
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You were right, I didn't think of that. Now it works, thanks a lot for your suggestion.
Daniel