|January 25, 2011, 12:35||
UDF for linear PTT model implementation
Join Date: Jan 2011
Location: Curitiba, Brazil
Posts: 4Rep Power: 6
I've been using Polyflow to perform simulations of a PTT fluid in axisymmetric geometries. My problem is that Polyflow has only the exponential PTT model implemented, and I would like to perform simulations using the linear PTT model, in order to compare my results with some data that I have from some authors.
My first attempt was to create an UDF for the eps parameter, in order to eliminate the exponential term from the constitutive equation of the exponential PTT model.
Here is the line from my UDF where I rewrite the eps parameter:
(bind ?R (* ?n0 (/ 1 (* ?lbd ?tr)) (log (+ 1 (* ?lbd ?reps ?tr (/ 1 ?n0))))))
I've tested my UDF file in qa.exe, and it works fine.
Unfortunately, I couldn't obtain any good results from my simulations using this UDF; most of them diverge, and some converge to a wrong result (I have only simulated cases of low Reynolds and Deborah numbers).
I think the difficulty to obtain convergency is due to the presence of the log term, but I couldn't find another way to do what I need.
I hope someone have an alternative suggestion to implement the linear PTT model in Polyflow, or an explanation for the instability of the numerical solutions using the UDF that I've created.
Thanks in advance!
|linear ptt model, polyflow, udf|
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