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 markus67 January 23, 2013 06:37

calculating output parameter in cfd post

Hi Everybody,
Iīm doing a cfd based design optimization in Ansys Workbench.
The goal is to maximize the flow uniformity in depending of a geometric parameter.

So my problem is to set up the calculation of the output parameter, the flow uniformity index, in cfd post.

I use the mathematical formular as follows:
Gamma=1-0,5*(sum(wi-wa))/wa

where wi is the local velocity on any position along a line and wa is the average velocity over the line. The sum goes all along the line for every local velocity from i=1 to n. n is about 200 or 300 the number of nodes at the line.
For this I set up a polyline through the area of interest.

The Problem now is how do I get the local velocity on any position along this polyline, to use it in an Expression?

When I do one single simulation there is no Problem to export the data from a chart and calculating the Parameter in excel. But how can I manage to calculate it in an optimization in workbench?

I allready seperated the polyline in segements with isoclips in depending of the y-axis of the COOS and calculated on every isoclip the local velocity, what worked fine. But when the geometry, as an input parameter in the optimization, changes, the iso clips are not at there right position anymore.

I hope I could express my problem sufficiently and there is a solution to my problem. I really appreciate everey help.

Thanks

 oj.bulmer January 24, 2013 06:33

Not sure if this answers your question, but you can give it a try by creating expressions in CFD post

wa=ave(Velocity)@Line 1
wi=Velocity
gamma=0.5*(sum(wi-wa)@Line 1) /wa

1-gamma is what you are looking for.

I didn't directly use "1-" in gamma itself, since the value may be too small and CFX may round it up to 1

Cheers
OJ

 markus67 January 28, 2013 09:20

Thanks a lot!
I donīt get the same values as when I calculate it in excel (modulus about 10 times lower). But I it works somehow and I think I can use it for my purpose.
Greets
Markus

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