# calculating output parameter in cfd post

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 January 23, 2013, 05:37 calculating output parameter in cfd post #1 New Member   markus kammann Join Date: Jan 2013 Posts: 2 Rep Power: 0 Hi Everybody, I´m 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

 January 24, 2013, 05:33 #2 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 19 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

 January 28, 2013, 08:20 #3 New Member   markus kammann Join Date: Jan 2013 Posts: 2 Rep Power: 0 Thanks a lot! I don´t 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

 August 26, 2015, 09:28 #4 Senior Member   Join Date: Jun 2014 Location: Taiwan Posts: 100 Rep Power: 10 Could you tell me why gamma has to be multiplied by 0.5? Thank you!

 Tags cfd post, optimization, parameter, workbench