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Ratio of velocity in CFD-post

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Old   October 15, 2013, 04:56
Default Ratio of velocity in CFD-post
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Hi

My question is about the post-process of a simulation using CFX. I already run a simulation of wind blowing on a opaque wall. Now I would like to visualise de velocity regions behind of the barrier. With the option of CFD-Post contour on
a plane I can show contours of velocity. But the experiment that I am using as a base worked with a-dimensional expressions, where contours represent a ratio: U+ = U/Uref
U= ameliorated speed (leeward side of the barrier)
Uref= speed of reference before the barrier
Is it possible to express this function U/Uref with contours?

Regards
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Old   October 15, 2013, 05:33
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Im not sure I understand you correctly, but I'll give it a shot.
Create an expression in cfd-post, e.g something like
Velocity/Uref
where Uref is an other expression you defined
Then create a variable of your first expression and plot it as the contour.
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Old   October 15, 2013, 06:25
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Quote:
Originally Posted by Lance View Post
Im not sure I understand you correctly, but I'll give it a shot.
Create an expression in cfd-post, e.g something like
Velocity/Uref
where Uref is an other expression you defined
Then create a variable of your first expression and plot it as the contour.
Thanks for your response.
What I mean: I want to replicate this isocurves:

this isocurves represent how much the wind speed changes around a building.
If the inlet wind is 5m/s and after the wall the speed decrease to 1.5m/s then, the region is represented as an area with the a-dimensional number of 0.3 (1.5/5).
If the area >1 that means the wind speed increases, if it is <1 the wind speed decreases.

Now, I don't know how to write the expression for the the wind speed after and before the barrier.
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Old   October 15, 2013, 06:52
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Generate the CFD-Post variable as Lance suggests. This is quite simple to do, have a look at the tutorials if you need help on how to introduce post processing variables.

Then put a plane through your domain and generate a contour plot on the plane of your variable and that will generate the equivalent plot.
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Old   October 16, 2013, 06:39
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On the same note, is it possible to show those values in different regions in the contour like the figure above? I tried once doing that but couldn't figure out how to do that.

OJ
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Old   October 16, 2013, 06:50
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I think you have to do that manually using text objects. I cannot think of a way of doing it automagically.
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Old   October 16, 2013, 07:18
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Quote:
... I cannot think of a way of doing it automagically.
Freudian?
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Old   October 16, 2013, 17:26
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Not at all. It is a very useful term: http://www.urbandictionary.com/defin...=automagically
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