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-   -   Forces results on multiple elements (https://www.cfd-online.com/Forums/fluent/91875-forces-results-multiple-elements.html)

 Santos-Dumont August 25, 2011 05:15

Forces results on multiple elements

Hi,

Quick question, I'm looking to plot the forces results on different elements connected to each others (antenna and video turret fixed on an aircraft). I want to have the results on the different elements separately.
I made multiple "Wall" BC on the antenna, turret, and fuselage, but to be honest my results are sometimes quite strange and I get artefacts on my results table.

Is my multiple walls method good ?

Thanks
Charles

 Santos-Dumont August 26, 2011 03:41

 _Denis_ August 26, 2011 06:30

Hi
As far as I know, dividing the boundary into the set of non-overlapping boundaries via named selections souldn't cause any troubles, although special considerations might be needed in some cases (e.g. mulitphase case). For those see the manual.

 Santos-Dumont January 23, 2013 10:31

Hi there,

I'm digging this old post to give answers to the one that might be seeking it in a similar. I've been working again on that case and also had some negative drag on some elements, and positive on others.

I used trigonometry to project the speed vector on the axis (I have pitch and yaw so it needs quiet thinking not to do any mistake). Of course the drag was also computed with the projected vector (something like 0.99, 0.06, 0.06).
Finally I understand the thing. I was overzaelous and after computing the reference value from the inlet I manually added the atmospheric pressure. That screwed up the whole force thing as I think it is related to gauge pressure or things like that. So I entered 0 for pressure on the reference value and bam my Cd jumped over zero.

So there is nothing wrong in making multiple walls to have details about the forces applied on a system.
As my boss says, when you are a fool it's forever !

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