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-   -   Force vs. pressure integration CFX-post (http://www.cfd-online.com/Forums/cfx/64982-force-vs-pressure-integration-cfx-post.html)

realanony87 May 30, 2009 16:37

Force vs. pressure integration CFX-post
 
Hello I have simulated flow around a 3D wing and I want to extract the lift distribution along the wing span. There are two ways that should be equivalent but aren't .
First I check the total lift force of the whole wing.
Then I make a polyline at a specific location on the wing and calculate the forceNorm in the direction I want. If I do this along the whole wing (with a macro automatically) I get a reasonable distribution that integrates to the total lift force of the wing.

However just to be sure I tried to make a usersurface by the intersection between a plane and a wing. Then I calculate the force on this user surface in the direction perpendicular to the flow, and I normalize it (divide by the usersurfaces width) so that its equivalent to the forceNorm, and I get terrible results . the values are just too low . However when I Integrate the pressure and wallshear in the direction I want, I get the same results as the polyline method.

It seems to me that CFX-post is not recognizing that the usersurface is actually at a wall, and so is giving me a very low force. Why is this so ? the user surface is specified as an intersection between a plane and a wing !.
Thanks.


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