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-   -   Find location @ Line where a variable has a certain value (https://www.cfd-online.com/Forums/cfx/74269-find-location-line-where-variable-has-certain-value.html)

 camoesas March 29, 2010 06:18

Find location @ Line where a variable has a certain value

Hello!

I want to calculate the boundary layer thickness on a plate. For this I have created several Lines vertical on the plate an now I want to know the altitude atop the plate where the velocity reaches 99% of Uinf for the first time.

Is there any function that can tell me the coordinates of a certain variable on a Line?

 dvolkind March 29, 2010 07:13

If Uinf is constant and Y is my plane normal and starts with zero at the wall, I would use CEL:
MyFunction1 = v - 0.99*Uinf
MyFunction2 = step (MyFunction1)
Then I would make a plot MyFunction2 = f(Y)
Axis segment where MyFunction2 = 0.5 is my boundary layer thickness +-tolerance
It's the first thing that comes to my narrow mind, still I think there must be a better way.

 camoesas March 29, 2010 08:20

Hey Dvolkind,

Thanks for your reply! I have tried your solution but its still not working.
I get the Warning: "No Data exists for variable "my variable..."
I am working on that keep you updated.

cheers

 ghorrocks March 29, 2010 20:10

The problem with Dmitry's approach is it does not interpolate correctly between nodes. If you are going to do a lot of this I would export the nodal values along the line and do it either with a program or in excel/matlab/whatever. Then you will be able to batch a few of them together to do it more efficiently.

 camoesas April 6, 2010 03:51

Hey Glenn,

Thats what I am about to do. Export all the data to matlab.
However I thought maybe there is a easy solution for this first step in Ansys.

Thanks

Camoesas

 brunoc April 6, 2010 12:02

Can't you just create an isosurface of 0.99*Vinf and then export this surface? When calculating the isosurface Post will interpolate values fine.

(remeber to clip it to the are you're interested in)

 dvolkind May 6, 2010 01:52

It's probably too late, but I think extracting a polyline from a velocity contour plot is a good idea.

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