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-   -   y+ in fluent (http://www.cfd-online.com/Forums/fluent/99133-y-fluent.html)

 mazdak March 26, 2012 17:20

y+ in fluent

i simulated turbulent flow in a pipe. how can i calculate y+ in the first grid near the pipe wall via fluent?
to make sure that my results are correct, the mentioned y+ should be over 30? or over 11?

 Far March 26, 2012 18:11

At least 11.06 and 30 for better performance of wall function.

 scipy March 26, 2012 18:56

Graphics and animations -> Contours -> pick Turbulence then in the drop down menu below pick Wall Yplus. Ticked "Filled" in the upper left corner and select your pipe wall in the list of surfaces, then display.. You can adjust your scales by unticking Auto range and putting in a manual minimum and maximum.

 mazdak March 26, 2012 18:58

I DONT need the contour of y+. i need value of y+ in the first gird near the wall.

 scipy March 26, 2012 19:00

That is what the contour is going to be showing.. You can right click anywhere on the wall and it will read out the y+ value in the textual interface part of Fluent.

 mazdak March 26, 2012 19:03

if i need the y+ on nodes what should i do? cause if i right click on the geometry
in fact i am picking up a random point.

 scipy March 26, 2012 19:12

OK, so if I'm understanding correctly you want a list of y+ values at a certain cross section of the pipe for example..

Plots -> XY Plot -> Set up -> Y Axis again Turbulence, beneath that Yplus, leave X Axis as Direction vector. Then beneath the list of surfaces click New surface -> Iso-surface -> on the right pick your pipe wall -> on the left pick under "Surface of constant" pick Mesh -> then (this part I'm going to guess as I can't see your geometry) you'd pick either X, Y or Z coordinate in the drop down menu beneath the upper Mesh choice. Basically, let's say your pipe centerline is the Z axis.. you would choose Z-Coordinate and then if the pipe goes from (0 0 0) to (0 0 10) meaning it's 10 meters long, you would enter anything between 0 and 10 in the Iso-Values field and that would be the cross section position where it's gonna display the y+ plot. So for example you'd put 5 in the Iso-Values and click Create.

Then you're back at the plot window and now you select the newly created surface named "z-coordinate-bla", in the upper left Node values is probably ticked, if not - tick it. Then you'd put 1 in the X or Y field (test for urself) under plot direction and click Plot.. there goes your plot of y+ values over a pipe cross section. If you tick Write to file in the upper left corner Plot button will change to a Write button and you can write the values over node positions in the .txt file.

/edit .. Correction, 1 doesn't go in the Z field since that's the cross section position..

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