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-   -   display and roughness (http://www.cfd-online.com/Forums/fluent/30037-display-roughness.html)

nicolas July 16, 2002 12:17

display and roughness
 
I have two questions : One about roughness in simulation : I use an realisable K epsilon model with no equilibrum wall fonction.I have some problems with convergence.I m not sure if it dues to the mesh size near the wall.What must the value of Y+ or y* be near the wall? How to display it ? The second question is about display : I have a big volume with a restriction in a pipe. Restriction involves big velocity gradient.In comparaison in the big part of the volume the gradient is smaller, so I can visualize it? Is it possible to adapt the range of velocity for the display (I already use 100 colors and the log visualisation only works with velocity vectors and not with contours, is it normal?) Thanks very much.

Matt July 23, 2002 20:07

Re: display and roughness
 
Your standard y+ value should be between 50-500. Make sure you are observing this. You can check your y+ value for your solution by going to Adapt --> y+/y* and then compute your y+ value. FLUENT should be able to refine or coarsen your grid if you need to get your y+ value in a different region. This usually never works for me, though. You can also display your y+ values through the contour options--under turbulence.

You can display different velocity contours between a range by unselecting the "auto" range on the contour panel and then typing in the range of velocities you are interested in.

matt

Matt July 23, 2002 20:09

Re: display and roughness
 
The manual is really good at explaining this y+ thing. Also, FLUENT has an advanced turbulence modeling training cd available for about 250 that is also really good.


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