Learning Forum

[thamilmani]

How to access yplus values at all cells as my UDF needs to return different values based on different range of yplus. ANSYS Fluent only provide Wall yplus in the cell macros, which has first cell y plus next to the wall. How to map y plus distributed values across the domain?

yplus = ustar * y / nu where ustar needs wall shear stress value at y = 0

Let's say even if I am trying to create my own UDMI or UDS for yplus, it is essential to access the near wall (y=0) values for calculating the yplus, which I am not sure how to handle it?

Any information or help regarding this would be valuable.

[Rob]

Once you're not in the near wall cell Fluent may not know the distance to the "nearest" wall so y+ may not be valid. The near wall cell ought to have a value, although it may not be trivial to access it. 

[thamilmani]

C_WALL_DIST(c, t) can be used to get the near wall distance right?

I am more concerned about not just accessing the distance from the wall but also the wall variables like, velocity gradient at y = 0 and thereby wall shear.

[Rob]

Near wall cell, yes. Beyond that it's complicated: how does Fluent know which wall a cell is nearest to? 

[thamilmani]

I can understand that it is complicated. But I have seen that a research paper has implemented that and mentioned in ANSYS Fluent as Face mapping of y+ in their algorithm, hence the question.

I am not able to see any way ahead to go with that. Anyone knows how that can be implemented?

https://linkinghub.elsevier.com/retrieve/pii/S0017931023009742

[Rob]

Nothing I can comment on as staff are limited to public domain knowledge.