# y+ calculator for equilibrium flows

 Register Blogs Members List Search Today's Posts Mark Forums Read

Rate this Entry

# y+ calculator for equilibrium flows

Posted April 10, 2014 at 03:58 by sbaffini
Updated December 21, 2016 at 09:08 by sbaffini

y+ calculation is, possibly, the most pervasive topic among CFD practitioners and, certainly, anybody doing CFD for more than a month already has his own tool to compute it.

Still, all the y+ calculators i am aware of rely on a very specific flow condition, namely, a flat plate boundary layer. This is probably the most common practical case but not the only option. For example, the fully developed flow in a pipe is cretainly different and possibly requires a different input for the y+ calculation.

The tool in the attached file is intended to provide an y+ calculator for the three most common equilibrium flows: channel flow, pipe flow and boundary layer. For the latter, a typical input would thus be the depth of the boundary layer and the external velocity. Analogous input are required for the remaining two flows.

All the relations are taken from the Pope's book. You will notice that, as much as in wall function calculations, an iterative loop is required, but i'm not an Excel fan, so i arranged it in a very trivial way over 10 consecutive rows (still, i know is possible to use some Excel feature to do it more elegantly).

Hope it helps someone, at least in clarifying that such y+ calculation is not uniquely done for all flows.

Edit: as for all the recent attachments, remember to rename it correctly instead of the dummy .php extension (i.e., .xlsx in this case).
Attached Files yplus.xlsx (12.6 KB, 491 views)
« Prev     Main     Next »
1. This is great, thanks for sharing! Seeing these equations laid out in Excel helped me better understand the enigma that is the value of y+ Posted January 13, 2021 at 18:59 by aero_head 2. Quote: Originally Posted by aero_head This is great, thanks for sharing! Seeing these equations laid out in Excel helped me better understand the enigma that is the value of y+ Thanks! However, note that, with respect to a classical y+ calculator (say, like this https://www.cfd-online.com/Wiki/Y_pl...nce_estimation), this one is peculiar in that, instead of using explicit formulas for the skin friction, it uses implicit ones (actually 3 different versions, one for each kind of flow), so iterations are needed in determining u_tau. But, besides this, it is identical to other y+ calculators. Posted January 14, 2021 at 03:24 by sbaffini 