# BUG: nut{k,U}WallFunction: incorrect y+ estimations for viscous sublayer

### Summary

In a nutWallFunction-simulation, when `yPlus`

FO is called, the FO calls `yPlus()`

of the nutWallFunction (unless the new commit 3e41c100 is in place).

`yPlus()`

contains the y+ definition specific to the chosen nutWallFunction rather than the formal definition of y+ in order to ensure various consistencies.

`yPlus()`

of some of the nutWallFunctions produces incorrect results for y+<10 (i.e. approximately viscous sublayer).

The affected items are:

### Minimal working example

See !381 (closed) for a MWE.

### Problem

Although each nutWallFunction correctly computes and blends nut predictions for viscous and inertial sublayers according to their definitions, `yPlus()`

computes only the inertial sublayer y+.

Therefore, predictions for viscous sublayer y+ from `yPlus()`

are incorrect.

### Environment

- OpenFOAM version : 7be30924/all maintained versions
- Operating system : opensuse
- Compiler : gcc/clang

### Possible fixes

- Compute viscous and inertial sublayer y+
**nominal**(theoretical?) predictions in`yPlus()`

, and blend them according to the chosen blending method. The missing information = how can we compute the**nominal**y+ for the sub-inertial region from dependent variables, e.g.`k`

. - Extend the analytical expression of the inertial sublayer up to the boundary by covering the viscous sublayer by using Spalding's law of the wall.