Yeah I forgot to say that I'm interested in a wall resolving approach (y+ is <1 everywhere). I did not use kqRWallFunction since it is suitable for high-Re flow, as it is written in the source code guide. This is also why I selected fixedValue as wall boundary condition for R (basically, no wall functions are used and the equations for R components are integrated up to the wall). On the other hand, the epsilonWallFunction is suitable for both low- and high-Re approaches (but I think that also a zeroGradient for epsilon at the wall would work in a wall resolving approach). For nut I used nutLowReWallFunction