Dimensionless Distance y+

Dimensionless distance of the normal to the wall for the numerical modeling of the near wall flow in the boundary layer

y^{+} = \frac{ρ \cdot y \cdot u_{τ}}{μ}

ρ	Fluid density (homogeneous and incompressible flow)
y	Distance of the normal to the wall
u_τ	Friction velocity
μ	Dynamic viscosity of the fluid

Do you have any questions?