What This Calculator Does
In computational fluid dynamics (CFD), y+ is a non-dimensional wall distance that determines whether the mesh near a solid surface is fine enough to resolve the boundary layer for a given turbulence model. This calculator estimates the first cell height needed near the wall to hit a target y+ value.
The Formula
The Reynolds number is Re = ρUL/μ. The skin friction coefficient is approximated with the flat-plate estimate Cf = 0.026 / Re^(1/7). Wall shear stress is τ = 0.5 × Cf × ρ × U², the friction velocity is uτ = √(τ/ρ), and the required wall distance is y = y+ × μ / (ρ × uτ).
Note: This uses the standard flat-plate approximation commonly used for initial mesh sizing estimates. Complex geometries, separation, or laminar flow will require CFD-specific tools or post-processing for exact values.