Y+ Calculator
y+ = ρ u_τ y / μ, with y the wall-normal distance to first cell center.
How to Use This Calculator
1
Enter fluid properties and u_τ
Use representative near-wall density and viscosity, and an estimate of friction velocity.
2
Optionally enter y or target y+
Compute current y+ or required y for a desired y+.
3
Calculate
Use the outputs to guide mesh resolution near walls.
Formula
y+ = (ρ u_τ y) / μ
y = (y+ · μ) / (ρ u_τ)
u_τ = √(τ_w/ρ). Choose target y+ (e.g., ~1 for wall-resolved LES, ~30 for wall functions).
Frequently Asked Questions
How do I estimate u_τ?
Use friction correlations (e.g., from Cf) or prior simulations/experiments to estimate τ_w and compute u_τ.
Which y is used?
Use the wall-normal distance from the wall to the first cell center.