y+ First Cell Height

Estimate first-cell center height and friction velocity for a target y+.

visual calculatorTurbulence & Wall Modeling

Read the flow shape before trusting the number.

This page turns a CFD setup into regime, scale, and dominant-effect cues. Adjust the calculator below and compare the moving graphic with the computed result.

input scale

model

check

y+wall modelingmeshSST

formula

KaTeX rendered

\begin{aligned}\text{y = y+ mu / (rho u\_tau)}\\[0.35em]\text{u\_tau = U sqrt(Cf / 2)}\end{aligned}

ASCII source

y = y+ mu / (rho u_tau), u_tau = U sqrt(Cf / 2)

rho (kg/m^3)mu (Pa·s)U_inf (m/s)reference length L (m)target y+Cf estimate

Re_L

2.042e+6

0.00326

u_tau (m/s)

1.2117

first-cell y (mm)

0.0121

This is a fast estimate for wall-normal spacing. Use y+ ≈ 1 for wall-resolved SST and roughly 30 to 100 for wall-function setups.

y+wall modeling mesh SST