y+ wall distance calculator
When meshing geometry for a CFD analysis, it is often useful to estimate the wall distance to obtain a certain y+. With the calculator below you can calculate this wall distance.
Formulas used to calculate the wall distance from y+
The Reynolds number for a given free stream velocity U∞ is:
$${Re = \frac{\rho \cdot U_{\infty} \cdot L_{boundary\,layer}}{\mu}}$$
The Schlichting formula to obtain the skin friction coefficient Cf is used in this calculator and is valid for Rex < 109:
$${C_f = [ 2 \cdot log_{10}(Re_x) - 0.65 ] ^{-2.3} \quad \mbox{voor} \quad Re_x < \; 10^9}$$
The wall shear stress is calculated from the skin friction coefficient Cf:
$${\tau_w = C_f \cdot \frac{1}{2} \, \rho \, U_{\infty}^2}$$
The friction velocity u* is a function of the fluid density and the wall shear stress:
$${u^* = \sqrt{\frac{\tau_w}{\rho}}}$$
And eventually the wall distance for a desired y+ is:
$${y = \frac{y^+ \mu}{\rho \, u^*}}$$
y+ wall distance calculator
The predefined values for density and dynamic viscosity in the calculator are for air at p = 1 atm and T = 20°C.
The density and dynamic viscosity for water at the same conditions are respectively 998.21 kg/m3 and 1.002e-3 Pa.s.
Disclaimer: The tools, calculators, and formulas provided on this website are intended for educational and informational purposes only. While we strive to ensure accuracy, we cannot guarantee that the results generated by these tools will be applicable to your specific circumstances. Users are encouraged to verify the results independently and consult with a qualified professional if necessary. By using these tools, you acknowledge that the use of any information obtained from this site is at your own risk. We accept no liability for any loss or damage incurred as a result of the use of the provided tools or information.