# First cell height calculation

 Introduction Mesh classification Structured mesh generation Unstructured mesh generation Special topics Mesh adaptation First cell height calculation

While performing CFD simulations, it is critical that one capture boundary layer near the wall properly. In order to do that, the mesh should be generated in such a manner that it captures boundary layer properly. For turbulent flows, calculation of the Y plus value of the first interior node/gridpoint helps in doing that. This dimensionless distance is defined as

$y^+ := \frac{u_* \, y}{\nu}$

where $u_*$ is the friction velocity defined as

$u_* := \sqrt{\frac{\tau_w}{\rho}}.$

The wall shear $\tau_w$ can probably not be determined until after a simulation has been completed, so it is usually necessary to estimate a value, and then check after a simulation is complete.