Relationship between mesh size and sediment size (d50)
 

When doing a scour analysis with movable bed usually the mesh size and sediment size cannot be considered independent unless a certain relationship is satisfied. In my case grid size is 0.02 m and d50 is 0.0002 m. Then how scour and boundary layer is calculated?

The boundary layer is not resolved, instead wall functions for velocities and turbulence parameters are used.

The mesh size and particle diameter are not connected.