Page "Boundary layer" Paragraph 32

The treatment of turbulent boundary layers is far more difficult due to the time-dependent variation of the flow properties.

One of the most widely used techniques in which turbulent flows are tackled is to apply Reynolds decomposition.

Here the instantaneous flow properties are decomposed into a mean and fluctuating component.

Applying this technique to the boundary layer equations gives the full turbulent boundary layer equations not often given in literature: