# Boundary Layer Physics and Bernoulli Principle

I was taught that the relative velocity of all fluid particles directly in contact with the boundary in a fluid flow is zero. In other words, that the relative velocity of fluid particles in the boundary layer decreases as the distance from the body decreases, from the relative velocity of the fluid outside the boundary layer, to zero at the surface of the body.

Bernoulli principle says that the total pressure in a non-compressible fluid flow must remain constant everywhere, and that therefore, the pressure normal to the surface of a body is decreased when the pressure parallel top the surface increases (when relative velocity increases). If this is true, the natural assumption is that the pressure normal to the surface must always be equal to the total pressure, i.e., constant, and lift due to decreased normal pressure is impossible.

This is clearly not the case, as anyone using an atomizer, or blowing across the top of a curved piece of paper can attest. Is the Bernoulli principle not applicable, or invalid, inside the boundary layer? Or is some other phenomenon or factor at work here?

Can anyone explain this?