# Turbulent boundary layer

1. Apr 17, 2009

### p3t3r1

Hey, in my lecture notes, it states that at high Re numbers, the boundary layer becomes turbulent and friction drag increases.

I am confused about why it is the friction drag that increases but not the pressure drag? I thought pressure drag is related to turbulence? It would make sense if the sentence states, at high Re numbers, the friction drag increases. This is because high Re number = less boundary layer = steeper velocity gradient = high sheer force = more friction drag but I just don't understand how friction drag would increase with turbulence in the boundary layer.