2.4 BOUNDARY LAYERS & VELOCITY PROFILES

Question 1

What is a boundary layer?

Answer 1

Region of fluid next to the boundary across which the velocity of the fluid grades from that of the boundary to that of the unaffected part of the flow “free stream”.

In practise, upper limit of boundary layer usually taken where u = 99% that of free stream

Question 2

When do boundary layers stop expanding downstream?

Answer 2

Flow passes an obstruction & viscous forces degrade sharing in boundary.
Boundary layer meets another one growing from another surface.

Question 3

What is flow separation?

Answer 3

Near the point where the surface of the solid boundary diverges from the direction of the mean flow, the boundary layer separates/breaks away from the boundary, e.g. for flow past a sphere or cylinder.