The free-stream flow outside a boundary layer is:
A) Either laminar or turbulent, depending on the Reynolds number
B) A smooth flow free of disturbances
C) An irrotational flow
D) Neither laminar nor turbulent

Question

Quizplus · Accepted Answer

Neither laminar nor turbulent
The free-stream flow certainly has fluctuations but they are not turbulence, i.e., the
velocity fluctuations are not correlated: for example,
 $\overline { u ^ { \prime } v ^ { \prime } } = 0$ Any turbulence
would occur inside the boundary layer. The flow outside the boundary layer is
usually irrotational (a potential flow) but it could have rotation (vorticity) if the
oncoming flow possessed velocity gradients.

The Free-Stream Flow Outside a Boundary Layer Is