Page 111 - Aeronautical Engineer Data Book

Basic fluid mechanics 87
Steady flow The flow is steady, relative
to the axes of the body

Unsteady flow The flow is not steady ‘Wake’ eddies move
relative to any axes slower than the rest
of the fluid

Boundary layer
Boundary layer of Area of turbulent flow
thickness (δ)

Wake
Area of laminar flow

Velocity distributions in laminar and turbulent flows

Laminar flow
v
Turbulent flow
u max
u

Fig. 5.8 Flow regimes

Low Reynolds numbers (below about 2000)
result in laminar flow. High Reynolds numbers
(above about 2300) result in turbulent flow.