where V and D are a fluid characteristic velocity and distance.
For example, for fluid flowing in a pipe,
V could be the average fluid velocity, and D would be the pipe diameter.
Typically, viscous stresses within a fluid tend to stabilize and organize the flow, whereas
excessive fluid inertia tends to disrupt organized flow leading to chaotic turbulent behavior.
Fluid flows are laminar for Reynolds Numbers up to 2000. Beyond a Reynolds Number of 4000, the flow
is completely turbulent. Between 2000 and 4000, the flow is in transition between laminar and turbulent,
and it is possible to find subregions of both flow types within a given flow field.