Fluid Mechanics

Reynolds Number

The ratio of inertial to viscous forces in a flow, which decides whether it is laminar or turbulent.

For flow in a pipe the Reynolds number is Re = VD/ν, with V the mean velocity, D the diameter and ν the kinematic viscosity. Low values mean viscosity dominates and the flow is smooth and layered; high values mean inertia dominates and the flow is turbulent.

Pipe flow is laminar below about 2,000, where the friction factor is simply 64/Re. Most water pipes run at Reynolds numbers in the tens or hundreds of thousands, fully turbulent, where the friction factor depends on relative roughness as well.

How much of the FE Civil exam is Fluid Mechanics?