Darcy Friction Factor

Definition

The friction factor depends on flow regime. In laminar flow it follows directly from the Reynolds number: f = 64/Re. In turbulent flow it is obtained from the Colebrook-White equation, 1/√f = −2 log(ε/3.7D + 2.51/(Re√f)), or, when a non-iterative solution is selected, from the Haaland approximation. In the transition region between laminar and turbulent flow, FluidFlow applies a linear interpolation between the friction factor where laminar flow ends and where turbulent flow begins. Here f is the friction factor, Re the Reynolds number, D the pipe diameter, and ε the absolute roughness.

Engineering context

Because the friction factor carries both the Reynolds number — which reflects fluid properties, temperature, and viscosity — and the relative roughness ε/D — which reflects pipe condition — the Darcy-Weisbach method stays valid across fluids and flow regimes, unlike empirical correlations limited to water at ambient conditions. Every friction pressure-drop result in a FluidFlow model is built on a friction factor solved this way, so pipe sizing, pump selection, and energy studies share one consistent basis.

Related definitions

Darcy-Weisbach equation · Reynolds number · Absolute roughness

See it in FluidFlow

See the friction factor solved across a whole network. FluidFlow computes f for every pipe from the Reynolds number and relative roughness — Colebrook-White in turbulent flow, 64/Re in laminar — so every pressure-drop result rests on the same method.