# Darcy friction factor - Free surface flow

## Description

In fluid dynamics, the Darcy friction factor formulae are equations that allow the calculation of the Darcy friction factor, a dimensionless quantity used in the Darcy–Weisbach equation, for the description of friction losses in pipe flow as well as open-channel flow.

The Darcy friction factor is also known as the Darcy–Weisbach friction factor, resistance coefficient or simply friction factor; by definition it is four times larger than the Fanning friction factor.

The shown formula is another form of the Colebrook-White equation exists for free surfaces. Such a condition may exist in a pipe that is flowing partially full of fluid.

Related formulas## Variables

f | Darcy friction factor (dimensionless) |

ϵ | Pipe's effective roughness height (m) |

R_{h} | Hydraulic radius (m) |

Re | Reynolds number (dimensionless) |