Friction Loss Methods
Of these, two - the Colebrook-White Equation and the Manning's Equation - are of interest to UK Engineers.
Colebrook-White Equation
The Colebrook-White equation is used to iteratively calculate for the Darcy-Weisbach friction factor:
Free Surface:
Full Flow (Closed Circuit):
Darcy-Weisbach Equation
Because of non-empirical origins, the Darcy-Weisbach equation is viewed by many engineers as the most accurate method for modeling friction losses. It most commonly takes the following form:
For section geometries that are not circular, this equation is adapted by relating a circular section's full-flow hydraulic radius to its diameter:
D = 4R
This can then be arranged to the form:
The Kinematic Viscosity is used in determining the friction coefficient in the Darcy-Weisbach Friction Method. The value for this is set in the Calculation Options, and depends on the water temperature. Temperatures of 10 or 15 degrees are normally used.
Manning's Equation