Cress Help - Flow - Pipe flow - A17.2

Averaged flow with turbulent flow 

Calculation of the average flow velocity in turbulent flow in a pipeline. The coefficient of Chézy varies with the wall roughness and the thickness of the boundary layer. The distinction between hydraulically smooth and hydraulically rough wall is made, in between the technical roughness is used.

Average flow velocity in turbulent flow:

in which:

C: coefficient of Chézy [m½/s]

With a hydraulically smooth wall (δ > 4 k) for C:

With a hydraulically rough wall (k > 6 δ) for C:

If 1/6 ≤ δ/k ≤ 4, the technical roughness is used. Then for C:

with

in which:

in which:

k: wall roughness (see following table) [m]
δ: thickness of the laminar boundary layer [m]
κ: Von Karman of constant (= 0.4) [-]