Flow in Tubes in Noncircular Cross Section

FLOW IN TUBES IN NONCIRCULAR CROSS SECTION

Discussion of flow in pipes has been restricted to pipes of circular cross section. The previous exposition may be applied to turbulent flow in noncircular ducts by introducing a dimension equivalent to the diameter of a circular pipe. This is known as the mean hydraulic diameter, d_m, which is defined as four times the cross-sectional area divided by the wetted perimeter. A few examples are as follows:

For a square channel of side b,

For an annulus of outer radius r₁ and inner radius r₂,

This simple modification does not apply to laminar flow in noncircular ducts.