Flow of Water around Bends in Pipes

In condensed form, this paper presents the more outstanding results of series of experiments on the flow of water around bends of various shapes and various degrees of curvature in 6-in. pipes. Only the most salient points are discussed. These experiments are believed to be unique in that, with the same quantity of flow, the effect on the loss of head resulting from unequal velocity distribution in the pipe approaching the bend was fully investigated.

The experiments show: (1) That it is possible to have conditions such that the resistance to flow may be very small or unusually large in the same pipe bend carrying identical quantities of water; (2) that in a standard 90°, 6-in. pipe bend, for the same quantity of flow, with high velocity on the inside, and low velocity on the outside, of the approach pipe, the loss of head may be four times as much as would be measured in the same bend when high velocity exists on the outside, and low velocity on the inside, of the tangent leading to the bend; (3) that present formulas for computing loss of head due to bends appear to apply only to cases in which approximately uniform velocity distribution exists in the approach pipe; ( 4) that the losses of head in the bends experimented upon appear to vary as the square of the velocity, and not as the 2.25 power as suggested by some writers; (5) that a pipe bend may be as useful as any other device for the measurement of discharge; (6) that the direction of flow of the secondary currents in pipe bends depends entirely upon the velocity distribution in the approach pipe; and (7) that the same fundamental laws of flow through bends apply to both closed conduits and open channels.