Treatise on hydraulics by Merriman Mansfield 1848-1925

Author:Merriman, Mansfield, 1848-1925. [from old catalog]
Language: eng
Format: epub
Tags: Hydraulics
Publisher: New York, J. Wiley & sons; London, Chapman & Hall, limited
Published: 1906-03-25T05:00:00+00:00

When water is admitted to a channel from a reservoir or pond through a rectangular sluice there occurs a contraction similar to that at the entrance into a pipe, and which may be often observed in a slight depression of the surface, as at D in the diagram. At this point, FlG -117a

therefore, the velocity is greater than the mean velocity v, and a loss of energy or head results from the subsequent expansion, which is approximately measured by the difference of the depths d x and d v the former being taken at the entrance of the channel, and the latter below the depression where the uniform flow is fully established. According to the experiments of Dubuat, the loss of head is

in which tn ranges between o and 2 according to the condition of the entrance. If the channel be small compared with the reservoir, and both the bottom and side edges of the entrance be square, m may be nearly 2; but if these edges be rounded, m may be very small, particularly if the bottom contraction is suppressed. The remarks in Chapter V regarding suppression of the contraction apply also here, and it is often important to prevent losses due to contraction by rounding the approaches to the entrance. Screens are sometimes placed at the entrance to a channel in order to keep out floating matter; if the cross-section of the channel is n times that of the meshes of the screen, the loss of head, according to (74), is (n— i)v 2 /2g.

The loss of head due to bends or curves in the channel is small if the curvature be slight. Undoubtedly every curve offers a resistance to the change in direction of the velocity, and thus requires an additional head to cause the flow beyond that needed to overcome the frictional resistances. Several formulas have been proposed to express this loss,

Flow in Conduits and Canals

Chap. IX

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