Adaptation of Venturi Flumes to Flow Measurements in Conduits
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VIEW THE REPLYPublication: Transactions of the American Society of Civil Engineers
Volume 101, Issue 1
Abstract
A weir can be considered as a control section through which water flows at critical depth. The sharp angle at the face and the fact that the flow is convex where it passes the critical section introduce energy losses between the point of measurement and the control section, the amount of these losses depending upon the setting of the weir in the channel. The ordinary weir formula is an empirical equation that is accurate only as long as the fundamental conditions upon which it was developed can be duplicated. These conditions can rarely be complied with in a confined channel, such as a sewer or an irrigation canal.
This paper presents the theoretical hydraulic principles involved, and the results of special tests made, in the adaptation and construction of various Venturi flumes for measuring flow in conduits of uniform cross-section, where weirs have proved unsatisfactory.
Since the uncertainties or variations in weir coefficients are due to indeterminable energy losses, it is reasonable to suppose that if these losses can be eliminated or reduced to a negligible amount by the use of some other device, the uncertainties in the rating curve will be eliminated. Such conditions are found in the so-called Venturi flume which, in this paper, includes any streamlined device placed in an open channel, or a closed channel partly full, having a sufficient constriction to cause water to flow at critical depth with parallel filaments.
Any shape of throat may be used, and the flow can be determined from a single depth measurement, using a rating curve drawn from rational formulas. Several of these Venturi flumes have been constructed, including one that was simply a flat slab on the bottom, and had no side contractions; one that was rectangular in cross-section; and several with trapezodial-shaped throats, all of which have given good results.
The writers show how the rating curve may be drawn, and give graphs for use with circular conduits.
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Published In
Transactions of the American Society of Civil Engineers
Volume 101 • Issue 1 • January 1936
Pages: 1195 - 1216
Copyright
© 1936 American Society of Civil Engineers.
History
Published in print: Jan 1936
Published online: Feb 10, 2021
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