Unformatted text preview: | Textbook Table of Contents | Study Guide 10.7 Flow Measurement and Control by Weirs 689 1
2 V1 Nappe
Ventilation 1 Y Weir
Weir Y L Fig. 10.16 Flow over wide, wellventilated weirs: (a) sharp-crested;
(b) broad-crested. (b) A very complete discussion of weirs, including other designs such as the polygonal
“Crump” weir and various contracting flumes, is given in the text by Ackers et al. .
See Prob. 10.122. Analysis of Sharp-Crested Weirs It is possible to analyze weir flow by inviscid potential theory with an unknown (but
solvable) free surface, as in Fig. P8.71. Here, however, we simply use one-dimensionalflow theory plus dimensional analysis to develop suitable weir flow-rate correlations.
A very early theoretical approach is credited to J. Weisbach in 1855. The velocity
head at any point 2 above the weir crest is assumed to equal the total head upstream;
i.e., Bernoulli’s equation is used with no losses:
2g H h V2
2g H or V2(h) 2gh V2
1 where h is the vertical distance down to point 2, as shown in Fig. 10.16a. If we accept
for the moment, without...
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