Chapt10

E it should spring clear of the weir crest

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Unformatted text preview: | Textbook Table of Contents | Study Guide 10.7 Flow Measurement and Control by Weirs 689 1 ≈H 3 h H 2 V1 Nappe Ventilation 1 Y Weir (a) H yc V1 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. [19]. 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: V2 2 2g H h V2 1 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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