Chapt10

81 is too high and should be replaced by an

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Unformatted text preview: ). Finally, the flow rate follows from wide-channel critical flow, Eq. (10.32): 1 3 3 gyc Broad-crested theory: q 2 3 V2 1 2g 2g H 3/2 (10.54) Again we may usually neglect the upstream velocity head V 2/(2g). The coefficient 1 1/ 3 0.577 is about right, but experimental data are preferred. Experimental Weir Discharge Coefficients Theoretical weir-flow formulas may be modified experimentally as follows. Eliminate the numerical coefficients 2 and 2, for which there is much sentimental attachment 3 in the literature, and reduce the formula to Qweir Cdb gH V2 1 2g 3/2 gH3/2 Cdb (10.55) where b is the crest width and Cd is a dimensionless, experimentally determined weir discharge coefficient which may vary with the weir geometry, Reynolds number, and Weber number. Many data for many different weirs have been reported in the literature, as detailed in Ref. 19. An accurate ( 2 percent) composite correlation for wide ventilated sharp crests is recommended as follows [19]: Wide sharp-crested weir: Cd 0.564 0.0846 H Y for H Y 2 (10.56) The Reynolds numbers V1H/ for these data varied from 1 E4 to 2 E6, but the formula should app...
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