Unformatted text preview: ather sensitive to small effects, such as plate
thickness and sidewall boundary-layer growth. Small heads (H 75 mm) and small
slot widths (b 30 cm) are not recommended. See Refs. 19 and 20 for further details.
The V notch, in Table 10.2c, is intrinsically interesting in that its overfall has only one
length scale, H — there is no separate “width.” The discharge will thus be proportional to
H5/2, rather than a power of 2 . Application of Bernoulli’s equation to the triangular opening, in the spirit of Eq. (10.52), leads to the following ideal flow rate for a V notch:
V notch: Qideal 8 2
15 tan 2 g1/2H5/2 (10.59) where is the total included angle of the notch. The actual measured flow is about 40
percent less than this, due to contraction similar to a thin-plate orifice. In terms of an
experimental discharge coefficient, the recommended formula is
QV notch Cd tan 2 g1/2H5/2 Cd 0.44 for 20° 100° (10.60) for heads H 50 mm. For smaller heads, both Reynolds-number and Weber-number
effects may be imp...
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- Spring '08
- Fluid Dynamics, Fig, e-Text Main Menu, subcritical flow