[Illustration: FIG. 43.]
§ 39. _Large Rectangular Jets from Orifices in Vertical Plane
Surfaces._--Let an orifice in a vertical plane surface be so formed
that it produces a jet having a rectangular contracted section with
vertical and horizontal sides. Let b (fig. 43) be the breadth of the
jet, h1 and h2 the depths below the free surface of its upper and
lower surfaces. Consider a lamina of the jet between the depths h and
h + dh. Its normal section is bdh, and the velocity of discharge
[root](2gh). The discharge per second in this lamina is therefore
b[root](2gh) dh, and that of the whole jet is therefore
_
/h2
Q = | b [root](2gh) dh
_/h1
= 2/3 b[root](2g) {h2^(3/2) - h1^(3/2)}, (6)
where the first factor on the right is a coefficient depending on the
form of the orifice.
Now an orifice producing a rectangular jet must itself be very
approximately rectangular. Let B be the breadth, H1, H2, the depths to
the upper and lower edges of the orifice. Put
b [h2^(3/2) - h1^(3/2)] / B [H2^(3/2) - H1^(3/2)] = c. (7)
Then the discharge, in terms of the dimensions of the orifice, instead
of those of the jet, is