Qa = cω √(2gh),
where c is called the coefficient of discharge. Thus for a sharp-edged plane orifice c = 0.97 × 0.64 = 0.62.
§ 18. Experimental Determination of cv, cc, and c.—The coefficient of contraction cc is directly determined by measuring the dimensions of the jet. For this purpose fixed screws of fine pitch (fig. 16) are convenient. These are set to touch the jet, and then the distance between them can be measured at leisure.
The coefficient of velocity is determined directly by measuring the parabolic path of a horizontal jet.
Let OX, OY (fig. 17) be horizontal and vertical axes, the origin being at the orifice. Let h be the head, and x, y the coordinates of a point A on the parabolic path of the jet. If va is the velocity at the orifice, and t the time in which a particle moves from O to A, then
x = vat; y = 1⁄2 gt2.
Eliminating t,
va = √ (gx2/2y).
Then
cv = va √ (2gh) = √ (x2/4yh).