HYDKAULIUS AND 1TJS APPLICATIONS 



o -Length of Tube divided by Length or Side of Squar 

 OS /-O /-5 20 2-5 3-0 



A 



If 4 6 8 10 



Length of Tube In Feet 

 FIG. 72. 



less than about 5 feet 

 observations showed an 

 upstream current located 

 at the upper side of the 

 tube, this reducing the 

 effective discharge area. 

 This effect was found to 

 become less marked as 

 the velocity was increased. 

 For greater lengths of out- 

 let tube this current was 

 absent, and the conditions 

 permitted the formation of 

 a region of less than 

 normal pressure at the 

 vena contracta (p. 117). If 

 n represents the number 

 of sides on which the con- 

 traction is suppressed, the 

 following relationships give 

 the minimum values of 

 C within about 2 per 

 cent. : 



For L -f- D < O'l ; 

 C = -605 + -019 w a . 



For L -r- D ~ 3-0 ; C = -786 + '0055 n 2 . 



FIG. 73. 



Partially Submerged Orifice (Fig. 73). 

 Here the portion of the orifice I m, 

 below the normal water level on the 

 discharge side, may be considered as 

 a submerged orifice, while the portion 

 k I above this level may be looked upon 

 as discharging freely into air, the 

 quantity passing each portion being 

 calculated separately on these assump- 

 tions. 



Thus in a rectangular orifice of 

 breadth b and depth d, having a head 

 of water on the supply side = H above 



