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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from a document discussing the coefficient of contraction and discharge for fluid flow through various orifices.

Identifier  ExFiles\Box 36\1\  scan 015
Date  16th February 1916
  
R.R. 82A a (400) T(S.C. 656 16-2-16) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 1546.

Contd. -3-

(3) The contraction is imperfect and Cc is increased if the orifice is placed in a confined part of the vessel or if the water approaches the orifice through a channel.
(4) Ditto. if the inner edge of the orifice is rounded.

Cc between .63 & 1.00
Vena contracta orifice.
Cc = 1

(5) See notes concerning value of C.
Notes concerning the value of C :-
(1) C diminishes as the head increases, but at a diminishing rate. Thus for a circular sharp edged orifice 1/16 sq inch area.
C = .62 at 1 foot head.
C = .61 " 2 feet "
C = .60 " 10 " "
(2) C is slightly greater (about 4%) for rectangular orifices of the same area at the same head.
(3) C increases slightly as the area of the orifice.
(4) C may be made nearly equal to Cv (i.e. Cc = 1) by properly shaping the orifice to suit the natural stream line flow.
(5) C for a cylindrical orifice is about .825.
Loss by shock occurs.
Cv = C or Cc = 1.
EFC.
  
  


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