Coefficient of contraction

The coefficient of contraction is a term used in fluid mechanics to describe the ratio of the area of the fluid stream at the vena contracta (the point of maximum constriction) to the location of the orifice through which the fluid is flowing. It is denoted by the symbol “C_c.”
The coefficient of contraction can be expressed mathematically as:
C_c = A_c / A_0
where A_c is the area of the fluid stream at the vena contracta, and A_0 is the area of the orifice.
The coefficient of contraction is used to determine the actual flow rate of a fluid through a given orifice. This rate is typically less than the theoretical flow rate due to various system losses. These losses include frictional losses due to the fluid's viscosity and losses due to the fluid's contraction as it passes through the orifice.