Vena contracta:

Vena contracta is the point in a fluid stream where the diameter of the stream is the least, and fluid velocity is at its maximum.

How is vena contracta formed in fluid flow?

The reason for the phenomenon Vena contracta is that the fluid streamline cannot abruptly changes direction  and they are unable to closely follow the sharp angles in orifices, nozzles and pipes. When fluid passes through the orifices, the gradual contraction of fluid takes place. The fluid stream begins to converge and passes through orifice.  The streamline continues to converging in smooth path even after it passes through the orifices. Fluid converges to the minimum section in downstream of flow and then it diverges again. This minimum cross section is known as vena contracta.

Types of orifices:

Orifice is defined as the small opening on side or bottom of a tank through which any kind of fluid is flowing.

Orifices are classified into small orifice and large orifice dependin....

Vena contracta is the point in a fluid stream where the diameter of the stream is the least, and fluid velocity is at its maximum.

How is vena contracta formed in fluid flow?

The reason for the phenomenon Vena contracta is that the fluid streamline cannot abruptly changes direction  and they are unable to closely follow the sharp angles in orifices, nozzles and pipes. When fluid passes through the orifices, the gradual contraction of fluid takes place. The fluid stream begins to converge and passes through orifice.  The streamline continues to converging in smooth path even after it passes through the orifices. Fluid converges to the minimum section in downstream of flow and then it diverges again. This minimum cross section is known as vena contracta.

Types of orifices:

Orifice is defined as the small opening on side or bottom of a tank through which any kind of fluid is flowing.

Orifices are classified into small orifice and large orifice depending upon the size of orifice and head of fluid in that orifice.

 Small orifice is the one in which has the head of fluid from the centre of orifice is more than five times the depth of orifice. 

Also, the large orifice is the one which has the head is less than five times the depth of orifice.

Based on shape of orifice they are classified as following:

• Rectangular orifice

• Circular orifice

• Triangular orifice

• Square orifice

Hydraulic Co-efficients

There are mainly 3 hydraulic coefficients, they are as follows:

• Co efficient of contraction, Cc

• Coefficient of discharge, Cd

• Coefficient of velocity, Cv

Coefficient of Contraction (Cc)

It is the ratio of area of water jet at vena-contracta to the area of the orifice.

`C_c=a_c/a`

Where,

`a_c` = Area of jet at vena-contracta

a = Area of the orifice

Coefficient of Velocity (Cv)

It is the ratio of velocity of water jet at vena-contracta to the theoretical velocity.

Coefficient of discharge (Cd)

It is the ratio of actual discharge to the theoretical discharge.

The relation between the coefficient of contraction, coefficient of velocity and coefficient of discharge can be expressed as,

`C_d=C_c*C_v`