What is the definition of v-notch used in fluid machinery?

A V-notch, also known as a triangular notch or a 90-degree notch, is a type of notch used in fluid machinery to measure the flow rate of liquids or gases. It consists of a sharp-edged opening cut into a thin plate or wall, forming a V-shaped cross section. The V-notch is usually symmetrical, with the included angle between the sides of the notch being 90 degrees.

V-notches are commonly used in conjunction with weirs, which are barriers placed in a flowing stream of fluid to raise the liquid level upstream of the weir. The V-notch is positioned at the crest of the weir, and the flow rate of the fluid passing through the notch can be determined by measuring the height of the liquid surface above the bottom of the notch.

The flow rate through a V-notch is given by the following formula:

Q = C_d * (2/3) * √(2g) * H^(5/2)

where:

- Q is the flow rate in cubic meters per second (m^3/s)

- C_d is the discharge coefficient, which is a dimensionless factor that takes into account the effects of friction and other losses

- g is the acceleration due to gravity (9.81 m/s²)

- H is the height of the liquid surface above the bottom of the notch in meters (m)

The discharge coefficient for a V-notch can be determined experimentally and depends on the specific design of the notch and the fluid flowing through it. Typical values for the discharge coefficient of V-notches range from 0.58 to 0.62, but can vary depending on the specific conditions.

V-notches are widely used in various applications, including:

- Measuring the flow rate of water in open channels and streams

- Flow measurement in industrial processes

- Calibration of flow meters and other flow measurement devices

- Laboratory experiments related to fluid mechanics and hydraulics.