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How does a pitot tube measure the speed of a moving fluid?

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differential manometer, Torricellian barometer, and siphon — fluid mechanics Figure 1: Schematic representations of (A) a differential manometer, (B) a Torricellian barometer, and (C) a siphon.

A pitot tube measures the speed of a moving fluid by utilizing the principles of fluid mechanics, specifically Bernoulli’s law.

The instrument consists of a tube with a right-angled bend, which is placed in the fluid flow with its opening directed upstream. As the fluid approaches the blunt end of the tube, the streamlines divide, and the fluid at the opening is brought to a complete stop, creating a point of stagnation.

According to Bernoulli’s law, the kinetic energy of the moving fluid is converted into pressure at this stagnation point. By measuring the difference between this stagnation pressure and the static pressure of the fluid, the velocity of the fluid can be calculated. This method is widely used in anemometers to determine airspeed for aircraft and to monitor the flow of liquids in industrial applications.12