Henri Pitot

PitotHenri Pitot (1695-1771) was a hydraulic engineer who invented a device that is still in use today. That device, the pitot tube, measures the velocity of a fluid flow at a given point. Pitot used his pitot tube to measure the flow of water in rivers and canals.

Pitot_tube_diagram

Diagram of Modern Pitot Tube

The pitot tube is a deceptively simple device. Pitot’s original tube had two tubes. The first was a tube that stuck straight up, open at one end and inserted vertically into the water. This tube measured the static pressure – the pressure of the water at rest. The second tube was bent at a right angle. The open end of the right angle faced directly in the fluid flow. Pitot used his tubes to measure the velocity of the Seine River. He stood on a bridge and lowered his apparatus into the water.

Pitot’s contemporaries were convinced that flow velocity increased with depth because it was proportional to the mass above it. Pitot used his innovation to prove that the velocity of the flow decreased as the depth decreased.

Today the Pitot tube is used to successfully calculate the velocity of both the flow of water and the flow of air at given points in the flow. How is it possible that one device can work for both water and air? Water and air are both fluids. The principles that apply to one, apply to the other because they are both governed by the principles of fluid dynamics. As a result, the pitot tube can give accurate readings of both water flow velocity and air flow velocity.

Today the pitot tube is used to calculate air speed on aircraft. It is also used to calculate the speed of ships in the water.

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