The other end of the Pitot tube is connected to a pressure gage, such as point C. That is, the plane of the opening of the tube is perpendicular to the flow, as shown at point B in Fig. In contrast, consider that a Pitot tube is now inserted into the flow, with an open end facing directly into the flow. Such a small hole in the surface is called a static pressure orifice, or a static pressure tap. Because the flow moves over the opening, the pressure felt at point A is due only to the random motion of the molecules i.e., at point A, the static pressure is measured. The plane of the role is parallel to the flow, as shown at point A in Fig. Furthermore, consider a boundary of the flow, such as a wall, where a small hole is drilled perpendicular to the surface. In engineering, whenever a reference is made to "pressure" without further qualification, that pressure is always interpreted as the static pressure. Static pressure is a measure of the purely random motion of molecules in the gas it is the pressure you feel when you ride along with the gas at the local flow velocity. We now give this pressure a specific name: the static pressure. The gas molecules, because of their random motion, will still bump into you, and you will feel the pressure p1 of the gas. Now imagine that you hop on a fluid element of the flow and ride with it at the velocity V1. This motion is very random, with molecules moving in all directions with various velocities. Pressure is associated with the time rate of change of momentum of the gas molecules impacting on or crossing a surface i.e., pressure is clearly related to the motion of the molecules. Let us consider the significance of the pressure p1 more closely. Moreover, a Pitot tube is the most common device for measuring flight velocities or airplanes.Ĭonsider a flow with pressure p1 moving with the velocity V1, as sketched at the left of Fig. This was the first time in history that a proper measurement of fluid velocity was made, and Pitot's invention has carried through to the present day as the Pitot Tube - one of the most common and frequently used instruments in any modern aerodynamic laboratory. In turn, he used the pressure inside this tube to measure the water flow velocity. ![]() Pitot oriented one of the open ends of the tube so that it faced directly into the flow. One of the instruments he used was his own invention - a strange-looking tube bent into L shape, as shown in Fig. ![]() In 1732, the Frenchman Henri Pitot was busy trying to measure the flow velocity of the Seine River in Paris.
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