Pitot tube

Recalling the definition of stagnation pressure as the maximum pressure that can be obtained by stopping the fluid isoentropically and adiabati – cally, it can be measured in an orifice drilled in the stagnation point of a body. The simplest body is a tube aligned with the direction of the stream with the open end facing the stream (Figure 2.3) called a Pitot tube after its inventor, Henri Pitot (1732). The other end of the tube is connected to a pressure-indicating instrument so that in equilibrium there is no motion in the tube (U = 0, stagnation).

If the opening is also normal to the tube axis and with circular cross­section, free of obstacles, the reading of the instrument is, in the subsonic regime, virtually independent from the shape of the front and the length of the tube.