In a Pitot tube design, what does the stagnation port measure?

The stagnation port in a Pitot tube design measures the fluid pressure as it impacts the port. The basic principle behind this measurement is that when a fluid flows into the opening of the stagnation port, it comes to a stop, resulting in an increase in pressure due to the kinetic energy of the fluid being converted into potential energy.

This pressure, known as stagnation or total pressure, encompasses both the static pressure exerted by the fluid at rest and the dynamic pressure due to the fluid's velocity. By utilizing the stagnation port, we can obtain critical information about the fluid's flow characteristics, which can then be correlated to determine the velocity of the fluid using Bernoulli's principle. This principle links the stagnation pressure measured at the port to the basic parameters of flow dynamics.

Fluid velocity, temperature, and density are not directly measured by the stagnation port itself, but they can be derived from the stagnation pressure in conjunction with other measurements and equations. Hence, the primary function of the stagnation port is the measurement of pressure, specifically at the point where fluid impact occurs.