pitottubes

Pitot tubes are pressure-measuring devices used to determine fluid flow velocity by converting the kinetic energy of a moving fluid into a pressure signal. They are named after Henri Pitot, a French engineer who developed the instrument in the 18th century to measure wind speeds. A typical pitot tube consists of a hollow, tube-like probe oriented so its opening faces the oncoming flow.

Principle: The open end captures stagnation (total) pressure Pt. Static pressure Ps is measured separately by ports on the side of the tube or by a nearby static port. The pressure difference ΔP = Pt − Ps is the dynamic pressure. For incompressible flow, v = sqrt(2 ΔP / ρ), where ρ is fluid density. At high speeds, compressibility effects require corrections.

Applications: In aviation, pitot tubes are part of the pitot-static system that feeds air data to instruments such as the airspeed indicator. The indicated airspeed is derived from dynamic pressure, and modern aircraft often use electronic air data computers to process Pt and Ps readings. Pitot tubes are typically heated to prevent icing, and they must remain free of debris; blockage can lead to erroneous readings or loss of airspeed indication if static ports are compromised as well.

Other uses: Pitot tubes are employed in wind tunnels and hydrodynamic research, as well as in open-channel and pipe-flow measurements, sometimes with differential manometers or electronic sensors.

Limitations: They are susceptible to icing, fouling, and debris; readings can be affected by yaw, angle of attack, and misalignment. Regular maintenance, proper positioning, and calibration are essential for accurate measurements.