The effect of turbulence on a multi-hole Pitot calibration

• This paper analyses a multi-holed Pitot tubes calibration in a low-turbulence wind tunnel.
• Hysteresis was discovered under certain conditions.
• Flow visualization was done in order to find the source of the hysteresis.
• The calibrations dependence on turbulent intensity was determined.

Accurate calibrations of multi-hole Pitot tubes require thousands of measurements spanning ranges of the fluid's velocity, and the pitch and yaw angles. When calibrating a commercially-manufactured multi-hole Pitot tube in NIST's low-turbulence wind tunnel, we found hysteresis in certain ranges of airspeed, pitch angle, and yaw angle. In the worst case, the hysteresis caused a calibration error of 30%. We demonstrate that the hysteresis was caused by a flow instability associated with flow separation. A turbulence intensity of only 1% removes the hysteresis; however, the calibration depends on the turbulence intensity over the entire range of our measurements (0.25–2%). Therefore, multi-hole Pitot tubes should be calibrated and used at the same turbulence levels.