Effects of the Reynolds number
For Reynolds numbers lower than 1000 (based on the diameter of the orifice), corrections are required due to the presence of a completely viscous flow; Figure 2.11 shows the calibration curve for very low Reynolds numbers. For Reynolds numbers less than 50, the error increases rapidly and the curve tends to become
pOI _ p = 1 + 112
Such small values of the Reynolds number are typical of measurements made in the boundary layer, where speeds are low (down to zero) and
Effects of low Reynolds numbers on the readings of a Pitot tube (d/D = 0.64)
Pitot tubes are very small to avoid both the displacement of the virtual centre in the presence of velocity gradients and the effects of proximity to the wall.