Effects of the proximity of a wall

The correction to the reading of a Pitot tube placed near a wall are less immediate than the corrections for the gradient of stagnation pressure since the error depends on the whole speed profile between the tube and the wall. A process of successive approximations could be developed to deduce the true profile from the profile measured but this procedure would require a large amount of experimental work. As said above, for

Подпись: Figure 2.8

Pitot probes for boundary layer

measurements in thin boundary layers very small tubes are used for which the correction for the effect of proximity to a wall can be ignored; for cylindrical tubes the effect tends to zero at distances greater than 2 diameters from the wall (Figure 2.9); the correction for a flattened tube is more uncertain since the effect of the wall is to prevent the deviation of the streamlines induced by the presence of the Pitot tube and a flattened tube deforms the streamlines more than a circular pipe.

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