The behaviour of a Pitot tube in transverse shear

Abstract

This paper presents an experimental investigation of the displacement of the total-head profile in a shear flow from its true position when it is measured with a flat-ended round Pitot tube. The experiments showed that at least two forms of displacement may exist depending on the flow conditions.In a wake the displacement of the effective centre of pressure towards the higher velocity was found to obey the law deduced theoretically by Hall (1956), provided that changes in flow direction were not large. In the presence of large eddies the behaviour of the Pitot is further modified by its characteristics in yaw. This introuduces a total-head error reducing the observed total head.In a turbulent boundary layer the experiments showed that the displacements were an order of magnitude smaller than in a wake and could be regarded as negligible for a round Pitot, even when it was touching the wall.An empirical method for correcting the observations made with a round Pitot which is of the same width as the wake is given in an appendix.