Head geometry effects on pneumatic three-hole pressure probes for wide angular range

Recent investigations Argüelles et al. (2008) [5] have demonstrated that it is possible to increase the operative angular range of pneumatic three-hole pressure probes (THP) using a two-zoned method in the data reduction procedure. In this study, the influence of the head geometry on the performance of this type of probes is addressed, especially in the extended regions of the angular range, previously unconsidered in the literature. Three different geometries have been built to carry out the analysis, corresponding to cylindrical, trapezoidal and cobra type probes, with a separation angle of 60° between the holes. Additionally, cylindrical and cobra type probes have been manufactured with angular distances of 30° and 45° between the holes, in order to advance the effect of the construction angle on the probes performance. The uncertainty transmitted from the measurements to the resultant flow variables has been also addressed. Moreover, the sensitivity of the different head designs to variations in the Reynolds number or deviations of the flow with respect to the measurement plane of the probe (pitch misalignments) has been addressed. Major conclusions indicate that cobra type probes provide the largest operative angular range, while cylindrical designs minimize the errors in the determination of both pressure and velocity flow variables when the Reynolds number or the pitch angle differ from the baseline calibration.