This paper introduces a pneumatic 9-hole probe which can measure flow angles, stagnation and static pressures, and spatial derivatives of stagnation pressure. It does this through direct measurement at a single location, rather than empirical corrections using measurements at multiple points.

The new design resembles a 5-hole probe with 4 additional holes positioned around the side of the probe head. This arrangement enables the probe to distinguish between flows with stagnation pressure gradient and flows at an angle. Mapping between the inputs, the probe hole pressures, and outputs, the calibration reference measurements, is achieved with a trained neural network which takes the place of a conventional calibration map.

Measurements of an unknown wake are performed in a calibration tunnel. The 9-hole probe data is compared with measured reference data and a “conventional” analysis of the 5 forward facing holes. The 5-hole probe analysis results in a maximum yaw angle error of 8.4°, while the 9-hole probe matches the reference to within 0.8°. Mass-averaged stagnation pressure and kinetic energy loss coefficients, evaluated with the 5-hole probe analysis, result in errors of +2.8% and −48% respectively, while the 9-hole probe gives +0.5% and −4.5%.

The new probe is used to perform an area traverse of an inlet guide vane in a research compressor. The 5-hole probe analysis gives a ±5.5° variation in yaw angle across the wake and this reduces to ±1.0° when the 9-hole probe is used. Measurement of stagnation pressure gradient and curvature, based on single point measurements, is also demonstrated.

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