Calibration of Pneumatic Multi-hole Probes for Transonic Turbomachinery Flows

Abstract

The calibration data of a five-hole probe and a six-hole probe designed for measurements in transonic turbomachinery flows is presented. The probes feature a special base pressure hole on the back side to avoid the Mach number insensitivity of pressure probes near Mach number unity. There is only little literature available on the performance of such probes, escpecially in flows with large radial flow angles. In order to close this gap, the probes are calibrated for radial flow angles up to 32°. A significant influence of this flow angle on the coefficients used for Mach number determination is shown. At large positive flow angles, the relationship between the pressure coefficient using the base pressure and the Mach number is not biunque, which can lead to high measurement inaccuracies. Therefore, an experimental study of Mach number measurement deviations is conducted for the six-hole probe at the calibration wind tunnel. Different evaluation methods are examined. The sample standard deviation over 210 randomly distributed points is reduced by 66 % compared to the same probe design without the base pressure hole. This is achieved by using two calibration coefficients for the Mach number simultaneously in a multidimensional interpolation.