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 are 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, especially in flows with large radial flow angles. To close this gap, the probes are calibrated for radial flow angles up to 32 degrees. 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 biunique for the six-hole probe. Therefore, an experimental study of Mach number measurement deviations is performed 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 using two calibration coefficients for the Mach number simultaneously in a multidimensional interpolation.