Uncertainty Quantification for Multi-Hole Pneumatic Probe Measurements in Transonic Turbomachinery Flows

The continuous pursuit of turbomachinery performance improvements leads to constantly increasing demands on measurement data from turbomachinery flows. Accurate measurements with intrusive multi-hole probes are particularly challenging in transonic flow due the Mach number insensitivity of conventional multi-hole probes near Mach number unity. This has led to the development of probes featuring an additional pressure hole which is not affected by the insensitivity. The paper aims to quantify the effect resulting from random errors on a probe measurement in transonic flow. Two operating modes, the Front Pressure Mode (FPM), a conventional five-hole probe method, and the Base Pressure Mode (BPM), using the base pressure, are compared. This constitutes the first published comprehensive uncertainty quantification for a multi-hole probe with a base pressure hole. Uncertainties from the probe calibration and the turbomachinery measurement are considered. Uncertainties resulting from the interpolation in the lookup table containing the calibration data are determined experimentally. The overall uncertainty of the probe yaw angle and the total pressure in the transonic turbomachinery flow remains relatively unaffected by the mode of operation. In contrast, uncertainties of the pitch angle and the static pressure are reduced by about 40 % and 75 % respectively in BPM.