The investigation on a hybrid interpolated additional zonal method for a conventionally calibrated five-hole probe

Abstract

For the highly three-dimensionality and large-span Mach number properties in modern turbomachinery, the five-hole probe calibrated by the conventional method might be incapable of accurate measurement. An additional zonal calibration method which can extend the valid deviation angle from 30° to 60° with low workload was introduced in this study. Besides, the data reduction process was modified to improve the measurement precision. Firstly, the Grubbs criterion and the spline interpolation approach were used to correct the gross error of calibration coefficients. Secondly, under the condition with a known Mach number, the univariate linear interpolation method was found to be more stable than the bivariate biharmonic spline interpolation method in restoring the real flow properties, especially in extended sectors. In addition, the investigation of the calibration coefficients behavior in the Mach-number range of 0.3 to 0.7 showed that the sensitivity of angle and total pressure coefficients to Mach number only appeared near the boundary of the five sectors, while the sensitivity of the static pressure coefficient remained seriously throughout the calibration region. When the measured and calibrated Mach numbers were placed within 0.4 or close to each other, the error caused by the compressibility effect could be ignored. Accordingly, the hybrid interpolation algorithm was developed to minimize the measurement error. Moreover, the hybrid interpolated additional method was confirmed in the measurement of the outlet flow field of the highly loaded compressor cascade. The measurement accuracy of the yaw angle and the total pressure loss were improved by 7.5° and 11.63%, respectively.