A METHOD OF CALIBRATION OF A 7-HOLE PRESSURE PROBE FOR MEASURING HIGHLY 3-DIMENSIONAL FLOWS

In this paper, a non-nulling calibration method using a seven-hole pre ssure probe in the range of +/-54 degrees at 9 degrees intervals both in yaw and in pitch planes is developed and reported. Calibration is c arried out in two stages, low angles (for the maximum centre hole pres sure) and high angles (other cases). On the basis of the maximum probe pressure reading, the calibration region is divided into seven zones; one central zone and six side zones. The calibration coefficients are derived for each zone. For interpolation, a localized two-variable po lynomial is used at each point with the calibration data surrounding i t. Zone extension is another useful feature developed here, in which e ach boundary point of every zone is extended to the nearest calibratio n point of the adjacent zone. By doing so, for a measuring point falli ng in between the boundaries of two adjacent zones, one employs the ex tended zone boundary data for fitting a polynomial. In addition to cal ibration data, additional data are acquired in the calibration tunnel. These data are used as measured data and calibration curves of suitab le zones are used to derive flow parameters. In general, the interpola tion errors in flow angles are found to be within +/-1 degrees and the errors in total and static pressures are within 0.5% and 1% of the dy namic pressure respectively.