A method of calibration of a seven-hole pressure probe for measuring highly three-dimensional flows

In this paper, a non-nulling calibration method using a seven-hole pressure probe in the range of ±54° at 9° intervals both in yaw and in pitch planes is developed and reported. Calibration is carried out in two stages, low angles (for the maximum centre hole pressure) 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 polynomial is used at each point with the calibration data surrounding it. Zone extension is another useful feature developed here, in which each boundary point of every zone is extended to the nearest calibration point of the adjacent zone. By doing so, for a measuring point falling in between the boundaries of two adjacent zones, one employs the extended zone boundary data for fitting a polynomial. In addition to calibration data, additional data are acquired in the calibration tunnel. These data are used as measured data and calibration curves of suitable zones are used to derive flow parameters. In general, the interpolation errors in flow angles are found to be within ±1° and the errors in total and static pressures are within 0.5% and 1% of the dynamic pressure respectively.